The landscape is constantly changing under the effects of erosion. Erosion is a wearing away of the Earth's surface. How does this happen? Moving glaciers crumbling the soil; the force of the ocean waves against the coast; the strength of ice or wild running rivers.... Under the influence of all these forces, the great mountainous massifs are changed into undulating countryside- after many million of years. As soon as the mountain is created, erosion starts to destroy it. When we look at a dry desert, without water, we say to ourselves, 'There is no life here.' On sandy soil, vegetation is very sparse. In some places a strong, dry wind can clean rocks of sand and remains of erosion. In the desert regions the wind blows and moves the sand against the rocks. The softer parts are worn away rapidly, the harder parts last longer. There is a great temperature change from day to night which weakens the rock. The wind and water are continually changing the Earth's appearance.