Rocks are constantly changing and being transformed through various geological processes. Weathering breaks down rocks into sediments which are then eroded and transported by water, wind or ice. The sediments may settle and become compacted into sedimentary rocks through cementation. Heat and pressure metamorphose sedimentary and igneous rocks into different types of metamorphic rocks. Extreme heat melts rocks into magma and their subsequent cooling forms new igneous rocks, completing the continuous rock cycle.