The Mars Exploration Rover “Spirit” provided us with a serendipitous opportunity to traverse a section of the ancient martian crust, acquiring a trove of imaging, geochemical, and mineralogical measurements along the way. This small window looking out on the Noachian period (>3.7 Ga), dubbed the Columbia Hills, pokes out from the younger, volcanically resurfaced floor of Gusev Crater. It was our first detailed look at early Mars, a time when liquid water appears to have played a much more prominent role in shaping and modifying the planet than later in its history.
The abundance of rocks that appear to be...
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