[img]2012q1/ct_etoefm_etoefspeakc_0777_20121[/img] [originaltext]W: During the L

W: During the Late Pleistocene stage of Earth’s history, there was a period of mass
  extinctions that resulted in the loss of two thirds of all the large mammals
  on the planet. Animals like mammoths, saber-toothed cats, and mastodons
  disappeared during this extinction event. Now the cause of the Late Pleistocene
  extinctions isn’t known for certain.., but some scientists are convinced that global
  climate change was primarily responsible. Between 18,000 and 15,000 years ago,
  climbing global temperatures may have initiated a period of mass extinctions.
  A researcher at the University of Alaska at Fairbanks says that the increase in
  moisture and the warmer temperatures caused many plant species to spread
  farther north, where mammoths primarily lived. You might think this was a
  good thing, since it would have given them a larger food supply. But what really
  happened was that the milder climate allowed trees to grow farther north too.
  And these trees out-competed the smaller plants that the mammoths ate. So
  their food supply quickly vanished, and with nothing to eat, the species vanished
  too.
  There’s a paleontologist with the Denver Museum of Nature and Science who
  claims that the changing climate had a similar effect on mastodons. When
  the climate warmed up, the savannahs and the forests that mastodons lived
  in became less diverse. Not only that, they began to shrink. Of course, as that
  happened, mastodon populations themselves began to shrink too. You know,
  the mastodons couldn’t find enough food or shelter to survive. Eventually, they
  totally died out, and all we’re left with now are fossils.