During the last Ice Age before humans arrived, the North American continent belonged to various forms of enormous, fantastic creatures. By the end of the Ice Age, most of these large animals had become extinct. Numerous attempts have been made to explain the disappearance of these animals, but there has yet to be a consensus. Among the theories that have been debated, two are predominant. They are the climatic change theory, and the overkill theory. The climatic change theory advocates the idea that the global warming, which brought about the end of the Ice Age, caused the animals to die off. The other is the overkill theory, which maintains that humans, by over hunting the animals, are responsible for the extinctions. It is likely that many of these animals became extinct at the end of the Ice Age due to a combination of climatic change and overkill.

The Ice Age, which began about one and a half million years ago, is also referred to as the Pleistocene Epoch. Much of the Pleistocene falls within the geological time period called the Quaternary stage. We are still in the Quaternary today. The Ice Age consisted of a series of

The expanding glaciers in the Ice Age forced sea levels to drop between 330 and 490 feet, opening a passage between Siberia in northeastern Asia and Alaska in North America. This passage was a strip of land, called the Bering Land Bridge. The land bridge still exists today, but is immersed under water. When sea levels were lowered by 330 feet, a 1000 mile wide strip of land was exposed. It surfaced and submerged many times throughout the Ice Age, and is believed to have been exposed for much of the time between 75,000 and 14,400 years ago. New research shows that the land bridge may have even been exposed until as late as 11,000 years ago.

One may wonder why, if the climatic change ended the existence of the megafauna, did it not affect the smaller animals in such dramatic ways. The likely answer that large animals have more difficulty adapting to new environments than do smaller animals. Larger animals are safer from predators than small animals are, but it is also harder for them to sustain in trying conditions. Many of the larger animals such as mammoths and bison travel in herds, and that, along with their large size, protects them from predators. However, when the predator is Mother Nature, there is virtually no defense. For modern day elephants, drought is the biggest concern. It can take twenty percent of a herd every year, but the elephants continue to exist (Ward, 1997). It would have been harder though, for the mammoths and mastodons to survive a drought. Because of their size and weight, the Ice Age Proboscidea had longer gestation periods, which meant lower birth rates. If too much of the population was lost due to a severe drought, the population would be at risk.

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Approximate Word count = 3464
Approximate Pages = 14 (250 words per page double spaced)