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Did Life Survive the Late Heavy Bombardment?

John on May 21, 2009 at 4:07 pm

From Science Daily, an announcement that is almost certainly more important than the “missing link” story earlier this week:

The bombardment of Earth nearly 4 billion years ago by asteroids as large as Kansas would not have had the firepower to extinguish potential early life on the planet and may even have given it a boost, says a new University of Colorado at Boulder study.

Impact evidence from lunar samples, meteorites and the pockmarked surfaces of the inner planets paints a picture of a violent environment in the solar system during the Hadean Eon 4.5 to 3.8 billion years ago, particularly through a cataclysmic event known as the Late Heavy Bombardment about 3.9 billion years ago. Although many believe the bombardment would have sterilized Earth, the new study shows it would have melted only a fraction of Earth’s crust, and that microbes could well have survived in subsurface habitats, insulated from the destruction.

“These new results push back the possible beginnings of life on Earth to well before the bombardment period 3.9 billion years ago,” said CU-Boulder Research Associate Oleg Abramov. “It opens up the possibility that life emerged as far back as 4.4 billion years ago, about the time the first oceans are thought to have formed.”


The researchers concluded subterranean microbes living at temperatures ranging from 175 degrees to 230 degrees Fahrenheit would have flourished during the Late Heavy Bombardment. The models indicate that underground habitats for such microbes increased in volume and duration as a result of the massive impacts. Some extreme microbial species on Earth today — including so-called “unboilable bugs” discovered in hydrothermal vents in Yellowstone National Park — thrive at 250 F.

The Hadean Era is so named for the Hades which is of course the mythical Greek version of hell. My understanding is that scientists in the field have also argued about whether the first life received energy from the sun or from undersea vents. These two options are sometimes called the “heaven and hell” scenarios. Based on this discovery it sounds like hell has the upperhand.

Related: Evidence for ancient life on Earth.

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