The concept of the rock cycle is attributed to James Hutton in the 18th century, also the founder of modern geology. The main idea is that rocks are continually changing from one type to another and back again, as forces inside the earth bring them closer to the surface (where they are weathered, eroded, and compacted) and forces on the earth sink them back down (where they are heated, pressed, and melted). So the elements that make up rocks are constantly being recycled.
Sediments can be compressed and cemeted to form sedimentary rocks. These rocks can then be changed by intense heat and/or pressure to become metamorphic rocks. They can then be melted and re-crystallized to make igneous rock. Weathering and erosion create sediments, and the cycle continues. Each rock type can remain relatively stable for long periods of time. Notice that between the different formations of each rock material is lost or formed. Precambrian rocks are mostly covered by rock systems of more recent origin, but where visible they commonly display evidence of having been altered by intense metamorphism.
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