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Seminar Detail
Can Rocks from Mars Yield Definitive Evidence of Past Life?
Presenter: J. William Schopf (University of California, Los Angeles)
February 25, 2008 11:00 AM Pacific
Throughout recorded Earth history, microbial life has been ubiquitous, abundant, metabolically diverse, and, for the Precambrian four billion years of geologic time, biotically predominant. In the search for life elsewhere in the Cosmos, the prokaryote-dominated world of the Precambrian is the best analogue we know. Though evidence of microbe-level life will thus be sought in rocks returned from Mars, for the first such missions only minimal samples will be available. This raises important questions: What amount of rock is needed to detect past life? What evidence is required to establish biogenicity? How can true fossils be distinguished from contaminants?
The Precambrian fossil record holds the answer. Given the minute size of fossil microbes and their prodigious abundance in some Precambrian rocks, firm evidence of ancient life has been adduced from samples weighing as little as 0.1 g (in volume, about half the size of a grain of rice). Backed by other lines of evidence, the biogenicity of such fossils is shown by their (1) biological, cellular, morphology and (2) carbonaceous (kerogenous) composition. And their indigenousness is established by showing that (3) the geochemical maturity of the fossil-comprising kerogen is consistent with the rock matrix in which they occur.
The presence of these three fossil-identifying traits can be shown by use of confocal laser scanning microscopy and Raman imagery, two techniques new to astrobiology. By providing micron-scale three-dimensional images of organic-walled fossils, both yield firm evidence of biological morphology, and Raman imagery can establish the molecular-structural composition as well as the geochemical maturity of the analyzed kerogen. Both of these non-intrusive and non-destructive techniques can be used to study fossils embedded in petrographic thin sections such as those to be prepared for mineralogical studies of Mars rocks.
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2) You can watch the Realplayer webcast at: http://vanseg-1.arc.nasa.gov/2008/AB080225-01.ram and view the slides in WebEx (see WebEx instructions above) There is a 30 second delay for the webcast, so you will need to control the slides manually using the arrow buttons in WebEx. Questions for the speaker can be posted in the WebEx chat area to be answered at the end of the talk. Do not try to watch the Realplayer webcast at the same time as the Polycom or the phone.December 21, 2007
The Director’s Seminar series features talks from scientists who are invited by the NAI Director to present their research results to the community. A primary goal of the seminars is to encourage interdisciplinary collaboration across NAI teams and within the astrobiology community at large.
Team Overview Seminars describe the work of the fourteen NAI teams and NAI Central. They offer an opportunity to find out more about the science, E/PO and other activities being performed by the NAI teams and the NAI Central office.
The Forum for Astrobiology Research (FAR) provides an opportunity for graduate students to present their research results and to meet as a student community for networking and mutual support.
The University of Washington seminar series is hosted by the NAI Virtual Planetary Lab (VPL) team from the UW campus in Seattle.
