A team of UK researchers has revealed how the arrival of the first plants 470 million years ago triggered a series of ice ages.

In the study, published today in the journal Nature Geoscience, the team attempts to identify the effects that the first land plants had on the climate during the Ordovician Period, ended around 444 million years ago.

During this period, the climate gradually cooled, leading to a series of ice ages. It has been previously known that this global cooling was caused by a dramatic reduction in atmospheric carbon, which this study now suggests was triggered by the arrival of plants.

The team used the modern moss, Physcomitrella patens for their study. They placed a number of rocks, with or without moss growing on them, into incubators. Over three months they were able to measure the effects the moss had on the chemical weathering of the rocks. They then used an Earth system model to establish what difference plants could have made to climate change during the Ordovician Period.

The findings show that the first plants, the ancestors of mosses, extracted minerals such as calcium, magnesium, phosphorus and iron from rocks in order to grow. In so doing, they caused chemical weathering of the surface of Earth. This had a dramatic impact on the global carbon cycle and subsequently on the climate.

“This study demonstrates the powerful effects that plants have on our climate,” said Professor Timothy Lenton of the University of Exeter, a co-author on the study. “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.”

The study also suggests that the first plants caused the weathering of calcium and magnesium ions from silicate rocks, such as granite, in a process that removed carbon dioxide from the atmosphere, forming new carbonate rocks in the ocean. This cooled global temperatures by around 5 oC.

“For me the most important take-home message is that the invasion of the land by plants – a pivotal time in the history of the planet – brought about huge climate changes,” said Professor Liam Dolan of Oxford University, a co-author on the study. “Our discovery emphasizes that plants have a central regulatory role in the control of climate: they did yesterday, they do today and they certainly will in the future.”