Fossilized Emu Eggshells Give Clues To 65,000 Years Of Vegetation And Climate Changes In Australia


Between 28,000 and 15,000 years ago, during the peak of the last glacial period, C4 grasses were almost totally absent because of the colder temperatures. Their range should have expanded again when the Earth warmed during the Holocene (10,000 years ago). However, data from the emu eggshell documents that the ecosystem did not revert to its state that prevailed prior to the arrival of humans. C4 grass abundances were below the levels established before the glacial period. Over the last 65,000 years, the researchers conclude, environmental factors other than climate have significantly influenced Australian ecology.

Vegetation changes in north- and south-eastern Australia, brought about by more frequent fires, is attributed to the arrival of the first human immigrants at about 60,000 years ago. The transfer of moisture from the plants and soils to the atmosphere is an important feedback mechanism that enhances the transfer of monsoon rainfall into the interior of the continent. Changes in the types of plants across northern Australia, brought about by the burning practices of the first human colonizers, may have reduced this mechanism and thus diminished the amount of rainfall reaching what is now the arid Australian interior. The influence of humans with their recurrent fires has been suggested as the cause of extinction for a least one Australian megafauna, the flightless bird Genyornis newtoni at 50,000 years ago (Science, vol. 283, no. 5399, p. 182).

Measurements since European colonization (about 150 years ago) indicate a further depletion of the C4 grasses. Instead of being related to climate, the shift is believed to result from overgrazing, the introduction of exotics and other activities associated with human expansion.

According to Marilyn Fogel, "Our isotopic data on the emu's eggshells are consistent with a human overprint on natural climate changes. The effect of precipitation from the summer monsoon in central Australia decrease

Contact: Marylin Fogel
202 686-2410 x 2480
Carnegie Institution

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