Arrival of plants triggered ice ages

Posted by Kate Taylor

The arrival of the first plants 470 million years ago triggered a series of ice ages.

During the Ordovician Period, which ended 444 million years ago, the climate gradually cooled, leading to a series of 'ice ages'.

And the reason, says the team, was a dramatic fall in atmospheric carbon, triggered by the arrival of plants.

The team, from the Universities of Exeter and Oxford, studied the modern moss Physcomitrella patens. They placed a number of rocks, with or without moss growing on them, into incubators, and then measured the effects the moss had on the the rocks over three months.

They then used this data with an Earth system model to establish what difference plants could have made to climate change during the Ordovician Period.

Mosses were among the first plants to grow on land. And, the research suggests, they caused the weathering of calcium and magnesium ions from silicate rocks, such as granite. This process removed carbon dioxide from the atmosphere, forming new carbonate rocks in the ocean - and cooling global temperatures by around five degrees Celsius.

In addition, by weathering the nutrients phosphorus and iron from rocks, the plants increased the quantities of both these nutrients going into the oceans. This removed yet more carbon from the atmosphere, cooling the climate by another two to three degrees.

It could also have had a devastating impact on marine life, leading to a mass extinction that has puzzled scientists, says ther team.

"This study demonstrates the powerful effects that plants have on our climate," says one of the lead researchers, Professor Tim Lenton of the University of Exeter.

"Although plants are still cooling the Earth's climate by reducing atmospheric carbon levels, they cannot keep up with the speed of today's human-induced climate change. In fact, it would take millions of years for plants to remove current carbon emissions from the atmosphere."