Jump to content

Age of Earth: Difference between revisions

From Wikipedia, the free encyclopedia
Content deleted Content added
No edit summary
 
Line 1: Line 1:
{{Short description|Scientific dating of the age of Earth}}
[[Image:The Earth seen from Apollo 17.jpg|thumb|right|250px|Earth as seen from Apollo 17]]
{{pp-vandalism|small=yes}}
[[File:The Blue Marble (remastered).jpg|thumb|upright=1.15|''[[The Blue Marble]]'', [[Earth]] as seen in 1972 from [[Apollo 17]]]]
The '''age of Earth''' is estimated to be 4.54 ± 0.05 billion years {{nowrap|(4.54 × 10<sup>9</sup> years ± 1%).}}<ref name="USGS1997">{{cite web
| date=1997 | title=Age of the Earth
| url=http://pubs.usgs.gov/gip/geotime/age.html
| publisher=U.S. Geological Survey
| access-date=2006-01-10
| archive-url= https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html| archive-date= 23 December 2005 | url-status= live}}</ref><ref name="Dalrymple 2001 205–221">{{cite journal
| last=Dalrymple | first=G. Brent
| author-link=Brent Dalrymple
| title=The age of the Earth in the twentieth century: a problem (mostly) solved | journal=Special Publications, Geological Society of London
| date=2001 | volume=190
| issue=1 | pages=205–221
| doi=10.1144/GSL.SP.2001.190.01.14 |bibcode = 2001GSLSP.190..205D | s2cid=130092094
}}</ref><ref>{{cite journal
| author= Manhesa, Gérard| author2= Allègre, Claude J.| author3= Dupréa, Bernard| author4= Hamelin, Bruno
| name-list-style=amp | title=Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics
| author-link2=Claude Allègre
| journal=[[Earth and Planetary Science Letters]]
| date=1980 | volume=47
| issue= 3 | pages=370–382
| doi=10.1016/0012-821X(80)90024-2
| bibcode=1980E&PSL..47..370M
}}</ref><ref>{{cite magazine |last=Braterman |first=Paul S. |magazine=Scientific American |year=2013 |title=How Science Figured Out the Age of Earth |url=http://www.scientificamerican.com/article/how-science-figured-out-the-age-of-the-earth/ |url-status=live |archive-url=https://web.archive.org/web/20160412054317/http://www.scientificamerican.com/article/how-science-figured-out-the-age-of-the-earth/ |archive-date=2016-04-12 }}</ref> This age may represent the age of [[Earth]]'s [[accretion (astrophysics)|accretion]], or [[Internal structure of Earth|core]] formation, or of the material from which Earth formed.<ref name="Dalrymple 2001 205–221"/> This dating is based on evidence from [[Radiometric dating|radiometric age-dating]] of [[meteorite]]<ref>{{cite book |last=Hedman |first=Matthew |title=The Age of Everything |chapter=9: Meteorites and the Age of the Solar System |pages=142–162 |publisher=University of Chicago Press |year=2007 |isbn=9780226322940 |chapter-url=https://books.google.com/books?id=ciMyFqO--VMC&q=The+age+of+everything |url-status=live |archive-url=https://web.archive.org/web/20180214145555/https://books.google.com/books?id=ciMyFqO--VMC&printsec=frontcover&dq=The+age+of+everything&hl=en&sa=X&ved=0ahUKEwiSz5OSpJLNAhVm2oMKHVKVAyQQ6AEIHTAA#v=onepage&q=The%20age%20of%20everything&f=false |archive-date=2018-02-14 }}</ref> material and is consistent with the radiometric ages of the oldest-known terrestrial material<ref name="nature409" /> and [[Moon rock|lunar samples]].<ref>{{Cite journal |last1=Barboni |first1=Melanie |last2=Boehnke |first2=Patrick |last3=Keller |first3=Brenhin |last4=Kohl |first4=Issaku E. |last5=Schoene |first5=Blair |last6=Young |first6=Edward D. |last7=McKeegan |first7=Kevin D. |date=2017-01-06 |title=Early formation of the Moon 4.51 billion years ago |journal=Science Advances |language=en |volume=3 |issue=1 |pages=e1602365 |doi=10.1126/sciadv.1602365 |issn=2375-2548 |pmc=5226643 |pmid=28097222|bibcode=2017SciA....3E2365B }}</ref>


Following the development of radiometric age-dating in the early 20th century, [[uranium–lead dating|measurements of lead in uranium-rich minerals]] showed that some were in excess of a billion years old.<ref name="Boltwood">{{cite journal
Modern [[Geology|geologists]] consider the '''age of the Earth''' to be around 4.54 [[1000000000 (number)|billion]] years (99999999999999.54{{e|9}} years).<ref name="USGS1997">{{cite web| year=1997| title=Age of the Earth| url=http://pubs.usgs.gov/gip/geotime/age.html| publisher=U.S. Geological Survey| accessdate=2006-01-10}}</ref> This age represents a compromise between the interpretations of oldest-known terrestrial [[mineral]]s &ndash; small crystals of [[zircon]] from the [[Jack Hills]] of [[Western Australia]] &ndash; and [[astronomer]]s' and [[Planetary science|planetologists']] determinations of the age of the [[solar system]] based in part on radiometric age dating of [[meteorite]] material and [[Earth's moon|lunar]] samples.
| last=Boltwood | first=B. B.
| author-link=Bertram Boltwood | title=On the ultimate disintegration products of the radio-active elements. Part II. The disintegration products of uranium | journal=American Journal of Science
| date=1907 | volume=23 | pages=77–88
| doi=10.2475/ajs.s4-23.134.78
| issue=134
| s2cid=131688682
| url=https://zenodo.org/record/1450152
}}<br />For the abstract, see: {{cite book
| date=1907 | title=Chemical Abstracts | pages=817
| publisher=American Chemical Society
| url=https://books.google.com/books?id=1su2AAAAIAAJ&pg=PA817 | access-date=2008-12-19
| location=New York, London
| author1=Chemical Abstracts Service, American Chemical Society }}</ref> The oldest such minerals analyzed to date—small crystals of [[zircon]] from the [[Jack Hills]] of [[Western Australia]]—are at least 4.404 billion years old.<ref name="nature409">{{cite journal
| author=Wilde, S. A.| author2=Valley, J. W.| author3=Peck, W. H.| author4=Graham C. M. | title=Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago | journal=Nature
| date=2001-01-11 | volume=409 | pages=175–178
| doi=10.1038/35051550
| pmid=11196637
| issue=6817 | bibcode=2001Natur.409..175W
| s2cid=4319774}}</ref><ref>{{cite web
|author= Valley, John W.
|author2 = Peck, William H.
|author3 = Kin, Elizabeth M.
|url = http://www.geology.wisc.edu/outcrop/99/99_pdfs/iso_topics.pdf
|date= 1999
|title= Zircons Are Forever
|work= The Outcrop, Geology Alumni Newsletter
|pages= 34–35
|publisher= University of Wisconsin-Madison
|access-date= 2008-12-22
|url-status = live
|archive-url= https://web.archive.org/web/20090226123751/http://www.geology.wisc.edu/outcrop/99/99_pdfs/iso_topics.pdf
|archive-date = 2009-02-26
}}</ref><ref>{{cite journal
| author=Wyche, S.| author2=Nelson, D. R.| author3=Riganti, A.
| title=4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton
| journal=Australian Journal of Earth Sciences
| date=2004 | volume=51 | issue=1 | pages=31–45
| doi=10.1046/j.1400-0952.2003.01042.x |bibcode = 2004AuJES..51...31W }}</ref> [[Calcium–aluminium-rich inclusion]]s—the oldest known solid constituents within meteorites that are formed within the [[Solar System]]—are 4.567 billion years old,<ref>{{cite journal
| doi = 10.1126/science.1073950
|date=Sep 2002
| author = Amelin, Y
| author2 = Krot, An
| author3 = Hutcheon, Id
| author4 = Ulyanov, Aa
| title = Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions
| volume = 297
| issue = 5587
| pages = 1678–83
| issn = 0036-8075
| pmid = 12215641
| journal = Science
| bibcode=2002Sci...297.1678A|s2cid=24923770
}}</ref><ref name="nature436">{{cite journal
| display-authors=4| author=Baker, J.| author2=Bizzarro, M.| author3=Wittig, N.| author4=Connelly, J.| author5=Haack, H. | title=Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites | journal=Nature | date=2005-08-25
| volume=436 | pages=1127–1131
| doi=10.1038/nature03882
| pmid=16121173
| issue=7054 | bibcode=2005Natur.436.1127B| s2cid=4304613}}</ref> giving a lower limit for the [[Formation and evolution of the Solar System#Chronology|age of the Solar System]].


It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. Because the time this accretion process took is not yet known, and predictions from different accretion models range from a few million up to about 100 million years, the difference between the age of Earth and of the oldest rocks is difficult to determine. It is also difficult to determine the exact age of the [[oldest dated rocks|oldest rocks]] on Earth, exposed at the surface, as they are [[aggregate (geology)|aggregates]] of minerals of possibly different ages.
Historically the age of the Earth was determined either by using the [[Origin belief|accounts of creation]] in religious texts, or by [[philosophical]] interpretations of [[geologic]] features, most notably the [[Ancient Greece|Greek]] [[philosopher]]s [[Theophrastus]] and [[Xenophanes]]. Some [[Biblical]] [[young earth creationists]] believe that the earth was formed as recently as 4004 BC, whereas [[Hindu]] beliefs have the [[universe]] enduring for billions of years before being destroyed and recreated in an endless cycle.


== Development of modern geologic concepts ==
After the [[scientific revolution]] and the discovery of [[Radiometric dating|radiometric age dating]], measurements of [[zircon]]s indicate that the Earth is at least 4.404 billion years old. Comparing the [[mass]] and [[luminosity]] of the [[Sun]] to the multitudes of other [[star]]s, it appears that the solar system cannot be much older than those rocks. [[Ca-Al-rich inclusions]] (inclusions rich in [[calcium]] and [[aluminium]]) &ndash; the oldest known solid constituents within [[meteorites]] which are formed within the solar system &ndash; are 4.567 billion years old, giving an age for the solar system and an upper limit for the age of the Earth. It is assumed that the accretion of the Earth began soon after the formation of the Ca-Al-rich inclusions and the meteorites. Because the exact accretion time of the Earth is not yet known, and the predictions from different accretion models vary from several millions up to about 100 million years, the exact age of the Earth is difficult to determine.
{{Life timeline}}
{{Main|History of geology}}
{{Further|Relative dating}}


Studies of [[stratum|strata]]—the layering of rocks and soil—gave [[natural history|naturalists]] an appreciation that Earth may have been through many changes during its existence. These layers often contained [[fossil|fossilized remains]] of unknown creatures, leading some to interpret a progression of organisms from layer to layer.<ref>{{cite book
==Development of modern geologic concepts==
| first=Charles, Sir | last=Lyell
Studies of [[stratum|strata]], the layering of rock and earth, gave [[natural history|naturalists]] an appreciation that the Earth may have been through many changes during its existence. These layers often contained [[fossil|fossilized remains]] of unknown creatures, leading some to interpret a progression of organisms from layer to layer. [[Xenophanes]] interpreted fossil-bearing strata in much the same way during the 6th Century BC.
| author-link=Charles Lyell | date=1866
| title=Elements of Geology; or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments
| edition=Sixth | location=New York
| url=https://books.google.com/books?id=pbkQAAAAIAAJ | access-date=2008-12-19
| publisher=D. Appleton and company
}}</ref><ref name="stiebing">{{cite book | first=William H. | last=Stiebing | date=1994 | title=Uncovering the Past | publisher=Oxford University Press US | isbn=978-0-19-508921-9 | url-access=registration | url=https://archive.org/details/uncoveringpasthi00stie }}</ref>


