Volcanic activity caused mass extinction of marine species

Dharam Shourie

New York, Jul 20 (PTI) The mass extinction of marine
life 93 million years ago which resulted in a thick mat of
organic matter on sea floor that ultimately became a major
source of oil resulted from volcanic activity, researchers
say.

"It certainly caused an extinction of several species
in the marine environment," says University of Alberta Earth
and Atmospheric Science researcher Steven Turgeon. "It wasn't
as big as what killed the dinosaurs, but it was what we call
an extreme event in the Earth's history, something that
doesn't happen very often."

Researchers Turgeon and Robert Creaser say the lava
fountains that erupted altered the chemistry of the sea and
possibly of the atmosphere.

"Of the big five mass extinctions in the Earth's
history, most of them were some kind of impact with the
planet's surface," said Turgeon. But this one is completely
Earth-bound, it's strictly a natural phenomenon.

They found specific isotope levels of the element
osmium, an indicator of volcanism in seawater, in black
shale-rocks containing high amounts of organic matter drilled
off the coast of South America and in the mountains of central
Italy.

"Because the climate was so warm back then, the
oceanic current was very sluggish and it initially buffered
this magmatic pulse, but eventually it all went haywire,"
Turgeon said. "The oxygen was driven from the ocean and all
the organic matter accumulated at the bottom of the sea, and
now we have these nice, big, black shale deposits worldwide,
source rocks for the petroleum we have today."

According to their research, the eruptions preceded
the mass extinction by a geological blink of the eye. The
event occurred within 23 thousand years of the extinction.

The underwater volcanic eruption had two consequences:
first, nutrients were released, which allowed mass feeding and
growth of plants and animals. When these organisms died, their
decomposition and fall towards the sea floor caused further
oxygen depletion, thereby compounding the effects of the
volcanic eruption and release of clouds of carbon dioxide in
to the oceans and atmosphere.

The result, was a global oceanic anoxic event, where
the ocean is completely depleted of oxygen. Anoxic events --
while extremely rare -- occur in periods of very warm climate
and a raise in carbon dioxide levels, which means that their
research could not only help prove a mass-extinction theory,
but also help scientists studying the effects of
global warming.

Due to the anoxic events temperatures and carbon
dioxide levels on the Earth's surface actually dropped.

"Organic matter that's decaying returns components
like carbon and CO2 to the atmosphere," said Turgeon. "But
this event locked them up at the bottom of the ocean, turning
them into oil, drawing down the carbon dioxide levels of the
ocean and the atmosphere."

After 10,000 to 50,000 years, the carbon dioxide
levels rose again. "Business as usual," he said, adding that
this might hold a warning for organic life on the planet
today.

"There's a bit of an analogy for what's going on
today," he said. "What happens if we pump more carbon dioxide
into the atmosphere? This tells me that the oceans may have
limited buffering capacity for carbon dioxide," he added.