If
you think that Early Earth, without industrial pollutants from
humankind whatsoever, smelled fresh and natural, you'd be in for a rude
and stinky surprise.
Scientists have determined that billions of years ago, Earth smelled of rotten eggs (irony: no chicken then, either):
Their
work has revealed spherical and rod-shaped bacteria dining on the
cylindrical outer shells of another, larger bacterium known as
Gunflintia. To digest those Gunflintia sheaths, the feeding bacteria
would have had to use oxygen atoms taken from salts, or "sulfates," in
seawater. In the process, the microbes formed gaseous carbon dioxide,
which would have been released into the atmosphere.
Another
byproduct of this biochemical process is hydrogen sulfide, which
produces a stench commonly known as "the rotten egg smell," explained
Martin Brasier, a paleobiologist at Oxford University in London.
"The
whole world didn't smell of rotten eggs," said Brasier, "but if you had
a sensitive nose, it would have been very widespread indeed."
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