SUMMARY: 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.
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