THE first bacteria on Earth had a much easier time of it than previously
thought, despite living through massive asteroid bombardments.
Between 4.15 and 3.8 billion years ago, storms of asteroids battered the Moon
and Earth. While this “late heavy bombardment” was going on, the Earth’s surface
was uninhabitable, or so researchers used to think.
That assumption was challenged a few years ago when Steve Mojzsis of the
University of California at Los Angeles discovered hints of ancient
life—in the form of telltale ratios of carbon isotopes—in rocks that
appeared to be more than 3.85 billion years old.…
