Slowing of continental shift could be the cause of major volcanic extinction events

A slowing of continental plate movement may have been the critical event that drove some of Earth's most devastating extinction events, according to a new study published in Science Advances.

The study's lead author, Dr. Micha Ruhl, tells IE that the new model debunks the generally held view that major volcanic events are linked to the 'upwelling' of magma from deep in Earth's interior.

And that's not all.

The study also provides a fresh boost in evidence for volcanic events being the cause of past mass extinction events. Until now, such a connection has been extremely complicated to prove.

Sites of major volcanic activity coincide with a reduction in the speed of continents

Earth’s history has been marked by major volcanic events, called Large Igneous Provinces (LIPs). The largest of which have caused major increases in atmospheric carbon emissions that warmed Earth’s climate drove unprecedented changes to ecosystems and resulted in mass extinctions on land and in the oceans.

In an age of figuring out the tipping points controlling Earth's climate system, it is therefore important for scientists to further their understanding of climate-sensitive processes - and that includes LIPs.

"The cause of the major volcanic events is commonly thought to be linked to the 'upwelling' of magma from deep in Earth's interior, which is called a mantle plume," explains Ruhl. When this magma reaches the base of the continent, it is assumed that it will relatively quickly erode (or melt) the continent from below to allow for volcanic activity to take place at the surface.

However, when the scientists compared the age of volcanic activity with models of plate reconstruction (models that show where the continents were in the past), they observed a co-occurrence.

"The Karoo-Ferrar Large Igneous Province, but also several other Large Igneous Provinces in Earth's past (e.g. the Siberian Traps, which are linked to the End-Permian mass extinction) all coincide with a significant reduction in the velocity of the continents. To less than 2cm per year," reveals Dr. Micha Ruhl.

'Just imagine you have a candle and a piece of paper

The professor likens the new model to that of a piece of paper that moves horizontally over a candle. "If you move the paper fast enough, then it may blacken the paper to some degree, but it will not burn a hole in it. Only when the paper moves over the flame slow enough then the candle has enough time to burn a hole in the paper," explains Ruhl.

The scientists believe a similar mechanism may be at play on a global continental scale. In other words, it is not the arrival of the mantle plume (the candle), but rather a slow-down in the velocity of the continental movement (the piece of paper) that allows the volcanic activity to happen.

Analyzing 183 million year deposits- a direct link to mass extinctions

Modern-day volcanoes on land and on the seafloor release mercury (Hg) into the atmosphere and oceans, respectively. It is hypothesized that a large volcanic event in Earth's past would have released a lot of Hg into Earth's surface environments.

Therefore the team studied a ~1.5 kilometer-long drillcore from Wales (UK), which contained sedimentary layers that formed before, during, and after the Toarcian Oceanic Anoxic Event (T-OAE).

The (T-OAE) occurred 183 million years ago and is characterized by significant ocean acidification, widespread ocean anoxia, and seawater warming leading to major ocean extinction. Today, this volcanic activity resides in Southern Africa and Antarctica- a place that is known as the Karoo-Ferrar Large Igneous Province.

"We analyzed the sedimentary layers [from the Karoo-Ferrar LIP] for their mercury (Hg) content," Ruhl explains to IE.

The results showed highly elevated levels of Hg in orders of magnitude higher than sediments that formed before and after [the ancient volcanic deposits]. Dr. Ruhl explains to IE that this observation "suggests indeed there was a direct temporal link between volcanism and associated greenhouse gas release." And therefore the catastrophic climatic change that followed after.

Next steps

Still, the new study is not quite the plethora. The team admits that more understanding of how mercury gets from the atmosphere and oceans into sediments is still required.

Additionally, uncertainties do exist in plate reconstruction models.

It's also unclear as to why continental plates slow down at some times and speed up at others.

Since the work is part of an ongoing research program by a large international team, the Early Jurassic Earth System and Timescale (JET) project, future work could bring the scientists closer to addressing the uncertainties.

Either way, learning more about volcanoes always makes for an interesting topic.