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Single-grain OSL needs specialised equipment and skilled personnel to analyse results, making it twice as expensive and more time-consuming than multi-grain analysis.Warratyi samples were first analysed with multi-grain OSL, giving dates of well over 50,000 years, but later analysis with single-grain OSL brought the oldest dates in to around 44,000 years (plus or minus 3,000 years).Once the organism dies, it stops replenishing its carbon supply, and the total carbon-14 content in the organism slowly disappears.Scientists can determine how long ago an organism died by measuring how much carbon-14 is left relative to the carbon-12.
Previous multi-grain OSL dating at a number of ancient sites have suggested humans arrived in Australia well over 50,000 years ago, but Spooner is sceptical of many of these dates.
“Unlike bone or charcoal, carbon preserved in eggshell is very stably locked in and unlikely to have been contaminated,” says Nigel Spooner, a physicist at the University of Adelaide in Australia who specialises in dating techniques.
For archaeologists such as Spooner trying to date the first occupation of Australia, older age limitations of radiocarbon dating are frustrating, as it is exactly this period in which they are most interested.
Over time, carbon-14 decays radioactively and turns into nitrogen.
A living organism takes in both carbon-12 and carbon-14 from the environment in the same relative proportion that they existed naturally.