Timeline
of human history
version 2 - by
Finn Sivert Nielsen
|
|
||
|
Timeline
3 - 2,000,000,000 BP to Present
|
||
|
Life
since the Huronian Glaciation. Sexual reproduction, predators & prey.
Animals diverge from plants
|
||
|
|
||
| During
the Huronian Glaciation life had kept alive in the deep oceans, perhaps
around underwater volcanic vents, under kilometer-thick layers of ice. When
released from the ice, life proceeded to diversify at a (relatively speaking)
rapid rate. Complex cell structures, large-scale colony structures (such
as reefs), sexual reproduction (assuring more rapid natural selection),
predators, and the fundamental division of animals from plants - all seem
to emerge during the next 2 billion years. And in the meantime, one supercontinent
has formed and disintegrated and another is reaching its maximum. As the second supercontinent (Rodinia) in turn starts disintegrating, at least two new "snowball earth" episodes take place. Clearly, the oxygen-to-CO2 ratios of the atmosphere are not robustly stable. But once again, the catastrophic glacial conditions seem to stimulate rather than obstruct the development of life, for shortly after the end of the last (Marioan) glaciation, the Cambrian Explosion takes place - the explosive evolution of complex life - plants and animals as we know them - in the geological epoch known as the Phanerozoic (which occupies 542 million years - a mere 12 percent of the Earth's age). This, among other things, is when life spreads from the sea to dry land - 420 million years ago. The Phanerozoic, moreover, coincides more or less with the age of the formation and disintegration of the third supercontinent (Pangea). Note finally the near-complete extinction of life in the great Permian Extinction (252 mill BP), while Pangea is at its maximum and the prevalent cold and arid conditions exacerbate the effects of the Permian catastrophe still further. |
||
© 2018 Finn Sivert Nielsen (fsnielsen.com)