Literature

In 1969, a large meteorite fell to the ground about 100 miles north of Melbourne, Australia. It broke apart before impact, and the science community has been left with numerous fragments. It is a carbonaceous chondrite, which is commonly thought to be closest in composition to the source materials that formed the terrestrial planets. There has been extensive research into the organic contents of this meteorite, and some of this has concerned contamination. There are some evidences for contamination and some evidences supporting an extraterrestrial origin for the organic molecules. The latest research claims that there are "extraterrestrial nucleobases in the Murchison meteorite".

The Murchison Meteorite continues to attract interest from scientists and the media (source here)

What has been found? The researchers report "many biologically relevant organic molecules" and highlight uracil and xanthine for attention. These are the nucleobases referred to in the title of their paper. They are described as "precursors to the molecules that make up DNA and RNA". Uracil is used to store information contained in RNA, and xanthine is a metabolic intermediate in the breakdown of purine nucleotides (which only works in conjunction with suitable enzymes). What they are not are "genetic material" (as announced by the Imperial College Press Release and repeated by several other forums: ScienceDaily, PhysOrg.com, popsci.com).

Having reported the presence of these molecules, the authors go on to speculate about their significance. Since these molecules represent primordial material, they can be inferred to have been transported to the Earth's surface in the Hadean Period of Earth history. They "may have played a key role in life's origin." Their presence allows a more critical appraisal of theories about the endogenous production of amino acids (which no longer look viable as a source of these building blocks).

"Our data advance proposals that life's raw materials were delivered to the early Earth and other planetary bodies by exogenous sources, including carbonaceous meteorites. In contrast, the endogenous synthesis of prebiotic organic compounds may have been constrained by the conditions on the young Earth, perhaps most importantly by the oxidation state of the atmosphere. For example, only low yields of amino acids were produced under non-reducing conditions in the Miller-Urey-type experiment. Yet, whatever the inventory of endogenous organic compounds on the ancient Earth, it would have been augmented by extraterrestrial material. It is estimated that these sources delivered ~10^9 kg of carbon per year to the Earth during the heavy bombardment phase 4.5-3.9 billion years ago."

The researchers are very excited about their find and its potential for helping theories of abiogenesis:

"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." (Zita Martins)
"Because meteorites represent left over 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." (Mark Sephton)

This message is echoed in the media reports. For example, popsci.com says: "If the basic ingredients are zipping around throughout the cosmos, the likelihood of life taking shape wherever the chemistry is right is most certainly increased." Comments like this do not provide a service to anyone, for they confuse rather than clarify. The same point applies to the search for liquid water on other astronomical bodies - as though finding water is the key to life springing forth wherever the right chemistry is present. Research has shown over and over again that life does not self-assemble. Put all the ingredients of life together in a soup and you do not get life! Those who present the issue as one for chemists to solve are seriously astray. It is crucially important to focus on biological information and where it comes from. Law and chance do not deliver. Abiogenesis research that considers only these options has confirmed repeatedly that life does not emerge from a chemistry set. What is needed is a reorientation to the role of information, and for this, we need design perspectives in science.

"In my opinion, there is no basis in known chemistry for the belief that long sequences of reactions can organize spontaneously - and every reason to believe that they cannot. The problem of achieving sufficient specificity, whether in aqueous solution or on the surface of a mineral, is so severe that the chance of closing a cycle of reactions as complex as the reverse citric acid cycle, for example, is negligible." Orgel, Leslie, (Dec 1998) "The origin of life - a review of facts and speculations," Trends in Biochemical Sciences, 23: 491-495.

Extraterrestrial nucleobases in the Murchison meteorite
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, 270(1-2), 15 June 2008, 130-136

Abstract: Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of [delta]13C [. . .] indicate a non-terrestrial origin for these compounds. 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.