Rock cycle

The rock cycle is a basic concept in geology that describes the time-consuming transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. As the adjacent diagram illustrates, each of the types of rocks is altered or destroyed when it is forced out of its equilibrium conditions. An igneous rock such as basalt may break down and dissolve when exposed to the atmosphere, or melt as it is subducted under a continent. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the three rock types are related to each other, and how processes change from one type to another over time. This cyclical aspect makes rock change a geologic cycle and, on planets containing life, a biogeochemical cycle.

The original concept of the rock cycle is usually attributed to James Hutton, from the eighteenth century Father of Geology. The rock cycle was a part of Hutton's uniformitarianism and his famous quote: no vestige of a beginning, and no prospect of an end, applied in particular to the rock cycle and the envisioned cyclical nature of geologic processes. This concept of a repetitive non-evolutionary rock cycle remained dominant until the plate tectonics revolution of the 1960s. With the developing understanding of the driving engine of plate tectonics, the rock cycle changed from endlessly repetitive to a gradually evolving process. The Wilson cycle (a plate tectonics based rock cycle) was developed by J. Tuzo Wilson during the 1950s and 1960s. The world is made out of rocks.

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