[meteorite-list] Abundant Ammonia Found in Antarctic Meteorite Aids Life's Origins

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 1 Mar 2011 17:31:13 -0800 (PST)
Message-ID: <201103020131.p221VDZc029773_at_zagami.jpl.nasa.gov>

http://asunews.asu.edu/20110301_ammonia

Abundant ammonia aids life's origins
Arizona State University
March 01, 2011

An important discovery has been made with respect to the possible inventory
of molecules available to the early Earth. Scientists led by Sandra
Pizzarello, a research professor at Arizona State University, found large
amounts of ammonia in a primitive Antarctic asteroid. This high
concentration of ammonia could account for a sustained source of reduced
nitrogen essential to the chemistry of life.

The work is being published in this week?s Proceedings of the National
Academy of Sciences (PNAS). The paper is titled, "Abundant ammonia in
primitive asteroids and the case for a possible exobiology," and is
co-authored by Pizzarello, geologist Lynda Williams, chemists Gregory
Holland and Jeffery Yarger, all from ASU and Jennifer Lehman of UC Santa
Cruz.
 
The finding of a high concentration of nitrogen-bearing molecules in an
asteroidal environment shown by the new study is very provocative. Besides
the noble gases, nitrogen is the fourth most abundant element in the Sun and
the universe overall. On the Earth, it is an indispensable ingredient of the
biosphere, being essential to DNA, RNA and proteins. In other words, it is
necessary for life's information transfer and catalytic processes.
 
"All origins-of-life theories need to account for a sustained source of
reduced nitrogen in order to make amino acids and nucleobases," said
Pizzarello, who works in ASU's Department of Chemistry and Biochemistry in
the College of Liberal Arts and Sciences.
 
On the early Earth, on the other hand, the prebiotic inventory of reduced
nitrogen necessary for the formation of N-containing biomolecules has been
difficult to predict. The hypotheses of a reducing atmosphere had initially
allowed one to envision considerable ammonia abundance as well as
evolutionary pathways for the production of amino acids. However, the
current geochemical evidence of a neutral early Earth atmosphere, combined
with the known photochemical destruction of ammonia, has left prebiotic
scenarios struggling to account for a constant provision of ammonia.

An abundant exogenous delivery of ammonia, therefore, might have been
significant in aiding early Earth's molecular evolution, as we should expect
it to have participated in numerous abiotic as well as prebiotic reactions.

It also is interesting to note that the new PNAS work was made possible by
the finding in Antarctica of these exceptionally pristine,
ammonia-containing, asteroidal meteorites. Antarctic ices are good
"curators" of meteorites. After a meteorite falls ? and meteorites have been
falling throughout the history of Earth ? it is quickly covered by snow and
buried in the ice. Because these ices are in constant motion, when they come
to a mountain, they will flow over the hill and bring meteorites to the
surface.
    
 
Jenny Green, jenny.green at asu.edu
480-965-1430
Department of Chemistry and Biochemistry
Received on Tue 01 Mar 2011 08:31:13 PM PST