Sydney, Aug 22 (IANS) Marine life faces far greater risk of large-scale extinctions than at any previous time in human history, world's leading marine scientists have warned.

Researchers from Australia, United States, Canada, Germany, Panama, Norway and Britain compared events which drove massive marine life extinctions in the past with what is observed to be taking place in the seas and oceans globally today.

We wanted to understand what had driven past extinctions of sea life and see how much of those conditions prevailed today, said study co-author John Pandolfi, professor at the ARC Centre of Excellence for Coral Reef Studies, an authority on the fate of coral reefs in previous mass extinction events.

It is very useful to look back in time - because if you forget your history, you're liable to repeat it, said Pandolfi, the journal Trends in Ecology and Evolution reports.

Three of the five largest extinctions of the past 500 million years were linked with global warming and acidification of the oceans - trends which also apply today, according to an ARC statement.

Other extinctions were driven by loss of oxygen from sea water, pollution, habitat loss and pressure from human hunting and fishing - or a combination of these factors.

Currently, the earth is again in a period of increased extinctions and extinction risks, this time mainly caused by human factors, the scientists said.

In the 'Great Death' during the Permian period 250 million years ago, for example, an estimated 95 percent of marine species died out due to a combination of warming, acidification, loss of oxygen and habitat.