for National Geographic News
A Martian "layer cake" of clay minerals sliced open by an ancient channel adds to evidence of the red planet's watery past, according to a new study.
The clays could be key to determining which areas of Mars, if any, were habitable and how long life-sustaining conditions might have lasted.
(Related: "Mars Was Warm, Wet, May Have Hosted Life, Study Says" [July 16, 2008].)
"We see big, deep clay deposits, so there must have been water for a long time," said study co-author Janice Bishop of the SETI Institute and NASA Ames Research Center in Mountain View, California.
"And we see different types of clays, so there must have been some interesting chemistry going on."
Bishop and colleagues pored over images from NASA's Mars Reconnaissance Orbiter and mapped the distribution of clays known as phyllosilicates in the Mawrth Vallis channel.
A deposit of four-billion-year-old clays—some of the oldest exposed minerals on the planet—extends over a wide area in the western part of the channel, suggesting that a large body of water once covered the region.
"Clays really need standing water [to form]," Bishop said, "and we can see that this is a huge clay deposit."
An instrument on board the Mars orbiter records the unique wavelengths of light given off by different minerals on the Martian surface.
Using these so-called spectral images, the team identified a layer of clays rich in iron and magnesium exposed in the Mawrth Vallis channel. The findings are detailed in this week's issue of the journal Science.
Based on the way clay minerals form on Earth, the scientists think the iron- and magnesium-rich layer was most likely created as water altered basalt, a volcanic rock that is common on Mars.
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