Near the center of the Martian Gale Crater (about the size of Connecticut), hundreds of exposed rock layers form a tower as tall as the Rockies and reveal a record of major environmental changes on Mars billions of years ago. Gale crater, like the Gusev crater, sits near the boundary between Mars’ southern highlands and northern lowlands. Its interior is filled with layer upon layer of rocks standing 5.5 kilometers (3.4 miles) higher than the northern crater floor, but it is unknown whether these are sediments came in with ancient floods, or lava flows, or windblown ash deposits. The geological history told by the rock layers matches what has been proposed in recent years as the dominant planet-wide pattern for early Mars, according to a new report by geologists using instruments on NASA’s Mars Reconnaissance Orbiter
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