Historical geology

Historical geology is the use of the principles of geology to reconstruct and understand the history of the Earth. It focuses on geologic processes that change the Earth's surface and subsurface; and the use of stratigraphy, structural geology and paleontology to tell the sequence of these events. It also focuses on the evolution of plants and animals during different time periods in the Geological timescale. The discovery of radioactivity and the development of a variety of radiometric dating techniques in the first half of the 20th century provided a means of deriving absolute versus relative ages of geologic history.

Economic geology, the search for and extraction of energy and raw materials, is heavily dependent on an understanding of the geological history of an area. Environmental geology, including most importantly the geologic hazards of earthquakes and volcanism, must also include detailed knowledge of the geologic history of an area.

Historical development

Nicolaus Steno, also known as Niels Stensen, was the first to observe and propose some of the basic concepts of historical geology. One of these concept was that fossils originally came from living organisms. The other, more famous, observations are often grouped together to form the laws of stratigraphy.

James Hutton and Charles Lyell also contributed to early understanding of the Earth's history with their observations at Edinburgh in Scotland concerning angular unconformity in a rock face. Hutton first proposed the theory of uniformitarianism, which is a basic principle in all branches of geology. Hutton also supported the idea that the Earth was very old as opposed to prevailing concept of the time which said the Earth had only been around a few thousand years. Uniformitarianism describes an Earth created by the same forces of nature that are at work today.

The prevailing concept of the 18th century was that of a very short Earth history dominated by catastrophic events. This view was stronly supported by religious thinkers based on a largely literal interpretation of biblical passages. The concept of uniformitarianism met with considerable resistance and the catastrophism vs. gradualism debate of the 19th century resulted. A variety of discoveries in the 20th century provided ample evidence that Earth history is a product of both gradual incremental processes and sudden cataclysmic events. Violent events such as meteorite impacts and large volcanic explosions do shape the Earth's surface along with gradual processes such as weathering, erosion and deposition much as they have throughout Earth history. The present is the key to the past - includes catastrophic as well as gradual processes.