“Big Five” should be “Big Six” say extinction researchers

Brachiopods

There are five generally acknowledged key mass extinction events in Earth’s history. Now new evidence led by a researcher at the University of Hull argues that a sixth extinction – which took place 262 million years ago – should be added to the list.

The Capitanian extinction event occurred during the Middle Permian period in China. Since the only evidence for the event was found in tropical regions, there has been some uncertainty on its global impact.

But new evidence led by Dr David Bond from Hull’s Department of Geography, Environment and Earth Sciences shows this extinction also occurred in Spitsbergen (Arctic Norway), proving that extinctions also took place in the Arctic, making it global in scale.

Global extinction

Dr Bond said: “Our research means we can now say this is a true global extinction.

“The disappearance of fossils in tropical waters and Arctic waters provide strong evidence that the Capitanian extinction was global, not just regional, as first thought.

“This qualifies it to become a key mass extinction event that should join the ‘Big Five’ events already recognized by most scientists.”

The event was first identified some 20 years ago when evidence of fossil extinctions in rock formations were found in China. The rocks had originally formed on the floor of a shallow tropical sea. Most tiny-shelled micro organisms called foraminifera were wiped out, along with many species of clamlike brachiopods.

Dr Bond, working with Prof. Paul Wignall at the University of Leeds, and colleagues at the Norwegian Polar Institute, the Geological Survey of Canada and the University of Erlangen in Germany, began looking at the event in 2011 and for evidence of extinction elsewhere besides the tropics.

Ancient volcanic eruptions

On the island of Spitsbergen in Arctic Norway the team examined layers of ancient rock and found a rich and diverse community of brachiopod shells that were almost completely wiped out at a level they correlated with the known extinction level in the tropics.

They found there was also a possible trigger to blame: a set of ancient volcanic eruptions in faraway China that would have released huge amounts of sulphur and carbon dioxide into the air, potentially causing a quick global chill followed by a longer period of global warming. The gases could have also driven acidification and oxygen depletion in the oceans.

Dr Bond explained: “This event should be seen as yet another example from Earth’s past of the harmful effects of massive volcanism and CO2 emissions.

“Carbon dioxide causes warming and ocean acidification, both factors in the Middle Permian crisis, and both concerns today when we think about the future of the planet. Human CO2 emissions are not vastly dissimilar to those associated with the biggest volcanic events in history.

“Indeed, at current rates of anthropogenic pollution, if fossil fuel resources permitted, in just 1000-3000 years we will release the same amount of CO2 as the ‘Siberian Traps’ which caused the biggest extinction of them all. Our concerns for the future are well founded in happenings in Earth’s past.”

 

Top picture: Fossil Brachiopods Daniela Nature Photography (CC BY-SA 2.0)

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