Oxygen drives the biosphere—we can’t live without
it. But most scientists now agree that there was
no free oxygen in the air during the earliest portion
of Earth’s history. The first oxygen came from a
group of bacteria—the cyanobacteria—that had
developed a new method of photosynthesis. Their
method was so efficient that they spread rapidly
throughout the oceans of the world and overtook
their less-efficient predecessors. But their success
may have created a catastrophic climate disaster
that plunged Earth into a global deep freeze for
tens of millions of years and almost wiped out life
on the planet forever. That, at least, is a scenario
I have developed in collaboration with geobiology
grad student Bob Kopp
