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15-Apr-2010

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A new look at the oldest Martian meteorite



Thomas Lapen, assistant professor of geosciences at the University of Houston, holding a sample of a Martian meteorite.
Image courtesy of Thomas Campbell, University of Houston

The oldest known Martian meteorite, known as ALH 84001, appears to be about half a billion years younger than previously thought, researchers report. These findings suggest that the Mars rock probably isn't a piece of the planet's very first crust, which formed as an ancient magma ocean cooled and hardened.

Until now, scientists have figured that ALH 84001 is about 4.51 billion years old, which would mean that it was a remnant of Mars' primordial crust that survived a period of intense bombardment between approximately 4.25 and 4.10 billion years ago.

Using a different form of radioisotope dating than was previously used on ALH 84001, Thomas Lapen of the University of Houston and colleagues have now revised the age of this meteorite to about 4.09 billion years. This age suggest that the meteorite—though still the oldest known version of its kind—came from crust that formed just at the end of the bombardment period.

The findings also suggest that the formation of crust from magma was ongoing on Mars over much of the planet's history. The research appears in the 16 April issue of the journal Science.

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