CANBERRA - Greenhouse gases may expand ' ocean dead zones' and could cause a mass extinction of marine life, Australian scientists warned on Tuesday.

An Australian research team analyzed ocean rocks back from 85 million years ago from the Late Cretaceous Period, which experienced greenhouse conditions similar to those predicted in 2050.

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Within the ancient rocks, drilled from ocean beds off the western coast of Africa, the researchers found huge amounts of marine life buried within deoxygenated layers.

According to Adelaide University Environmental Sciences Professor Martin Kennedy, his research looked at the rapid expansion of ocean dead zones created by rising temperatures in prehistoric times.

"They are areas without oxygen in them and the marine animals within them are no longer capable of living there - they are responsible for major fish kills," the Australia Associated Press quoted Kennedy as saying on Tuesday.

"What we see from going back to the past is what our future ocean will probably do in response to those conditions, he said.

"Our research points to a mass mortality in the oceans at a time when the Earth was going through a greenhouse effect, with high levels of carbon dioxide in the atmosphere," said the professor.

Kennedy said the rocks analyzed over a 400,000-year period suggested the ocean 'corrects itself' naturally, but over thousands of years.

He said observations of a mass extinction of marine life in prehistoric times serve as a warning that a similar event could occur again.