About 183 million years ago massive volcanic eruptions occurred and lava deposits rivaling the size of continents covered the Earth’s surface, causing mass extinctions and changing ocean chemistry and global climate. What triggered it has been a mystery for the past 183 million years, but a new paper published in Science Advances offers a fascinating explanation. One of the paper’s co-authors, Ricardo L. Silva, Assistant Professor of Paleoenvironmental Sedimentology in the Department of Earth Sciences at the University of Manitoba, explains that what probably enabled this catastrophic sequence of events was the slowing down of tectonic plates. In short, the team found the long-awaited mechanism linking Earth’s interior and surface processes and arrived at an explanation for one of the most important global climate events and mass extinctions in Earth’s past. “Imagine using a pressure washer on the side of your house, but then you stop moving the nozzle and spray water in one place,” says Silva. “Eventually, you’re going to blow a hole in your house. Now build a magma plume from deep within the Earth the pressure washer and tectonic plates in your home. That’s what happened. And when the magma penetrated the plates, huge amounts of carbon dioxide were released, and when the magma heated the surrounding rocks, even more carbon was released.” These large volcanic events, called Major Igneous Provinces (LIPs), occur every 20 million years or so, and the largest release enough carbon into the atmosphere to disrupt Earth’s climate, alter ecosystems, and cause mass extinctions. Examining ancient mudstone deposits from a 1.5km-deep borehole in Wales, the team found that these catastrophic events coincided directly with the onset of major volcanic activity and the associated release of greenhouse gases in the southern hemisphere, in what is now South Africa. Antarctica and Australia. The crucial new information came when the research team’s plate reconstruction models helped them discover the key fundamental geological process that appeared to control the timing and initiation of this and other large-scale volcanic events: plate deceleration. (Why tectonic plates decelerate to such an extent to trigger LIPs is not yet known.) “Scientists have long believed that the initiation of molten volcanic rock, or magma, from deep inside the Earth as a mantle plume was the instigator of such volcanic activity, but new evidence shows that the normal rate of continental plate movement of several centimeters per year effectively prevents magma from penetrating the Earth’s continental crust,” says lead author Micha Ruhl, Assistant Professor at Trinity College Dublin, Ireland. “It appears that only when the speed of continental plate motion slows to near zero can magmas from mantle plumes effectively rise to the surface, causing large volcanic eruptions of large igneous provinces and the associated climate disturbances and mass extinctions.” Such catastrophic environmental events in Earth’s history are of great interest to Silva, who recently came to UM, and rounds out the expertise of the Basin, Environment, and StratigraphY (BETY) research group. Scientists are beginning to recognize that these large volcanic episodes led to profound changes in ocean ecosystems due to the expansion of coastal dead zones and ocean acidification, disrupting the biological flow of carbon between the atmosphere and oceans. However, we still know very little about these processes, so we lack an understanding of how the oceans and ocean productivity affect climate and the environment on different time scales. The BETY research group at UM will fill this gap in knowledge. Research at the University of Manitoba is supported in part by funding from the Government of Canada Research Support Fund. UM Today Staff
