Creative Destruction on a Cosmic Scale

In a paradox of creation, new evidence suggests that devastating avalanches of cosmic debris may have fostered life on Earth, not annihilated it.

Astronomers world-wide have been transfixed by a roiling gash the size of Earth in the atmosphere of Jupiter, caused by an errant comet or asteroid that smashed into the gas giant last month. The lingering turbulence is an echo of a cataclysmic bombardment that shaped the origin of life here 3.9 billion years ago, when millions of asteroids, comets and meteors pummeled our planet.

Until recently, many researchers thought that this rain of rocks, lasting 20 million years or more, almost certainly wiped out early life on Earth -- perhaps more than once. No one knows. The earliest known traces of life belong to a period shortly after the asteroid showers slackened.
In their super-heated plunge through the atmosphere, these asteroids and meteors may have helped create conditions ideal for emerging life. "Everyone focuses on the meteor that hits the ground," says geochemist Richard Court at London's Imperial College. "No one thinks about the products of its journey that get pumped into the atmosphere."

As they vented, they collectively could have imported billions of tons of life-sustaining water into the air every year, Dr. Court and his colleague Mark Sephton recently determined. They calculated that these showers of volatile rocks delivered 10 times the daily outflow of the Mississippi River every year for 20 million years. By analyzing the fumes emitted under such extreme heat, they discovered these rocks also could have injected billions of tons of carbon dioxide into the air every year.

Combined with so much water vapor, the carbon dioxide could have induced a global greenhouse effect. That could have kept any life emerging on Earth safely in a planetary incubator at a time when the planet might easily have frozen because the Sun radiated 25% less energy than today. "The amount of CO2 that was produced is about the same we produce today through fossil fuel use and we know that is a climate-changing volume," says Dr. Court.

In fact, evolving microbes of the sort considered ancestral to all life forms today may have flourished underground in water heated by the impacts. Such habitable havens actually expanded during the bombardment, the computer simulation showed. Microbes able to live at temperatures ranging from 175 degrees to 230 degrees Fahrenheit could have survived unscathed. Some bacteria today thrive in even hotter water, such as those in hydrothermal vents at Yellowstone National Park.

In a report released Wednesday, a panel of experts convened by the U.S. National Research Council warned that Earth could still be blindsided. They are studying ways to safely deflect any that do come too close.

In this game of orbital roulette, Dr. Yeomans does have his eye on one large near-Earth asteroid called Apophis. On its next close approach past Earth, there is a 1-in-45,000 chance that the interplay of gravitational forces could nudge it onto a potential collision course.

"In the unlikely event that happens, it will come back and hit us on April 13, 2036," Dr. Yeomans says. "That's Easter Sunday."

by Robert Lee Hotz
Printed in The Wall Street Journal