The Rock Cycle
The rock cycle is a conceptual model of how earth materials form and change in the Earth’s crust over time. The rock cycle represents the series of events in which a rock of one type is converted to one or more other types and then back to the original type. Both products (rocks and sediments) and processes (such as melting, cooling, erosion, deposition, metamorphism, remelting) are part of this idealized cycle. The passage of geologic time is the essential component, although some processes are much faster than others. Note that all these types of processes are taking place simultaneously, but at different locations on and within the crust. It is important to note that rock cycle processes also occur on other rocky planets or moons, but rates may vary due to the presence (or lack of) atmospheric gases or fluids (including water) or availability of heat enough to melt rocks.