Biggest mass extinction in history 250 million years ago was triggered by an enormous volcanic eruption in Siberia which spewed huge amounts of carbon dioxide into the atmosphere

 

• Life on Earth was almost totally wiped out by CO2 around 252 million years ago
• The huge eruption in Siberia ejected massive quantities of the greenhouse gas
• It killed of around 90 per cent of the world's creatures by making the seas acidic
• New research provides the first precise reconstruction of the source of carbon

The biggest mass extinction event in Earth's history was caused by a volcanic eruption in Siberia that spewed carbon dioxide (CO2) into the atmosphere, scientists say. 

The Permian–Triassic extinction event, also known as the 'Great Dying', wiped out 95 per cent of marine species and 70 per cent of terrestrial species at the time. 

When the CO2 dissolved in the oceans, they became highly acidic and the level of oxygen in the water was reduced, killing sea life. 

Other extreme changes and multiple stressors – high temperatures and sulphide poisoning – also helped wipe out a large variety of marine organisms. 

The Great Dying was driven by an immense multi-millennial carbon injection and can be used as an example of what can happen following long-term CO2 production.  

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Approximately 252 million years ago, long before the emergence of dinosaurs, at the Permian-Triassic boundary, the largest of the known mass extinctions on Earth occurred, triggered by a  volcanic eruption in Siberia (stock photo)

'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.'

During the Great Dying, a supercontinent called Pangaea covered the Earth

The 'Great Dying' is a period where life on Earth has never been so close to becoming completely extinct without recovering, either before or since. 

During the Great Dying, all land on Earth was stuck together in a supercontinent called Pangaea, which was surrounded by a thriving and diverse ecosystem of sea life. 

In total, it is believed that around 90 per cent of all life was wiped out by the Great Dying in the space of several thousands of years – a geological 'blink of an eye'.

Scientists have long debated the theories of the cause of the extinction ranging from a meteor impact to volcanoes, which could have caused climatic and environmental changes making Earth inhospitable. 

For this study, experts analysed fossils of clam like shellfish called brachiopods that once lived on the seafloor.

They were able to work out pH readings of the ocean 250 million years ago from the ancient fossilised shells of these animals. 

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Dr Jurikova's team analysed fossils of clam like shellfish called brachiopods (pictured) that lived on the seafloor

Seawater pH is an indicator of ocean acidity, which varies depending on the amount of absorbed CO2. The higher the CO2 level, the more acidic an ocean becomes. 

The team was able to determine that the trigger of the Permian-Triassic crisis was a large pulse of CO2 to the atmosphere originating from a massive flood basalt province, the result of a giant volcanic eruption in today's Siberia. 

Analyses showed that the volcanisms released more than 100,000 billion tonnes of carbon into the atmosphere, triggering the onset of the extinction. 

This is more than 40 times the amount of all carbon available in modern fossil fuel reserves including carbon already burned since the Industrial Revolution.

The research team used computer modelling to reconstruct the effect of such large CO2 release on global bio-geochemical cycles and the marine environment. 

The findings showed that initially, CO2 led to extreme warming and acidification of the ocean that was lethal to many organisms, especially those building calcium carbonate shells and skeletons. 

The greenhouse effect, however, led to further dramatic changes in chemical weathering rates on land.This resulted in vast de-oxygenation and likely sulphide poisoning of the oceans too, killing the remaining organism groups.

The Permian-Triassic mass extinction was therefore 'a cascading collapse of vital global cycles' that were sustaining the environment. 

Studies have shown modern ocean acidification is endangering marine life and communities whose livelihoods depend on it.

The experts warn that ocean acidication is currently being observed, from the ongoing 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.' 

GREAT DYING 'TRIGGERED SWITCH TO WARM-BLOODEDNESS' 

University of Bristol palaeontologist Professor Mike Benton has said that the ancestors of both mammals and birds became warm-blooded at the same time, some 250 million years ago. 

Around this time, life was recovering from the greatest mass extinction of all time - the Great Dying. 

The Great Dying mass extinction killed around 90 per cent of life on Earth and the very few survivors faced a turbulent world, repeatedly hit by global warming and ocean acidification crises. 

But two main groups of tetrapods survived - the synapsids and archosaurs, including ancestors of mammals and birds respectively.

Palaeontologists had identified indications of warm-bloodedness, or technically endothermy, in these Triassic survivors, including evidence for a diaphragm and possible whiskers in the synapsids.

More recently, similar evidence for early origin of feathers in dinosaur and bird ancestors has come to light. 

In both synapsids and archosaurs of the Triassic, the bone structure shows characteristics of warm-bloodedness.

The evidence that mammal ancestors had hair from the beginning of the Triassic has been suspected for a long time, but the suggestion the archosaurs had feathers from 250 million years ago is new. 

Professor Benton said: 'Modern amphibians and reptiles are sprawlers, holding their limbs partly sideways.

'Birds and mammals have erect postures, with the limbs immediately below their bodies. This allows them to run faster, and especially further. There are great advantages in erect posture and warm-bloodedness, but the cost is that endotherms have to eat much more than cold-blooded animals just to fuel their inner temperature control.'

The evidence from posture change and from early origin of hair and feathers, all happening at the same time, suggested this was the beginning of a kind of 'arms race'. 

In ecology, arms races occur when predators and prey have to compete to with each other, and where there may be an escalation of adaptations. 

The lion evolves to run faster, but the wildebeest also evolves to run faster or twist and turn to escape.

Something like this happened in the Triassic, from 250 to 200 million years ago. 

Today, warm-blooded animals can live all over the Earth, even in cold areas, and they remain active at night. 

They also show intensive parental care, feeding their babies and teaching them complex and smart behaviour. 

These adaptations gave birds and mammals the edge over amphibians and reptiles and in the present cool world allowed them to dominate in more parts of the world.

Professor Benton added: 'The Triassic was a remarkable time in the history of life on Earth. You see birds and mammals everywhere on land today, whereas amphibians and reptiles are often quite hidden.

'This revolution in ecosystems was triggered by the independent origins of endothermy in birds and mammals, but until recently we didn't realise that these two events might have been coordinated.

'That happened because only a tiny number of species survived the Permian-Triassic mass extinction – who survived depended on intense competition in a tough world. 

'Because a few of the survivors were already endothermic in a primitive way, all the others had to become endothermic to survive in the new fast-paced world.'