More than 1.5 million years ago, during the Pleistocene epoch a rapid cooling of the climate occurred. This was the beginning of an ice age. At that time, large areas of the Northern Hemisphere were covered by an ice sheet. In Europe, it started to grow on the Scandinavian Peninsula. From there, it reached the area of Poland. The Scandinavian ice sheet in our country grew smaller or bigger, depending on the climate warming up or cooling down. The ice sheet grew bigger when the climate became cooler, and grew smaller when the climate warmed up. It is a fact that the area of Poland was covered by the ice sheet at least three times.