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How a comet impact may have jump-started life on Earth -- and elsewhere

Did life on Earth come from space? The scientific evidence is mounting.

A new report suggests amino acids, the chemical building blocks necessary for life as we know it, may be scattered throughout the solar system, created when high-speed comets smacked into the icy moons of Jupiter and Saturn, and rocky planets like our very own Earth.

"Amino acids have very basic starting materials -- you need some kind of carbon source like methane or carbon dioxide, a nitrogen source like ammonia, and water ice," said Nir Goldman, a physical chemist at the Lawrence Livermore National Laboratory in California and a co-author of the study published Sunday in the journal Nature Geoscience. "Comets have all these things in abundance."

PHOTOS: Moons of the solar system

Since 2006, Goldman has been working on a theory known as shock synthesis. It predicts that when a comet slams into another rocky or icy body, the heat and pressure from the impact cause the chemical bonds in the comet's head to break apart while new bonds form.

"Amino acids are just one of the things that are formed, but they are almost guaranteed to form," he said.

Goldman tested his theory using elaborate computer models. Then a team of scientists put shock synthesis to test in the lab. 

After meeting Goldman at a conference, Mark Price of the University of Kent in England offered to re-create the conditions of a comet impact in his lab. Price, who has one of the coolest jobs ever, works with a powerful gun more than 15-feet long that can shoot a projectile faster than 4 miles per second. 

Price and his team created a block of ice with the same chemical composition observed in comets like Halley and Hale-Bopp. The scientists split each block of ice in two, then shot one half with a 2-mm round steel ball -- "basically a ball bearing," Price said.

Both samples were melted down, the water was allowed to evaporate, and then Zita Martins, a chemist at the Imperial College London, analyzed the remaining mixture for amino acids. 

They did the experiment twice. Each time, Martins found amino acids in the sample that had been shot -- but no amino acids in the control sample. 

"When we got the results, I was like, 'What do you mean it worked?'" said Price. "It wasn't that I disbelieved Nir Goldman's theory, but it raised some eyebrows in the lab. But we got repeatable results, and that's when we were finally convinced it was working."

In the paper, the scientists write that the results of their experiment present a significant step forward in our understanding of the origin of the building blocks of life and where we might find them.

"What is interesting about this work is that the amino acids could be synthesized regardless of the chemical conditions of the impact site," Goldman said. "In that sense, a comet could hit Earth, or a moon of Saturn or Jupiter and the same process would occur."  

Martins puts it this way: "This study increases enormously the places where we might look for life."

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