Boiling seas linked to mass extinction
Methane belches may have catastrophic consequences.
Nature Science Update
22 August 2003
A massive methane explosion frothing out of the world's
oceans 250 million years ago caused the Earth's worst
mass extinction, claims a US geologist.
Similar, smaller-scale events could have happened since,
which might explain the Biblical flood, for example,
suggests Gregory Ryskin of Northwestern University in
Evanston, Illinois. And they could happen again: "It's a
very conjectural idea but it's too important to ignore," says
Up to 95% of Earth's marine species disapeared at the end
of the Permian period. Some 70% of land species, including plants,
insects and vertebrates, also perished. "It's arguably the single most
important event in biology but there's no consensus as to what
happened," says palaeontologist Andrew Knoll of Harvard University
in Cambridge, Massacheusetts.
Ryskin contends that methane from bacterial decay or from frozen
methane hydrates in deep oceans began to be released. Under the
enormous pressure from water above, the gas dissolved in the water
at the bottom of the ocean and was trapped there as its concentration
Just one disturbance - a small meteorite impact or even a fast
moving mammal - could then have brought the gas-saturated water
closer to the surface. Here it would have bubbled out of solution
under the reduced pressure. Thereafter the process would have been
unstoppable: a huge overturning of the water layers would have
released a vast belch of methane.
The oceans could easily have contained enough methane to explode
with a force about 10,000 times greater than the world's entire
nuclear-weapons stockpile, Ryskin argues. "There would be
mortality on a massive scale," he says.
"It's a wacky idea," says geologist Paul Wignall of the University of
Leeds, UK, "but not so wild that it shouldn't be taken seriously."
There is evidence that the oceans stagnated at the end of the
Permian period. And the chemical signature in fossils of the time
hints there was a massive change in the amount of atmospheric
carbon dioxide. Carbon dioxide would have been produced as
methane broke down or exploded in the atmosphere.
After all, belches of trapped methane from lakes and oceans are "a
rare but well-known maritime hazard", Wignall adds.
The same phenomenon could explain more recent events, such as the
Biblical flood, Ryskin also argues. An eruption from Europe's
stagnant Black Sea would fit the bill. There is even some geological
evidence that such an event took place 7,000-8,000 years ago.
Other sluggish seas might still be accumulating methane at their
depths and could represent a future hazard, Ryskin adds.
"Even if there's only a small probability that I am right, we
should start looking for areas of the ocean where this might be
happening," he argues.
1. Ryskin, G. Methane driven oceanic eruptions and mass
extinctions. Geology, 31, 737 - 740, (2003).
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