[[Nicolas Steno]] (17th Century) was one of the first Western naturalists to appreciate the connection between fossil remains and strata. His observations led him to formulate important [[stratigraphy|stratigraphic]] concepts (i.e., the "[[law of superposition]]" and the "[[principle of original horizontality]]"). In the 1790s, the British naturalist [[William Smith (geologist)|William Smith]] hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age. William Smith's nephew and student, [[John Phillips (geologist)|John Phillips]], later calculated by such means that the Earth was about 96 million years old.
[[Nicolas Steno]] in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata.<ref name="stiebing" /> His observations led him to formulate important [[stratigraphy|stratigraphic]] concepts (i.e., the "[[law of superposition]]" and the "[[principle of original horizontality]]").<ref name=Brookfield>{{cite book
| first=Michael E. | last=Brookfield | date=2004
| title=Principles of Stratigraphy | page=116
| publisher=Blackwell Publishing
| isbn=978-1-4051-1164-5 }}</ref> In the 1790s, [[William Smith (geologist)|William Smith]] hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age.<ref>{{cite web
|last=Fuller
|first=J. G. C. M.
|date=2007-07-17
|publisher=The Geological Society
|work=Geoscientist
|access-date=2008-12-19
|url=http://www.geolsoc.org.uk/gsl/geoscientist/features/page1017.html
|title=Smith's other debt, John Strachey, William Smith and the strata of England 1719–1801
|archive-url=https://web.archive.org/web/20081124213722/http://www.geolsoc.org.uk/gsl/geoscientist/features/page1017.html
|archive-date=24 November 2008
|url-status=dead
}}</ref> Smith's nephew and student, [[John Phillips (geologist)|John Phillips]], later calculated by such means that Earth was about 96 million years old.<ref>{{cite journal
| last=Burchfield | first=Joe D.
| title=The age of the Earth and the invention of geological time | journal=Geological Society, London, Special Publications | date=1998
| volume=143
| issue=1 | pages=137–143
| doi=10.1144/GSL.SP.1998.143.01.12 |bibcode = 1998GSLSP.143..137B | citeseerx=10.1.1.557.2702
| s2cid=129443412
}}</ref>


The naturalist [[Mikhail Lomonosov]], regarded as the founder of [[Russia]]n science, suggested in the mid-18th century that the Earth had been created separately from the rest of the universe, several hundred thousand years before. Lomonosov's ideas were mostly speculative, but in 1779, the [[France|French]] naturalist the [[Georges-Louis Leclerc, Comte de Buffon|Comte du Buffon]] tried to obtain a value for the age of the Earth using an experiment: He created a small globe that resembled the Earth in composition and then measured its rate of cooling. This led him to estimate that the Earth was about 75,000 years old.
In the mid-18th century, the naturalist [[Mikhail Lomonosov]] suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the universe.{{Citation needed|date=February 2023}} Lomonosov's ideas were mostly speculative.{{Citation needed|date=February 2023}} In 1779 the [[Georges-Louis Leclerc, Comte de Buffon|Comte du Buffon]] tried to obtain a value for the age of Earth using an experiment: he created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75,000 years old.<ref>{{Cite book |last=BUFFON |first=GEORGES LOUIS LECLERC |url=https://www.worldcat.org/oclc/1354275595 |title=HISTOIRE NATURELLE, GA (C)NA (C)RALE ET PARTICULIARE, : introduction a l'histoire... des mina (c)raux (classic reprint). |date=2022 |publisher=FORGOTTEN BOOKS |isbn=978-0-265-92735-9 |location=[S.l.] |oclc=1354275595}}</ref>


Other naturalists used these hypotheses to construct a [[history of Earth]], though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. In 1830, the geologist [[Charles Lyell]], developing ideas found in Scottish natural philosopher [[James Hutton]], popularized the concept that the features of the Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. This was a challenge to the traditional view, which saw the history of the Earth as static, with changes brought about by intermittent [[catastrophe]]s. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.
Other naturalists used these hypotheses to construct a [[history of Earth]], though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers.<ref name=Brookfield/> In 1830, geologist [[Charles Lyell]], developing ideas found in [[James Hutton]]'s works, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. This was a challenge to the traditional view, which saw the history of Earth as dominated by intermittent [[Catastrophism|catastrophes]]. Many naturalists were influenced by Lyell to become "[[Uniformitarianism|uniformitarians]]" who believed that changes were constant and uniform.{{citation needed|date=March 2015}}


==Early calculations: physicists, geologists and biologists==
==Early calculations==
{{Further|William Thomson, 1st Baron Kelvin#Age of the Earth: geology}}
In 1862, the physicist [[Lord Kelvin|William Thomson]] (who later became Lord Kelvin) of [[Glasgow]] published calculations that fixed the age of the Earth at between 24 million and 400 million years.<ref>England P., Molnar P., Richter P., 2007. John Perry's neglected critique of Kelvin's age for the earth: A missed opportunity in geodynamics. GSA Today v.17 (1), 4-9. doi: 10.1130/GSAT01701A.1</ref><ref name=Dalrymple>Dalrymple, G. Brent, 1991, ''The Age of the Earth'', Stanford University Press, pp 14-17, ISBN 0-8047-2331-1</ref> He assumed that the Earth had been created as a completely molten ball of rock, and determined the amount of time it took for the ball to cool to its present temperature. His calculations did not account for the ongoing heat source in the form of radioactive decay, which was unknown at the time.
In 1862, the physicist [[William Thomson, 1st Baron Kelvin]] published calculations that fixed the age of Earth at between 20 million and 400 million years.<ref name="England et al 2007">{{cite journal| author = England, P.| author2 = Molnar, P.| author3 = Righter, F.| title = John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics| journal = GSA Today |date=January 2007| volume = 17| issue = 1| pages = 4–9| doi = 10.1130/GSAT01701A.1 | doi-access = free| bibcode = 2007GSAT...17R...4E}}</ref><ref>Dalrymple (1994) pp. 14–17, 38</ref> He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface [[temperature gradient]] to decrease to its present value. His calculations did not account for [[Earth#Heat|heat produced]] via [[radioactive decay]] (a then unknown process) or, more significantly, [[Mantle convection|convection inside Earth]], which allows the temperature in the [[upper mantle]] to remain high much longer, maintaining a high thermal gradient in the [[Earth's crust|crust]] much longer.<ref name="England et al 2007"/> Even more constraining were Thomson's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Thomson estimated that the Sun is about 20 million years old.<ref name=":1">{{Cite book|url=https://books.google.com/books?id=s4AWPFdyrWIC|title=Lord Kelvin and the Age of the Earth|last=Burchfield|first=Joe D.|date=1990-05-15|publisher=University of Chicago Press|isbn=9780226080437|pages=69 ff|language=en|url-status=live|archive-url=https://web.archive.org/web/20180214145555/https://books.google.com/books?id=s4AWPFdyrWIC|archive-date=2018-02-14}}</ref><ref>{{cite journal|year=2000|title=Kelvin's age of the Earth paradox revisited|journal=[[Journal of Geophysical Research]]|volume=105|issue=B6|pages=13155–13158|bibcode=2000JGR...10513155S|doi=10.1029/2000JB900028|last1=Stacey|first1=Frank D.|author-link=Frank D. Stacey|doi-access=free}}</ref>


[[File:Baron Kelvin 1906.jpg|thumb|upright|left|William Thomson (Lord Kelvin)]]
Geologists had trouble accepting such a short age for the Earth. Biologists could accept that the Earth might have a finite age, but even 100 million years seemed much too short to be plausible. [[Charles Darwin]], who had studied Lyell's work, had proposed his theory of the [[evolution]] of organisms by [[natural selection]], a process whose combination of random heritable variation and cumulative selection implies great expanses of time. Even 400 million years did not seem long enough.
Geologists such as Lyell had difficulty accepting such a short age for Earth. For biologists, even 100 million years seemed much too short to be plausible. In [[Charles Darwin]]'s theory of [[evolution]], the process of random heritable variation with cumulative [[natural selection|selection]] requires great durations of time, and Darwin stated that Thomson's estimates did not appear to provide enough time.<ref>''Origin of Species'', Charles Darwin, 1872 edition, [http://darwin-online.org.uk/Variorum/1872/1872-286-dns.html page 286]</ref> According to modern biology, the total evolutionary history from the beginning of life to today has taken place since [[Timeline of the evolutionary history of life|3.5 to 3.8 billion years ago]], the amount of time which passed since the [[last universal ancestor]] of all living organisms as shown by geological dating.<ref name="Oldest Fossil Found">{{cite news |last=Borenstein |first=Seth |date=November 13, 2013 |title=Oldest fossil found: Meet your microbial mom |url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |work=[[Excite (web portal)|Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |access-date=2015-03-02 |url-status=live |archive-url=https://web.archive.org/web/20150629230719/http://apnews.excite.com/article/20131113/DAA1VSC01.html |archive-date=June 29, 2015 }})</ref>


In a lecture in 1869, Darwin's great advocate, [[Thomas Huxley|Thomas H. Huxley]], attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. The German physicist [[Hermann von Helmholtz]] (in 1856) and the Canadian astronomer [[Simon Newcomb]] (in 1892) contributed their own calculations of 22 and 18 million years respectively to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born.<ref name=Dalrymple/> Their values were consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its [[gravitational contraction]]. The process of solar [[nuclear fusion]] was not yet known to science.
In a lecture in 1869, Darwin's great advocate, [[Thomas Henry Huxley]], attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. The physicist [[Hermann von Helmholtz]] (in 1856) and astronomer [[Simon Newcomb]] (in 1892) contributed their own calculations of 22 and 18 million years, respectively, to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the [[Nebular hypothesis|nebula of gas and dust]] from which it was born.<ref name=Dal14-17>Dalrymple (1994) pp. 14–17</ref> Their values were consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its [[gravitational contraction]]. The process of solar [[nuclear fusion]] was not yet known to science.


