Over millions of years, the world's climate has undergone a series of dramatic changes that have most likely resulted from oscillations, or pendulum like swings, in the rotation of the earth. One such dramatic climate change was what is commonly called the Ice Age and was in reality a serious of phases o colder and warmer weather that commenced approximately two million years ago. What we today refer to as the Ice Age was in reality a series of weaker and stronger glacial periods during which sheets of ice expanded and moved varying distances south followed by inter-glacial periods when the glaciers melted to varying degrees and retreated to the north. These successive periods of colder and warmer weather  have had striking effects on the world's landscape and on the life forms that inhabit the land. Each glacial period in the series of colder and warmer phase had a different impact, depending on how far south the ice extended, how long it lasted before melting, and how much it changed the landscape and sea levels.

The effect on the world's landscape that resulted from the changing climate was dramatic. Vast sheets of glacial ice in the northern latitudes of the world cut deep u-shaped valleys that still exist today and caused huge boulders and enormous amount of clay and dust to be deposited across North America, Europe and Asia and to reshape the landscape of these areas. As the glacial sheets of ice crept southward on the northern continents, they trapped large amounts of water. This served to reduce the amount of moisture in the atmosphere that could fall as rain or snow, reducing the amount of rainfall and leading to further aridity and the expansion of deserts in the tropical and subtropical regions.

In addition, with so much water held in the glacial ice, the sea level fell, resulting in the exposure of land that today is covered with water. During glacial periods there was a land bridge from France to England, the islands of Japan and Java were connected to the Asian mainland, and Asia was linked to North America over what is today the Bering Strait. Then, during interglacial periods, when the glacial ice retreated to the north, more water became available as glaciers melted. Vegetation expanded with the increase in rainfall, and coastlines changed with the increase in ocean water, during interglacial periods, many areas that today are landmasses were covered with water.

Prehistoric people seem to have adapted well to these environmental changes. They moved from place to place in response to climatic changes. They could be found living in the grasslands of Asia, in the forests of southeast Asia, and in the temperate areas of southern Europe, and they moved into and out of the more northerly regions as the glacial regions retreated and advanced. Their diet changed to adapt to the changes in plant and animal life during succeeding glacial and interglacial periods, and the use fo stone tools, the building of shelters, and the use of clothing came about during this period. It was these sorts of adaptations that enabled humans to survive and progress while many other species failed to survive and thrive during this period in the way that prehistoric people did.

Source: My TOEFL preparation package