San Francisco
DID comet power spark life on Earth? Researchers in California are suggesting
that comets might not only have provided the starting material, but could also
have supplied the energetic push that got biological chemistry rolling.
About 4 billion years ago, comet impacts were a thousand times as frequent as
they are now. Comets are made up of volatile ices and carbon compounds, which at
first glance seem the perfect ingredients to get life鈥檚 chemistry started.
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However, comets must have reached temperatures of more than 10 000 掳C as
they burnt up in the atmosphere. 鈥淭hey were coming in so fast and so hot that
any decently sized molecule got blown to smithereens,鈥� says Chris McKay, a
geochemist at NASA Ames Research Center in Moffett Field, California.
Despite this, McKay has shown that the comets may have been the source of
complex molecules after all. He calculated that if a comet鈥檚 molecules broke up
into elements at high temperatures, they would recombine as they cooled to leave
water, carbon dioxide, methane, nitrogen and hydrogen sulphide.
What鈥檚 more, says McKay, his team鈥檚 experiments suggest that subsequent
impacts might have provided the energy to transform these compounds into more
complex ones. The researchers took a jar filled with the comet gases, and
focused a laser onto them to deliver a 30 000 掳C pulse of heat. As they
report in last week鈥檚 Science (vol 276, p 390), this created at least a
dozen new compounds, some with chains six carbon atoms long.
鈥淢ost people think of these impacts as bad and destructive,鈥� says Norman
Sleep of Stanford University in California. 鈥淗ere they show they can actually
provide the basic building blocks of life.鈥