Robert Owen (firstname.lastname@example.org)
Fri, 01 Oct 1999 17:45:41 -0400
Larry Klaes wrote:
> >Date: Fri, 1 Oct 1999 19:16:22 GMT
> >From: Ron Baalke <BAALKE@KELVIN.JPL.NASA.GOV>
> >To: email@example.com
> >Subject: [ASTRO] Study Shows Carbonates In Martian Meteorite Are 3.9
> > Billion Years Old
> >MARTIAN METEORITE CARBONATES 3.9 BILLION YEARS OLD
> >A new study of the carbonate minerals found in a meteorite from Mars
> >shows they were formed about 3.9 billion years ago. Scientists believe
> >the planet had flowing surface water and warmer temperatures then,
> >making it more Earth-like. Giant meteorites were blasting huge craters
> >in its surface.
> >This study doesn't directly address the possibility that life once
> >existed on Mars. But "It's another piece in the puzzle," said Larry E.
> >Nyquist of the Planetary Sciences Branch of Johnson Space Center's Earth
> >Science and Solar System Exploration Division. Nyquist, one of the
> >authors of an article in Science, a weekly publication of the American
> >Association for the Advancement of Science, was the principal
> >Researchers at Johnson Space Center in Houston and the University of
> >Texas at Austin did the study, using different techniques. Both produced
> >similar results, establishing the carbonatesí age within comparatively
> >narrow limits.
> >The 4.2 pound meteorite is believed to be part of an igneous rock
> >formation formed about 4.5 billion years ago as Mars solidified from a
> >molten mass. The meteorite probably was blasted from the planet when a
> >huge comet or asteroid struck Mars 16 million years ago.
> >It fell in Antarctica about 13,000 years ago, and was found in 1984 by
> >an annual expedition sponsored jointly by NASA, the National Science
> >Foundation, and the Smithsonian Institution. Called ALH84001, after the
> >Allan Hills in Antarctica where it was found, it was returned to Johnson
> >Space Center, and has been preserved at the Meteorite Processing
> >Laboratory there.
> >It subsequently was recognized as one of more than a dozen meteorites
> >with unique Martian characteristics.
> >Just how the carbonates were deposited within this igneous rock is the
> >topic of lively debate. Some scientists believe water saturated with
> >carbon dioxide from the atmosphere seeped down to the subsurface site
> >where the igneous rock formed and created the carbonate deposits. On
> >Earth, living organisms often play a role in carbonate formation. In
> >1996 scientists at Johnson Space Center and Stanford University examined
> >the carbonates in ALH84001 using electron microscopy and laser mass
> >spectrometry, and reported evidence suggesting primitive life may have
> >existed in them.
> >Other scientists believe the carbonates formed when hot,
> >carbon-dioxide-bearing fluids were forced into cracks in the rocks when
> >a meteor struck Mars. The 3.9-billion-year age of the carbonates
> >eliminates neither possibility.
> >The carbonates themselves are tiny deposits, reddish globules, some with
> >purplish centers and many surrounded by white borders. The different
> >colors are due to variations in the compositions of the carbonates:
> >purplish manganese-bearing calcium carbonate, reddish iron carbonate,
> >and white magnesium carbonates. The globules were found along fractures
> >in the meteorite and make up about 1 percent of its volume.
> >The JSC-UT team, using a binocular microscope and tools resembling
> >dental picks, over a period of months painstakingly separated out enough
> >of the carbonate material for their analyses. After experimenting with
> >terrestrial calcium, iron, and magnesium carbonates, they developed a
> >way to selectively dissolve carbonate material of differing
> >compositions, enabling them to separate different elements from the
> >carbonate solutions.
> >The study established the age of the carbonate deposits by measuring the
> >decay of rubidium to strontium and of uranium to lead. The techniques
> >are similar to carbon dating, which is used for much shorter time
> >periods. The investigators used the dual approach because "we wanted to
> >make sure we had a result we could believe in and that other people
> >could believe in," Nyquist said.
> >The leading author of the Science article is Lars E. Borg, formerly of
> >the National Research Council and Johnson Space Center and now at the
> >University of New Mexico in Albuquerque. Other authors are James N.
> >Connelly of the University of Texas at Austin, Chi-Yu Shih, Henry
> >Weismann, and Young Reese, of Lockheed Engineering and Science in
> >Houston. K. Manser of the University of Texas contributed to the
> >The age of the carbonates, said Everett K. Gibson of Johnson Space
> >Center and an author of the 1996 study that reported evidence of
> >microbial life in the carbonates, had been "one of the real mysteries"
> >of indications of life on Mars. Had the carbonates been formed more
> >recently, when the planet's surface was devoid of water, it would have
> >been unlikely they were associated with primitive life on Mars. Dating
> >them at 3.9 billion years, when there apparently was surface water on
> >Mars is, Gibson said, very important, and could "suggest events were
> >very similar in the inner solar system" as primitive life arose.
Robert M. Owen
The Orion Institute
57 W. Morgan Street
Brevard, NC 28712-3659 USA
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