Research by scientists from Oxford and Exeter universities, published this week, has shed new light on the cause of a series of ice ages that affected the earth 475 million years ago.
Until now, it has been assumed that global cooling began 200 to 300 million years ago with the emergence of large plants with large rooting systems. This new research reveals a significant change in climate occurring 100 million years earlier in the Ordovician Period (488-444 million years ago), due to the emergence of the first land plants.
Where a rise in carbon dioxide levels in the atmosphere causes an increase in temperature, a decrease results in the cooling of the climate. Scientists claim that the interaction of the first land plants with rocks resulted in a significant decrease in the carbon dioxide levels due to silicate weathering – the process by which mosses extract nutrients from rock formations by dissolving them with acid, leading to carbon dioxide reacting with the rocks and being removed from the atmosphere. The expansion of non-vascular plants (mosses) around 475 million years ago may therefore have accelerated this chemical weathering, causing a fall in atmospheric carbon dioxide and triggering formation of the polar ice caps.
Professor Liam Dolan from University of Oxford Department of Plant Sciences, one of scientists involved in the research, told Cherwell, “The most important message is that the invasion of the land by plants, a pivotal time in the history of the planet, brought about huge climate changes. It should also remind us that the removal of large areas of the world’s vegetation, which act as carbon stores, will increase atmospheric carbon dioxide levels and cause dramatic climate change.”
Third year Earth Scientist Tom Phelan commented, “Currently climate change is a global problem and scientific research into previous climatic events is not only important for the scientific community but also for the global community.” He added, “The recent discovery is important as it is clear evidence for the world to see that deforestation and removing plants from the Earth’s surface is only going to enhance the rate of climate change.”
Timothy Lenton from Exeter University, who headed the team of researchers, added, “Although plants are still cooling the Earth’s climate by reducing the atmospheric carbon levels, they cannot keep up with the speed of today’s human-induced climate change. It would take millions of years for plants to remove current carbon emissions from the atmosphere.”