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Climate change, not human activity, led to megafauna extinction

Climate change, not human activity, led to megafauna extinction | Science Communication from mdashf | Scoop.it
Most species of gigantic animals that once roamed Australia had disappeared by the time people arrived, a major review of the available evidence has concluded.

 

The research challenges the claim that humans were primarily responsible for the demise of the megafauna in a proposed "extinction window" between 40,000 and 50,000 years ago, and points the finger instead at climate change.

 

An international team led by the University of New South Wales, and including researchers at the University of Queensland, the University of New England, and the University of Washington, carried out the study. It is published in the Proceedings of the National Academy of Sciences.

 

"The interpretation that humans drove the extinction rests on assumptions that increasingly have been shown to be incorrect. Humans may have played some role in the loss of those species that were still surviving when people arrived about 45,000 to 50,000 years ago -- but this also needs to be demonstrated," said Associate Professor Stephen Wroe, from UNSW, the lead author of the study.

 

"There has never been any direct evidence of humans preying on extinct megafauna in Sahul, or even of a tool-kit that was appropriate for big-game hunting," he said.

 

About 90 giant animal species once inhabited the continent of Sahul, which included mainland Australia, New Guinea and Tasmania.

 

"These leviathans included the largest marsupial that ever lived -- the rhinoceros-sized Diprotodon - and short-faced kangaroos so big we can't even be sure they could hop. Preying on them were goannas the size of large saltwater crocodiles with toxic saliva and bizarre but deadly marsupial lions with flick-blades on their thumbs and bolt cutters for teeth," said Associate Professor Wroe.

 

The review concludes there is only firm evidence for about 8 to 14 megafauna species still existing when Aboriginal people arrived. About 50 species, for example, are absent from the fossil record of the past 130,000 years.


Via Dr. Stefan Gruenwald
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Marco Bertolini's curator insight, May 7, 2013 3:21 AM

Des scientifiques sont à présent certains qu'un changement climatique a détruit la mégafaune d'Australie.  Et non pas l'action humaine, comme on l'a longtemps cru.  Un avertissement ?

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Radiocarbon Dating: Nature's Timepiece Gets a Tune-Up

Radiocarbon Dating: Nature's Timepiece Gets a Tune-Up | Science Communication from mdashf | Scoop.it

It’s relatively easy for scientists to see the signature of droughts and other climate events in the prehistoric past by digging into underground or seafloor sediments, or drilling into ancient ice. In order to say exactly when these events happened, though, you need a reliable natural dating method, and even the best of these is flawed.

 

However, one of the most familiar of these timelines, known as radiocarbon dating, just got a lot more precise. According to a paper published in the journal Science, measurements from the bottom of Japan’s Lake Suigetsu have allowed scientists to improve the technique dramatically.

 

Now, thanks to those lake sediments, scientists can narrow that range down to just 10 years or less -- but only if the sample is between 11,000 and 53,000 years old. Younger and there hasn't been enough breakdown in the radioactive carbon. Older, and the lake's sediments don't go back that far.

 

This impressive achievement comes thanks to Lake Suigetsu’s calm waters, and also from the lucky fact that the plant matter that drifts into the water and sinks to the bottom is light-colored in winter and dark in summer. The result: alternating layers under the lake bottom that make it easy to identify every year, one after the other, going well back into the last Ice Age.


Via Dr. Stefan Gruenwald
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Rare Fossil Points to Toxic Oceans in Devonian Period Possibly Causing Global Mass Extinction

Rare Fossil Points to Toxic Oceans in Devonian Period Possibly Causing Global Mass Extinction | Science Communication from mdashf | Scoop.it
A well-preserved crab-like fossil that was found by scientists from Curtin University, Australia, has provided evidence of a toxic ocean environment in the Devonian Period, potentially responsible for the mass extinction 380 million years ago.

 

A study, published in the journal Geology, shows that hydrogen sulphide dependant organisms –known as Chlorobi – and sulphate-reducing bacteria had preserved the shell and the muscles of the crab-like creature. “The research presents organic geochemistry as a new tool for paleontologists, enabling them to identify invertebrate fossils and reconstruct their environments from a molecular point of view,” explained lead author Ines Melendez, a PhD student at the Curtin University.

 

“It’s like walking in on a crime scene, when all the evidence is still intact. Not only do we know the organism was a crustacean from the abundance of cholestane it contained, but we also know it was in a toxic ocean environment, from the biomarkers associated with the sulfate–reducing bacteria and Chlorobi. By looking at the biomarkers and stable isotopes of fossils, we are able to reconstruct past environments, and can apply this technique to other ages of geological time,” Melendez said.

 

Curtin University scientists collected the unique fossil from the Gogo Formation in the Kimberley Region of Western Australia. “This research suggests the Devonian Period had similar paleoenvironmental conditions to the largest extinction event in the past 600 million years, where it was proved toxic concentrations of hydrogen-sulfide in ancient oceans, rather than a meteorite, were largely responsible for wiping out mass populations,” said study co-author Prof Kliti Grice of the Curtin University.


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