Remember that there are three main types of rock:
The Earth's rocks do not stay the same forever. They are continually changing because of processes such as weathering, erosion and large earth movements. The rocks are gradually recycled over millions of years. This is called the rock cycle.
For example, sedimentary rocks can be changed into metamorphic rocks. These can be weathered, eroded, and the pieces transported away. The pieces of rock could be deposited in a lake or sea, eventually forming new sedimentary rock. Many routes through the rock cycle are possible.
The processes in the rock cycle are summarised in this diagram:
|A||Weathering breaks down rocks on the surface of the Earth. There are three types of weathering (biological physical and chemical). Wind and water move the broken rock particles away. This is called erosion.|
|B||Rivers and streams transport rock particles to other places. Rock particles are deposited in lakes and seas.|
|C||Rock particles form layers.|
|D||Compaction and cementation presses the layers and sticks the particles together. This creates sedimentary rock.|
|E||Rocks underground get heated and put under pressure, and are changed into metamorphic rock.|
|F||Rocks underground that get heated so much they melt turn into magma. Magma also comes from deeper inside the Earth, from a region called the mantle. Pressure can force magma out of the ground, creating a volcano. When the magma (lava) cools quickly, it turns into solid extrusive igneous rock. Magma that cools slowly underground forms solid intrusive igneous rock.|
|G||Areas of rock can move slowly upwards, pushed up by pressure of the rocks forming underneath. This is called uplift.|