Volcanoes and extinctions
Trip Start Jan 30, 2007
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29 May 2009
Researchers show the first ever concrete link between massive ancient volcanic activity and global mass extinctions.
Geologists have long been aware that vast and explosive volcanic activity seems to coincide with some of the planet's largest mass extinctions. But, until now, they had no tangible evidence for a cause and effect link.
In a new study published in Science this week, a team of geologists shows that massive volcanic explosions in the Emeishan province in southwest China happened right before a global mass extinction 260 million years ago.
Scientists have debated the cause of mass extinctions for years with asteroid impacts, volcanic eruptions and changes in sea level suggested as the likely triggers. Most agree the extinction of the dinosaurs at the end of the Cretaceous was down to a massive asteroid impact 65 million years. But all other large mass extinctions were probably linked to major volcanic activity.
Volcano sandwich in limestone
An explosion in volcanic activity would have led to sharp cooling - limiting the growth of photosynthetic creatures - and long periods of acid rain. The planet is likely to have then warmed up gradually, because of the carbon dioxide released from the many volcanoes.
But finding a direct cause-effect link between volcanic activity and mass extinctions is difficult, because the fossils that mark the extinctions are rare in volcanic regions.
In 1994, scientists unearthed evidence for a global mass extinction that happened 260 million years ago, druing the Middle Permian. Just a few years later, they discovered the relics of huge volcanic eruptions in the Emeishan province in southwest China. The eruptions were massive and unleashed around one million cubic kilometres of lava, covering an area five times the size of Wales.
Professor Paul Wignall of the University of Leeds soon realised this presented a perfect opportunity to study the fossil record and the volcanic history of the area at the same time. 'I thought the two must be linked,' says Wignall.
Wignall and his team - including researchers from the China University of Geosciences - took rock samples from two locations at Wuhan in China where volcanic rock is sandwiched between layers of limestone in Emeishan province.
Since the limestone contains easily datable marine fossils it was possible to see which creatures were present before the increase in volcanic explosions and which ones disappeared afterwards.
The researchers built up a picture of the types of marine creatures that lived at various times before and after volcanic explosions. They found several groups of tiny marine creatures disappeared after the start of the volcanic explosions, which suggests the devastation unleashed by the volcanoes spelt disaster for many species.
'Nowhere in the world is as good as this as a place to study both volcanic activity and mass extinction at the same time. Because this plate is being uplifted towards the Himalayas, the area is exposed and is ripe for studying,' says Wignall. Most of the evidence in other places around the world is buried under the sea.'
While the extinction of the dinosaurs is the best-known mass extinction, the largest in the Earth's history happened around 250 million years ago. Called the Permian-Triassic event, it led to nine out of every ten marine animals dying out and was probably caused by either massive volcanic eruptions in an area known as the Siberian traps, a meteorite impact or both.
'This less well-known mass extinction has been hiding in the shadow of the well-known Permian-Triassic extinction,' says Wignall.
Volcanism, Mass Extinction, and Carbon Isotope Fluctuations in the Middle Permian of China
Paul B. Wignall et al
Science 29 May 2009, Vol. 324. no. 5931, pp. 1179 - 1182