The earth is always changing.One way it changesis by erosion.Some is caused by the weather.For example,the wind causes erosion .in a desert,the wind blows the sand around.Rain also causes erosion . it washes away earth and even changes the shape of some rocks .A nother kind of erosion is caused by rivers . When a river goes through a mountain,it cuts into mountain.After a long time,the mountain is lower and the land is flatter