Earliest known life forms

The earliest known life forms found on Earth are fossils of microorganisms in 3.46 billion year old rocks in Western Australia.^[1] Life forms, as microorganisms, may have lived much earlier.

The earliest time that life forms first appeared on Earth is unknown. Life forms may have existed as early as 4.28 billion years ago, not long after the oceans were formed 4.41 billion years ago. That is not long after the formation of the Earth 4.54 billion years ago.^[2]

A life form, or lifeform, is an organism that is living. Estimates of the number of species of life forms on Earth range from 14 million, to as many as 1 trillion species.^[3] More than 99% of all species of life forms that have ever lived on Earth are thought to be extinct.^[4] Life forms may be found everywhere on Earth. This includes underground,^[5] possibly at least 12 miles deep underground,^[6] and the deepest parts of the oceans. Life can be found at least 47 miles high in the atmosphere^[7] and, under test conditions, it survives the vacuum of outer space.^[8]

According to one researcher, "You can find microbes everywhere – [they are] extremely adaptable to conditions, and survive wherever they are".^[9]

1. ↑ Tyrell, Kelly April (18 December 2017). "Oldest fossils ever found show life on Earth began before 3.5 billion years ago". University of Wisconsin-Madison. Retrieved 16 December 2018.
2. ↑ Betts, Holly C.; et al. (20 August 2018). "Integrated genomic and fossil evidence illuminates life's early evolution and eukaryote origin". Nature Ecology & Evolution. 2 (10): 1556–1562. doi:10.1038/s41559-018-0644-x. PMC 6152910. PMID 30127539.
3. ↑ Staff (2 May 2016). "Researchers find that Earth may be home to 1 trillion species". National Science Foundation. Retrieved 16 December 2018.
4. ↑ Kunin, W.E.; Gaston, Kevin, eds. (31 December 1996). The biology of rarity: causes and consequences of rare—common differences. Springer. ISBN 978-0412633805. Retrieved 16 December 2018.
5. ↑ Klein, JoAnna (19 December 2018). "Deep Beneath Your Feet, They Live in the Octillions - The real journey to the center of the Earth has begun, and scientists are discovering subsurface microbial beings that shake up what we think we know about life". The New York Times. Retrieved 21 December 2018.
6. ↑ Hadhazy, Adam (12 January 2015). "Life might thrive a dozen miles beneath Earth's surface". Astrobiology Magazine. Archived from the original on 16 August 2018. Retrieved 17 December 2018.
7. ↑ Loeb, Abraham (4 November 2019). "Did Life from Earth Escape the Solar System Eons Ago? - There's no proof that it happened—but it's not impossible". Scientific American. Retrieved 5 November 2019.
8. ↑ Dvorsky, George (13 September 2017). "Alarming Study Indicates Why Certain Bacteria Are More Resistant to Drugs in Space". Gizmodo. Retrieved 16 December 2018.
9. ↑ Choi, Charles Q. (17 March 2013). "Microbes thrive in deepest spot on Earth". Live Science. Retrieved 16 December 2018.