Lesson 3 of 7
The rock cycle
Goal: Explain how rocks change from one type to another.
Over millions of years, rocks change from one type to another. This is the rock cycle.
Follow the arrows once round the cycle. There are short cuts too: any rock at the surface can be weathered, and any rock can be changed by heat and pressure, or melted.
- Weathering wears rock down. Frost cracks it, plant roots split it and slightly acidic rain slowly dissolves it. The pieces stay where they are.
- Erosion moves the pieces away. Rivers, ice and wind carry them.
- Deposition, compaction and cementation make new rock. The pieces settle in layers. The weight on top squashes them, and minerals from the water glue the grains together.
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Key words in this lesson
Magma Molten rock below the surface of the Earth
Igneous rock Formed when magma cools and turns solid
Sedimentary rock Formed from layers of sediment squashed and stuck together
Metamorphic rock Formed when heat and pressure change an existing rock without melting it
Sediment Small pieces of rock that settle in layers
Weathering The wearing down of rock by physical, chemical or biological processes
Erosion The movement of pieces of rock by water, ice or wind
Rock cycle The processes that change rocks from one type to another