(CN) – Geologists have uncovered evidence that the largest extinction event in the history of planet Earth was an inside job.
Rather than asteroids hitting Earth and killing a majority of the planet’s terrestrial and marine life during the Permian extinction event, a new paper written by three scientists and published in Nature Communications on Monday argues that new clues unearthed in Siberia demonstrate the abrupt intrusion of igneous rock onto the earth’s surface and the changes to the climate it brought triggered widespread extinction.
“There have been five major mass extinctions since life originated on Earth more than 600 million years ago,” said Seth Burgess, lead author of the study and a geologist at the U.S. Geological Survey who explores the nexus of volcanic and tectonic processes. “Most of these events have been blamed, at various times, on volcanic eruptions and asteroids impacts. By reexamining the timing and connection between … the movement of magma, climate change and extinction, we’ve created a model that explains what triggered the end-Permian mass extinction.”
The study – co-written by James Muirhead, researcher with the Syracuse University Department of Earth Sciences and Samuel Bowring, geologist at the Massachusetts Institute of Technology – explored an igneous province in Russia known as the Siberian Traps. Encompassing an area of approximately 500,000 square miles, the rocky outpost serves as a record for more than a million years of volcanic activity.
Unlike the tall cone-like volcanoes, these were broad and flat and abetted the flow of significant volumes of lava and the release of copious amounts of gases like sulfur dioxide, carbon dioxide and methane which altered the climate enough to trigger the extinction event.
The Permian extinction was massive, eradicating 96 percent of the Earth’s marine species and 70 percent of its terrestrial species. It was the only one of Earth’s five extinction events that resulted in a mass extinction of insects.
Researchers say advancements in pinpointing the time of the extinction event and its relation to geologic events led to a fuller understanding of how volcanoes played a role.
“Our model is based on new, high-resolution age data that suggests surface lava flows erupted too early to drive mass extinction,” Muirhead said. “Instead, there was a subinterval of magmatism – a shorter, particular part of the LIP – that triggered a cascade of events causing mass extinction.”
In other words, the subterranean flow of magma in the area gave off an extreme heat and formed sills, or layers of intrusive igneous rock that broke the surface bearing an array of harmful gases.
“Heat from sills exposed untapped, gas-rich sediments to contact metamorphism thus liberating the massive greenhouse gas volumes needed to drive extinction,” Muirhead said.
Metamorphism is the process by which rock minerals are altered due to exposure to extreme heat or pressure.
“Our model links the onset of extinction with the initial pulse of sill emplacement,” Muirhead said. “It represents a critical juncture in the evolution of life on Earth.”
It also argues for an alternative theory to extinction events being driven primarily by external events, such as asteroid impacts.
There are two ways magma forms. The first, more popularly known and decidedly more spectacular, is extrusion, whereby magma is thrown to the Earth’s surface by a volcanic eruption. The other, lesser known method, is called intrusion, where magma settles between layers of already formed rock.
Common types of intrusion are sills, dikes and batholiths.
The sills in Siberia, where the research was conducted, pushed through layers of limestone, coal and clastic rocks. The mixture of magma and the hydrocarbon-bearing coals in the sedimentary layers is what set the stage for the massive greenhouse gas release and a global-scale climate change event that nearly wiped out all vestiges of life from earth, according to the study.
“Mass extinction can take 10,000 years or less – the blink of an eye, by geological standards – but its effects on the evolutionary trajectory of life are still observable today,” Burgess said.