The massive mass extinction incident in Earth’s history was caused by a volcanic eruption in Siberia that poured out carbon dioxide (CO2) into the atmosphere, scientists explain.
The Permian–Triassic extinction incident, also understood as the ‘Great Dying’, annihilated 95 per cent of marine species and 70 per cent of terrestrial species at the time.
When the CO2 disintegrated in the oceans, they came to be highly acidic and the level of oxygen in the water was decreased, destroying sea life.
Additional extreme alterations and multiple stressors – elevated temperatures and sulphide poisoning – also helped annihilate a large species of marine organisms.
About 252 million years ago, years prior to the emergence of dinosaurs, at the Permian-Triassic boundary, the largest of the known mass extinctions on Earth happened, triggered by a volcanic eruption in Siberia.
‘Our research provides the first precise reconstruction of the carbon source and with it the trigger of the crisis, as well as uncovers the subsequent chain of processes that resulted in Earth’s largest mass extinction,’ said Dr Hana Jurikova at the University of St Andrews, Scotland.
‘It took several hundreds of thousands to millions of years for the ecosystem to recover from the catastrophe which profoundly altered the course of evolution of life on Earth.’
At the time of the Great Dying, a supercontinent called Pangaea covered the Earth. It was encompassed by a thriving and diverse ecosystem of sea life.
The ‘Great Dying’ is a time where life on Earth has never been so close to coming to be totally extinct without restoring, either before or since.
It is speculated that around 90 per cent of all life was annihilated by the Great Dying in the space of many thousands of years – a geological ‘blink of an eye’.
Scientists have long disputed the theories of the reason for the extinction varying from a meteor impact to volcanoes, which could have resulted in climatic and environmental alterations making Earth inhospitable.
For this study, experts examined fossils of clam like shellfish called brachiopods that once lived on the seafloor.
They could work out pH readings of the ocean 250 million years ago from the ancient fossilised shells of these animals.
Seawater pH is a pointer of ocean acidity, which fluctuates based on the amount of absorbed CO2. The more the CO2 level, the more acidic an ocean becomes.
The team could deduce that the trigger of the Permian-Triassic disaster was a massive pulse of CO2 to the atmosphere emerging from a large flood basalt province, the outcome of a giant volcanic eruption in today’s Siberia.
Analyses revealed that the volcanisms spewed more than 100,000 billion tonnes of carbon into the atmosphere, activating the onset of the extinction.
This is over 40 times the amount of all carbon available in modern fossil fuel reserves comprising carbon already burned since the Industrial Revolution.
The research team utilized computer modelling to reconstruct the impact of such large CO2 release on global bio-geochemical cycles and the marine environment.
The findings revealed that originally, CO2 led to severe warming and acidification of the ocean that was lethal to several organisms, particularly those building calcium carbonate shells and skeletons.
The greenhouse effect, regardless, caused further dramatic alterations in chemical weathering rates on land.
This resulted in substantial de-oxygenation and probable sulphide poisoning of the oceans too, destroying the remaining organism groups.
The experts notify that ocean acidication is presently being examined, from the continuous decrease in their pH levels.
‘A coupled increase in atmospheric CO2 and decrease in surface ocean pH, global warming, changes in productivity and oxygen depletion have been reported worldwide.’ the team said in Nature Geoscience.
‘[This] suggests that the scenario outlined here for [the Great Dying] may also be relevant to understanding future environmental and climatic trends.’