Joel Achenbach writes:

The young Earth got beat up a lot, including one day 3.26 billion years ago when a rock four times the size of Mount Everest slammed into the planet. Scientists believe that the rock, which was much bigger than the Chicxulub object that ended the reign of the dinosaurs, probably landed in the ocean, since Earth had barely begun to form continents.

The collision was so violent it boiled off the top layer of that ocean and, near the impact site, created a tsunami as high as a New York skyscraper. Molten rock rained from the sky. The atmosphere was choked with ash and dust. The planet descended into darkness.

But it wasn’t all bad.

That was the counterintuitive implication of three presentations at the American Geophysical Union’s fall meeting in San Francisco this month. The scientists, working independently, found that the bludgeoning of young Earth by giant space rocks may have primed the planet to be more congenial to life.

Calamity is followed by opportunity: There is a lesson here for everyone, written in the geophysical record. Earth has been through hell and back — smashed, melted, frozen, depending on which eon or epoch is under discussion.

But the first couple billion years of Earth’s history remain hazy. No one knows how, amid the chaos and tumult of that time, life emerged and evolved into more complex organisms.

The story of how this planet became habitable is relevant to the young science of astrobiology, which probes the hypothetical existence of life on other worlds. Our own solar system has abundant examples of planets and moons that are inhospitable. Earth is an anomaly, riotous with living things. What happened to make it so?

As researchers probe the distant past, giant impacts loom large. [Continue reading…]