Down-to-Earth Theory : Science Ponders If Life Got Off to a Rocky Start

Some scientists have a down-to-earth theory about how life began: The chemicals needed for life already were in rocks on Earth and were freed when meteorites bombarded the planet.

Rocks were not previously considered a source for the building blocks of life but were thought to be potential sites for chemical reactions that helped produce the more complex substances leading to life, the authors of a new study said.

“What we are trying to do is examine a potential source of organic material that has not been examined,” said chemist Sherwood Chang of the National Aeronautics and Space Administration.

Citing the controversial theory that asteroids smashing into Earth caused extinction of dinosaurs and other creatures, Chang said it seems “appropriate to ask whether the (earlier) impact of meteorites played a role in the origin of the materials necessary for life.”

Chang and other researchers conducted an experiment in which olivine, a mineral common in Earth’s rock, was cracked open in a vacuum chamber.

Complex Organic Gases

The scientists found that carbon, hydrogen, oxygen and nitrogen--which were dissolved in olivine as impurities--migrated to the freshly cracked surface. There, they combined to form water vapor, carbon dioxide, methane and a surprising variety of the fairly complex organic gases needed for life to begin, Chang said.

The scientists calculated that under ideal conditions, rocks on the early Earth cracked open by meteorites could release about a million-billion tons of organic compounds, an amount roughly equal to that on Earth today. That does not count any organic chemicals released from meteorites as they cracked.

“We therefore conclude that, if the processes described here have occurred on the early Earth, a large reservoir of organic compounds may have been produced by biogenic elements dissolved in solid rocks,” the researchers wrote.

The study was conducted by chemists Friedemann Freund and Chang, from NASA’s Ames Research Center in Mountain View; physicist J. Thomas Dickinson of Washington State University in Pullman; and Christopher Becker and Minoru Freund, physicists at SRI International, a private research center in Menlo Park.

Scientists have proposed numerous possible sources of the organic gases needed for life to start. Most believe that the building blocks of life developed from gases already in Earth’s primitive atmosphere, although there is debate about the makeup of that atmosphere.

Quantity Questioned

Chang said it is uncertain whether rocks struck by meteorites could release enough organic compounds to start life, even though extraterrestrial objects once bombarded Earth far more frequently than they do today.

Jeffrey Bada, a marine chemist at the Scripps Institution of Oceanography, agreed, saying it is premature to consider rocks cracked by meteorites “a viable source of organics.”