Building Up and Breaking Down

When the crust moves, the rocks of the crust can change. They can change position. These changes may cause mountains to be made. The most common type of mountain is made mostly of rock layers folded by being squeezed together. This is called a fold mountain. A fault is a large crack in rocks along which there is movement. A mountain made by huge tilted blocks of rocks separated from surrounding rocks by faults is called a fault-block mountain. At the same time that forces are building up the crust, other forces are breaking down the crust. The two main forces breaking down the crust are weathering and erosion. The breaking down of rocks into smaller pieces by natural processes is called weathering. The picking up and removal of rock fragments and other particles is called erosion.  The end result of weathering is soil. Soil is a mixture of weathered rock, decayed plant and animal matter, living things, air, and water.  Plants and animals live in and on the soil. When they die, their remains enrich the soil. Rocks in the soil break down into smaller and smaller pieces.  Slowly the soil develops distinct layers. Any of the layers of soil from the surface to the bedrock below are called soil horizons. Below the soil is weathered rock and rock layers. Water that soaks into soil and rock by collecting in the spaces between the rock particles is called groundwater.  Poor soil can be improved by adding fertilizers. It can also be improved by adding humus. Humus is material in soil produced by the breakdown of plant and animal material. Humus helps soil absorb and retain water. And is what I learn.