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The Geologic History of Mars: An Astrobiology PerspectiveFourteen SNC meteorites contain information which must be incorporated with recent spaceflight data for developing Mars' geologic history. SNCs have crystallization ages of 4500 to 160 m.y. Tle oldest meteorite ALH84001 contains information on the Noachian period of Mars' history. There are no meteorites from the Hesperian period and the remaining 13 meteorites fall into two age groups within the Amazonian: The nakhlites around 1300 m.y. and the shergottites between 800-160 m.y. Oxygen isotopic analysis of Martian samples shows two distinct O2 reservoirs throughout Martian history indicating late additions of volatiles and a lack of plate tectonics prior to 3.9 Gy. Evidence for percolation of aqueous brines through impact-produced fractures in the rocky surface is contained in the 3.9 Gy-old ALH84001 carbonate deposits. These carbonates precipitated at approx. 100 C. At this time life had already evolved on Earth. Early Mars could have hosted life similar to the bacteria that inhabited early Earth. Potential microorganisms could have been transported into fractures by carbonate-bearing waters and their remains could have become incorporated into the precipitated carbonate. Since Mars had a weak magnetic field at this time, it can be hypothesized that some of the Martian microorganisms may have been similar to terrestrial magnetotactic bacteria. Over geologic time episodic cratering, and tectonic events have occurred on Mars along with the periodic release of subsurface waters which may have produced clays within SNC meteorites. The geochemical data contained within SNC meteorites complements previous observational data and the recent Mars Global Surveyor data to provide a geological and environmental history which spans almost the entire lifespan on Mars. One of the outstanding features of this model is the possible creation of an early (about 4 Gy) volatile reservoir distinct from the outgassed Mars volatiles, and the persistence of this reservoir throughout most, if not all of subsequent Mars' history. Within the framework of this history a potential scenario for a possible record of living organisms is provided by suggestive structures and organic signatures trapped within secondary mineral deposits and alteration features of some SNC meteorites. Tracing the differences in oxygen isotopic compositions within Martian components allows us to gain insight in the history of Mars.
Document ID
20000041375
Acquisition Source
Johnson Space Center
Document Type
Preprint (Draft being sent to journal)
Authors
Gibson, Everett K.
(NASA Johnson Space Center Houston, TX United States)
Westall, Frances
(NASA Johnson Space Center Houston, TX United States)
McKay, David S.
(NASA Johnson Space Center Houston, TX United States)
Thomas-Keprta, Kathie
(Lockheed Martin Corp. Houston, TX United States)
Socki, Richard A.
(Lockheed Martin Corp. Houston, TX United States)
Date Acquired
August 19, 2013
Publication Date
January 1, 2000
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: Astrobiology Science
Location: Mountain View, CA
Country: United States
Start Date: April 3, 2000
End Date: April 5, 2000
Sponsors: NASA Ames Research Center
Funding Number(s)
PROJECT: RTOP 344-50-92
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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