The rock cycle — Earth science, 7–10 years
Rocks are not always the same forever. Heat, pressure, water and time can change one kind of rock into another.
Rocks can change
A rock may melt, cool, break into pieces, or be squeezed deep underground. These changes happen very slowly, so one rock can take a very long time to become another kind. The rock cycle is this continuing journey.
Why have a cycle?
People once saw different rocks but needed to explain how they formed and why new rocks keep appearing. The cycle solves this puzzle: Earth does not simply make rocks once and finish. Its heat, movement, rain and wind keep recycling old material.
A piece of sandstone
Imagine a sandstone cliff. First, rain and wind loosen sand grains. Next, the grains collect in a layer and are pressed together, forming sandstone. If it is buried and heated, it may change into another rock; if it melts, cooling magma can form a new rock.
The common mix-up
It is easy to think that every rock follows one neat path: pebble, rock, then nothing else. That seems reasonable because rocks look solid and permanent. In fact, different rocks take different routes, and the same rock may change more than once.
Reading a landscape
Geologists use the rock cycle to work out what happened in a place long ago. Layers, crystals and cracks can show whether rock cooled from melted material, formed from layers, or changed underground. This helps people study mountains, volcanoes and useful stone.
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