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SOME 2.5 billion years ago, the sun was so faint the oceans should have been ice. They weren鈥檛, and this 鈥渇aint young sun paradox鈥� has puzzled scientists for decades. Now a modelling study suggests the answer lies with well-known greenhouse gases aided by an extra helping of nitrogen.
Previous modelling attempts to resolve the paradox by loading the early atmosphere with greenhouse gases assumed that it has always had the same amount of nitrogen. But Colin Goldblatt of NASA Ames Research Center in California ran a model in which the pressure of nitrogen was twice what it is today.
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Nitrogen is not a greenhouse gas, but the increased pressure would have led to more frequent collisions between nitrogen molecules and greenhouse gases, causing them to absorb at more infrared wavelengths. Goldblatt found that this would have raised global temperatures by 4.4 掳C (Nature Geoscience, ). He admits that this doesn鈥檛 close the temperature gap entirely, but it could be part of the answer.
Goldblatt says he has evidence that the crust and mantle have since absorbed the extra nitrogen.