'The rock cycle has no beginning and no end.' Justify this statement with examples.

The continuous process of transformation of old rocks into new ones is known as rock cycle. The cycle may also pass through the process of formation of sedimentary, metamorphic and igneous rocks.

1. The igneous rocks are the primary source of all other rocks. They are formed on the outer surface of the earth due to volcanic activities. Rocks are disintegrated and eroded by climatic factors. The disintegrated material is removed and transported to lower levels by the forces of running water, winds, glaciers and ocean currents. In the basins, lakes or ocean beds the sediments accumulate.
2. The accumulations undergo lithification through the processes of evaporation, compaction and cementation.
3. Once the loose sediment is transformed into sedimentary rock, it is carried in depressions or on the sea floor further down under the earth. There may be further disintegration and recrystallisation into igneous rock and then it may be transformed into metamorphic rock.
4. In case the rock melts it may again result in formation of igneous rock. The disintegrated material may again form sedimentary rock. In completing any of these changes hundreds and thousands of years are involved.

In the operation of the rock cycle, the earth is kept young and movements of adjustments specially through horizontal flow or convection currents maintain the balance between various elements of the earth like oceans and continents.