Was life founded on cyanide from space crashes?
By David Shiga (Image: P. H. Schultz, Brown University and AVGR) Life may have been built on a foundation of cyanide formed in the fiery wakes of asteroids plunging through Earth’s atmosphere, high-speed impact experiments suggest. Earth was probably not born with much in the way of organic material – the complex molecules containing carbon that life requires. It formed too close to the sun for such compounds to condense from the swirling primordial disc of gas and dust. One possibility is that organic matter formed on Earth after the planet coalesced, for example in chemical reactions induced by lightning arcing through the atmosphere, as experiments by Stanley Miller at the University of Chicago in the 1950s suggested. But the chemical reactions in this process could happen only in an early atmosphere full of methane and hydrogen, and later studies of the ancient geological record have suggested that was unlikely. Others have suggested the building blocks came from comets and asteroids that struck Earth, because these objects are known to contain high concentrations of organic material. But the tremendous heat of impact would have burned up much of that material, converting it into simpler molecules like carbon dioxide. Now another way for organic material to appear on Earth has been demonstrated. New experiments show that although impacts destroy the original organic molecules in comets and asteroids, they may help create new ones at the same time. “The idea in the past has been, ‘Any of this stuff coming through the atmosphere would be heated to the point where it would get wasted,'” says Peter Schultz of Brown University in Providence, Rhode Island, one of the experimenters. “What this new work did was to show that we might actually revive these compounds.” With Seiji Sugita of the University of Tokyo, Japan, Schultz simulated asteroid and comet impacts by firing projectiles made of polycarbonate plastic, an organic material, as fast as 6 kilometres per second at metal targets in a laboratory at the NASA Ames Research Center in Moffett Field, California. The projectiles were vaporised in a flash of light, just as an asteroid or comet would be on impact with Earth’s surface. Analysis of the spectrum of the flashes revealed abundant cyanide – a compound consisting of a carbon atom bound to a nitrogen atom – formed by chemical reactions between the projectile’s carbon and nitrogen in the air. Cyanide compounds are very reactive, so further reactions involving them on early Earth could have led to more complex carbon-containing molecules important to life, Sugita and Schultz argue. The nitrogen in the cyanide compounds could have been especially important, since it is an ingredient of amino acids – key building blocks for life – but is relatively scarce in the raw organic material of asteroids. Donald Brownlee of the University of Washington in Seattle, who was not involved in the study, says some of early Earth’s organic material undoubtedly formed this way. But he adds that there were probably other sources too, including organic-rich particles of interplanetary dust, which fall to Earth more gently than asteroids and comets. “It gets warmed but it doesn’t get extremely hot,” he says. Journal reference: Geophysical Research Letters, DOI: 10.1029/2009gl040252 More on these topics: