Did Plants Cool the Earth and Spark Explosion of Life?

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Before plants drifted in from the sea, the Earth was a fairly barren wasteland of rocks, sometimes buried in ice.

Hedges and his collaborators suggest that as plants colonized Earth, they changed the climate, making it cooler by removing carbon dioxide from the atmosphere.

"Lots of plants would remove carbon dioxide from the atmosphere and increase the amount of oxygen," said Hedges. "It's the reverse of the global warming we see today, when we're releasing more carbon dioxide into the atmosphere by burning fossil fuels."

At the same time, plants release more oxygen into the atmosphere. "One widely entertained idea is that the Cambrian Explosion had something to do with an increase in oxygen at the time," said Hedges. The lack of oxygen would limit animal size because the larger an animal is, the higher its requirement for oxygen.

"The plants conceivably boosted oxygen levels in the atmosphere high enough for animals to develop skeletons, grow larger, and diversify," said Hedges.

The theory is bound to engender controversy; there is some question as to whether there would be enough plants to have caused the changes proposed by Hedges and company. But Hedges, whose area of expertise is astrobiology—the study of the relationship between life and the environment—is excited about the possibility.

"This study suggests that there's a lot more synergy between biological evolution and the Earth's geologic history."

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