1 July 1998

Human History Recorded in a Grain of Sand

Scientists pioneering a revolutionary way to date single grains of sand are hoping to open a spectacular new volume in the history of Australia - including the impact of human settlement over thousands of years. By scrutinizing tiny grains of quartz buried in layers of sediment, they expect to "read" the story of the continent's landscape with dazzling accuracy.

"Humans are like glaciers in their impact on a landscape," says team leader Jon Olly of the Commonwealth Scientific and Industrial Research Organization. "We remove cover, increase erosion, change things profoundly. The traces of this activity can be seen in the layers of sediment that line our river systems."

The trick is to see grains of quartz as minuscule clocks. When they encounter sunlight, they release energy stored in the crystal lattice, setting the timer to zero. But once the grain is buried away from light, it begins to accumulate radioactive energy from the surrounding soil, and from this the time since burial can be calculated.

The process, known as optically stimulated luminescence, has the power to explain everything from how Aboriginal land management changed Australia to how the continent's rivers functioned when grazed by giant marsupials before humans arrived. The team is currently dating a site on the Murrumbidgee which they believe records major flood events for the last two millennia, and shows a clear change in the river from the time of European settlement.