Australia's mass extinction
What caused an extinction in Australia during the late Pleistocene? Climate change? Human impact?
When exactly did the extinction occur?
Although most elements of the biota modify their environment, only humans deliberately modify their environment to meet perceived needs. In prehistoric times, controlled use of fire was the most effective tool for landscape modification. Unlike Africa and much of Eurasia, where there was a long adjustment period as human tool kits and social structures evolved, the Americas and Australia were only colonized after the appearance of H. sapiens sapiens. In these regions more dramatic impacts may have occurred following human arrival.
Our research focuses on the impact of Pleistocene colonization of Australia by modern humans. We hypothesize that their burning activities destabilized ecosystems across the interior such that a large segment of the dependent fauna became extinct, and that this ecosystem change ultimately led to reduced effective moisture over the interior. By combining tightly focussed field campaign to acquire primary collections, and a coordinated analytical program for these samples concentrating on their physical characteristics, geochronology, and d13C as a paleovegetation proxy we aim test specific predictions of our hypothesis.
Through the years, our research has developed a continuous time-series of eggshells of two large flightless birds, the extant emu (Dromaius) and the extinct Genyornis from several sites across central Australia. More than 100,000 years of eggshells are represented in each collection. From these time-series we can evaluate the timing of megafauna extinction, and from the isotopic records of diet (vegetation) preserved in the eggshells, we can evaluate ecosystem change and test whether systematic shifts in diet occurred as Genyornis approached extinction. We can also measure d13C in biomarkers for terrestrial vegatation extracted from long (100,000 years), continuous sediment records in NW Australia to evaluate whether changes in regional vegetation occurred following human colonization.
By evaluating the diets of Dromaius and Genyornis, we aim to determine the cause of the megafauna extinction. If the cause of the extinction was human predation, we would not expect to see a dietary shift (a shift in vegetation). However, ecosystem collapse might be recorded as a change in diet. Precise geochronology is essential in addressing the timing and cause of this extinction, therefore we employ state of the techniques to meet this requirement (amino acid geochronology, optically stimulated luminescense dating and uranium-thorium dating).