Earth hit by 'mass extinction'

2006-11-24 07:18

Washington - About 95% of Earth's marine species and 70% of its land species were wiped out during a "mass extinction" about 250 million years ago, according to Australian and US researchers.

The phenomenon fundamentally changed which species survived in the world's oceans. And the experts at James Cook University in Townsville, Queensland and the Field Museum in Chicago warned that modern human-induced changes to the ecosystem could have a similar impact.

The experts told in the latest edition of the journal Science how they came across the culling of species while examining figures on the numbers of marine life forms in communities over the past 540 million years.

Simple species that did not move or search for food were largely wiped out, they concluded. More complex life forms such as crabs and snails that went looking for food took over.

The biological devastation occurred at the end of the Permian age about 250 million years ago, when the Earth was believed to have had only one continent, surrounded by a single ocean.

The US and Australian researchers did not go into the cause of what they called a "mass extinction" but, using a new palaeobiology database, they gave what they say are the most exhaustive details ever assembled of the impact.

So-called "ecologically simple" species such as stationary shells and other forms that filtered food out of the water were replaced by "complex communities", mobile species such as crabs and clams.

"We think these are the first analyses of this type at this large scale," said Peter Wagner, associate curator of fossil invertebrates at The Field Museum and lead author of the study, who worked with Matthew Kosnik of James Cook University.

"They show that the end-Permian mass extinction permanently altered not just taxonomic diversity but also the prevailing marine ecosystem structure," Wagner said.

The results of the study could provide a warning on how we treat the ecosystem now, the experts said.

"Studies by modern marine ecologists suggest that humans are reducing certain marine ecosystems to something reminiscent of 550 million years ago, prior to the explosion of animal diversity," Wagner said.

"The asteroid that wiped out the dinosaurs couldn't manage that."

- AFP