for National Geographic News
Some of life's raw ingredients may have originated in space, says a new analysis of an Australian meteorite that adds more fuel to the controversial theory.
Researchers discovered the organic molecules uracil and xanthine in the meteorite and confirmed they could not have formed on Earth.
These molecules, called nucleobases, are precursors to DNA, a set of genetic instructions for organisms on Earth. (Get the facts on DNA.)
Uracil and xanthine may also have been stepping-stones to RNA, which builds proteins in organisms.
"Emergent life systems may have adopted nucleobases from meteoritic fragments for use in an early and primitive genetic material, enabling them to pass on their successful features to the next generations," said study leader Zita Martins of Imperial College London.
The finding supports an idea first proposed by astronomer Carl Sagan and a colleague in 1992. Some of life's crucial building blocks, they said, were forged in the hearts of roving comets and asteroids, which seeded them throughout the cosmos.
(Related: "Did Comets Make Life on Earth Possible?" [October 2, 2003].)
"It could be that these molecules landed in just the right place at the right time and helped to make us what we are," said Max Bernstein, an astrochemist at NASA Ames Research Center in California who was not involved in the study.
The team dissolved and analyzed samples of the Murchison meteorite. The asteroid fragment had crashed into Australia in 1969 and is thought to be 4.5 billion years old—as old as our solar system.
The results also showed that the nucleobases contained a large ratio of a heavy form of carbon rarely found on Earth.
The nucleobases could have formed in space or in the interiors of asteroids, where the molecules would have been shielded from harsh ultraviolet light and other radiation, study leader Martins said.
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