Doubt Cast on Australia Discovery
SYDNEY, Australia (AP) _ Two years ago, Australian scientists stunned the world by announcing they had found Aboriginal tools in layers of sand at least 116,000 years old and rock art up to 75,000 years old.
Their revelation contradicted the long-accepted belief that Aborigines came to Australia from Asia just 60,000 years ago, as well as current theories about how humans evolved and migrated across the continents.
New research published Thursday in the science journal Nature, however, suggests their dating methods were flawed _ and that the Aboriginal tools and nearby Jinmium rock carvings in the Northern Territory are very recent.
``It’s definitely not a very ancient occupation site. It’s no more than 10,000 years old,″ Richard Roberts of La Trobe University in Melbourne told The Associated Press.
The art at the Jinmium site is thousands of dot-like indentations engraved on rock monoliths in the Kimberley region, 280 miles southwest of Darwin. The naturally positioned rocks were apparently chosen to mark out boundaries and trails to caves and tunnels.
The Aboriginal tools were found in quartz sand originally dated two years ago by scientists at the Australian Museum and University of Wollongong.
David Price of Wollongong University heated groups of quartz crystals in a process called thermoluminescence, indicating they were 116,000 to 176,000 years old. Chips and crystals off the nearby Aboriginal rock carvings dated the same way appeared to be 50,000 to 75,000 years old, Price found.
The findings were published in 1996 in the archaeological journal ``Antiquity,″ but were released to the press first, making a huge splash worldwide.
Using a different dating method, Roberts and his colleagues found that the Jinmium sediments ranged in age from 4,000 years in the upper levels to 10,000 years deeper down. The base of the Jinmium deposit is no more than 22,000 years old, he found.
Roberts’ group studied the age of individual quartz crystals in a process called optically stimulated luminescence, which analyzes how long it has been since quartz was last exposed to sunlight.
Roberts suggested the Australian Museum and University of Wollongong research was contaminated with weathered quartz crystals that had been buried since the formation of the rock, and therefore appeared far more ancient.
``If some of the grains didn’t see sunlight, you’ll get the wrong dates,″ he said.
The new study looks at individual quartz crystals, which allowed Roberts to identify and discard atypical crystals.
This dating method was available to Price’s group but Roberts said it chose to proceed to publication rather than spend time reanalyzing its samples.
Roberts and his colleagues also used radiocarbon dating on charcoal samples in the excavation to check his single-crystal dating _ and found they matched his method, not the earlier dates.
Price wanted to see the Nature article before commenting, but added, ``there isn’t any reason at this time to say this (original research) isn’t valid.″
Australian Museum archaeologist Richard Fullagar, who led the Jinmium dig, was both an author on the original study and a co-author with Roberts. He said Roberts’ single-crystal dates ``do provide some agreement with some of the carbon dating that we think is more accurate.″
``The thermoluminescence dates (in the original study) appear to be too early,″ he said.
Most scientists believe Homo sapiens did not emerge from Africa until about 100,000 years ago and the oldest reliably dated rock art had been 32,000-year-old cave paintings at Chauvet in France.