Australian site jumps forward in time.Prehistoric Australians have taken a chronological roller-coaster ride at the Jinmium rock shelter A rock shelter is a shallow cave-like opening at the base of a bluff or cliff. Another term is rockhouse. Rock shelters form because a rock stratum such as sandstone that is resistant to erosion and weathering has formed a cliff or bluff, but a softer stratum, more subject in the past few years. What once looked like a surprisingly ancient occupation site in northern Australia The term northern Australia is generally considered to include the States and territories of Australia of Queensland and the Northern Territory. The part of Western Australia (WA) north of latitude 26° south — a definition widely used in law and State government policy , with implications for explaining modern human evolution, now appears to date back only a short way into the Stone Age, a new study finds. Previous thermoluminescence dating at Jinmium yielded ages of 50,000 to 75,000 years for quartz sands found near buried circular engravings and ages of 116,000 to 176,000 years for lower, artifact-bearing deposits (SN: 9/28/96, p. 196). However, a related dating method, known as optically stimulated luminescence In physics Optically stimulated luminescence or (OSL) is a method for measuring doses from ionizing radiation (commonly known as radioactive radiation). The method makes use of electrons trapped between the valence and electron band in the crystaline structure of certain (OSL OSL Open Source Lab OSL Office of Student Life OSL Open Source License OSL Oregon State Library OSL Order of St Luke the Physician OSL Optical Stimulated Luminescence OSL Oud Strijders Legioen (Dutch) OSL Order of Saint Luke ), now indicates that the oldest Jinmium layers date to 22,000 years ago at most, report geoscientist Richard Roberts of La Trobe University 1. u/r = unranked 2.AsiaWeek is now discontinued. Student life During the 1970s and 1980s, La Trobe, along with Monash, was considered to have the most politically active student body of any university in Australia. in Melbourne and his colleagues. Both techniques estimate the time elapsed e·lapse intr.v. e·lapsed, e·laps·ing, e·laps·es To slip by; pass: Weeks elapsed before we could start renovating. n. since minerals such as quartz were last exposed to sunlight, taking into account their radioactive exposure while buried. Some Jinmium quartz grains have inflated ages because they received little or no exposure to sunlight before burial, Roberts' group contends in the May 28 Nature. For example, weathering of buried bedrock releases quartz grains that have had little or no exposure to the sun. OSL allows for the dating of single quartz grains and the detection of those that show signs of insufficient bleaching from the sun, the scientists say. The oldest thermoluminescence thermoluminescence Emission of light from certain heated substances as a result of previous exposure to high-energy radiation. The radiation causes displacement of electrons within the crystal lattice of the substance. ages for human occupation of Australia now come from two other sites dated at 50,000 to 60,000 years old. Roberts' team is using single-grain optical dating methods to verify these measurements. "Personally, I believe that Jinmium's age lies somewhere in between the [thermoluminescence] results and the OSL estimates," remarks archaeologist Paul S.C. Tacon of the Australian Museum in Sydney. It remains possible that humans reached Australia more than 60,000 years ago, he adds. A widely recognized geologic disturbance within the Jinmium deposit may have affected age estimates produced by both dating methods, Tacon asserts. The circular engravings at Jinmium resemble those at other Australian sites dated as early as 40,000 to 50,000 years ago, according to a study directed by Tacon and published in the December 1997 Antiquity. |
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