( Massive extinctions of animals and the ...)Did humans cause ecosystem collapse in ancient Australia?

Massive extinctions of animals and the arrival of the first humans in ancient Australia may be linked, according to scientists at the Carnegie Institution, University of Colorado, Australian National University, and Bates College.* The extinctions occurred 45,000 to 55,000 years ago. The researchers traced evidence of diet and the environment contained in ancient eggshells and wombat teeth over the last 140,000 years to reconstruct what happened. The remains showed evidence of a rapid change of diet at the time of the extinctions. The researchers believe that massive fires set by the first humans may have altered the ecosystem of shrubs, trees, and grasses to the fire-adapted desert-scrub of today. The work is published in the July 8, issue of Science.

The scientists plotted diet changes over 140,000 years of two species of large, flightless birds--the now-extinct Genyornis and the surviving emu (Dromaius)--in three Australian locations. They then corroborated their findings by analyzing ancient wombat teeth. "What your mother told you is true: You are what you eat," stated co-author of the study Marilyn Fogel of Carnegie. "Eggshells and teeth both contain evidence of these animals' diets in different forms of carbon. All three animals were plant eaters. Different types of plants metabolize different forms of carbon in distinctive ways from the CO2 they take up during photosynthesis. The tell-tale carbon varieties were preserved in the eggshells and teeth and told us what types of plants the animals ate. We saw a sudden shift in plant type coincident with the arrival of humans. The shifting diet shed light on the extinctions. The animals that relied mostly on the more palatable plant forms died out, such as Genyornis, while the animals that adapted to the less nutritious plants survived, including the emu."

There are three isotopes, or varieties, of carbon found in nature--12C, 13C and 14C. They differ in the number of neutrons in the nucleus. By far
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Source:Carnegie Institution

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