Cascading greenhouse gas catastrophe sparked Earth’s deadliest mass extinction, scientists find

The most famous of all mass extinctions is surely the one which suddenly wiped out around three-quarters of all life, including the dinosaurs, around 66 million years ago.

Next, perhaps, is the current one - also known as the sixth mass extinction, with more than 500 species currently on course to go disappear in next two decades, according to recent research.

But the earth’s third mass extinction event was the most deadly of all. This came around 252 million years ago at the end of the Permian Epoch and the beginning of the Triassic Epoch, just before the first dinosaurs evolved.

During this turbulent time, around three quarters of all land life and about 95 per cent of life in the oceans disappeared within just a few thousand years.

It has not been known exactly what triggered the cascade of death which caused so many plants and animals to die out so quickly, but gigantic volcanic activity in what is now Siberia, combined with the release of large amounts of methane from the seafloor have been long debated as potential triggers of the Permian-Triassic extinction.

But new research based on geochemical modelling provides for the first time “a conclusive reconstruction” of the key events that led to the mega-catastrophe, the team of scientists from Germany, Italy and Canada said.

The international team led by Hana Jurikova, at GEOMAR Helmholtz Centre for Ocean Research Kiel, in Germany, studied isotopes of the element boron in the calcareous shells of fossil brachiopods - clam-like organisms.

This allowed the team to determine the rate of ocean acidification over the Permian-Triassic boundary.

Ocean acidity and atmospheric carbon dioxide (CO2) are closely coupled, so the team was able to reconstruct changes in atmospheric CO2 at the onset of the extinction from boron and carbon isotopes.

They then used a new geochemical model to study the impact of the CO2 injection on the environment.

Their findings showed that volcanic eruptions, from the then active flood basalt province known as the Siberian Traps, released immense amounts of CO2 into the atmosphere.

This huge CO2 release lasted several millennia and led to a strong greenhouse effect on the late Permian world, causing extreme warming and acidification of the ocean.

This then caused dramatic changes in chemical weathering on land, which altered productivity and nutrient cycling in the ocean, and ultimately led to vast de-oxygenation of the ocean, the researchers said.

These multiple new stresses on the environment combined to wipe out a wide variety of animal and plant groups.

Dr Jurikova said: “We are dealing with a cascading catastrophe in which the rise of CO2 in the atmosphere set off a chain of events that successively extinguished almost all life in the seas.

“This domino-like collapse of the inter-connected life-sustaining cycles and processes ultimately led to the observed catastrophic extent of mass extinction at the Permian-Triassic boundary.”

The research also offers  “bleak lessons” for the future, the scientists said.

"Ancient volcanic eruptions of this kind are not directly comparable to anthropogenic carbon emissions, and in fact all modern fossil fuel reserves are far too insufficient to release as much CO2 over hundreds of years, let alone thousands of years as was released 252 million years ago.

“But it is astonishing that humanity’s CO2 emission rate is currently fourteen times higher than the annual emission rate at the time that marked the greatest biological catastrophe in Earth's history,” said Dr Jurikova.

The study is published in the journal Nature Geoscience.