The Rock Cycle

Rocks are constantly exposed to various physical and chemical conditions that can change them over time. The interaction of processes that change rocks from one type to another is called rock cycle. Three kinds of rocks—igneous, sedimentary, and metamorphic—are involved in a worldwide recycling process. Internal heat from the tectonic cycle produces igneous rocks from molten material near the surface, such as lava from volcanoes. These new rocks weather when exposed. The process of weathering produces sediments, including boulders, pebbles, sand, silt, and clay, as well as dissolved chemical elements. These sediments are transported by wind, water, or the movement of glaciers.

The weathered materials accumulate in depositional basins. These can be in the ocean, where the sediments are compacted by material deposited above them, and then converted to sedimentary rocks. After sedimentary rocks are buried to sufficient depth (usually tens to hundreds of kms), they may be altered by heat, pressure, or chemically active fluids. They are transformed again, to metamorphic rocks. These may start the rock cycle again, by being transported to the surface by plate tectonics (movement of the plates by the force

originating deep within Earth), and subjected to weathering.

     Fig.: Rock Cycle

 It is the weathering, erosion, and transport of sediment, with tectonic processes of uplift that produce the tremendously varied topography on Earth. It is through the combined actions of plate tectonics, the hydrologic cycle, and life processes that rocks and minerals so important to modern civilization are formed and concentrated, and by which chemical elements required for life are returned to the surface, after they have been weathered, transported, and deposited on ocean basins.