Earth's most recent glacial period peaked about 26,500 years ago. At that time, around 10 million square miles (26 million square kilometers) of ice covered the Earth. The Laurentide ice sheet covered Canada and the American Midwest, stretching over Minnesota and Wisconsin south to New York and the Rocky Mountains. Across the Atlantic, ice blanketed Iceland and stretched down over the British Isles and northern Europe, including Germany and Poland. The Patagonian ice sheet crept north from Antarctica to cover parts of Chile and Argentina. The climate was colder and drier globally; rain was scarce, but pockets of rainforest survived in the tropics. With so much of the planet's water tied up in ice, global sea level was more than 400 feet lower than it is today.
Low sea level meant that some land masses that are currently submerged were accessible to people. One of the best known is the Bering Land Bridge, which connected Alaska to Siberia. The first people to reach the Americas migrated across the land bridge and settled here. Land animals also made the journey over the bridge in both directions to colonize new continents. As the world's glaciers and ice sheets melted during the following millennia, the Bering Land Bridge was flooded and disappeared beneath the ocean's surface, cutting off the migration route.