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That is probably the most remarkable thing I've ever seen as a scientist, given the difficulty of the analyses," Farley says.This also helps researchers looking for evidence of past life on Mars.At 80 million years ago, wind would have caused this scarp to migrate across the surface and the rock below the scarp would have gone from being buried—and safe from cosmic rays—to exposed," Farley explains.Geologists have developed a relatively well-understood model, called the scarp retreat model, to explain how this type of environment evolves.The smooth floor of Yellowknife Bay is made up of a fine-grained sedimentary rock, or mudstone, that researchers think was deposited on the bed of an ancient Martian lake.In March, Curiosity drilled holes into the mudstone and collected powdered rock samples from two locations about three meters apart.
However, because the rock at Yellowknife Bay has only been exposed to cosmic rays for 80 million years—a relatively small sliver of geologic time—"the potential for organic preservation at the site where we drilled is better than many people had guessed," Farley says.Furthermore, the "young" surface exposure offers insight into the erosion history of the site."When we first came up with this number, the geologists said, ' Yes, now we get it, now we understand why this rock surface is so clean and there is no sand or rubble,'" Farley says.The exposure of rock in Yellowknife Bay has been caused by wind erosion.Over time, as wind blows sand against the small cliffs, or scarps, that bound the Yellowknife outcrop, the scarps erode back, revealing new rock that previously was not exposed to cosmic rays."Imagine that you are in this site a hundred million years ago; the area that we drilled in was covered by at least a few meters of rock.