Many Paleolithic bands were nomadic. They moved from place to place as the weather changed. They followed herds of animals that they hunted from their winter feeding places to their summer feeding places. If there was a drought,flood, or some other disaster, the herds and the people might haved moved a long distance, looking for food. During the "Ice Age" a lot of the water on Earth turned to ice. This made sea much lower than it is now. People were able to walk through Beringia from Siberia to Alaska. Bands of "Homo sapiens" ( another word for people) travelled to that area from Asia. At that time there were rich grasslands with many large animals that are now extinct. It is believed that many groups of people travelled there over a long time and later spread to other parts of America, as the weather changed.