Plants saved planet Earth from freezing over during last ice age
2 Jul 2009, 1156 Hrs

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Washington, July 2 In a new research, scientists have suggested that plants may have played a crucial role in putting a limit on the last ice age.

When glaciers advanced over much of the Earth's surface during the last ice age, the planet did not freeze over entirely.

This has been a puzzle to climate scientists because leading models have indicated that over the past 24 million years geological conditions should have caused carbon dioxide levels in the atmosphere to plummet, possibly leading to runaway "icehouse" conditions.

Now, scientists report on the missing piece of the puzzle - plants.

"Atmospheric CO2 concentrations have been remarkably stable over the last 20 or 25 million years despite other changes in the environment," said research co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology.

"We can look to land plants as the primary buffering agent that's held CO2 in such a narrow range during this time," he added.

The research team, led by Mark Pagani of Yale University, found that the critical role of plants in the chemical breakdown and weathering of rocks and soil gave them a strong influence on carbon dioxide levels.

It was a link that earlier studies had missed.

The rise of the Andes, Himalayas, Tibetan Plateau, and mountain ranges in western North America over the past 25 million years would have been expected to have cause faster weathering and erosion, and therefore a faster burial of carbon drawn from the atmosphere.

But the stability of carbon dioxide levels indicate that this didn't happen.

This is where the plants come in.

"The rates of weathering reactions are largely controlled by plants. Their roots secrete acids that dissolve minerals, they hold soils, and they increase the amount of carbon dissolved in groundwater," said Caldeira.

"But when levels of carbon dioxide get too low, the plants basically suffocate and the weathering slows down. That means less sediment is eroded from the uplands and less carbon can be buried. It's a negative feedback on the system that has kept carbon dioxide levels from dropping too low," he added.

Extremely low carbon dioxide levels would have reduced the atmosphere's ability to retain heat, putting the planet into a deep freeze.

"So you could say that by limiting the drawdown of CO2 by chemical weathering and sedimentation, plants saved the planet from freezing over," said Caldeira. (ANI)

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