A very large percentage of the earth’s land masses were covered by glacial ice during the last glaciation. Right now it is about 10%, but during the Ice Age it was much more. Enough of the earth’s water was trapped in this glacial ice that the oceans were about 120 to 150 meters lower than they are now. The thicker ice sheets were one or two kilometers thick, and they tended to slide around quite a bit, grinding down the surface of the earth and turning bedrock into dust and cobbles.