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It's hard to think of rocks as moving objects unless you pick one up and throw it! But rocks do move—slowly— as they are created, destroyed, and changed into new types of rock. The way rocks change over time is called the rock cycle.

The rock cycle takes place over a very long period of time. It may take millions of years for a rock to change from one type to another. Understanding the rock cycle can help us understand how the Earth was formed and continues to change.

Geology This diagram on the facing page shows you the entire cycle. Look it over, and then examine each part of the cycle.

Geology The rock cycle begins far below the Earth's surface. The incredibly hot temperatures cause rock to turn to magma. The magma emerges as lava from a volcano. As the lava cools, it forms igneous rock.

Geology Weathering begins the process of breaking down the igneous rock. Erosion continues the process and transports the sediment along.

Geology Over time, the sediments form sedimentary rock layers at the bottom of rivers, lakes, and streams. Pressure from layer after layer of sedimentary rock causes the rock to change form. Metamorphic rock is created.

Geology As pressure pushes the rock deeper into the Earth, it heats up and turns into magma. The cycle begins again.

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Science Encyclopedia for KidsGeology