OXYGEN is a good thing, in moderation. Too little, and oxygen-breathing organisms would all suffocate. But if the atmosphere contained too much, firestorms would sweep the world. Now two geochemists believe they have unravelled the feedback mechanism that prevents a global catastrophe of either kind. The atmosphere's oxygen content is regulated by bacteria living in sediments on the seabed, they say.
The amount of oxygen in the atmosphere is always roughly in balance with the oxygen content of the oceans - if one of these reservoirs of the gas becomes depleted, oxygen diffuses into it from the other. Much of the oxygen in the atmosphere is produced by photosynthetic algae floating near the surface of the sea. Over millions of years, excess oxygen is consumed by the process of weathering, in which the gas combines with minerals in rocks.
Weathering also releases phosphorus, which eventually finds its way into the ...
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