By Emily Sohn, Wed. Sep 7, 2011 — The great die off 250 million years ago may have been due to a change in the pH level of the oceans.

 

THE GIST

• Rising levels of acidity in the oceans probably contributed to the biggest extinction event in Earth’s history, 250 million years ago.
• As the ocean’s become more acidic again today, fears of another impending extinction crisis are escalating.
• Marine creatures that make shells are hardest hit by ocean acidification.
  

 

Earth experienced its most dramatic extinction crisis of all time 250 million years ago when about 90 percent of ocean-dwelling species and 70 percent of land-dwellers disappeared. Exactly what caused the massive die-off, however, has long been a matter of debate.

Now, a new study offers new clues.

 

High levels of atmospheric carbon dioxide would have turned the oceans more than acidic enough to kill off marine animals, a computer simulation indicates.

 

 

 

Ocean acidification caused by rising levels of carbon dioxide in the air, the study suggests, may have played a major role in the ancient extinction event, which was particularly hard on marine creatures that make calcium carbonate shells — a process that’s much harder for them to do in acidic conditions.

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The findings have potentially major implications for what we can expect to happen on Earth in the near future. As atmospheric CO2 levels rise in the coming decades and the oceans absorb the gas, which ends up making the water more acidic, we might be headed for another round of serious extinction events.

“While it’s hard to actually quantify the magnitude of the role played by ocean acidification compared to many other things going on, our results clearly show that ocean acidification played a role and maybe an important role in this extinction event,” said Alvaro Montenegro, a physical oceanographer at St. Francis Xavier University in Nova Scotia.

“It is quite evident that we have pushed and continue to push the oceans toward more acidic conditions, and we already can foresee impacts on certain types of ocean organisms become significant quite soon,” he added, with clams, mussels and other shellfish at biggest risk. “Our results are showing that organisms don’t necessarily adapt quickly or quick enough to changes in ocean pH.”

The history of life on Earth has been punctuated by a number of major extinction events, including the one that knocked off most of the dinosaurs about 65 million years ago. By far the most extreme sequence of events, though, struck just over 250 million years ago.

 

Read the rest of the story here.