Thursday, November 10, 2011

Meteorites and Prebiotic Organic Matter

It has been long understood that in the early history of the earth before the appearance of life, there were present organic substances that were the precursors to the complex compounds that are the essential ingredients for all living things.  These molecular precursors are referred to as prebiotic organic matter.  In addition, the cosmological data has established that the earth along with all the other planetary bodies within our solar system were formed from material expelled from the sun during its formation – the so-called “protoplanetary disk.”

A fundamental question that arises from these known occurrences is the actual origin of prebiotic organic matter.  One of the possible answers to this question is that these materials may have been seeded as a result of collisions of meteorites on the earth’s surface.  This postulate is made even more plausible if one takes into account the fact that in the early history of the planet collisions with meteorites were exceeding common.
Of particular interest is a class of meteorites referred to as the carbonaceous chondrite meteors that are believed to be samples of primitive meteorites that contain the material that was part of the formation of planet earth some 4.6 billion years ago.  These generally consist of insoluble organic matter (IOM) and soluble organic matter ((SOM). 

Dr. Christopher D. K. Herd from the Department of Earth and Atmospheric Sciences at the University of Albert, Canada and his colleagues systematically analyzed the Tagish Lake – in the Southwest region of the Yukon in Canada - meteorite specimens that fell on the frozen lake and were harvested within a few days.  The freshness of the samples effectively ruled out the possibility of contamination from the local environment – an issue that is always of major concern in these types of studies.  The investigative group chose four samples for detailed evaluation. 

Their findings were of extreme interest, for they discovered that the water extracts from these samples were dominated by monocarboxylic acids (MCAs) including formic and acetic acids that play key and ubiquitous roles in the biochemical metabolism of life on the planet.  They isolated eleven different examples of this class of organic compound.  In addition to these, amino acids were also identified.  Amino acids are the basic building blocks from which all proteins are constructed.  The evidence that was accumulated in these studies supports an extraterrestrial origin for these compounds.

This conclusion, if true, is of immense value in understanding the evolution of life on planet earth as well as encouraging speculation as to the possibility of life on other worlds or so-called “exoplanets.”

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