Tuesday, August 2, 2016

What Caused The Demise of Mammoth?

It wasn’t humans: The first people on Saint Paul were Russian whalers who landed there in 1787, well after the last mammoth had gone. It wasn’t polar bears: They also came later. It wasn’t volcanoes: There were no traces of volcanic sediments in the lake during the extinction window. It wasn’t a lack of space: Although Saint Paul had certainly shrunk since its isolation from the mainland, it had reached its minimum size at least 3,000 years before the mammoths disappeared. And it wasn’t a lack of food: Pollen and plant remains in the lake sediments revealed that vegetation on the island was stable when the mammoths were declining.

Instead, the final killer was probably thirst, brought about by changing climate. Saint Paul never had rivers or springs. The only sources of freshwater were shallow lakes—and these were slowly disappearing. When sea levels rise around an island, the salt water also seeps beneath it, creating a wedge that intrudes into lakes, aquifers, and other sources of freshwater. On Saint Paul, this happened between 7,850 and 5,600 years ago, as Graham’s team discovered by analyzing microbes and chemical isotopes in their sediment cores.

This, combined with a drying climate, meant that Saint Paul’s water supplies were getting smaller, shallower, and saltier. That was disastrous for the mammoths. Modern elephants need to drink between 70 and 200 liters of water every day, and mammoths probably needed more to keep cool. An elephant can get rid of heat by sweating, relying on the evaporating moisture to cool its skin. But a mammoth’s dense, waterproof fur would have wicked sweat away from the skin before it could evaporate. To compensate, they must have sweated a lot more, which in turn gave them a truly mammoth thirst.

Ironically, the mammoths probably made things worse for themselves. As they were forced into a dwindling number of waterholes, they would have destroyed the surrounding vegetation, eroded the banks, stirred up the sediments, and slowly filled up the lakes. “They sort of hastened their own demise,” says Graham.

- More Here

No comments: