July 26, 2006

World’s Oldest Open Caves Near Sydney: Scientists

SYDNEY -- A series of limestone caves west of Sydney, best known as a popular family tourist attraction, are in fact the world's oldest open caves, dating back 340 million years, Australian scientists say.

The Jenolan Caves in the Blue Mountains west of Sydney were thought to be only a few thousand years old but actually predate dinosaurs, said Armstrong Osborne, a member of a Sydney University scientific team which recently dated the caves.

"We've shown that these caves are hundreds of millions of years older than any reported date for an open cave anywhere in the world," Osborne said in a statement.

"No one imagined they would be more than 300 million years old from the Carboniferous period," he said.

Until now, the oldest open caves were thought to exist in New Mexico, dating back 90 million years, Osborne told Reuters on Wednesday. Open caves are caves which can be walked into.

Osborne said the dating team studied tiny amounts of radioactive potassium in clay to determine the age of the caves. By measuring the ratio of radioactive potassium and trapped argon gas, which was produced when the potassium decayed, scientists determined the age of the clay.

"Working out the age of a cave is working out the age of the stuff that's filling it," he said.

Osborne said it was amazing The Jenolan Caves had survived "as most landscape pieces this old would have been destroyed."