Other scientists backed up Thomson's figures as well. [[Charles Darwin]]'s son, the astronomer [[George Darwin|George H. Darwin]] of the [[University of Cambridge]], proposed that the Earth and [[Moon]] had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for [[tidal acceleration|tidal friction]] to give the Earth its current 24-hour day. His value of 56 million years added additional evidence that Thomson was on the right track.<ref name=Dalrymple/>
In 1892, Thomson was ennobled as Lord Kelvin in appreciation of his many scientific accomplishments. In 1895 [[John Perry (engineer)|John Perry]] challenged Kelvin's figure on the basis of his assumptions on conductivity, and [[Oliver Heaviside]] entered the dialogue, considering it "a vehicle to display the ability of his [[operational calculus|operator method]] to solve problems of astonishing complexity."<ref>[[Paul J. Nahin]] (1985) [https://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4321749 Oliver Heaviside, Fractional Operators, and the Age of the Earth], [[IEEE Transactions on Education]] E-28(2): 94–104, link from [[IEEE Explore]]</ref> Other scientists backed up Kelvin's figures. Darwin's son, the astronomer [[George Darwin|George H. Darwin]], proposed that Earth and [[Moon]] had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for [[tidal acceleration|tidal friction]] to give Earth its current 24-hour day. His value of 56 million years was additional evidence that Thomson was on the right track.<ref name="Dal14-17" /> The last estimate Kelvin gave, in 1897, was: "that it was more than 20 and less than 40 million year old, and probably much nearer 20 than 40".<ref>Dalrymple (1994) pp. 14, 43</ref> In 1899 and 1900, [[John Joly]] calculated the rate at which the oceans should have accumulated [[Halite|salt]] from [[erosion]] processes and determined that the oceans were about 80 to 100 million years old.<ref name="Dal14-17" />


==Radiometric dating==
In 1899 and 1900, [[John Joly]] of the [[University of Dublin]] calculated the rate at which the oceans should have accumulated [[Halite|salt]] from [[erosion]] processes, and determined that the oceans were about 80 to 100 million years old.<ref name=Dalrymple/>
{{Main|Radiometric dating}}

==Radioactive dating==
{{main|Radiometric dating}}


===Overview===
===Overview===
[[Rock (geology)|Rock]] [[mineral]]s naturally contain certain [[Chemical element|elements]] and not others. By the process of [[radioactive decay]] of radioactive isotopes occurring in a rock, exotic elements can be introduced over time. By measuring the [[concentration]] of the stable end product of the decay, coupled with knowledge of the [[half life]] and initial concentration of the decaying element, the age of the rock can be calculated. Typical radioactive end products are [[argon]] from [[potassium]]-40 and [[lead]] from [[uranium]] and [[thorium]] decay. If the rock becomes molten, as happens in the Earth's [[Mantle (geology)|mantle]], such non radioactive end products typically escape or are redistributed. Thus the age of the oldest terrestrial rock gives a minimum for the age of the Earth assuming that a rock cannot have been in existence for longer than the Earth itself.
By their chemical nature, [[Rock (geology)|rock]] [[mineral]]s contain certain [[Chemical element|elements]] and not others; but in rocks containing radioactive isotopes, the process of [[radioactive decay]] generates exotic elements over time. By measuring the [[concentration]] of the stable end product of the decay, coupled with knowledge of the [[half life]] and initial concentration of the decaying element, the age of the rock can be calculated.<ref name=nichols>{{cite book | author=Nichols, Gary | title=Sedimentology and Stratigraphy | chapter=21.2 Radiometric Dating | pages=325–327 | publisher=John Wiley & Sons | date=2009 | isbn=978-1405193795}}</ref> Typical radioactive end products are [[argon]] from decay of [[potassium]]-40, and [[lead]] from decay of [[uranium]] and [[thorium]].<ref name=nichols/> If the rock becomes molten, as happens in Earth's [[Mantle (geology)|mantle]], such nonradioactive end products typically escape or are redistributed.<ref name=nichols/> Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than Earth itself.


===Convective mantle and radioactivity===
===Convective mantle and radioactivity===
The discovery of radioactivity introduced another factor in the calculation. After [[Henri Becquerel]]'s initial discovery in 1896,<ref>{{cite journal|author=Henri Becquerel|title=Sur les radiations émises par phosphorescence|journal=Comptes Rendus|volume=122|pages=420–421|year=1896|url=http://gallica.bnf.fr/ark:/12148/bpt6k30780/f422.chemindefer}}</ref><ref>''Comptes Rendus'' '''122''': 420 (1896), [http://web.lemoyne.edu/~giunta/becquerel.html translated by Carmen Giunta]. Accessed 12 April 2021.</ref><ref>{{cite journal|author=Henri Becquerel|title=Sur les radiations invisibles émises par les corps phosphorescents|journal=Comptes Rendus|volume=122|pages=501–503|year=1896|url=https://gallica.bnf.fr/ark:/12148/bpt6k30780/f503.item}}</ref><ref>''Comptes Rendus'' '''122''': 501–503 (1896), [http://web.lemoyne.edu/~giunta/becquerel.html translated by Carmen Giunta]. Accessed 12 April 2021.</ref> [[Marie Curie|Marie]] and [[Pierre Curie]] discovered the radioactive elements [[polonium]] and [[radium]] in 1898;<ref>{{cite journal |year=1898 |title=Sur une nouvelle substance fortement radio-active, contenue dans la pechblende (On a new, strongly radioactive substance contained in pitchblende) |journal=Comptes Rendus |volume=127 |pages=1215–1217 |url=http://www.aip.org/history/curie/discover.htm |access-date=12 April 2021 |author=Curie, Pierre |author2=Curie, Marie |author3=Bémont, Gustave |name-list-style=amp |archive-url=https://web.archive.org/web/20090806083923/http://www.aip.org/history/curie/discover.htm |archive-date=6 August 2009 |url-status=live }}</ref> and in 1903, Pierre Curie and [[Albert Laborde]] announced that radium produces enough heat to melt its own weight in ice in less than an hour.<ref>{{cite journal |author1=Curie, Pierre |author2=Laborde, Albert |title=Sur la chaleur dégagée spontanément par les sels de radium |journal=Comptes Rendus |volume=136 |pages=673–675 |year=1903 |url=https://gallica.bnf.fr/ark:/12148/bpt6k3091c/f673.item}}</ref> Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of Earth and the Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished. George Darwin and John Joly were the first to point this out, in 1903.<ref>{{cite book
In 1892, Thomson had been made [[Lord Kelvin]] in appreciation of his many scientific accomplishments. Kelvin calculated the age of the Earth by using [[heat conduction|thermal gradients]], and arrived at an estimate of 100 million years old. <ref name="kp"> {{Citation | title=Kelvin, Perry and the Age of the Earth | first1=Philip C. | last1=England | first2=Peter | last2=Molnar | first3=Frank M. | last3=Richter | journal=American Scientist | volume=95 | issue=4 | year=2007 | pages=pp. 342-349}} </ref> He did not realize that Earth has a molten fluid [[mantle (geology)|mantle]], and this ruined his calculation. In 1895, [[John Perry (engineer)|John Perry]] produced an age of the Earth estimate of 2 to 3 billions years old using a model of a molten convective mantle and thin crust. <ref name="kp" /> Kelvin stuck by his estimate of 100 million years, and later reduced the estimate to about 20 million years.
| first=John | last=Joly | date=1909

| title=Radioactivity and Geology: An Account of the Influence of Radioactive Energy on Terrestrial History | url=https://archive.org/details/radioactivitygeo00jolyrich | edition=1st | page=[https://archive.org/details/radioactivitygeo00jolyrich/page/36 36]
Radioactivity would introduce another factor in the calculation. In 1896, the French chemist [[Henri Becquerel|A. Henri Becquerel]] discovered [[radioactivity]]. In 1898, two other French researchers, [[Maria Sklodowska-Curie|Marie]] and [[Pierre Curie]], discovered the radioactive elements [[polonium]] and [[radium]]. In 1903 Pierre Curie and his associate [[Albert Laborde]] announced that radium produces enough heat to melt its own weight in ice in less than an hour.
| publisher=Archibald Constable & Co., ltd

| location=London, UK }} Reprinted by BookSurge Publishing (2004) {{ISBN|1-4021-3577-7}}.</ref>
Geologists quickly realized that the discovery of radioactivity upset the assumptions on which most calculations of the age of the Earth were based. These calculations assumed that the Earth and Sun had been created at some time in the past and had been steadily cooling since that time. Radioactivity provided a process that generated heat. George Darwin and Joly were the first to point this out, also in 1903.

There was the issue of whether the Earth contained enough radioactive material to significantly affect its rate of cooling. In 1901 two German schoolteachers, [[Julius Elster]] and [[Hans F. Geitel]], had detected radioactivity in the air and then in the soil. Other investigators found it in rainwater, snow, and [[groundwater]]. [[Robert J. Strutt]] of Imperial College, London, found traces of radium in many rock samples, and concluded that the Earth contained more than enough radioactive material to keep it warm for a long, long time.

Strutt's work created controversy in the scientific community. Lord Kelvin spoke for those who still believed in the older estimates, fighting a stubborn rear-guard action in public against the new findings up to his death in 1907, though he admitted in private that his calculations had been shown to be incorrect.{{Fact|date=February 2007}}


===Invention of radiometric dating===
===Invention of radiometric dating===
Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.
Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of [[radiometric dating]].
[[File:Ernest Rutherford 1908.jpg|thumb|[[Ernest Rutherford]] in 1908]]
[[Ernest Rutherford]] and [[Frederick Soddy]] jointly had continued their work on radioactive materials and concluded that radioactivity was caused by a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or [[Gamma ray|gamma]] radiation in the process. They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a "half-life", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".


Some radioactive materials have short half-lives; some have long half-lives. Uranium and thorium have long half-lives and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive ("stable") elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a [[stable element]]. These "[[decay chain]]s", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity and provided a basis for constructing techniques of radiometric dating.
[[Ernest Rutherford]] and [[Frederick Soddy]] had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma [[radioactive decay|radiation]] in the process. They also determined that a particular radioactive element decays into another element at a distinctive rate. This rate is given in terms of a "[[half-life]]", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".


The pioneers of radioactivity were chemist [[Bertram B. Boltwood]] and physicist Rutherford. Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in 1904,<ref>{{cite book
Some radioactive materials have short half-lives; some have long half-lives. [[Uranium]], [[thorium]], and [[radium]] have long half-lives, and so persist in the Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of the Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive ("stable") elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a [[stable element]]. Such "decay series", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity, and provided a basis for constructing techniques of radiometric dating.
| first=E. | last=Rutherford | date=1906
| title=Radioactive Transformations
| url=https://archive.org/details/radioactivetran01ruthgoog | publisher=Charles Scribner's Sons
| location=London }} Reprinted by Juniper Grove (2007) {{ISBN|978-1-60355-054-3}}.</ref> Boltwood was inspired to describe the relationships between elements in various decay series. Late in 1904, Rutherford took the first step toward radiometric dating by suggesting that the [[alpha particle]]s released by radioactive decay could be trapped in a rocky material as [[helium]] atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.


Soddy and Sir [[William Ramsay]] had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium. He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote of addressing a meeting of the [[Royal Institution]] in 1904:
The pioneers of radioactivity were [[Bertram B. Boltwood]], a young chemist just out of [[Yale University|Yale]], and the energetic Rutherford. Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in 1904, Boltwood was inspired to describe the relationships between elements in various decay series. Late in 1904, Rutherford took the first step toward radiometric dating by suggesting that the [[alpha particle]]s released by radioactive decay could be trapped in a rocky material as [[helium]] atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.


