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Much of the northern hemisphere is covered by ice sheets up to one and a half miles thick.
北半球多被厚达2.5公里的冰层覆盖。
With trillions of gallons of water locked up as ice, sea levels fall.
数万亿加仑的水凝结成冰，海平面下降。
A strip of land emerges from the ocean between Siberia and Alaska.
一块土地出现在西伯利亚与阿拉斯加之间的海洋，
It's a bridge between two vast continents, a gateway that takes humans from Asia to a new world, the Americas.
它是连接两块大陆的桥梁，这个通道使人类从亚洲进入一个新世界，即美洲。
They're the last great continents to be colonized,
这是最后一块未被殖民的大陆，
the last great human migration,
最后一次人类大迁徙，
and the first Americans.
也是第一批美洲人。
Now, 14,000 years ago, the changes that triggered the ice age reverse.
14000年前，引发冰河时期的变化逆转，
As the ice retreats, it reveals a very different northern hemisphere.
冰融化后露出截然不同的北半球，
The huge depressions that the glaciers create fill with water to become North America's Great Lakes.
冰河挖出巨大洼地，填满水后成为了北美的五大湖。
6,000 years ago, the ice retreats back to the poles, toward the Arctic and Antarctic.
6000年前，冰退回到北极与南极。
