Through the Looking Glass

By Carl Zimmer|Thursday, August 01, 1996
RELATED TAGS: METEORS & ASTEROIDS
The dozen or so small rocks in Jeffrey Bada’s lab are nondescript but far from ordinary. They come from a crater near Sudbury, Ontario, that formed 1.85 billion years ago, when a meteorite the size of Mount Everest slammed into Earth. Canadian geologists sent the rocks to Bada, a geochemist at the Scripps Institution of Oceanography, to see if they contained any organic carbon molecules. Not likely, Bada thought: if the molecules hadn’t been incinerated on impact, they would have been destroyed--probably by hungry microbes--long ago. Bada put the rocks on a shelf for a few years.

That was a mistake. The rocks, it turns out, do contain organic carbon--in the form of buckyballs, the molecular soccer balls named for Buckminster Fuller and his geodesic domes. And not just any buckyballs-- these seem to have been made outside the solar system, near a red giant star.

Buckyballs have popped up in some strange places in the decade since their discovery, and that’s what finally led Bada to take a look at his Sudbury rocks. If buckyballs can form in candle soot and lightning- struck soil, he reasoned, maybe they formed in a meteorite impact as well, from other organic carbon molecules vaporized in the explosion. Unlike amino acids that Bada has extracted from more recent impact deposits, buckyballs might stick around forever--or at least 1.85 billion years. They’re stable, and nothing’s going to eat them, says Bada.

He gave the rocks to a graduate student named Luann Becker to analyze. She dissolved away bits of rock until she was left with a black, powdery carbon residue. Then she dissolved the residue in a solvent called toluene. The solution turned purple--which is what buckyballs invariably do to toluene.

Although interesting, this was hardly startling. But not long after Becker and Bada published their results, other labs managed to trap atoms inside the cagelike structure of buckyballs. If, as the Scripps team thought, their buckyballs had formed during an impact, this new research suggested the buckyballs might have engulfed some atoms from the 1.85- billion-year-old air. Becker and Bada worked with Robert Poreda at the University of Rochester to see what was inside their buckyballs. They heated some slowly to split the molecular bonds and release any trapped atoms--and that’s when they found something surprising.

One in every million of the Sudbury buckyballs burped out a helium atom. That doesn’t sound like a lot, but it’s actually so many that the buckyballs couldn’t have formed after the meteorite impact, in Earth’s helium-poor atmosphere. In fact, they must have formed in a place where the pressure of helium was 500 times the pressure of Earth’s entire atmosphere. More proof came in the ratio of different types of helium isotopes in the buckyballs: it was unlike anything found in the solar system. That blew our minds, says Bada.

The only place with such abundant helium is the neighborhood of dying red giant stars. Apparently, Bada says, the buckyballs formed near another star billions of years ago, got swept into a meteor as our solar system formed, and survived its impact in Canada--an event that released 1,000 times the energy of all the world’s nuclear arsenals. Perhaps, Bada speculates, the surviving buckyballs were in small pieces that broke off the meteorite in the atmosphere and didn’t crash as hard as the main rock.

In any case, says Bada, the buckyballs’ survival has an important implication. Life on Earth needed carbon-based molecules to get started. But according to the best estimates, Earth’s early atmosphere didn’t have much organic carbon. That has led some researchers to suggest that meteorites or comets could have delivered the organic carbon. One of the many critics of that hypothesis had been Bada. I’d always been an opponent of the impact-delivery scenario. These are high-energy events, and organic molecules are fragile and get destroyed when you heat them, he explains.

Now Bada thinks the idea is not so far-fetched after all. It’s not often that researchers prove themselves wrong, he says. But here at Sudbury, we have an example of at least one kind of organic carbon molecule surviving.
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