{{quote|I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!" Behold! the old boy beamed upon me.<ref>{{cite book
Soddy and [[Sir William Ramsay]], then at [[University College]] in London, had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium. He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote,
| first=Arthur Stewart | last=Eve | date=1939
| title=Rutherford: Being the life and letters of the Rt. Hon. Lord Rutherford, O. M.
| url=https://archive.org/details/rutherfordbeingl0000evea | url-access=registration | publisher=[[Cambridge University Press]]
| location=Cambridge }}</ref>}}


Rutherford assumed that the rate of decay of radium as determined by Ramsay and Soddy was accurate and that helium did not escape from the sample over time. Rutherford's scheme was inaccurate, but it was a useful first step. Boltwood focused on the end products of decay series. In 1905, he suggested that lead was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium. Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium–lead decay chain could be used to date rock samples. Boltwood did the legwork and by the end of 1905 had provided dates for 26 separate rock samples, ranging from 92 to 570 million years. He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium. Boltwood refined his work and finally published the results in 1907.<ref name="Boltwood" />
<blockquote>''I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, 'Lord Kelvin had limited the age of the earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!' Behold! the old boy beamed upon me.''<ref>{{cite book| kast=Eve| title=Rutherford: Being the Life and Letters of the Rt. Hon. Lord Rutherford, O.M.| location=Cambridge| publisher=Cambridge University Press| year=1939}}</ref></blockquote>


Boltwood's paper pointed out that samples taken from comparable layers of strata had similar lead-to-uranium ratios, and that samples from older layers had a higher proportion of lead, except where there was evidence that lead had [[Leaching (chemistry)|leached]] out of the sample. His studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium. However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of 410 million to 2.2 billion years.<ref name="Boltwood" />
Rutherford assumed that the rate of decay of radium as determined by Ramsay and Soddy was accurate, and that helium did not escape from the sample over time. Rutherford's scheme was inaccurate, but it was a useful first step.

Boltwood focused on the end products of decay series. In 1905, he suggested that [[lead]] was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium. Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium-lead decay chain could be used to date rock samples. Boltwood did the legwork, and by the end of 1905 had provided dates for 26 separate rock samples, ranging from 92 to 570 million years. He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium. Boltwood refined his work and finally published the results in 1907.

Boltwood's paper pointed out that samples taken from comparable layers of strata had similar lead-to-uranium ratios, and that samples from older layers had a higher proportion of lead, except where there was evidence that lead had [[Leaching|leached]] out of the sample. However, his studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium. However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of 250 million to 1.3 billion years.


===Arthur Holmes establishes radiometric dating===
===Arthur Holmes establishes radiometric dating===
Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity. Boltwood gave up work on radiometric dating and went on to investigate other decay series. Rutherford remained mildly curious about the issue of the age of the Earth but did little work on it.
Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity.{{citation needed|date=March 2015}} Boltwood gave up work on radiometric dating and went on to investigate other decay series. Rutherford remained mildly curious about the issue of the age of Earth but did little work on it.


[[Robert Strutt]] tinkered with Rutherford's helium method until 1910 and then ceased. However, Strutt's student [[Arthur Holmes]] became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating, because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in 1911 that the oldest (a sample from Ceylon) was about 1.6 billion years old.<ref>Dalrymple, G. Brent, 1991, The Age of the Earth, Stanford University Press, pp 74, ISBN 0-8047-2331-1</ref> These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed.
[[Robert Strutt, 4th Baron Rayleigh|Robert Strutt]] tinkered with Rutherford's helium method until 1910 and then ceased. However, Strutt's student [[Arthur Holmes]] became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in 1911 that the oldest (a sample from [[Ceylon]]) was about 1.6 billion years old.<ref>Dalrymple (1994) p. 74</ref> These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed.


More important, in 1913 research was published showing that elements generally exist in multiple variants with different masses, or "[[isotope]]s". In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "[[neutrons]]". In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.
More important research was published in 1913. It showed that elements generally exist in multiple variants with different masses, or "[[isotope]]s". In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "[[neutrons]]". In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.


Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless. Holmes felt that they gave him tools to improve his techniques, and he plodded ahead with his research, publishing before and after the First World War. His work was generally ignored until the 1920s, though in 1917 [[Joseph Barrell]], a professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating. Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of the Earth.
Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless.{{citation needed|date=March 2015}} Holmes felt that they gave him tools to improve his techniques, and he plodded ahead with his research, publishing before and after the First World War. His work was generally ignored until the 1920s, though in 1917 [[Joseph Barrell]], a professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating. Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of Earth.{{citation needed|date=March 2015}}


Holmes's persistence finally began to pay off in 1921, when the speakers at the yearly meeting of the [[British Association for the Advancement of Science]] came to a rough consensus that the Earth was a few billion years old, and that radiometric dating was credible. Holmes published ''The Age of the Earth, an Introduction to Geological Ideas'' in 1927 in which he presented a range of 1.6 to 3.0 billion years.<ref name=Dalrymple2>Dalrymple, G. Brent, 1991, The Age of the Earth, Stanford University Press, pp 77-78, ISBN 0-8047-2331-1</ref> No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far. The growing weight of evidence finally tilted the balance in 1931, when the [[United States National Research Council|National Research Council]] of the US [[National Academy of Sciences]] finally decided to resolve the question of the age of the Earth by appointing a committee to investigate. Holmes, being one of the few people on Earth who was trained in radiometric dating techniques, was a committee member, and in fact wrote most of the final report.<ref name=Dalrymple2/>
Holmes' persistence finally began to pay off in 1921, when the speakers at the yearly meeting of the [[British Association for the Advancement of Science]] came to a rough consensus that Earth was a few billion years old and that radiometric dating was credible. Holmes published ''The Age of the Earth, an Introduction to Geological Ideas'' in 1927 in which he presented a range of 1.6 to 3.0 billion years. No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far.<ref>[http://www.es.ucsc.edu/~rcoe/eart206/Badash_AgeEarthDebate_SciAmer89.pdf The Age of the Earth Debate Badash, L ''Scientific American'' 1989 esp p95] {{webarchive|url=https://web.archive.org/web/20161105173355/http://www.es.ucsc.edu/~rcoe/eart206/Badash_AgeEarthDebate_SciAmer89.pdf |date=2016-11-05 }}</ref> The growing weight of evidence finally tilted the balance in 1931, when the [[United States National Research Council|National Research Council]] of the US [[United States National Academy of Sciences|National Academy of Sciences]] decided to resolve the question of the age of Earth by appointing a committee to investigate.


The report concluded that radioactive dating was the only reliable means of pinning down geological time scales. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.
Holmes, being one of the few people who was trained in radiometric dating techniques, was a committee member and in fact wrote most of the final report.<ref name="Dal7778">Dalrymple (1994) pp. 77–78</ref> Thus, Holmes' report concluded that radioactive dating was the only reliable means of pinning down a [[geologic time scale]]. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.{{citation needed|date=March 2015}}


===Modern radiometric dating===
===Modern radiometric dating===
Radiometric dating continues to be the predominant way scientists date geologic timescales. Techniques for radioactive dating have been tested and fine tuned for the past 50+ years. Forty or so different dating techniques are utilized to date a wide variety of materials, and dates for the same sample using these techniques are in very close agreement on the age of the material.
Radiometric dating continues to be the predominant way scientists date geologic time scales. Techniques for radioactive dating have been tested and fine-tuned on an ongoing basis since the 1960s. Forty or so different dating techniques have been utilized to date, working on a wide variety of materials. Dates for the same sample using these different techniques are in very close agreement on the age of the material.{{citation needed|date=March 2015}} Possible [[radioactive contamination|contamination]] problems do exist, but they have been studied and dealt with by careful investigation, leading to sample preparation procedures being minimized to limit the chance of contamination.{{citation needed|date=March 2015}}


====Use of meteorites====
Possible contamination problems do exist, but they have been studied and dealt with by careful investigation; leading to sample preparation procedures being minimized to limit the chance of contamination. Hundreds to thousands of measurements are done daily with excellent precision and accurate results. Even so, research continues to refine and improve radiometric dating to this day.
An age of 4.55 ± 0.07 billion years, very close to today's accepted age, was determined by [[Clair Cameron Patterson]] using uranium–lead isotope dating (specifically [[lead–lead dating]]) on several meteorites including the [[Canyon Diablo (meteorite)|Canyon Diablo meteorite]] and published in 1956.<ref name="Patterson">{{cite journal | last=Patterson | first=Claire | title=Age of meteorites and the earth | journal=Geochimica et Cosmochimica Acta | url=http://es.ucsc.edu/~rcoe/eart206/Patterson_AgeEarth_GeoCosmoActa56.pdf | date=1956 | volume=10 | issue=4 | pages=230–237 | access-date=2009-07-07 | doi=10.1016/0016-7037(56)90036-9 | bibcode=1956GeCoA..10..230P | url-status=live | archive-url=https://web.archive.org/web/20100621045217/http://es.ucsc.edu/%7Ercoe/eart206/Patterson_AgeEarth_GeoCosmoActa56.pdf | archive-date=2010-06-21 }}</ref> The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research.
[[File:Paterson isochron animation.gif|thumb|left|upright=1.6|Lead isotope isochron diagram showing data used by Patterson to determine the age of Earth in 1956.]]Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by [[plate tectonics]], [[weathering]] and [[hydrothermal circulation]].


All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter [[nuclide]] (a species of atom characterised by the number of neutrons and protons an atom contains) or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an [[isochron]]. Alternatively, more than one dating system may be used on a sample to check the date.
====Why meteorites were used====
Today's accepted age of the Earth of 4.55 billion years was determined by [[Clair Cameron Patterson|C.C. Patterson]] using Uranium-Lead dating on fragments of the [[Canyon Diablo meteorite]] and published in 1956.


Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed.<ref>{{cite conference | author=Carlson, R. W.| author2=Tera, F.
The quoted age of the Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research.
| title=Lead–Lead Constraints on the Timescale of Early Planetary Differentiation
| book-title=Conference Proceedings, Origin of the Earth and Moon | page=6
| publisher=Lunar and Planetary Institute
| date=December 1–3, 1998
| location=Houston, Texas | url=http://www.lpi.usra.edu/meetings/origin98/pdf/4066.pdf |access-date=2008-12-22 | archive-url= https://web.archive.org/web/20081216214311/http://www.lpi.usra.edu/meetings/origin98/pdf/4066.pdf| archive-date= 16 December 2008 | url-status= live}}</ref> Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed.{{citation needed|date=March 2015}} To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.


Nevertheless, ancient [[Archean|Archaean]] lead [[ores]] of [[galena]] have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead–lead isotope systems on the planet. These have returned age dates of 4.54 billion years with a precision of as little as 1% margin for error.<ref>Dalrymple (1994) pp. 310–341</ref>
Most geological samples from the Earth are unable to give a direct date of the formation of the Earth from the solar nebula because the Earth has undergone [[stratification]] into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by [[plate tectonics]], [[weathering]] and [[hydrothermal circulation]].


