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2389FWD: [UASR] Martian Meteorite Carbonates 3.9 Billion Years Old

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  • Frits Westra
    Oct 2, 1999
    • 0 Attachment
      Posted by : "Mark A. LeCuyer" <randydan@...>

      Source: Johnson Space Center
      October 1, 1999

      John Ira Petty
      Johnson Space Center, TX
      (281) 483-5111

      Release: J99-42

      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 carbonates´┐Ż 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

      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.


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