Perpetrators of mass deaths identified, motive remains unknown

September 9, 2022 —

About 183 million years ago, massive volcanic eruptions and continent-sized lava deposits covered the Earth’s surface, causing mass extinctions and altering ocean chemistry and global climate. What triggered this has been a mystery for the past 183 million years, but a new paper published in scientific advances offers a convincing explanation.

One of the publication’s co-authors, Ricardo L. Silva, assistant professor of paleoecological sedimentology in the University of Manitoba’s Department of Earth Sciences, explains that this catastrophic series of events was likely made possible by a slowing of the tectonic plates. In short, the team found the long-sought mechanism that connects Earth’s interior to near-surface processes and found an explanation for one of Earth’s greatest past global climate and mass extinction events.

“Imagine using a pressure washer on the side of your house, but then you stop moving the spout and spray water in one spot,” says Silva. “Eventually you will drill a hole through your house. Now, a plume of magma from deep within the Earth makes the high-pressure cleaner and tectonic plates your home. That’s what happened. And as the magma bored through the plates, huge amounts of carbon dioxide were released, and as the magma heated the surrounding rock, even more carbon was released.”

These large volcanic events, called Large Igneous Provinces (LIPs), occur about every 20 million years, and the largest release enough carbon into the atmosphere to disrupt Earth’s climate, alter ecosystems, and cause mass extinctions. By examining ancient mudstone deposits from a 1.5 km deep borehole in Wales, the team discovered that these catastrophic events coincided directly with the occurrence of major volcanic activity and the associated release of greenhouse gases in the southern hemisphere, in what is now southern Africa, in the Antarctica and Antarctica Australia.

The crucial new information came as the plate reconstruction models helped the research team discover the key fundamental geological process that appeared to drive the timing and onset of this volcanic event and other large-scale events: the slowing of the plates. (Why tectonic plates slow down enough to allow LIPs is not yet known.)

“Scientists have long assumed that the onset of rising molten volcanic rock, or magma, from deep within the Earth’s interior as mantle clouds was the trigger for such volcanic activity, but the new evidence shows that the normal rate of continental plate motion of several centimeters per year prevents it effective for magma to invade the Earth’s continental crust,” says lead author Micha Ruhl, Assistant Professor at Trinity College Dublin, Ireland. “It appears that magmas from mantle plumes can only effectively surface when the rate of continental plate motion slows to near zero, leading to large volcanic eruptions in magmatic provinces and the attendant climate disturbances and mass extinctions.”

Such catastrophic environmental events in Earth’s history are of great interest to Silva, who recently joined UM and rounds out the expertise of the Basin, Environment, and straTigraphY (BETY) research group. Scientists are beginning to see that these major volcanic episodes caused profound changes in ocean ecosystems as coastal dead zones expanded and the oceans acidified, disrupting the flow of biological carbon between the atmosphere and the oceans. However, we still know very little about these processes, so we lack an understanding of how oceans and ocean productivity affect climate and the environment over different timescales. The BETY research group at UM will fill this knowledge gap.

UM Today staff