When the sea was 120 m lower, and you could walk from Asia to America.
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Just 20,000 years ago, Britain wasn’t an island. Dry land (green) joined it to the rest of Europe, where the North Sea is now. So where was the sea? (The old land and ice in this lesson are drawn simpler than they really were.)
It was the peak of the last ice age. Giant ice sheets (white) covered nearly all of Canada and much of northern Europe, 2 to 4 km thick at the top. About a quarter of all the land on Earth was under ice; today it’s about a tenth.
All that ice was water taken from the sea. Water evaporated from the ocean and fell as snow on the land, where it piled up as ice instead of flowing back. So sea level was about 120 m lower than today, and the shallow edges of the continents turned into dry land.
Between Asia and Alaska, the sea floor became a wide land bridge, more than 1,600 km from north to south. Woolly mammoths, horses and camels crossed it. So did the people who became the first Americans.
Then the Earth warmed up, and the ice melted back into the sea. Drag the slider to raise the sea and watch Britain become an island. Then keep going, past today!
In the ice age, Borneo, Sumatra and Java were joined to mainland Asia in one big land called Sundaland. Drag the slider to bring the sea back. Then keep going: what happens to Bangladesh?
Today most of Earth’s ice is on Antarctica and Greenland. If it all melted, the sea would rise about 70 m and almost all of Florida would drown (blue), though that would take thousands of years. Right now the sea is rising a little over 4 mm a year, and getting faster.
In the ice age, people and animals walked from Asia to America.
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The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).