MARTIAN METEORITE CARBONATES 3.9 BILLION YEARS OLD



Oct. 1, 1999



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

<h4>Release: J99-42</h4> <h3>Martian Meteorite Carbonates 3.9 Billion 
Years Old</h3> 

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&rsquo;t directly address the possibility that life 
once existed on Mars. But &ldquo;It&rsquo;s another piece in the 
puzzle,&rdquo; said Larry E. Nyquist of the Planetary Sciences Branch 
of Johnson Space Center&rsquo;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 investigator.



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&rsquo; 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 &ldquo;we wanted to make sure we had a result we could 
believe in and that other people could believe in,&rdquo; 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 
investigation.



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 &ldquo;one of the real 
mysteries&rdquo; of indications of life on Mars. Had the carbonates 
been formed more recently, when the planet&rsquo;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 &ldquo;suggest events were very similar in the inner solar 
system&rdquo; as primitive life arose.

	
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