Cooling oceans helped biodiversity 500 mn yrs ago

MELBOURNE: A new study has revealed for the first time a link between a cooling climate and increasing biodiversity in ancient oceans 500 million years ago.

A team at Australian National University has based its conclusion on an analysis of microscopic tooth-like fossils of extinct eel-shaped sea creatures called conodonts -- in their study, they measured the oxygen isotope ratio of the fossils.

According to researchers, fossils preserve the oxygen over geological timescales much better than calcium carbonate from fossil seashells.

"Our research shows that over the period from about 490 to 470 million years ago, the equatorial sea surface cooled from about 40C to temperatures similar to the tropics of today.

"This new moderate temperature regime persisted for around 25 million years, during which there was an explosion in marine biodiversity -- it's actually recognised as one of the greatest evolutionary radiations in history.

"Oceans then cooled to glacial conditions, when there were major extinctions. Change the climate, change the life on Earth," lead researcher Dr Julie Trotter said.

To unlock this temperature record from the fossils, the team used a room-sized instrument called a 'SHRIMP' or the Sensitive High Resolution Ion MicroProbe. It measures isotopes from samples as small as five microns in diameter, or about one tenth the diameter of a human hair.

"Using the SHRIMP to measure oxygen from phosphate microfossils is a real breakthrough. The SHRIMP will let us track climate change over hundreds of millions of years more easily and reliably, and therefore help us to understand how life might respond to future climate change," Dr Trotter said.

The study has been published in the latest edition of the 'Science' journal.