Development of Earth and Its Inhabitants
- 4.5 billion years ago
What happened? Earth formed from particles and matter distributed throughout the developing solar system by the explosion of a dying star. This early Earth was hot, covered in magma and bombarded by a constant barrage of space debris (1).
How do we know?
Scientists are able to determine the age of radioactive isotopes trapped in rocks to figure out when our planet was formed. For more information, check out the wiki article on radiometric dating and the article’s associated source links (1).
- 4.3 billion years ago
What happened? Earth had cooled, over time, to less than 100 degrees Celsius, which is less than 212 degrees Fahrenheit. This was cool enough for condensed water to fall to Earth and for oceans to form.
How do we know? The mineral zircon holds some of these answers in the form of isotopic oxygen ratios trapped within its crystal matrix (1).
- 3.86 billion years ago
What happened? Further evidence that Earth was cool enough for liquid water.
How do we know? Geologists evaluated the chemical composition of some very old rocks in Greenland and realized that they formed under water. They dated these rocks as approximately 3.86 billion years old (1).
- 3.5 billion years ago
What happened? Microbial life was present on Earth.
How do we know? Scientists found stromatolite fossils, formed from Chloroflexus bacteria’s ancestors (1). Stromatolites, layered communities of phototrophic microbes, are believed to have been the first life on Earth (2). Fossilized stromatolites are commonly found on beaches, with the largest number at Shark Bay, Australia – which was designated a World Heritage Area in 1991 by the United Nations Educational, Scientific and Cultural Organisation, who realized the importance of these formations (3).
- 2.5 billion years ago
What happened? Oxygen present in Earth’s atmosphere in substantial levels.
How do we know? Significant development of oxygen on Earth is evident in banded iron formations of rock. These red lines in sedimentary formations show that oxygen was present in high enough levels to oxidize reduced iron. This is commonly known as the Great Oxidation Event (1). Availability of oxygen lead to further development of microbial life.
- Madigan, M. T., Martinko, J. M., Stahl, D. A., and Clark, D. P. (2012). Brock Biology of Microorganisms. San Francisco, CA. Benjamin Cummings.
- Tewari, V. C., & Seckbach, J. (2011). Stromatolites [electronic resource] : interaction of microbes with sediments / Edited by Vinod C. Tewari and Joseph Seckbach. Dordrecht ; New York : Springer, c2011.
- Government of Western Australia: Department of Parks & Wildlife (2009). Stromatolites of Shark Bay. Retrieved 6 Dec. 2014 from <http://www.sharkbay.org>.