EARLY EARTH WAS RIPE FOR LIFE, SCIENTISTS DISCOVER

Even during an extraordinarily violent era in Earth's early history, when our young planet was being whacked by asteroids and comets so frequently that scientists refer to it as "Late Heavy Bombardment," conditions most of the time at the Earth's surface were quite hospitable for the microbes that lived here.

That is the conclusion of research by Rochester scientists presented at the annual December meeting of the American Geophysical Union.

By making fine measurements of a kind of stardust carried to Earth by asteroids and comets some 4 billion years ago, a team led by geochemist Ariel Anbar and graduate student Gail Arnold has determined that only rarely-perhaps once every 30 to 100 million years-was the bombardment from the skies so severe that microbes would have had a difficult time surviving at the Earth's surface.

Even in such instances, scientists say, hardy bacteria and viruses could have found sheltered places, such as beneath the Earth's crust or deep in the ocean near thermal vents, to ride out the storm.

"It's been the conventional wisdom that with all this bombardment, life should be very hard to maintain, and some scientists have argued that the Earth's surface wasn't habitable," Anbar says.

"It was a violent period in Earth history. Sure, every 30 million years or so life would have been really challenging. But if microbes could find places to ride out the big impacts, there is no reason that they wouldn't be able to repopulate the surface and flourish."

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