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Originally Posted by blueend
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that's what they say,
big bang 13.7 billion years ago (bya)
solar system formed 12 bya
earth born 4.6 bya
surface cooled enough to solidify (oldest known rocks) 3.8 bya
life formed 3.5 bya
[immediately after the first rocks formed!!!]
oxygen build up 2.2 bya (almost wiped out
all life on earth!)
humans originated 200,000 years ago (ya)
It's amazing how quickly life formed after the surface of the earth was cool enough to solidify into rocks! The first fossils, dating 3.5 billion years are
Cyanobacteria (aquatic, photosynthetic bacteria), these little suckers are
still around today!! That's 3.5 billion years of continual existence!
At about 2.5 bya, after a billion years of Cyanobacteria releasing oxygen into the atmosphere, all life on earth was almost eradicated by the release of this oxygen. It plunged the earth into an ice age and killed off virtually every living creature on the planet.
Quote:
Organisms, which had lived on earth without oxygen, could no longer exist ever since oxygen was added in the atmosphere. Because once oxygen intrudes in cells of their body, all the components start to dissolve by oxidization. In other words, for creatures, which did not have mitochondria, oxygen worked as a highly toxic substance.
Today all life on earth can trace its lineage back to those few microorganisms which survived the great dying of 2,500,000,000 BC.
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http://www.damninteresting.com/?p=673
http://www.ucmp.berkeley.edu/bacteria/cyanointro.html
http://www.ersdac.or.jp/Others/geoes..._text_05_e.htm