Roughly 550 million years ago the first complex animals, such as
trilobites, appear in the fossil record. Many scientists have concluded
that an increase in the amount of atmospheric oxygen was critical to
the relatively sudden evolution of these animals.

They knew that
photosynthetic organisms had been producing oxygen for hundreds of
millions of years, but what might have led to the apparently rapid
accumulation of the stuff in the atmosphere was a mystery. Now a team
of researchers argues that clay may have played a key role.

Geologist Martin Kennedy and his colleagues from the University of
California, Riverside realized that clay minerals in marine sediments
are responsible for trapping the organic carbon that would otherwise
bond with highly reactive oxygen. Today such clay minerals form in soil
when organisms such as microbes or fungi interact with tiny bits of
weathered rock. The resultant clay then washes down to the sea and
settles on the bottom, where the clay’s chemical properties actively
attract organic carbon and then absorb it, much like kitty litter. The
scientists reasoned that this so-called clay mineral factory might have
produced the sharp rise in oxygen availability that preceded the
flowering of complex life forms.

By David Biello

More here.