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Life first arose on the Earth, 4.6 billion years ago.
When life first arose on the Earth, 4.6 billion years ago, the Sun was putting out 20-25% less energy - our planet should have been an iceball... why wasn't it? Evidence from ancient rocks shows that there was a large amount of carbon dioxide and methane in the Earth's atmosphere, which would have helped warm the planet. But these levels were tied to early weather and plate tectonics which carried the greenhouse gasses into and out of the atmosphere, leading to several early ice ages. New research from Stanford has turned up rocks that give an accurate picture of how these gas levels rose and fell over the first few billion years.
NASA's Opportunity rover is continuing to circle the rocky rim of Endurance Crater, searching for the right place to try and go in. At its deepest point, the crater descends 20 metres (66 feet), so operators are looking for a sheet of stable rock that will stop the rover from slipping in the Martian sand. So far, it looks like the slope is 18 to 20 degrees, which is within the rover's ability to climb back out - just barely. In Eagle crater, where Opportunity landed, the rover was unable to get out from a 17-degree slope because of fine dust at the top of the crater's rim.
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