英語聽力：長(zhǎng)毛象王國(guó)—7

The answer lies in the effects of North America’s immense and fluctuating ice sheets. As they grew, they locked up so much water that the sea levels began to fall.

The Bering Sea between Asia and North America began to drain away, leaving a bridge of land exposed, the Bering Land Bridge, roughly a thousand milse wide and covering an area twice that of modern Texas. This was the route by which lions, woolly mammoths and other creatures colonised the American continent.

During the last Ice Age, the Bering Land Bridge formed once more. And this time it allowed a different colonist to cross, one that would have a huge and permanent effect upon the continent. This is one of their first known haunts, the Mesa Site in Northern Alaska, a key point on the Ice Age map. Beautifully crafted spear-points found here are known to date back almost 14,000 years and tell us that the first people to cross the land bridge were skilled, sophisticated hunters.

But what were they doing on this particular spot? The climate was harsh, the location extremely exposed. It’s not a place you’d choose to make a campsite. But if you were a hunter, what you needed was a view. The Mesa was the perfect lookout point with panoramas of surrounding land and game. These early hunters had spread all the way from Asia. What did they find on the other side of the Bering bridge?