Earth’s most devastating mass extinctions triggered by slowing of continental plates, study finds

Earth’s history has been marked by major volcanic eruptions, some of which caused such climatic and biological upheaval that they drove some of the most devastating extinction events in Earth’s history.

Now scientists have shed new light on the timing and likely cause of these events that occurred millions of years ago.

A new study by Trinity College Dublin reveals that a slowing of continental plate movement was the critical event that enabled magma to rise to the Earth’s surface and deliver the devastating knock-on impacts.

The surprising discovery is based on chemical data from ancient mudstone deposits obtained from a mile deep borehole in Wales.

‘Scientists have long thought the onset of upwelling of molten volcanic rock, or magma, from deep in Earth’s interior, as mantle plumes, was the instigator of such volcanic activity,’ said lead author Dr Micha Ruhl, of Trinity College Dublin.

‘But the new evidence shows that the normal rate of continental plate movement of several centimetres per year effectively prevents magma from penetrating Earth’s continental crust.

‘It seems it is only when the speed of continental plate movement slows down to near zero magmas from mantle plumes can effectively make their way to the surface, causing major large igneous province volcanic eruptions and their associated climatic perturbations and mass extinctions.’

Model linking the reduced velocity of the African continental plate with the increased thermal erosion of the mantle and crust, leading to the emplacement of the Karoo-Ferrar Large Igneous Province (LIP) in Southern Pangea 183 million years ago.

The world’s biggest volcanoes lie in areas called Large Igneous Provinces (LIPs). 

These include the Siberian Traps in Russia, which span more than 500,000 square miles and were the site of nearly a million years of epic volcanic activity.

The biggest eruptions 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 the study, the international team was able to link two key events that occurred during the Toarcian period, around 183 million years ago.

This time period was characterised by some of the most severe climatic and environmental changes ever, and directly coincided with the occurrence of major volcanic activity and associated greenhouse gas release in the southern hemisphere. 

Computer reconstruction models showed that the slowing of continental plate movement was the key fundamental geological process that seemed to control the timing and onset of this volcanic event and others of great magnitude. 

‘Crucially, further assessment shows that a reduction in continental plate movement likely controlled the onset and duration of many of the major volcanic events throughout Earth’s history, making it a fundamental process in controlling the evolution of climate and life at Earth’s surface throughout the history of this planet,’ said Dr Ruhl.

Throughout the past 600 million years there have been five major mass extinctions. While some are well studied, others are more enigmatic.

The first three extinctions took place near the end of the Ordovician Period (around 445 million years ago), end of the Devonian Period (from 385 to 359 million years ago) and at the end of the Permian Period (252 million years ago).

The most devastating of all these events was the end of the Permian period, which wiped out some 96 per cent of all marine species and about 70 per cent of all known species on Earth.

Massive volcanic eruptions occurred on a scale never before seen, with other effects that include runaway greenhouse effect triggered by methane release from clathrates on the seafloor. Recovery took around 10 million years.

An extinction at the end of the Triassic, about 201 million years ago, mostly affected life in the oceans, with a third of marine species going extinct. Some reptile groups also went extinct on land.

Examples of when reduced plate velocity coincided with major volcanic eruptions – including the onset of Siberian Traps emplacement around 252 million years ago (A), the ’emergence’ of the Iceland Plume from underneath the Greenland craton around 56 million years ago (B), and the onset of East African Rift volcanism around 40 million years ago, which led to continued eruptions throughout the Late Cenozoic period (C).

The Late Triassic mass extinction 201m years ago was caused by a large-scale eruption of the Central Atlantic Magmatic Province, which heralded the splitting of the supercontinent Pangaea (left) and the initial opening of what would become the Atlantic Ocean

The study by Trinity College Dublin reveals that a slowing of continental plate movement was the critical event that enabled magma to rise to the Earth’s surface and deliver the devastating knock-on impacts

The last mass extinction happened 66 million years ago when an asteroid as big as a city smashed into the Gulf of Mexico. It killed off the dinosaurs.

The study helps disentangle the different processes that control global carbon cycle change and tipping points in Earth’s climate system.

It could have implications for today – as a sixth mass extinction is already thought to be underway owing to manmade global warming.