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updated 6/13/2008 5:33:19 PM ET 2008-06-13T21:33:19

We may all be aliens, it seems.

Some of the building blocks of life on Earth came from space, according to a new study of molecules in meteorite fragments.

The study confirmed that some of the raw material for DNA and RNA found in a meteorite did not contaminate the rock after it landed on Earth, but actually originated in space.

The materials in question are the molecules uracil and xanthine, which are precursors to the compounds that make up DNA and RNA, and are known as nucleobases.

"We believe early life may have adopted nucleobases from meteoritic fragments for use in genetic coding which enabled them to pass on their successful features to subsequent generations," said the study's lead author, Zita Martins, a researcher in the Department of Earth Science and Engineering at Imperial College London.

Martins and her colleagues detailed their findings in the June 15 issue of the journal Earth and Planetary Science Letters.

The team discovered the molecules in rock fragments of the Murchison meteorite, which crashed in Australia in 1969. The scientists analyzed the genetic building blocks and found that they contain a heavy form of carbon which could only have been formed in space. Materials formed on Earth are made of a lighter type of carbon.

The two molecules in this study are only a few of the organic molecules that have been detected in the famous Murchison meteorite, said David Deamer, a chemist at the University of California, Santa Cruz.

"There are about 70 different amino acids in the Murchison meteorite," Deamer told SPACE.com. "About six or so are the same kinds of amino acids associated with life on Earth."

Uracil is one of the four base molecules of RNA, so is vital for life.

Just because the molecules found on this meteorite and others came from space, doesn't mean the same compounds weren't also independently synthesized on Earth, Deamer pointed out. Scientists are unsure how many of the building blocks of life on Earth originated on this planet, and how many came from beyond.

"We don't know the answer yet," he said. "Most people would say that both contributed to the organic compounds available on Earth, but we don't know with certainty how much of one compared to the other."

Many space rocks similar to the Murchison meteorite rained down on Earth between 3.8 and 4.5 billion years ago, when primitive life was forming. The heavy bombardment would have dropped large amounts of meteorite material to the surface on planets such as Earth and Mars.

Martins and her colleagues say their discovery may help shed light on how life first evolved in our solar system.

"Because meteorites represent leftover materials from the formation of the solar system, the key components for life — including nucleobases — could be widespread in the cosmos," said co-author Mark Sephton, a professor of Earth science and engineering at Imperial College London. "As more and more of life's raw materials are discovered in objects from space, the possibility of life springing forth wherever the right chemistry is present becomes more likely."

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