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15 November 2009

Paradox lost: molecular collisions kept early Earth warm

Some 2.5 billion years ago, the sun was so faint, the oceans should have been ice. They weren’t, and this “faint young sun paradox” has puzzled scientists for decades. Now a modelling study suggests the answer lies with the greenhouse effect, and an extra helping of nitrogen.

Previous modelling efforts to resolve the paradox by loading the early atmosphere with greenhouse gases assumed that it has always had the same concentration of nitrogen. Instead, Colin Goldblatt of NASA Ames Research Center in California ran a model in which the pressure of nitrogen was twice what it is today.

Nitrogen is not a greenhouse gas, but the pressure rise would have led to more collisions between these molecules and greenhouse gases, causing them to absorb more infrared wavelengths.

Goldblatt found that this would have raised global temperatures by 4.4 degrees C (Nature Geoscience, DOI: 10.1038/ngeo692). He admits that this doesn’t 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.

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