Rocks change physically and chemically, in a cycle. To show this cycle a model expressing these changes was developed--the rock cycle. This model expresses the creation of the different kinds of rocks and their interactions, and which other cycles in nature affect these interactions and changes.
Features
In geology there are three types of rocks: igneous, metamorphic and sedimentary. Igneous rocks are cooled, solidified liquid rock; metamorphic rocks have been heated and undergone pressure but not melted; and sedimentary rock is a solidified mass via pressurization of sediment, weathered bits of rock.
History
It is the father of modern geology, James Hutton (1726-97), who is credited with forming the rock cycle. Hutton was the creator of uniformitarianism, which states that all geological processes continue at the same rate forever; and the rock cycle was part of this concept. Plate tectonics, though, altered geologists' opinion of this theory by showing that there are sudden upheavals.
The Cycle
Within the Earth there are areas where rock has heated to the point of melting. This melted rock (magma) eventually cools, either extrusively (being erupted via volcanic activity) or intrusively (cooling where it is). What happens to the erupted rock is part of the next stage in the basic model of the rock cycle.
When it is exposed to the weather, igneous rock begins to decompose, or erode, from conditions such as wind, moving water or temperature changes. These conditions break off small particles of rock, which are mixed with other substances. This mixture of particles is called sediment, and is swept away via natural forces. Eventually the sediment is deposited in layers, in such places as stream beds and lake beds, where it begins to go through lithification, a process that turns sediment into rock.
Eventually, the sedimentary rock comes under so much pressure and heat that it changes, becoming metamorphic rock. Metamorphic rock, in turn, may come under so much pressure and heat, that it melts, completing the cycle.
Considerations
This basic cycle isn't the only way rock can change. Alternative routes include sedimentary and metamorphic rock eroding; igneous rock being heated and coming under pressure to form metamorphic rock; and metamorphic rock being exposed to the surface before it has a chance to melt into igneous rock.
Significance
Understanding the rock cycle is important for building a basis of how the Earth works. The rock cycle isn't alone in its function. It also influences and is influenced by other systems and cycles such as the lithosphere (the Earth's crust and upper mantle), biosphere (all biological life forms on Earth) and water cycle (where water evaporates, condenses and precipitates). It is important to know the rock cycle to have a balanced concept of the Earth as a whole.
Tags: rock cycle, metamorphic rock, igneous rock, heat that, much pressure, much pressure heat
