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The Rock Cycle:
The movement of the earth's crust may carry the rock as much as 700km (454 miles) below the surface. Here the temperature and pressure will be even higher and the rock will begin to melt. Molten rock is lighter than solid rock and it will begin to rise up through the overlying rock towards the surface. If it reaches the surface as a lava flow it will immediately be ready for weathering and erosion and the start of a new cycle. More often the molten rock solidifies underground and then all the rock above it must be eroded away before it can begin the cycle again.The rock cycle [2] is the relationship between these three types of rocks. The first part of the rock cycle takes place on the earth's surface. This is the erosion and weathering of older rocks to soil and sand and the transportation of the resulting sediment by rivers down to the sea. Nearly all the sediment produced, whether on the land or along the coast, is eventually transported to deep basins under the sea.
The oceans evolved over billions of years—possibly more —as by-products of volcanism. Both the water and the gaseous constituents of the ocean, such as carbon dioxide and chlorine, came from the earth's deep interior. Rivers brought to the seas rock particles that contained sodium, magnesium, and potassium, as part of the weathering cycle on land. This huge chemical vat provided the raw materials and the environment for the start of life. In the future, the minerals locked in the water and the sea Floor and the food resources present in all parts of the marine biological cycle may be called upon to sustain that life.
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