Evidence of ancient life may have been scrubbed from parts of Mars (Martian geology)

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EXCERPTS: . . . The space agency's Curiosity rover made the surprising discovery while investigating clay-rich sedimentary rocks around its landing site in Gale Crater, a former lake that was made when an asteroid struck the Red Planet roughly 3.6 billion years ago.

[...] when Curiosity took two samples of ancient mudstone, a sedimentary rock containing clay, from patches of the dried-out lake bed, dated to the same time and place (3.5 billion years ago and just 400m apart), researchers found that one patch contained only half the expected amount of clay minerals. Instead, that patch held a greater quantity of iron oxides, the compounds that give Mars its rusty hue.

The team believes the culprit behind this geological disappearing act is brine: supersalty water that leaked into the mineral-rich clay layers and destabilized them, flushing them away and wiping patches of both the geological — and possibly even the biological — record clean.

"We used to think that once these layers of clay minerals formed at the bottom of the lake in Gale Crater, they stayed that way, preserving the moment in time they formed for billions of years," study lead author Tom Bristow, a researcher at NASA's Ames Research Center in Mountain View, California, said in a statement. "But later brines broke down these clay minerals in some places — essentially resetting the rock record."

[...] "We've learned something very important: There are some parts of the Martian rock record that aren't so good at preserving evidence of the planet's past and possible life," co-author Ashwin Vasavada, a Curiosity project scientist at NASA's Jet Propulsion Laboratory in California, said in the statement. "The fortunate thing is, we find both close together in Gale Crater and can use mineralogy to tell which is which." (MORE - details)

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