Earth

The Earth is home to millions of species of plants and animals, including humans.

Earth is the only planet in the galaxy which is known to support life. Earth has many places that are suitable for humans to live; although, some areas of the planet can be dangerous for humans or uninhabitable.

Science shows that Earth formed around 4.5 billion years ago. The organisms that live on Earth have completely changed its air (atmosphere); this is called a biosphere. 71% of Earth's surface is covered in salt water oceans. Earth is the only place in the Solar System where liquid water is known to exist at present. The other 29% is made of rocky land in the shape of continents and islands. Earth interacts with other objects in the Solar System, particularly the Sun and the Moon. The Earth orbits the Sun roughly once every 365.25 days. One spin is called a day and one orbit around the Sun is called a year. This is why there are 365 days in a year, but a leap day added to the calendar once every 4 years.^[1]

^ Steffen, Will; Richardson, Katherine; Rockström, Johan; Schellnhuber, Hans Joachim; Dube, Opha Pauline; Dutreuil, Sébastien; Lenton, Timothy M.; Lubchenco, Jane (2020-01). "The emergence and evolution of Earth System Science". Nature Reviews Earth & Environment. 1 (1): 54–63. doi:10.1038/s43017-019-0005-6. ISSN 2662-138X. {{cite journal}}: Check date values in: |date= (help)

[1] Steffen, Will; Richardson, Katherine; Rockström, Johan; Schellnhuber, Hans Joachim; Dube, Opha Pauline; Dutreuil, Sébastien; Lenton, Timothy M.; Lubchenco, Jane (2020-01). "The emergence and evolution of Earth System Science". Nature Reviews Earth & Environment. 1 (1): 54–63. doi:10.1038/s43017-019-0005-6. ISSN 2662-138X. {{cite journal}}: Check date values in: |date= (help)

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