In the heyday of the Quaternary Ice Age (starting about 2-3 million years ago and ending about1-20,000 years ago), about 25,000-20,000 years ago, the glacier ice sheet developed to the mid-latitude area in the northern hemisphere, and the global sea level dropped by at least 90 meters, while the Bering Strait had an average water depth of 42 meters and a maximum water depth of 52 meters. Therefore, at this time, Bering, the easternmost part of Northeast Asia, has spread in the American continent since then.

At this time, it was not the Bering Strait that was covered with ice and snow, but the Strait became land because of the lowering of sea level, and people and wild animals could come and go.

Ice and snow are not enough. The temperature dropped sharply this winter, with the lowest temperature below -45℃. It's the Ice Age in the Strait. The surface of the strait is frozen, and the ice layer is more than 2 meters thick. There is only an "ice bridge" connecting the two continents in the Bering Strait, and there is no "land bridge", so neither humans nor wild animals can pass through it. This period is from June 10 to April of the following year.

Of course, during the ice age 20,000 years ago, even if there was a land bridge, it was covered with thick ice sheets, similar to the current winter strait. So how did humans get through it? It is speculated that in the middle of the ice age, there will be a relatively warm period of several years to decades. At this time, the continental ice sheet had no time to melt and the sea level did not rise significantly. However, because the Bering Strait is close to the ocean, the ice sheet on the continental bridge may have partially or completely disappeared, green plants began to grow, and there are a considerable number of wild fruits and animals. Humans chased animals and plants all the way to the east and unconsciously came to the American continent.