Older rocks are recycled to make younger rocks, just as old aluminum cans are recycled to make new aluminum cans or old newspapers are recycled to make new cardboard boxes. Weathering and erosion at the earth's surface can break down a rock into small bits. These can be deposited as sediments that become sedimentary rocks. Burial, with rising pressure and temperature, can alter any rock to form a metamorphic rock. When the molten rock cools it forms an igneous rock.
Metamorphic rocks can form from either sedimentary or igneous rocks.
The sedimentary particles from which a sedimentary rock is formed can be derived from a metamorphic, an igneous, or another sedimentary rock. All three rock types can be melted to form a magma. Thus, the cycle has continued over the ages, constantly forming new rocks, breaking those down in various ways, and forming still younger rocks.