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Unformatted text preview: • The difference in crater crowding tells us that the southern highlands are a much older surface than the northern plains • Volcanism erased crater impacts • The frequency of volcanic eruptions on Mars has decreased steadily since at least about 3.5 billion years ago, just as we would expect for a planet small enough to have lost much of its internal heat by now What geological evidence tells us that water once flowed on Mars? • Photos that showed features that looked much like dry riverbeds on Earth seen from above • The branching nature of the channels suggests that they were carved gradually, os liquid water must have been stable at or just below the surface at that time • Rainfall • Rocks at the Opportunity landing site contain tiny spheres – nicknamed “blueberries” although they’re neither blue nor as large as the berries we find in stores – and odd indentations suggesting that they formed in standing water, or possibly groundwater percolating through rocks • Past existence of underground pockets of liquid water near volcanoes • Water still exists in the form of ice Why was Mars warmer and wetter in the past? • Greenhouse effect • Today Mars has such a thin atmosphere that it has only a weak greenhouse effect, despite the fact that 95% of its atmosphere is composed of the greenhouse gas CO2 •...
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- Fall '08
- Astrology, liquid water, Mars Reconnaissance Orbiter, Mars Science Lab