The meteorite that some suspect doomed the dinosaurs also carried with it extraterrestrial gases trapped in tiny carbon cages called buckyballs, scientists report in the 28 March Proceedings of the National Academy of Sciences. The discovery confirms earlier claims that meteors can bring gases to Earth--and, some say, perhaps even introduce new organic compounds that may alter the course of evolution.
Buckyballs, also called fullerenes, are molecular carbon cages of at least 60 atoms that resemble the geodesic domes designed by their namesake, R. Buckminster Fuller. Scientists first synthesized a buckyball on Earth in the mid-1980s by zapping carbon with high-intensity laser beams. Similar conditions can be found in the atmospheres of some middle-aged stars that have fused hydrogen and helium to produce a ready supply of carbon. When a buckyball forms, it traps nearby gas, leading many scientists to suggest that the nearly diamond-hard fullerenes could have survived interstellar travel and carried other materials to Earth.
In a 1996 study, geochemist Luann Becker of the University of Hawaii, Manoa, noble gas chemist Robert Poreda of the University of Rochester, and space scientist Ted Bunch of NASA's Ames Research Center in California treated small samples of two meteorites--the Mexican Allende meteorite and Australian Murchison meteorite--with an organic solvent to extract the fullerenes, then heated them up under a vacuum to drive out the trapped gases. Sure enough, they found helium and several other noble gases; the isotopes helium-3 and -4 appeared in a ratio found only in space.
But those meteorites were only about the size of charcoal briquettes, leaving scientists to wonder if buckyballs could also survive catastrophic impacts of giant meteorites and spread globally. The answer appears to be yes. Becker's team collected samples of sediment deposited around the world by the asteroid that slammed into Earth 65 million years ago, killing the dinosaurs and many other species. Using the same extraction technique, they isolated samples of fullerenes from each location, and again they found extraterrestrial helium preserved inside the buckyballs. "This is strong evidence that objects falling onto the Earth come in with fullerenes," says Martin Saunders, a chemist at Yale University in New Haven, Connecticut.
Although the team has not detected any organic molecules, Becker says it's possible that they, too, were part of some buckyballs' cargo. "If so, they could have contributed to the synthesis of new organic molecules on Earth," she says.