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Mammal Growth Tied to Air Oxygen Levels

October 01, 2005|From Times Staff and Wire Reports

Spurts in the size and diversity of mammals have occurred most commonly in periods marked by high concentrations of atmospheric oxygen, researchers reported this week in the journal Science.

Paul G. Falkowski of Rutgers University and colleagues estimated the amount of oxygen in the atmosphere at various times in the past. They found that the air contained about 10% oxygen when dinosaurs dominated the Earth. Those reptiles required one-third to one-sixth as much oxygen as mammals. By 50 million years ago, when oxygen levels had risen to 17%, mammals were flourishing. Today the level is about 21%.

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