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Alien impact
01 April 2000
From New Scientist Print Edition.
Hazel Muir

It's blamed for obliterating the dinosaurs, but that famous asteroid or comet impact did more—it sprinkled buckyballs containing extraterrestrial gases all over the Earth. Scientists say this backs the idea that earlier impacts enriched the primeval soup of organic chemicals that gave rise to life.

Several years ago, Luann Becker and Jeffrey Bada of the Scripps Institution of Oceanography in San Diego found buckyballs—tiny cages of carbon atoms—in the debris of an impact crater in Canada. Trapped inside these 60 and 70-carbon molecules was a mixture of helium isotopes more typical of interstellar space than Earth's atmosphere, hinting that they formed in space and travelled to Earth on the meteorite (New Scientist, 20 April 1996, p 17).

But critics argued that all these buckyballs might have formed in the heat of the impact, or in wildfires that followed it. So to find out more, Becker and her colleagues have looked at debris from another impact: the one thought to have wiped out the dinosaurs 65 million years ago. Debris from this bombshell, which sprayed into the atmosphere and rained down all over the world, is preserved in ancient sediments.

In samples of this debris from New Zealand, Denmark and Colorado, and in samples from two meteorites, Becker's team has again found buckyballs—some as large as C400. When opened up in the lab, these contained mixtures of inert gases that the team says "can only be described as extraterrestrial in origin". "We've pretty much nailed it this time," says Becker, now at the University of Hawaii in Honolulu.

She adds that if organic compounds could survive the plunge to Earth, this supports the idea that early impacts enriched the primordial soup of chemicals that gave rise to life. And buckyballs that have survived might provide the best record of Earth's impact history, giving clues to unexplained mass extinctions such as the one 250 million years ago. "It was close to complete sterilisation, wiping out nearly every living organism on the planet," says Becker. "But so far there's no evidence for an impact."

The work should also help astronomers to pinpoint the birthplaces of buckyballs in space. "Meteorites are like the garbage cans of the Universe—they pick up everything that's out there and give you hints about how they formed," says Becker. Buckyballs could have formed in the atmospheres of old stars called red giants in the twilight of their lives.

From issue 2232 of New Scientist magazine, 01 April 2000, page 9

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