It is known as ice ages at different times of the geological history of Earth, during which glaciers were formed, ie, masses of ice that cover large land areas. There were several ice ages in the Permian period of the Paleozoic Era (290 to 250 million years ago), and in the Quaternary, the latest period of the Cenozoic Era, which began with the appearance of man, two million years ago. In the latter period there were four ice ages in Europe, known as Würm, Riss, Mindel and Gunz, which correspond almost perfectly with those of Nebraska, Kansas, Illinois and Wisconsin, have occurred in North America. These glaciations were separated by as many interglacial stages with warmer climates. The last glaciation ended about 35,000 years. Currently, the Earth passes through an interglacial period. Among the various theories about the origin of ice ages is one that is based on changes in the tilt of the Earth. A second theory involves increasing the height of different parts of the world, along with a decrease in solar radiation, which had led to glacial regions. Other scientists maintain the idea that a reduction in carbon dioxide would have caused the drop in temperature, a fact which, coupled with snowfall, would have resulted in glacial areas.
The physical transformations glaciers on the Earth's surface, such as glacial lakes, valleys, "U" with steep slopes, waterfalls and waterfalls, fjords, mountain ranges with shaped ends.
There are three main types of glaciers: the plateau, which are the largest and amesetadas form in mountains, the mountain, which occur in valleys, depressions and ravines, and continental glaciers, which originate in the polar areas.