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Volcanoes, asteroids and mass extinctions

17.05.2004


Neither massive volcanic eruptions nor extraterrestrial impacts are sufficiently powerful on their own to cause mass extinctions of life on Earth, research by University of Leicester geologists suggests.



Instead, both events coincidentally occurring together may be required to cause the worst mass extinctions.

In the last 300 million years, life on Earth has suffered three major mass extinctions: those of the end-Permian, end-Triassic and end-Cretaceous periods.


The third of these, leading to the demise of the dinosaurs 65 million years ago, is believed to be caused by a meteorite colliding with the Earth, combined with the eruption of huge floods of basaltic lava.

Controversy rages over whether all three mass extinctions involve a similar combination of impact and volcanism, and if they did, whether this is due to random chance or whether there is any causal link between impact and volcanism.

Dr Rosalind White, Royal Society Dorothy Hodgkin Research Fellow, and Professor Andrew Saunders, both of the University of Leicester Department of Geology, recently looked at the statistical probability of any link between impact and eruptions to see whether it is credible that they occur during the same period by coincidence alone.

Their re-evaluation of the frequency of bolide (extraterrestrial) impacts and massive ‘flood basalt’ volcanism indicates that both events occur individually much more frequently than the incidence of mass extinctions.

This suggests that each, on its own, is not powerful enough to trigger a disastrous worldwide collapse of ecosystems that would lead to a mass extinction.

The occurrence of flood basalts (caused by the outpourings of basaltic lava) and bolide impact may both be necessary to lead to the largest mass extinctions the planet has known.

That begged the question as to what the likelihood was of the two events occurring over the same period, if they were not linked.

Here, Professor Saunders’ and Dr White’s statistical analysis showed that three random coincidences involving both impact and volcanism over the last 300 million years are likely, and there would not necessarily have to be any link between them.

They therefore suggest that theories implying that flood basalts are generated by bolide impacts are unnecessary and unproven.

Rosalind White explained the scale of events that cause flood basalts: “Massive continental flood basalt provinces occur when immense outpourings of basaltic lava are formed by localised partial melting in anomalously hot regions of the Earth’s mantle (the solid layer of rock between the Earth’s core and crust).

“A typical continental flood basalt would cover an area five times that of the UK, with lava exceeding 1 km in thickness, made up of hundreds of individual lava flows, each coming from an enormous volcanic eruption that may have lasted decades.

“Eruptions are separated by periods of inactivity that can last hundreds or thousands of years. The total time taken to erupt an entire continental flood basalt province is probably approximately 1-5 million years, though in most cases, the dating is not precise enough for us to know this duration accurately.”

A report on the research carried out by Dr Rosalind White and Professor Andrew Saunders is to be published later in the year by the geological journal Lithos.


Ather Mirza | University of Leicester
Further information:
http://www.le.ac.uk

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