A study finds that human activity has led to a severe decrease in Caribbean shark abundance.
Image credit: Sean Mattson (International Center for Tropical Agriculture, Cali, Colombia).
Edited* by Ronald Breslow, Columbia University, New York, NY, and approved January 24, 2011 (received for review October 6, 2010)
Abstract
Carbonaceous chondrites are asteroidal meteorites that contain abundant organic materials. Given that meteorites and comets have reached the Earth since it formed, it has been proposed that the exogenous influx from these bodies provided the organic inventories necessary for the emergence of life. The carbonaceous meteorites of the Renazzo-type family (CR) have recently revealed a composition that is particularly enriched in small soluble organic molecules, such as the amino acids glycine and alanine, which could support this possibility. We have now analyzed the insoluble and the largest organic component of the CR2 Grave Nunataks (GRA) 95229 meteorite and found it to be of more primitive composition than in other meteorites and to release abundant free ammonia upon hydrothermal treatment. The findings appear to trace CR2 meteorites’ origin to cosmochemical regimes where ammonia was pervasive, and we speculate that their delivery to the early Earth could have fostered prebiotic molecular evolution.
Footnotes
- 1To whom correspondence should be addressed. E-mail: pizzar{at}asu.edu.
Author contributions: S.P. designed research; S.P., L.B.W., J.L., and G.P.H. performed research; S.P., J.L., G.P.H., and J.L.Y. analyzed data; and S.P. wrote the paper.
The authors declare no conflict of interest.
*This Direct Submission article had a prearranged editor.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1014961108/-/DCSupplemental.
Abundant ammonia in primitive asteroids and the case for a possible exobiology
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- Physical Sciences
- Chemistry
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