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Phoenix666 [soylentnews.org] writes:

Since it landed more than three years ago in a 96-mile-wide depression known as Gale Crater, Curiosity has made a number of discoveries, notably that the crater once held lakes of fresh water. For most of that time, the rocks it encountered were generally basaltic, a volcanic composition typical on Mars.

“Now in the recent few months, that has changed,” Ashwin R. Vasavada, the project scientist for the mission, said at a news conference on Thursday at a meeting of the American Geophysical Union in San Francisco, where researchers were presenting some of their newest results.
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Each layer of sedimentary rock tells something about the geological conditions at the time the rock formed, meaning that Curiosity, which arrived at the base of the mountain in September 2014, is in a sense moving forward through the geological history of Mars as it climbs.

What has caught the attention of Dr. Vasavada and his colleagues lately is silica, a class of minerals made of silicon and oxygen [nytimes.com]. The evidence points to the action of liquid water even after the lakes disappeared.

“Groundwater passed through the rock multiple times, leaving different chemical signatures behind,” Dr. Vasavada said.

Basalt is generally half silica. Curiosity has been examining two rock units: one a mudstone of lake bed deposits, among the oldest rocks the rover will examine, and the other a sandstone of coarse grains that were blown in and draped onto the mountain. “It probably is among the youngest rocks we’ll encounter on the mission,” Dr. Vasavada said.

In the mudstone and the sandstone, Curiosity found much higher levels of silica, up to 90 percent more than it had observed previously in basaltic rocks.

More silica means a greater, longer presence of water, which in turn improves the chances for life having developed on Mars.

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