lunes, 25 de octubre de 2010

Building Up and Breaking Down

In this topic you will learn about how mountains are formed .
As the crust moves, the rocks of the crust can change. They change position. They can move up, down, or sideways.
Rocks can also be bent, squeezed, twisted, or broken. 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 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.
Soil can support the growth of rooted plants.
 
The soil develops many layers. Any of the layers of soil  are called soil horizons.
Water that soaks into soil and rock by collecting in the spaces between the rock particles is called groundwater.
Soil can easily lose minerals. Poor soil can be improved by adding fertilizers and 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.

                                          


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