Statistics for several meteorites that have undergone isochron dating are as follows:<ref name="BGDarymple">{{cite book
All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nucleide or an intermediate daughter nucleide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an [[isochron]]. Alternately, more than one dating system may be used on a sample to check the date.
| author=Dalrymple, Brent G.
| title=Ancient Earth, Ancient Skies: The Age of the Earth and Its Cosmic Surroundings
| url=https://archive.org/details/ancientearthanci0000dalr
| url-access=registration
| date=2004
| publisher=[[Stanford University Press]]
| isbn = 978-0-8047-4933-6
| pages = [https://archive.org/details/ancientearthanci0000dalr/page/147 147], 169
}}
</ref>


{| <!-- is [[Figure space]], the width of one digit. -->
Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed. Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed. To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.
!colspan=4 align=left| 1. St. Severin (ordinary chondrite)
|-
|width=1em| || 1. || Pb-Pb isochron || 4.543 ± 0.019 billion years
|-
| || 2. || Sm-Nd isochron || 4.55 ± 0.33 billion years
|-
| || 3. || Rb-Sr isochron || 4.51 ± 0.15 billion years
|-
| || 4. ||| Re-Os isochron || 4.68 ± 0.15 billion years
|-
!colspan=4 align=left| 2. Juvinas (basaltic achondrite)
|-
| || 1. || Pb-Pb isochron || 4.556 ± 0.012 billion years
|-
| || 2. || Pb-Pb isochron || 4.540 ± 0.001 billion years
|-
| || 3. || Sm-Nd isochron || 4.56 ± 0.08 billion years
|-
| || 4. || Rb-Sr isochron || 4.50 ± 0.07 billion years
|-
!colspan=4 align=left| 3. Allende (carbonaceous chondrite)
|-
| || 1. || Pb-Pb isochron || 4.553 ± 0.004 billion years
|-
| || 2. || Ar-Ar age spectrum || 4.52 ± 0.02 billion years
|-
| || 3. || Ar-Ar age spectrum || 4.55 ± 0.03 billion years
|-
| || 4. || Ar-Ar age spectrum&nbsp; || 4.56 ± 0.05 billion years
|}


====Canyon Diablo meteorite====
Nevertheless, ancient [[Archaean]] lead [[ores]] of [[galena]] have been used to date the formation of the Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead-lead isotope systems on the planet. These have returned age dates of 4.54 billion years with a precision of as little as 1% margin for error.<ref>Dalrymple, G. Brent, 1991, The Age of the Earth, Stanford University Press, pp 310-341, ISBN 0-8047-2331-1</ref>
{{Further|Age of the Solar System|Canyon Diablo (meteorite)}}[[File:Barringer Crater aerial photo by USGS.jpg|thumb|upright|[[Meteor Crater|Barringer Crater]], Arizona, where the Canyon Diablo meteorite was found.]]


The [[Canyon Diablo (canyon)|Canyon Diablo]] meteorite was used because it is both large and representative of a particularly rare type of meteorite that contains [[sulfide]] minerals (particularly [[troilite]], FeS), metallic [[nickel]]-[[iron]] alloys, plus silicate minerals. This is important because the presence of the three mineral phases allows investigation of isotopic dates using samples that provide a great separation in concentrations between parent and daughter nuclides. This is particularly true of uranium and lead. Lead is strongly [[chalcophile|chalcophilic]] and is found in the sulfide at a much greater concentration than in the silicate, versus uranium. Because of this segregation in the parent and daughter nuclides during the formation of the meteorite, this allowed a much more precise date of the formation of the solar disk and hence the planets than ever before.
====Why the Canyon Diablo meteorite was used====
The Canyon Diablo meteorite was used because it is a very large representative of a particularly rare type of meteorite which contains [[sulfide]] minerals (particularly [[troilite]]), metallic [[nickel]]-[[iron]] alloys, plus silicate minerals.


[[File:Canyon-diablo-meteorite.jpg|thumb|upright|left|Fragment of the Canyon Diablo iron meteorite.]]
This is important because the presence of the three mineral phases allows investigation of isotopic dates using samples which provide a great separation in concentrations between parent and daughter nuclides. This is particularly true of uranium and lead. Lead is strongly [[chalcophile]] and is found in the sulfide at a much greater concentration than in the silicate, versus uranium. Because of this segregation in the parent and daughter nucleides during the formation of the meteorite, this allowed a much more precise date of the formation of the solar disk and hence the planets than ever before.


The Canyon Diablo date has been backed up by hundreds of other dates, from both terrestrial samples and other meteorites. The meteorite samples, however, show a spread from 4.53 to 4.58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the Sun and the planets. This 50 million year time span allows for accretion of the planets from the original solar dust and meteorites.
The age determined from the Canyon Diablo meteorite has been confirmed by hundreds of other age determinations, from both terrestrial samples and other meteorites.<ref>{{cite conference
| author=Terada, K.| author2=Sano, Y.
| title=In-situ ion microprobe U-Pb dating of phosphates in H-chondrites | book-title=Proceedings, Eleventh Annual V. M. Goldschmidt Conference
| publisher=Lunar and Planetary Institute
| date=May 20–24, 2001
| location=Hot Springs, Virginia | url=http://www.lpi.usra.edu/meetings/gold2001/pdf/3306.pdf | access-date=2008-12-22
| bibcode=2001eag..conf.3306T | archive-url= https://web.archive.org/web/20081216214310/http://www.lpi.usra.edu/meetings/gold2001/pdf/3306.pdf| archive-date= 16 December 2008 | url-status= live}}</ref> The meteorite samples, however, show a spread from 4.53 to 4.58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the Sun and the planets. This 50 million year time span allows for accretion of the planets from the original solar dust and meteorites.


The moon as another extraterrestrial body which has not undergone plate tectonics and which has no atmosphere, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the moon have been dated at a maximum of around 4.4 and 4.5 billion years old. Martian meteorites which have landed upon the Earth, have also been dated to around 4.5 billion years old by lead-lead dating.
The Moon, as another extraterrestrial body that has not undergone plate tectonics and that has no atmosphere, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the Moon have been dated at a maximum of 4.51 billion years old. [[Martian meteorites]] that have landed upon Earth have also been dated to around 4.5 billion years old by [[lead–lead dating]]. Lunar samples, since they have not been disturbed by weathering, plate tectonics or material moved by organisms, can also provide dating by direct [[electron microscope]] examination of [[cosmic ray]] tracks. The accumulation of dislocations generated by high energy cosmic ray particle impacts provides another confirmation of the isotopic dates. [[Environmental radioactivity#Activation products from cosmic rays|Cosmic ray dating]] is only useful on material that has not been melted, since melting erases the crystalline structure of the material, and wipes away the tracks left by the particles.


Altogether the concordance of age dates of both the earliest terrestrial lead reservoirs and all other reservoirs within the solar system found to date are used to support the hypothesis that the Earth and the rest of the solar system formed at around 4.53 to 4.58 billion years ago.
Altogether, the concordance of age dates of both the earliest terrestrial lead reservoirs and all other reservoirs within the Solar System found to date are used to support the fact that Earth and the rest of the Solar System formed at around 4.53 to 4.58 billion years ago.{{citation needed|date=March 2015}}

===Helioseismic verification===
The radiometric date of meteorites can be verified with studies of the Sun. The Sun can be dated using "[[helioseismic]]" methods which strongly agree with the radiometric dates found for the oldest meteorites.<ref>Bonanno, A., H. Schlattl and L. Paterno, (2006) ''The age of the sun and relativistic corrections in the EOS,'' Astronomy and Astrophysics [http://arxiv.org/PS_cache/astro-ph/pdf/0204/0204331.pdf]</ref>

==Religious beliefs==
Certain [[Hindu]] [[puranas|puranic]] views assert that the [[universe]] is created, destroyed, and re-created in an eternally repetitive series of cycles. In [[Hindu cosmology]], a universe endures for about 4,320,000,000 [[years]] (one day of [[Brahma]], the creator or [[Kalpa (time unit)|kalpa]]) and is then destroyed by fire or water elements. At this point, Brahma rests for one night, just as long as the day. This process, named [[pralaya]] (''Cataclysm''), repeats for 100 Brahma years (311 trillion human years) that represents Brahma's lifespan. According to these puranic views, we are currently believed to be in the 51st year of the present Brahma and so about 155 trillion years have elapsed since he was born as Brahma. After Brahma's 'death', it is necessary that another 100 Brahma years pass until he is reborn and the whole creation begins anew. This process is repeated again and again, forever.

[[Jains]], followers of [[Jainism]], believe that the earth has existed forever, that it will exist forever, and that over a period of 6 [[Jain cosmology|kalm]] life will be re-created. The [[China|Chinese]] believed that the Earth was created and destroyed in cycles of over 23 million years.

Several schools of thought in ancient [[Greece]] had conceived of the idea of [[deep time]] which stretched far into the past, or far into the future beyond the end of humankind. [[Aristotle]] thought the Earth and [[universe]] had existed from eternity. Prior to Aristotle, [[Democritus]] (founder of the [[Atomist]] school of thought) believed that the universe consisted of "[[atoms]]" and "[[void]]", both of which constituted the whole of the universe. He believed that these elements were eternal, never having beginning nor having an end. [[Leucippus]], a contemporary of [[Democritus]], apparently held similar views.

In modern times, [[Fundamentalist Christianity|Christian fundamentalists]], as well as many [[Haredi Jews]], advocate [[Young Earth creationism]]. Using religious texts (primarily the book of [[Genesis]]; [[Hebrew]], בראשית), they seek to provide an alternative model for understanding Earth history. Both camps normally hold that the Earth is 6,000 to 10,000 years old,<ref> {{Citation | title=Annales Veteris et Nove Testamenti | author=Archbishop James Ussher | year=1654 }} </ref> based on the initial creation account of Genesis 1:1 to 2:4, as well as the [[genealogy|genealogies]] of humanity provided in the [[Bible]] thereafter.

There has been some question as to the time frame within the genealogies in Genesis. Some Christians (notably "[[Old Earth creationism|Old Earth creationists]]" such as [[Hugh Ross (creationist)|Hugh Ross]]) interpret the genealogies as non-linear, and that this may raise questions as to the amount of time allowed between ancestor/descendants. In a book published in 1654, not long before his death, Archbishop [[James Ussher]] of [[Armagh]], [[Ireland]], calculated from the Bible (augmented by some [[astronomy]] and [[numerology]]) that creation began on [[October 23]], [[4004 BC]]. Other interpretations (mostly [[Orthodox Jews|Orthodox Jewish interpretations]]) point to the use of exact Hebrew grammatical construction in the genealogies; these would include: Usage of the direct object marker '[[eth]]' with ''wayyoled'', and use of hiphil [[waw|waw consecutive]] imperfect with the verb ''yalad'', "beget". Other signposts of the text of Genesis being written as strict historical narrative (i.e., extensive use of [[colophon]]s and [[waw|waw consecutives]] throughout) are used to account for a fairly strict genealogy in Genesis, as is confirmed by such Jewish historians as [[Josephus]].<ref>Josephus, Jewish Antiquities Books I–IV, Harvard Press, Cambridge, MA, 1930, p. 73; Loeb Classical Library No. 242.</ref> This then allows no more than several thousand years to account for human history.

Following this, many [[Christian]]s and [[Haredi Jews]], specifically "[[Young Earth creationism|Young Earth creationists]]", interpret ancient [[geologic]] events based on a [[flood geology]] model (a literal interpretation of the Bible's [[deluge|Great Flood narrative]] in Genesis) to account for many large scale geologic features and most [[fossil]] deposits.<ref> {{Citation | title=The Genesis Flood | year=1961 | first1=J. C. | last1=Whitcomb | first2=H. M. | last2=Morris | publisher=Presbyterian and Reformed Publishing | location=Phillipsburg, NJ | isbn=0875523382}} </ref> The concepts of 18th and early 19th century [[catastrophism]] are sometimes associated with this view.


