Little fossils show how cooling oceans increased life forms

September 3rd, 2008 - 11:59 am ICT by IANS  

Sydney, Sep 3 (IANS) Microscopic tooth-like fossils have helped scientists correlate cooling climate and increasing biodiversity in ancient oceans 500 million years ago. An international team led by Julie Trotter of Australian National University (ANU) Research School of Earth Sciences (RSES) measured the oxygen isotope ratio of the fossils, less than two mm long, from extinct eel-shaped sea creatures called conodonts.

The oxygen isotope ratio in a conodont depends on the temperature of the water which the creature inhabited.

The fossils, made from material similar to fish teeth (calcium phosphate), preserve oxygen over geological timescales much better than the calcium carbonate from fossil seashells used in earlier studies.

The findings, published recently in Science, have shed new light on an ancient era and provide clues to oceanic life responses to climate change.

“Our research shows that over the period from about 490 to 470 million years ago, the equatorial sea surface cooled from about 40 degrees Celsius to temperatures similar to the tropics of today,” said Trotter.

“This new moderate temperature regime persisted for around 25 million years, during which there was an explosion in marine biodiversity - it’s 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.”

To unlock this temperature record from the fossils, the team used a room-sized instrument called a SHRIMP. The SHRIMP II (Sensitive High Resolution Ion MicroProbe Mark II) was invented by scientists from the ANU RSES. It measures isotopes from samples as small as five microns or a tenth the size of human hair.

“Using the SHRIMP to measure oxygen from phosphate microfossils is a real breakthrough,” said Trotter. “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.”

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