The formation of volcanic rock, and the release of extreme heat associated with the process, might have been to blame for the world's largest, most catastrophic mass extinction – the End-Permian Mass Extinction 252 million years ago.
Scientists have long wanted to find out more about the exact causes of the extinction event, in which 95% of marine species and 70% of land species are thought to have perished.
But until recently, the timing and duration of the mass extinction was imprecise, which meant researchers were unable to get the full picture on what caused the End-Permian Mass Extinction, also referred to as 'Great Dying'.
In a study now published in the journal Nature Communications, geologists have investigated the timing of the extinction and unveiled new clues about what caused it.
"There have been five major mass extinctions, since life originated on Earth more than 600 million years ago," lead author Seth Burgess, a geologist at the US Geological Survey, said in a statement.
"Most of these events have been blamed, at various times, on volcanic eruptions and asteroids impacts. By reexamining the timing and connection between magmatism [the movement of magma], climate change and extinction, we've created a model that explains what triggered the End-Permian Mass Extinction."
The scientists studied the role of intrusive igneous rock, known as sills. These are rocks that form when magma cools slowly below the Earth's surface, such as granite. They conducted their investigations in a large igneous province in Russia called the Siberian Traps. Spanning more than 500,000 square miles, this site bears witness to nearly a million years of intense volcanic activity.
Igneous intrusive rocks are formed via a process known as intrusion, whereby magma forces itself through existing formations of rock, without reaching the surface.
The scientists found that sills in Siberia likely pushed their way through limestone and coal. The mixture of hot, molten rock and hydrocarbon-bearing coals probably led to a massive release of heat and greenhouse gases, triggering global-scale climate change. This set the stage for the extinction of many species across the globe.
"Our model is based on new, high-resolution age data that suggests surface lava flows erupted too early to drive mass extinction. Instead, there was a subinterval of magmatism that triggered a cascade of events causing mass extinction," co-author James Muirhead explained.
"Heat from sills exposed untapped, gas-rich sediments to contact metamorphism [the process in which rock minerals and texture are changed by exposure to heat and pressure], thus liberating the massive greenhouse gas volumes needed to drive extinction. Our model links the onset of extinction with the initial pulse of sill emplacement. It represents a critical juncture in the evolution of life on Earth."