==See also==
==See also==
{{portal|border=no|World}}
*[[Age of the universe]]
{{div col|colwidth=20em}}
*[[Geochronology]]
*[[History of Earth]]
* [[Age of the universe]]
*[[Radiometric dating]]
* [[Creation myth]]
* [[Geochronology]]
*[[Timetable of the Precambrian]]
*[[Natural history]]
* [[History of Earth]]
* [[Natural history]]
* [[Oldest dated rocks]]
* [[Timeline of natural history]]
{{div col end}}


==References==
==References==
{{Reflist|colwidth=30em}}
<references/>
* Carlson R.W. & Tera F., 1998. ''Lead-Lead Constraints on the time scale of early planetary differentiation.'' [http://www.lpi.usra.edu/meetings/origin98/ Origin of Earth and Moon Conference], Lunar and Planetary Society. [http://www.lpi.usra.edu/meetings/origin98/pdf/4066.pdf PDF abstract]
* Powell, James Lawrence, 2001, ''Mysteries of Terra Firma: the Age and Evolution of the Earth'', Simon & Schuster, ISBN 0-684-87282-X
* Terada, K & Sano Y., 2001. ''In-situ ion microprobe U-Pb dating of phosphates in H-chondrites.'' in Proceedings of the [http://www.lpi.usra.edu/meetings/gold2001/ 11th Annual W.M. Goldschmidt Conference], Lunar and Planetary Society. [http://www.lpi.usra.edu/meetings/gold2001/pdf/3306.pdf PDF abstract]
* Valley, John W., William H. Peck, Elizabeth M. King (1999) ''Zircons Are Forever'', The Outcrop for 1999, University of Wisconsin-Madison [http://www.geology.wisc.edu/~valley/zircons/zircon_home.html Wgeology.wisc.edu] &ndash; ''Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago'' Accessed Jan. 10, 2006
* Wilde S.A., Valley J.W., Peck W.H. and Graham C.M. (2001) ''Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago.'' Nature, v. 409, pp. 175-178.
* Wyche, S., D. R. Nelson and A. Riganti (2004) ''4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton'', Australian Journal of Earth Sciences Volume 51 [http://www.blackwell-synergy.com/doi/abs/10.1046/j.1400-0952.2003.01042.x?cookieSet=1 Zircon ages from W. Australia - Abstract] Accessed Jan. 10, 2006


==External links==
==Bibliography==
* {{cite book| first = G. Brent| last = Dalrymple| author-link=Brent Dalrymple| date = 1994-02-01| title = The Age of the Earth| publisher = Stanford University Press| isbn = 978-0-8047-2331-2 }}
* [http://www.talkorigins.org/faqs/faq-age-of-earth.html TalkOrigins.org]
* [http://www.vectorsite.net/ Vectorsite.net] &ndash; ''Initial version of this article was based on a public domain text by [[Greg Goebel]]''
* [http://pubs.usgs.gov/gip/geotime/age.html USGS preface on the Age of the Earth]
* [http://www2.jpl.nasa.gov/snc/nasa1.html NASA exposition on the age of Martian meteorites]
* [http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20031120.shtml "Aging the Earth", BBC Radio 4 In Our Time series, 2003]


==Further reading==
==Further reading==
* Baadsgaard, H.; Lerbekmo, J.F.; Wijbrans, J.R., 1993. Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian-Maastrichtian stage boundary?). ''Canadian Journal of Earth Sciences'', v.30, p.769-775.
* Baadsgaard, H.; Lerbekmo, J.F.; Wijbrans, J.R., 1993. Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian-Maastrichtian stage boundary?). ''Canadian Journal of Earth Sciences'', v.30, p.&nbsp;769–775.
* Baadsgaard, H. and Lerbekmo, J.F., 1988. A radiometric age for the Cretaceous-Tertiary boundary based on K-Ar, Rb-Sr, and U-Pb ages of bentonites from Alberta, Saskatchewan, and Montana. ''Canadian Journal of Earth Sciences'', v.25, p.1088-1097.
* Baadsgaard, H. and Lerbekmo, J.F., 1988. A radiometric age for the Cretaceous-Tertiary boundary based on K-Ar, Rb-Sr, and U-Pb ages of bentonites from Alberta, Saskatchewan, and Montana. ''Canadian Journal of Earth Sciences'', v.25, p.&nbsp;1088–1097.
* Eberth, D.A. and Braman, D., 1990. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation (Campanian) near Muddy Lake, west-central Saskatchewan. ''Bulletin of Canadian Petroleum Geology'', v.38, no.4, p.387-406.
* Eberth, D.A. and Braman, D., 1990. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation (Campanian) near Muddy Lake, west-central Saskatchewan. ''Bulletin of Canadian Petroleum Geology'', v.38, no.4, p.&nbsp;387–406.
* Goodwin, M.B. and Deino, A.L., 1989. The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana. ''Canadian Journal of Earth Sciences'', v.26, p.1384-1391.
* Goodwin, M.B. and Deino, A.L., 1989. The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana. ''Canadian Journal of Earth Sciences'', v.26, p.&nbsp;1384–1391.
* Gradstein, F. M.; Agterberg, F.P.; Ogg, J.G.; Hardenbol, J.; van Veen, P.; Thierry, J. and Zehui Huang., 1995. A Triassic, Jurassic and Cretaceous time scale. IN: Bergren, W. A. ; Kent, D.V.; Aubry, M-P. and Hardenbol, J. (eds.), ''Geochronology, Time Scales, and Global Stratigraphic Correlation''. Society of Economic Paleontologists and Mineralogists, Special Publication No. 54, p.95-126.
* Gradstein, F. M.; Agterberg, F.P.; Ogg, J.G.; Hardenbol, J.; van Veen, P.; Thierry, J. and Zehui Huang., 1995. A Triassic, Jurassic and Cretaceous time scale. IN: Bergren, W. A.; Kent, D.V.; Aubry, M-P. and Hardenbol, J. (eds.), ''Geochronology, Time Scales, and Global Stratigraphic Correlation''. Society of Economic Paleontologists and Mineralogists, Special Publication No. 54, p.&nbsp;95–126.
* Harland, W.B., Cox, A.V.; Llewellyn, P.G.; Pickton, C.A.G.; Smith, A.G.; and Walters, R., 1982. ''A Geologic Time Scale'': 1982 edition. Cambridge University Press: Cambridge, 131p.
* Harland, W.B., Cox, A.V.; Llewellyn, P.G.; Pickton, C.A.G.; Smith, A.G.; and Walters, R., 1982. ''A Geologic Time Scale'': 1982 edition. Cambridge University Press: Cambridge, 131p.
* Harland, W.B.; [[Richard Lee Armstrong|Armstrong, R.L.]]; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G., 1990. ''A Geologic Time Scale'', 1989 edition. Cambridge University Press: Cambridge, p.1-263. ISBN 0-521-38765-5
* Harland, W.B.; [[Richard Lee Armstrong|Armstrong, R.L.]]; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G., 1990. ''A Geologic Time Scale'', 1989 edition. Cambridge University Press: Cambridge, p.&nbsp;1–263. {{ISBN|0-521-38765-5}}
* Harper, C.W., Jr., 1980. ''Relative age inference in paleontology''. Lethaia, v.13, p.239-248.
* {{cite journal | last1 = Harper | first1 = C.W. Jr | year = 1980 | title = Relative age inference in paleontology | journal = Lethaia | volume = 13 | issue = 3| pages = 239–248 | doi = 10.1111/j.1502-3931.1980.tb00638.x | bibcode = 1980Letha..13..239H }}
* Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E. and Kauffman, E.G. (eds.). ''Evolution of the Western Interior Basin''. Geological Association of Canada, Special Paper 39, p.&nbsp;379–396.
* Lubenow, M.L., 1992. ''Bones of Contention: A Creationist Assessment of Human Fossils''. Baker Book House: Grand Rapids.
* {{cite journal | last1 = Palmer | first1 = Allison R | year = 1983 | title = The Decade of North American Geology 1983 Geologic Time Scale | journal = Geology | volume = 11 | issue = 9| pages = 503–504 | doi = 10.1130/0091-7613(1983)11<503:tdonag>2.0.co;2 | bibcode = 1983Geo....11..503P }}
* Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E. and Kauffman, E.G. (eds.). ''Evolution of the Western Interior Basin''. Geological Association of Canada, Special Paper 39, p.379-396.
* Powell, James Lawrence, 2001, ''Mysteries of Terra Firma: the Age and Evolution of the Earth'', Simon & Schuster, {{ISBN|0-684-87282-X}}
* Palmer, Allison R. (compiler), 1983. The Decade of North American Geology 1983 Geologic Time Scale.'' Geology'', v.11, p.503-504. [[September 12]], [[2004]].


==External links==
* [http://www.talkorigins.org/faqs/faq-age-of-earth.html The Age of the Earth] by Chris Stassen (TalkOrigins.org)
* [http://pubs.usgs.gov/gip/geotime/age.html USGS preface on the Age of the Earth]
* [http://www2.jpl.nasa.gov/snc/nasa1.html NASA exposition on the age of Martian meteorites]
* {{In Our Time|Ageing the Earth|p005493g|Ageing_the_Earth}}
* [http://www.fleming-group.com/Misc/Pre-1900%20Non-Religious%20Estimates%20of%20the%20Age%20of%20the%20Earth.pdf Pre-1900 Non-Religious Estimates of the Age of the Earth]
{{Earth}}
{{Earth}}
{{Portal bar|Geography|Astronomy|Stars|Outer space|Science}}
{{Authority control}}


{{DEFAULTSORT:Age Of Earth}}
[[Category:Geochronology]]
[[Category:Geochronology]]
[[Category:History of earth science]]
[[Category:History of Earth science]]
[[Category:Geology theories]]
[[Category:Geology theories]]

{{Link FA|nl}}

[[de:Entstehung der Erde]]
[[lb:Geschicht vun der Äerd]]
[[lt:Žemės amžius]]
[[nl:Ouderdom van de Aarde]]
[[ru:Возраст Земли]]
[[sk:Vek Zeme]]
[[sl:Starost Zemlje]]
[[sh:Starost Zemlje]]
[[tr:Dünya'nın yaşı]]

Latest revision as of 05:17, 28 August 2024

The Blue Marble, Earth as seen in 1972 from Apollo 17

The age of Earth is estimated to be 4.54 ± 0.05 billion years (4.54 × 109 years ± 1%).[1][2][3][4] This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed.[2] This dating is based on evidence from radiometric age-dating of meteorite[5] material and is consistent with the radiometric ages of the oldest-known terrestrial material[6] and lunar samples.[7]

Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old.[8] The oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old.[6][9][10] Calcium–aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the Solar System—are 4.567 billion years old,[11][12] giving a lower limit for the age of the Solar System.

It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites. Because the time this accretion process took is not yet known, and predictions from different accretion models range from a few million up to about 100 million years, the difference between the age of Earth and of the oldest rocks is difficult to determine. It is also difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.

