Most likely, when most people think about the mighty Himalayas, the sweeping prairies or the various jagged coasts of the world, they see something permanent, ancient and forever. This vision of an unchanging landscape is simply not accurate though. Almost every region of the world has undergone massive changes in just the last 20,000 years. If you make that number 20,000,000, almost nothing we see now, is what it was then. The Sahara used to be covered with water in contrast to today, as was Texas. The Great Plains, largely vast treeless grassland now, was covered with spruce forest in the last ice-age. Much of what is now the Bering Sea was once dry land. And this was only thousands of years ago. The lesson to be learned is that geography is an ever changing thing due to the forces of wind, water, erosion, plate tectonics, heat, volcanism and others. Though some changes happen radically, most occur incredibly gradually. But no landscape is permanent and unchanging.