Scientists from Europe and the United States say that their research, recently published in the journal Earth and Planetary Science Letters, provides evidence that life's raw materials came from sources beyond the Earth.

"We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite," the authors of the paper, titled Extraterrestrial Nucleobases in the Murchison Meteorite, report. "These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin."

"Researchers say the finding makes it slightly more plausible that meteorite bombardments may have seeded ancient Earth with life's raw materials, potentially paving the way for life itself," Scientific American says of the study.

Science Daily dives into this theory, based on the recent findings, using material extracted from the Murchison Meteorite that crashed in Australia in 1969. Here's an excerpt:

Between 3.8 to 4.5 billion years ago large numbers of rocks similar to the Murchison meteorite rained down on Earth at the time when primitive life was forming. The heavy bombardment would have dropped large amounts of meteorite material to the surface on planets like Earth and Mars.

"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 lead author Dr. Zita Martins, of the Department of Earth Science and Engineering at Imperial College London.

Co-author Mark Sephton, also a professor of Imperial's Department of Earth Science and Engineering, adds:

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. 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.

Scientific American provides some input from researchers who are skeptical of the Murchison findings. Robert Shapiro, a professor emeritus and senior research scientist in chemistry at New York University, says that because of their low concentration, extraterrestrial nucleobases were unlikely to have played much of a role in kick-starting life.

"They're a subunit of a subunit of DNA," Shapiro says. "My opinion is that their amounts were utterly unimportant and insignificant."

Shapiro says he would be more impressed if whole nucleosides — bases plus sugars — were found in meteorites in concentrations similar to those of amino acids.

Scientific American also indicates that researchers may yet discover ways that Earthly chemistry — perhaps around hydrothermal vents — could have generated nucleobases and other compounds.

Adding additional levity is Conel Alexander, a geochemist at the Carnegie Institution of Washington who specializes in meteorites: "It really comes down to quantitative arguments about how much was made on Earth [and] how much was brought in from space.

"Any honest person would keep an open mind about the whole issue," Alexander says.

Resources

Extraterrestrial Nucleobases in the Murchison Meteorite
by Zita Martins, Oliver Botta, Marilyn L. Fogel, Mark A. Sephton, Daniel P. Glavin, Jonathan S. Watson, Jason P. Dworkin, Alan W. Schwartz and Pascale Ehrenfreund
Earth and Planetary Science Letters (Vol. 270, Iss. 1-2), June 15, 2008

Life's Raw Materials May Have Come From the Stars, Scientists Confirm
ScienceDaily, June 13, 2008

Were Meteorites the Origin of Life on Earth?
by JR Minkel
Scientific American, June 16, 2008