How the ROCK CYCLE Recycles Earth’s Crust

rock cycle

Last Updated: Jan 5, 2019

The rock cycle recycles the crust

Rock Cycle

If you could speed up time, you would see rocks continuously cycling from the surface down into the deep interior of the planet and back up again.

Like a well-oiled machine, rocks transform from igneous, sedimentary to metamorphic over long periods of time.

This process where rocks are created, altered and formed again is the rock cycle.

Igneous rocks from volcanoes


Volcanoes are the foundation for igneous rocks. Like a bottle of champagne with a cork in it, liquid rock pools in the magma chamber.

Once you pull the cork, the volcano erupts from the mouth spewing lava. Like wax dripping down the side of a candle, igneous rocks like feldspars form.

So hot lava drips on the side of volcanoes then cools, hardens and become igneous rocks like granite.

Without igneous rocks, there wouldn’t be the rock cycle.

Metamorphic rocks from heat and pressure

Metamorphic Rock

Metamorphic rocks change in form from pre-existing rocks.

For example, a rock that was once made of sand is changed or “metamorphosed” into another type of rock from heat and pressure.

When it’s metamorphosed, it’s soft and pliable like cookie dough. This intense pressure for metamorphic rocks comes from inside Earth.

Earth’s major mountain chains contain metamorphic rocks because it’s at plate tectonics boundaries where this intense pressure exists.

Sedimentary Rocks: Compaction and Cementation


Sedimentary rocks like shale, limestone and sandstone form from pre-existing rocks. If you start with sand, mud or organic material, these sediment deposits get eroded and transported over time.

This happens because shorelines move back and forth compacting material below like a steam roller. The new layers of sedimentary rock are on top and the older layers on the bottom.

Like glue, each successive layer cements over tens of millions of years.

For example, the Grand Canyon has sedimentary rock layers dating back to 2 billion years ago.

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