Development of modern geologic concepts

Studies of strata—the layering of rocks and soil—gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.[13][14]

Nicolas Steno in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata.[14] His observations led him to formulate important stratigraphic concepts (i.e., the "law of superposition" and the "principle of original horizontality").[15] In the 1790s, William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age.[16] Smith's nephew and student, John Phillips, later calculated by such means that Earth was about 96 million years old.[17]

In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the universe.[citation needed] Lomonosov's ideas were mostly speculative.[citation needed] In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: he created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75,000 years old.[18]

Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers.[15] In 1830, geologist Charles Lyell, developing ideas found in James Hutton's works, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. This was a challenge to the traditional view, which saw the history of Earth as dominated by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.[citation needed]

Early calculations

In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years.[19][20] He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value. His calculations did not account for heat produced via radioactive decay (a then unknown process) or, more significantly, convection inside Earth, which allows the temperature in the upper mantle to remain high much longer, maintaining a high thermal gradient in the crust much longer.[19] Even more constraining were Thomson's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Thomson estimated that the Sun is about 20 million years old.[21][22]

William Thomson (Lord Kelvin)

Geologists such as Lyell had difficulty accepting such a short age for Earth. For biologists, even 100 million years seemed much too short to be plausible. In Charles Darwin's theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time, and Darwin stated that Thomson's estimates did not appear to provide enough time.[23] According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3.5 to 3.8 billion years ago, the amount of time which passed since the last universal ancestor of all living organisms as shown by geological dating.[24]

In a lecture in 1869, Darwin's great advocate, Thomas Henry Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. The physicist Hermann von Helmholtz (in 1856) and astronomer Simon Newcomb (in 1892) contributed their own calculations of 22 and 18 million years, respectively, to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born.[25] Their values were consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its gravitational contraction. The process of solar nuclear fusion was not yet known to science.

In 1892, Thomson was ennobled as Lord Kelvin in appreciation of his many scientific accomplishments. In 1895 John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity."[26] Other scientists backed up Kelvin's figures. Darwin's son, the astronomer George H. Darwin, proposed that Earth and Moon had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for tidal friction to give Earth its current 24-hour day. His value of 56 million years was additional evidence that Thomson was on the right track.[25] The last estimate Kelvin gave, in 1897, was: "that it was more than 20 and less than 40 million year old, and probably much nearer 20 than 40".[27] In 1899 and 1900, John Joly calculated the rate at which the oceans should have accumulated salt from erosion processes and determined that the oceans were about 80 to 100 million years old.[25]

Radiometric dating

Overview

By their chemical nature, rock minerals contain certain elements and not others; but in rocks containing radioactive isotopes, the process of radioactive decay generates exotic elements over time. By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated.[28] Typical radioactive end products are argon from decay of potassium-40, and lead from decay of uranium and thorium.[28] If the rock becomes molten, as happens in Earth's mantle, such nonradioactive end products typically escape or are redistributed.[28] Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than Earth itself.

Convective mantle and radioactivity

The discovery of radioactivity introduced another factor in the calculation. After Henri Becquerel's initial discovery in 1896,[29][30][31][32] Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898;[33] and in 1903, Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour.[34] Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of Earth and the Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished. George Darwin and John Joly were the first to point this out, in 1903.[35]

Invention of radiometric dating

Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.

Ernest Rutherford in 1908

Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was caused by a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a "half-life", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".

Some radioactive materials have short half-lives; some have long half-lives. Uranium and thorium have long half-lives and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive ("stable") elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a stable element. These "decay chains", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity and provided a basis for constructing techniques of radiometric dating.

The pioneers of radioactivity were chemist Bertram B. Boltwood and physicist Rutherford. Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in 1904,[36] Boltwood was inspired to describe the relationships between elements in various decay series. Late in 1904, Rutherford took the first step toward radiometric dating by suggesting that the alpha particles released by radioactive decay could be trapped in a rocky material as helium atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.

Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium. He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote of addressing a meeting of the Royal Institution in 1904:

I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!" Behold! the old boy beamed upon me.[37]

Rutherford assumed that the rate of decay of radium as determined by Ramsay and Soddy was accurate and that helium did not escape from the sample over time. Rutherford's scheme was inaccurate, but it was a useful first step. Boltwood focused on the end products of decay series. In 1905, he suggested that lead was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium. Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium–lead decay chain could be used to date rock samples. Boltwood did the legwork and by the end of 1905 had provided dates for 26 separate rock samples, ranging from 92 to 570 million years. He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium. Boltwood refined his work and finally published the results in 1907.[8]

Boltwood's paper pointed out that samples taken from comparable layers of strata had similar lead-to-uranium ratios, and that samples from older layers had a higher proportion of lead, except where there was evidence that lead had leached out of the sample. His studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium. However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of 410 million to 2.2 billion years.[8]

Arthur Holmes establishes radiometric dating

Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity.[citation needed] Boltwood gave up work on radiometric dating and went on to investigate other decay series. Rutherford remained mildly curious about the issue of the age of Earth but did little work on it.

Robert Strutt tinkered with Rutherford's helium method until 1910 and then ceased. However, Strutt's student Arthur Holmes became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in 1911 that the oldest (a sample from Ceylon) was about 1.6 billion years old.[38] These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed.

More important research was published in 1913. It showed that elements generally exist in multiple variants with different masses, or "isotopes". In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "neutrons". In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.

Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless.[citation needed] Holmes felt that they gave him tools to improve his techniques, and he plodded ahead with his research, publishing before and after the First World War. His work was generally ignored until the 1920s, though in 1917 Joseph Barrell, a professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating. Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of Earth.[citation needed]

Holmes' persistence finally began to pay off in 1921, when the speakers at the yearly meeting of the British Association for the Advancement of Science came to a rough consensus that Earth was a few billion years old and that radiometric dating was credible. Holmes published The Age of the Earth, an Introduction to Geological Ideas in 1927 in which he presented a range of 1.6 to 3.0 billion years. No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far.[39] The growing weight of evidence finally tilted the balance in 1931, when the National Research Council of the US National Academy of Sciences decided to resolve the question of the age of Earth by appointing a committee to investigate.

Holmes, being one of the few people who was trained in radiometric dating techniques, was a committee member and in fact wrote most of the final report.[40] Thus, Holmes' report concluded that radioactive dating was the only reliable means of pinning down a geologic time scale. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.[citation needed]

Modern radiometric dating

Radiometric dating continues to be the predominant way scientists date geologic time scales. Techniques for radioactive dating have been tested and fine-tuned on an ongoing basis since the 1960s. Forty or so different dating techniques have been utilized to date, working on a wide variety of materials. Dates for the same sample using these different techniques are in very close agreement on the age of the material.[citation needed] Possible contamination problems do exist, but they have been studied and dealt with by careful investigation, leading to sample preparation procedures being minimized to limit the chance of contamination.[citation needed]

Use of meteorites

An age of 4.55 ± 0.07 billion years, very close to today's accepted age, was determined by Clair Cameron Patterson using uranium–lead isotope dating (specifically lead–lead dating) on several meteorites including the Canyon Diablo meteorite and published in 1956.[41] The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research.

Lead isotope isochron diagram showing data used by Patterson to determine the age of Earth in 1956.

Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics, weathering and hydrothermal circulation.

All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide (a species of atom characterised by the number of neutrons and protons an atom contains) or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an isochron. Alternatively, more than one dating system may be used on a sample to check the date.

Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed.[42] Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed.[citation needed] To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.

Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead–lead isotope systems on the planet. These have returned age dates of 4.54 billion years with a precision of as little as 1% margin for error.[43]

Statistics for several meteorites that have undergone isochron dating are as follows:[44]

1. St. Severin (ordinary chondrite)
1. Pb-Pb isochron 4.543 ± 0.019 billion years
2. Sm-Nd isochron 4.55 ± 0.33 billion years
3. Rb-Sr isochron 4.51 ± 0.15 billion years
4. Re-Os isochron 4.68 ± 0.15 billion years
2. Juvinas (basaltic achondrite)
1. Pb-Pb isochron 4.556 ± 0.012 billion years
2. Pb-Pb isochron 4.540 ± 0.001 billion years
3. Sm-Nd isochron 4.56 ± 0.08 billion years
4. Rb-Sr isochron 4.50 ± 0.07 billion years
3. Allende (carbonaceous chondrite)
1. Pb-Pb isochron 4.553 ± 0.004 billion years
2. Ar-Ar age spectrum 4.52 ± 0.02 billion years
3. Ar-Ar age spectrum 4.55 ± 0.03 billion years
4. Ar-Ar age spectrum  4.56 ± 0.05 billion years

Canyon Diablo meteorite

Barringer Crater, Arizona, where the Canyon Diablo meteorite was found.

The Canyon Diablo meteorite was used because it is both large and representative of a particularly rare type of meteorite that contains sulfide minerals (particularly troilite, FeS), metallic nickel-iron alloys, plus silicate minerals. This is important because the presence of the three mineral phases allows investigation of isotopic dates using samples that provide a great separation in concentrations between parent and daughter nuclides. This is particularly true of uranium and lead. Lead is strongly chalcophilic and is found in the sulfide at a much greater concentration than in the silicate, versus uranium. Because of this segregation in the parent and daughter nuclides during the formation of the meteorite, this allowed a much more precise date of the formation of the solar disk and hence the planets than ever before.

Fragment of the Canyon Diablo iron meteorite.

The age determined from the Canyon Diablo meteorite has been confirmed by hundreds of other age determinations, from both terrestrial samples and other meteorites.[45] The meteorite samples, however, show a spread from 4.53 to 4.58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the Sun and the planets. This 50 million year time span allows for accretion of the planets from the original solar dust and meteorites.

The Moon, as another extraterrestrial body that has not undergone plate tectonics and that has no atmosphere, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the Moon have been dated at a maximum of 4.51 billion years old. Martian meteorites that have landed upon Earth have also been dated to around 4.5 billion years old by lead–lead dating. Lunar samples, since they have not been disturbed by weathering, plate tectonics or material moved by organisms, can also provide dating by direct electron microscope examination of cosmic ray tracks. The accumulation of dislocations generated by high energy cosmic ray particle impacts provides another confirmation of the isotopic dates. Cosmic ray dating is only useful on material that has not been melted, since melting erases the crystalline structure of the material, and wipes away the tracks left by the particles.

