In middle school classrooms, the gist of the Ice Age is often explained as, "It got really cold and all the animals became extinct.” Recently, however, scientists have been taking a closer look at where and when human behavior affected the extinction of species, instead of climate change. Recent findings in Tasmania prove that certain ancient species, like the giant kangaroo and marsupial rhino and leopard, were still inhabiting the island when humans first arrived, leading the research team to conclude that the animals' extinction was due to human hunting, not the Ice Age.

Lots of amphibians (a third to a half of all species) are dying, and their deaths are the breaking-edge of what many scientists are calling the first mass extinction since the dinosaurs checked out 65 million years ago, researchers say in a new paper published online in the Journal Proceedings of the National Academy of Sciences.

What exactly killed the dinosaurs? One of the most popular theories holds that the extinction event was driven by an asteroid collision. Evidence for the theory can be found in a thin layer of iridium in what's known as the K-T boundary, a (similarly thin) layer of sediment in the ground which marks where the surface of the Earth was 65 million years ago. Iridium is common in asteroids and not common on Earth. Its presence in the sediment would indicate an impact and release of the material. What happened next is still a matter of debate.