Well Preserved Meteorite Yields Clues To Carbon Evolution In Space

Carbonaceous chondrite meteorites contain vital clues to the evolution of carbon compounds in our solar system preceding the origin of life.

The analysis, conducted by a team headed by chemist Sandra Pizzarello, a research scientist at Arizona State University, on 4.5 grams taken from the sealed interior of the meteorite, found organic compounds in the meteorite with some similarities to other known carbonaceous chondrites, but also clear differences -- most notably the near-absence of the amino acids found in some meteorites studied before.

In an article scheduled to appear in the August 24 issue of the online journal Science Express (with publication in Science to follow) the team notes that the chemistry of the Tagish Lake Meteorite appears to preserve organics that accumulated or developed in the early history of the Solar System – including molecular bubbles of carbon (fullerenes or “buckyballs”) containing the noble gasses helium and argon in a ratio similar to the gas and dust cloud that formed the planets -- and thus perhaps reflects an early stage in a process of evolution of complex carbon compounds in space.

“The chemistry here is different from that we have seen in any other meteorite,” said Pizzarello. “It’s simple, when compared with Murchison (a famous carbon meteorite found in Australia in 1969 that contained numerous amino acids and a variety of other organic compounds) and probably represents a separate line of chemical evolution. However, it still includes compounds that are identical to biomolecules.”

Other members of the research team include Yongsong Huang from the Department of Geological Sciences at Brown University; Luann Becker from the Institute for Crustal Studies at the University of California Santa Barbara; Robert J. Poreda from the Department of Earth and Environmental Sciences, University of Rochester; George Cooper from the NASA Ames Research Center; and Ronald A. Nieman and Michael Williams, both also from ASU.

The Science paper notes that many of the organic compounds found in the Tagish Lake sample have also been found in other meteorites, but that the distribution of compounds is different, particularly for the amino acids and carboxylic acids.

“Some people have been disappointed that we found virtually no amino acids, but scientifically this is very exciting,” Pizzarello said. “This meteorite shows the complexity of the history of organic compounds in space -- it seems to have had a distinct evolution.

“We found some compounds identical to some in Murchison that show the same ‘interstellar connection’ in their abundance of deuterium (heavy hydrogen), while some others differ from Murchison in amounts and variety,” said Pizzarello, meaning that for some groups of organic molecules, only the simplest species were found in Tagish Lake, as opposed to a broader distribution of species found in Murchison. “Overall, Tagish Lake represents a simpler, more unaltered stage than we have seen before.”

What emerges from the analyses is evidence for what Pizzarello calls “a different outcome” of organic chemical evolution in space likely to have happened during the formation and development of the solar system, “but one that still might have contributed molecular precursors of biomolecules to the origins of life,” she noted.