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Meteorites and the rise of organic life

Scientists interested in the rise of organic life have been intrigued with the "biological chemicals" found in some meteorites. But there are two nagging questions. Do these chemicals really come from space or are they contaminants that got into the meteorite after it landed? And if they are space chemicals, how were they formed? In short, is the evolution beyond Earth of protein building blocks and other prebiotic chemicals a believable proposition?

Several recent studies have given new reasons for answering "yes." Among other things, they suggest that nature uses the Fisher-Tropsch process that makes synthetic gasoline from hydrogen and carbon monoxide on Earth.

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The chemicals in meteorites include amino acids (the protein building blocks) , pyrimidines (a class of chemical found in the DNA and RNA molecules that carry the genetic code) and other biologically interesting types. Not all of these amino acids or pyrimidines play a role in organic life. This has strongly suggested that the meteoritic chemicals formed independently of any biological processes.

In November, Akira Shimoyama and Cyril Ponnamperuma of the University of Maryland and Keizo Yanai of Japan's National Institute of Polar Research described what they call "detailed evidence for the presence of amino acids of extraterrestrial origin" in Antarctic meteorites. Because these meteorite pieces were protected by being frozen in ice for much of the time since they landed, and because they show little change due to weathering since they were exposed on the glacial surface, the scientists believe them to be uncontaminated. Yet the chemical mix they contain is similar to that found in other meteorites, suggesting they are indeed space chemicals.

At the same time, James G. Lawless of the National Aeronautics and Space Administration, Ames Research Center, and George U. Yuen of Arizona State University reported finding meteoritic chemicals that fit predictions of a theory in which organic chemicals would be produced in a two step process, the first stage of which would be the Fischer- Tropsch synthesis. They believe their results point to "a naturally occurring chemical synthesis and support the chemical evolution theory."

More recently, Peter G. Stoks and Alan W. Schwartz of the University at Nijmegen in the Netherlands have reported the presence of the pyrimidine uracil in several meteorites. Uracil, a constituent of RNA, is the first biologically important pyrimidine identified in meteorites. Again, the researchers think its presence suggests that the Fischer- Tropsch process is involved in the creation of the pre-life chemicals.

While scientists still cannot prove beyond doubt that such chemicals do arise spontaneously beyond Earth, these recent findings -- all reported in Nature -- strengthen the case. They are one more reason for thinking that the potential for organic life is inherent in the physical laws that underly the universe.


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