Quote:
Originally Posted by RWebb
IIRC, the collision was pre- O2 Earth.
O2 was produced as a waste product by "blue-green algae" - a significant metabolic innovation that killed off almost everything else on the planet (except for tetanus and a few other anaerobes). It was the greatest extinction in Earth history, but usually not counted as little is known that far back.
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+1 on pre-O2. Wiki describes Earth as "proto-Earth" when impact occurred.
Cool factoid on introduction of oxygen.
https://en.wikipedia.org/wiki/Theia_(planet)