The Last Glacial Maximum was the time period about 20,000 years ago when the last glacial period was at its maximum extent and temperatures on the planet were lowest. Though the last glacial period lasted from 110,000 to between 15,000 and 10,000 years ago, it was most intense right before the end. During the Last Glacial Maximum, huge glaciers covered most of present-day Canada and the northern United States (Laurentide Ice Sheet), much of southern South America (Patagonian Ice Sheet), and large sectors of northern Europe and northwest Russia. The British Isles were almost completely under ice. Instead of the Baltic Sea, the area between Sweden and Norway would have been packed with gigantic glaciers, some as much as two miles thick.
Because so much water was locked up in glaciers during the Last Glacial Maximum, the world's sea levels were lower by a factor of about 100 m (328 ft). This temporarily revealed large areas of land that are underwater today, such as Beringia (a large region between Russia and Alaska), Doggerland (much of the present-day North Sea), Sundaland (most of the islands of Indonesia were connected), and Sahulland (Australia connected to New Guinea). The Black Sea was much shallower, and the Persian Gulf was dry. Both of these basins were later filled abruptly in flooding events that may have been catastrophic, and could have inspired Biblical and other flood myths.
Most archaeological signs of human habitation from the Last Glacial Maximum are found in Africa, southern Europe, the Middle East, southern Asia, Indonesia, and Australia. Northern Europe and Asia were largely uninhabited due to the cold, except for an ice-free refugium area called Beringia, located around the present-day Bering Strait, on large amounts of low-lying land that is currently submerged. The people that lived in Beringia during the Last Glacial Maximum would eventually take advantage of the low sea levels to migrate into the Americas. This is believed to have occurred sometime between about 22,000 and 12,000 BC -- the details are not yet fixed. It is known that the coasts of Alaska and western Canada would have become ice-free around 14,000 BC, which would have made coastal southern migration much more feasible.