The Quaternary period has been separated into two epochs: Pleistocene and recent. The Pleistocene epoch began about one million years ago and ended about 8-10 thousand years B.C. It is believed that due to unusual solar activity or certain unknown reasons repeated glaciation activities occurred, as a result of which ice was formed in the polar regions and on the mountains in temperate parts and high altitudes. When the ice retreated it left lakes, like the Swiss Lakes and those of Northern Italy, English and Scottish Lakes and Great Lakes. These glaciations resulted in the destruction and redistribution of many animals and plant species.