THE centuries-old idea that life was seeded from space was dusted off last week, thanks to a controversial study of a meteorite that struck Earth 40 years ago.
A team led by Zita Martins at Imperial College London claims it has found some of the fundamental chemical building blocks of our genetic code in the Murchison meteorite, which landed in Australia in 1969. In the mass of organic chemicals they isolated they found two ring-shaped carbon-containing molecules: uracil, a base that is essential for the creation of RNA, and xanthine, a close chemical relative of the DNA base, guanine.
Such chemicals have been found in a number of meteorites, but no one was sure whether they were extraterrestrial or the result of contamination since the meteorite landed. To find out where the bases formed, Martins and her colleagues measured the relative quantities of two different isotopes of carbon.
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The lighter version, carbon-12, is present on Earth in large amounts. Carbon-13 is more common in clouds of interstellar gas, and large amounts of it usually indicate the material did not form on Earth. The ratio of carbon-13 to carbon-12 was unusually high in the two bases, leading the team to conclude that the materials probably did not form on Earth (Earth and Planetary Science Letters, vol 270, p 130).
鈥淚t boosts the idea that the origin of life on Earth may have had an important contribution from an extraterrestrial object,鈥� says Martins.
鈥淭his boosts the idea that life on Earth may have had a contribution from space鈥�
It may be too early to conclude these bases formed beyond the Earth, says Sandra Pizzarello at Arizona State University, Tempe. Too many other chemicals were present in the samples to clearly distinguish the carbon ratio. 鈥淎nalytically, it鈥檚 not convincing,鈥� Pizzarello says. But she adds that the study 鈥渞aises a very interesting question that was raised a long time ago, but I don鈥檛 think it solves it鈥�.
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