London, May 12 (IANS) British researchers have debunked a long-prevailing theory that ocean acidification from the asteroid impact that killed the dinosaurs caused the extinction of marine molluscs.
The team from University of Southampton found that the acidification levels produced were too weak to have caused the disappearance of the calcifying organisms 66 million years ago when the asteroid hit the Earth.
Ammonites which were free-swimming molluscs of the ancient oceans and are common fossils went extinct at the time of the end-Cretaceous asteroid impact.
As did more than 90 percent of species of calcium carbonate-shelled plankton.
“Our results do not say that there was enough ocean acidification to cause global extinctions,” said professor Toby Tyrrell from ocean and earth science at University of Southampton.
In the first modelling study of ocean acidification which followed the asteroid impact, the researchers simulated several acidifying mechanisms, including wildfires emitting CO2 into the atmosphere.
“Out of several factors, we considered in our model simulation, only one (sulphuric acid) could have made the surface ocean severely corrosive to calcite. But even then, the amounts of sulphur required are unfeasibly large,” Tyrrell explained.
It throws up the question that if it was not ocean acidification then what was it?
“Possible alternative extinction mechanisms, such as intense and prolonged darkness from soot and aerosols injected into the atmosphere, should continue to be investigated,” the authors contended.
The study was published in the journal Proceedings of the National Academy of Sciences (PNAS).