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Thursday, April 12, 2007

Proterozoic Era

The Proterozoic, which lasted even longer than the Archean Era, saw the atmosphere changes from reducing to oxygenated, driving the original anaerobic inhabitants of the Earth into a few restricted anoxic refuges and enabling the rise of aerobic life (both prokaryote and the more complex eukaryotic cell, which requires the high octane boost that oxygen enables.) Stromatolites (colonial cyanobacteria), which had appeared during the Archean, were common. The modern regime of continental drift began, and saw the formation of supercontinent of Rodinia, and several extensive ice ages. Late in the Proterozoic a runaway icehouse effect meant that the preceding warm conditions were replaced by a "snowball" with ice several kilometers deep covering the globe. Warming conditions saw the short-lived Edicarian biota and finally the appearance of first metazoa.

Monday, April 02, 2007


Lasting more than twice as long as the Phanerozoic eon, the Archean was a time when diverse microbial life flourished in the primordial oceans, and the continental shields developed from volcanic activity. The reducing (anaerobic) atmosphere enabled archea (anaerobic microbes) to develop, and plate tectonics followed a regime of continental drift different to that of the Proterozoic and later. During this era, one type of organism, the Cyanobacteria (blue-green algae) produced oxygen as a metabolic by-product; the eventual build-up of this highly reactive gas was to eventually prove fatal to many life-forms, and converted the atmosphere from.