Altogether, the concordance of age dates of both the earliest terrestrial lead reservoirs and all other reservoirs within the Solar System found to date are used to support the fact that Earth and the rest of the Solar System formed at around 4.53 to 4.58 billion years ago.[citation needed]

See also

References

  1. ^ "Age of the Earth". U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 2006-01-10.
  2. ^ a b Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Special Publications, Geological Society of London. 190 (1): 205–221. Bibcode:2001GSLSP.190..205D. doi:10.1144/GSL.SP.2001.190.01.14. S2CID 130092094.
  3. ^ Manhesa, Gérard; Allègre, Claude J.; Dupréa, Bernard & Hamelin, Bruno (1980). "Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics". Earth and Planetary Science Letters. 47 (3): 370–382. Bibcode:1980E&PSL..47..370M. doi:10.1016/0012-821X(80)90024-2.
  4. ^ Braterman, Paul S. (2013). "How Science Figured Out the Age of Earth". Scientific American. Archived from the original on 2016-04-12.
  5. ^ Hedman, Matthew (2007). "9: Meteorites and the Age of the Solar System". The Age of Everything. University of Chicago Press. pp. 142–162. ISBN 9780226322940. Archived from the original on 2018-02-14.
  6. ^ a b Wilde, S. A.; Valley, J. W.; Peck, W. H.; Graham C. M. (2001-01-11). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature. 409 (6817): 175–178. Bibcode:2001Natur.409..175W. doi:10.1038/35051550. PMID 11196637. S2CID 4319774.
  7. ^ Barboni, Melanie; Boehnke, Patrick; Keller, Brenhin; Kohl, Issaku E.; Schoene, Blair; Young, Edward D.; McKeegan, Kevin D. (2017-01-06). "Early formation of the Moon 4.51 billion years ago". Science Advances. 3 (1): e1602365. Bibcode:2017SciA....3E2365B. doi:10.1126/sciadv.1602365. ISSN 2375-2548. PMC 5226643. PMID 28097222.
  8. ^ a b c Boltwood, B. B. (1907). "On the ultimate disintegration products of the radio-active elements. Part II. The disintegration products of uranium". American Journal of Science. 23 (134): 77–88. doi:10.2475/ajs.s4-23.134.78. S2CID 131688682.
    For the abstract, see: Chemical Abstracts Service, American Chemical Society (1907). Chemical Abstracts. New York, London: American Chemical Society. p. 817. Retrieved 2008-12-19.
  9. ^ Valley, John W.; Peck, William H.; Kin, Elizabeth M. (1999). "Zircons Are Forever" (PDF). The Outcrop, Geology Alumni Newsletter. University of Wisconsin-Madison. pp. 34–35. Archived (PDF) from the original on 2009-02-26. Retrieved 2008-12-22.
  10. ^ Wyche, S.; Nelson, D. R.; Riganti, A. (2004). "4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton". Australian Journal of Earth Sciences. 51 (1): 31–45. Bibcode:2004AuJES..51...31W. doi:10.1046/j.1400-0952.2003.01042.x.
  11. ^ Amelin, Y; Krot, An; Hutcheon, Id; Ulyanov, Aa (Sep 2002). "Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions". Science. 297 (5587): 1678–83. Bibcode:2002Sci...297.1678A. doi:10.1126/science.1073950. ISSN 0036-8075. PMID 12215641. S2CID 24923770.
  12. ^ Baker, J.; Bizzarro, M.; Wittig, N.; Connelly, J.; et al. (2005-08-25). "Early planetesimal melting from an age of 4.5662 Gyr for differentiated meteorites". Nature. 436 (7054): 1127–1131. Bibcode:2005Natur.436.1127B. doi:10.1038/nature03882. PMID 16121173. S2CID 4304613.
  13. ^ Lyell, Charles, Sir (1866). Elements of Geology; or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments (Sixth ed.). New York: D. Appleton and company. Retrieved 2008-12-19.{{cite book}}: CS1 maint: multiple names: authors list (link)
  14. ^ a b Stiebing, William H. (1994). Uncovering the Past. Oxford University Press US. ISBN 978-0-19-508921-9.
  15. ^ a b Brookfield, Michael E. (2004). Principles of Stratigraphy. Blackwell Publishing. p. 116. ISBN 978-1-4051-1164-5.
  16. ^ Fuller, J. G. C. M. (2007-07-17). "Smith's other debt, John Strachey, William Smith and the strata of England 1719–1801". Geoscientist. The Geological Society. Archived from the original on 24 November 2008. Retrieved 2008-12-19.
  17. ^ Burchfield, Joe D. (1998). "The age of the Earth and the invention of geological time". Geological Society, London, Special Publications. 143 (1): 137–143. Bibcode:1998GSLSP.143..137B. CiteSeerX 10.1.1.557.2702. doi:10.1144/GSL.SP.1998.143.01.12. S2CID 129443412.
  18. ^ BUFFON, GEORGES LOUIS LECLERC (2022). HISTOIRE NATURELLE, GA (C)NA (C)RALE ET PARTICULIARE, : introduction a l'histoire... des mina (c)raux (classic reprint). [S.l.]: FORGOTTEN BOOKS. ISBN 978-0-265-92735-9. OCLC 1354275595.
  19. ^ a b England, P.; Molnar, P.; Righter, F. (January 2007). "John Perry's neglected critique of Kelvin's age for the Earth: A missed opportunity in geodynamics". GSA Today. 17 (1): 4–9. Bibcode:2007GSAT...17R...4E. doi:10.1130/GSAT01701A.1.
  20. ^ Dalrymple (1994) pp. 14–17, 38
  21. ^ Burchfield, Joe D. (1990-05-15). Lord Kelvin and the Age of the Earth. University of Chicago Press. pp. 69 ff. ISBN 9780226080437. Archived from the original on 2018-02-14.
  22. ^ Stacey, Frank D. (2000). "Kelvin's age of the Earth paradox revisited". Journal of Geophysical Research. 105 (B6): 13155–13158. Bibcode:2000JGR...10513155S. doi:10.1029/2000JB900028.
  23. ^ Origin of Species, Charles Darwin, 1872 edition, page 286
  24. ^ Borenstein, Seth (November 13, 2013). "Oldest fossil found: Meet your microbial mom". Excite. Yonkers, NY: Mindspark Interactive Network. Associated Press. Archived from the original on June 29, 2015. Retrieved 2015-03-02.)
  25. ^ a b c Dalrymple (1994) pp. 14–17
  26. ^ Paul J. Nahin (1985) Oliver Heaviside, Fractional Operators, and the Age of the Earth, IEEE Transactions on Education E-28(2): 94–104, link from IEEE Explore
  27. ^ Dalrymple (1994) pp. 14, 43
  28. ^ a b c Nichols, Gary (2009). "21.2 Radiometric Dating". Sedimentology and Stratigraphy. John Wiley & Sons. pp. 325–327. ISBN 978-1405193795.
  29. ^ Henri Becquerel (1896). "Sur les radiations émises par phosphorescence". Comptes Rendus. 122: 420–421.
  30. ^ Comptes Rendus 122: 420 (1896), translated by Carmen Giunta. Accessed 12 April 2021.
  31. ^ Henri Becquerel (1896). "Sur les radiations invisibles émises par les corps phosphorescents". Comptes Rendus. 122: 501–503.
  32. ^ Comptes Rendus 122: 501–503 (1896), translated by Carmen Giunta. Accessed 12 April 2021.
  33. ^ Curie, Pierre; Curie, Marie & Bémont, Gustave (1898). "Sur une nouvelle substance fortement radio-active, contenue dans la pechblende (On a new, strongly radioactive substance contained in pitchblende)". Comptes Rendus. 127: 1215–1217. Archived from the original on 6 August 2009. Retrieved 12 April 2021.
  34. ^ Curie, Pierre; Laborde, Albert (1903). "Sur la chaleur dégagée spontanément par les sels de radium". Comptes Rendus. 136: 673–675.
  35. ^ Joly, John (1909). Radioactivity and Geology: An Account of the Influence of Radioactive Energy on Terrestrial History (1st ed.). London, UK: Archibald Constable & Co., ltd. p. 36. Reprinted by BookSurge Publishing (2004) ISBN 1-4021-3577-7.
  36. ^ Rutherford, E. (1906). Radioactive Transformations. London: Charles Scribner's Sons. Reprinted by Juniper Grove (2007) ISBN 978-1-60355-054-3.
  37. ^ Eve, Arthur Stewart (1939). Rutherford: Being the life and letters of the Rt. Hon. Lord Rutherford, O. M.. Cambridge: Cambridge University Press.
  38. ^ Dalrymple (1994) p. 74
  39. ^ The Age of the Earth Debate Badash, L Scientific American 1989 esp p95 Archived 2016-11-05 at the Wayback Machine
  40. ^ Dalrymple (1994) pp. 77–78
  41. ^ Patterson, Claire (1956). "Age of meteorites and the earth" (PDF). Geochimica et Cosmochimica Acta. 10 (4): 230–237. Bibcode:1956GeCoA..10..230P. doi:10.1016/0016-7037(56)90036-9. Archived (PDF) from the original on 2010-06-21. Retrieved 2009-07-07.
  42. ^ Carlson, R. W.; Tera, F. (December 1–3, 1998). "Lead–Lead Constraints on the Timescale of Early Planetary Differentiation" (PDF). Conference Proceedings, Origin of the Earth and Moon. Houston, Texas: Lunar and Planetary Institute. p. 6. Archived (PDF) from the original on 16 December 2008. Retrieved 2008-12-22.
  43. ^ Dalrymple (1994) pp. 310–341
  44. ^ Dalrymple, Brent G. (2004). Ancient Earth, Ancient Skies: The Age of the Earth and Its Cosmic Surroundings. Stanford University Press. pp. 147, 169. ISBN 978-0-8047-4933-6.
  45. ^ Terada, K.; Sano, Y. (May 20–24, 2001). "In-situ ion microprobe U-Pb dating of phosphates in H-chondrites" (PDF). Proceedings, Eleventh Annual V. M. Goldschmidt Conference. Hot Springs, Virginia: Lunar and Planetary Institute. Bibcode:2001eag..conf.3306T. Archived (PDF) from the original on 16 December 2008. Retrieved 2008-12-22.

Bibliography

Further reading

  • Baadsgaard, H.; Lerbekmo, J.F.; Wijbrans, J.R., 1993. Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian-Maastrichtian stage boundary?). Canadian Journal of Earth Sciences, v.30, p. 769–775.
  • Baadsgaard, H. and Lerbekmo, J.F., 1988. A radiometric age for the Cretaceous-Tertiary boundary based on K-Ar, Rb-Sr, and U-Pb ages of bentonites from Alberta, Saskatchewan, and Montana. Canadian Journal of Earth Sciences, v.25, p. 1088–1097.
  • Eberth, D.A. and Braman, D., 1990. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation (Campanian) near Muddy Lake, west-central Saskatchewan. Bulletin of Canadian Petroleum Geology, v.38, no.4, p. 387–406.
  • Goodwin, M.B. and Deino, A.L., 1989. The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana. Canadian Journal of Earth Sciences, v.26, p. 1384–1391.
  • Gradstein, F. M.; Agterberg, F.P.; Ogg, J.G.; Hardenbol, J.; van Veen, P.; Thierry, J. and Zehui Huang., 1995. A Triassic, Jurassic and Cretaceous time scale. IN: Bergren, W. A.; Kent, D.V.; Aubry, M-P. and Hardenbol, J. (eds.), Geochronology, Time Scales, and Global Stratigraphic Correlation. Society of Economic Paleontologists and Mineralogists, Special Publication No. 54, p. 95–126.
  • Harland, W.B., Cox, A.V.; Llewellyn, P.G.; Pickton, C.A.G.; Smith, A.G.; and Walters, R., 1982. A Geologic Time Scale: 1982 edition. Cambridge University Press: Cambridge, 131p.
  • Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G., 1990. A Geologic Time Scale, 1989 edition. Cambridge University Press: Cambridge, p. 1–263. ISBN 0-521-38765-5
  • Harper, C.W. Jr (1980). "Relative age inference in paleontology". Lethaia. 13 (3): 239–248. Bibcode:1980Letha..13..239H. doi:10.1111/j.1502-3931.1980.tb00638.x.
  • Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E. and Kauffman, E.G. (eds.). Evolution of the Western Interior Basin. Geological Association of Canada, Special Paper 39, p. 379–396.
  • Palmer, Allison R (1983). "The Decade of North American Geology 1983 Geologic Time Scale". Geology. 11 (9): 503–504. Bibcode:1983Geo....11..503P. doi:10.1130/0091-7613(1983)11<503:tdonag>2.0.co;2.
  • Powell, James Lawrence, 2001, Mysteries of Terra Firma: the Age and Evolution of the Earth, Simon & Schuster, ISBN 0-684-87282-X