years ago - cyanobacteria. They caused what was quite possibly the greatest die-
off in Earth’s history - termed the “oxygen holocaust” by the dramatic and the
“oxygenation catastrophe” by the somewhat more sedate. See - the earliest atmosphere
was anoxic - virtually no oxygen whatsoever. When cyanobacteria developed photosynthesis
they started cranking out oxygen. But since all of the iron and other metals in Earth’s
crust were in a reduced form, the oxygen was sucked up by the metals as soon as it was
formed. In effect, the Earth’s crust rusted. It took nearly 2 billion years for all of
the iron and other metals in the crust to fully rust - only then could oxygen start to
accumulate in the atmosphere. Oxygen - especially to an anaerobic organism - is incredibly
toxic. So as oxygen started to accumulate in the atmosphere, the organisms (mostly bacteria
and algae) started to die horrible deaths. Well…OK…maybe not horrible. But they died.
Only a handful of lucky survivors (about 1% of life on Earth) made it through to give
rise to all of the oxygenated glory we see around us today. So - yeah - earthly life
was almost extinguished by oxygen about 2.3 billion years ago. Compared to that, humanity
isn’t that big a deal - even with (Al Gore's) global warming.
- No Al Gore
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