Rock Cycle

The rock cycle describes how the three main kinds of rock, igneous, sedimentary and metamorphic, transform into one another over geologic time as each is moved out of the conditions that formed it. Weathering and erosion break existing rock into fragments that accumulate as sediment and, over time, compact and cement into sedimentary rock; heat and pressure deep underground can recrystallize any rock type into metamorphic rock without fully melting it; and sufficient heat and pressure can melt rock into magma, which cools and crystallizes into new igneous rock, completing the cycle. In 1967 the geophysicist J. Tuzo Wilson described the repeated opening and closing of ocean basins, now called the Wilson cycle, tying the rock cycle directly to plate tectonics as its underlying driving mechanism, alongside the water cycle.