The Great Geological Cycle
The earth is undergoing a constant, slow process of change, so slow by human standards that it is easy to gain the impression that everything is permanent and unalterable.
This diagram shows the way in which the bedrock and mountains have emerged as a result of the crystallization of molten magma to form solid rock.
The upward folding of the mountain ranges is also governed by plate tectonics, movements of segments of the earth’s crust and collisions between them. In the course of time the bedrock is worn down by weathering, the effects of water and the atmosphere and gravitational forces, and the rocks are reduced to sand and clay and eventually transported by water and wind into the seas. Here they are deposited on the sea bed and harden in time to form sedimentary rocks. Eventually, as a result of movements in the earth’s crust, these sedimentary rocks are pressed down further into the earth and melt to form magma once more. All this forms a cycle of the matter of which the earth is composed that takes place over a period of hundreds of millions of years, although the processes that contribute to it are active all the time.