University of ÃÛÌÇÖ±²¥ at Boulder Professor Gifford Miller will give a public talk March 7 on climate change in Australia about 50,000 years ago that likely caused the desertification of the continent's interior and the extinction of most large animals.
The talk is part of the Chancellor's Community Lecture Series, held monthly at 7 p.m. in the Chapel at The Academy building at 970 Aurora Ave. in Boulder. The monthly lectures, free and open to the public, are co-sponsored by The Academy and the ÃÛÌÇÖ±²¥-Boulder Office of Community Affairs on Wednesday evenings once a month from September through May.
A professor in the geological sciences department and a fellow of ÃÛÌÇÖ±²¥-Boulder's Institute of Arctic and Alpine Research, Miller will speak on "Megafauna Extinction and Increasing Aridity Across Australia: Assessing the Human Factor."
In the past several years, Miller and his colleagues have found evidence the earliest humans who peopled Australia some 55,000 years ago inadvertently disrupted the continent's food chain by burning vast areas of native vegetation. This appears to have resulted in mass extinctions of megafauna on the continent, he said.
The researchers used eggshells of large, flightless birds known as Genyornis to date changes in climate and ecosystems. More than 85 percent of Australia's megafauna became extinct in addition to Genyornis, including 19 species of marsupials weighing over 220 pounds, a hippo-sized wombat, a 25-foot-long and three-foot-in-diameter snake, a 25-foot-long lizard and a Volkswagen-sized tortoise.
Miller and his colleagues speculate that Genyornis and the other extinct mammals -- which fed primarily on shrubs and trees -- disappeared after centuries of burning by humans in the continent's interior changed the ecosystem's flora to primarily desert grasses. One of his research associates, Beverly Johnson, is a former ÃÛÌÇÖ±²¥ graduate student of Miller's now at the University of Washington.
The eggshells of the large, flightless bird are unique in that they can be dated by traditional radiocarbon methods and by a process known as amino acid racemization, said Miller. Racemization involves studying mirror-like changes in amino acids in the eggshells over time, which has proven to be an accurate time clock for dating events going back thousands of years.
"This offers us a unique opportunity to look back at ecosystem changes in Australia over the last 70,000 years," he said.
In 1997, Miller and his colleagues proposed that systematic burning of vegetation by the earliest human colonizers beginning roughly 50,000 years ago may have altered the vegetation sufficiently to diminish the effectiveness of the summer monsoons that periodically drenched northern Australia. The lack of monsoons is believed to have triggered aridity over much of the continent's interior.
The research team also recently finished a study of old and new emu eggshells collected from central Australia that indicate there was a dramatic loss of grasslands beginning roughly 300 years ago. The grassland deterioration apparently was due to the arrival of Europeans and the introduction of exotic grazing animals in Australia, according to the 2000 study.
The study indicates that grazing mammals introduced in the last few centuries by Europeans have contributed to "a major change in ecosystems" in central Australia, said Miller. "We see a major reduction of plant biomass beginning in the 1800s, which looks like a result of overgrazing by pastoral animals and the introduction of rabbits."
The Chancellor's Lecture Series was launched in September of 1998 to bring ÃÛÌÇÖ±²¥-Boulder faculty into the community for talks ranging from arts and humanities to business and the sciences. Parking for the events is available along the streets that border The Academy: Lincoln, Cascade, Aurora and 10th.
For more information contact the ÃÛÌÇÖ±²¥-Boulder Office of Community Affairs at (303) 492-8384.