What Is The Rock Cycle?

In this video you will learn about the dynamic rock cycle. Plant roots help to create new soil from the solid rock and they get nutrients and support from the soil. This solid rock is often sandstone or granite. They are made up of grains, but the granite has interlocking grains and sandstone has rounded grains. These are the two main types of rock – granite is formed by molten rock solidifying, an igneous rock. But sandstone was made by bits of other rock carried by rivers to the sea – the bits get smoothed and rounded like the pebbles on the beach. These grains settle on the sea bed forming sedimentary rocks. Rocks get broken up by a process called weathering. Mechanical weathering is when the heat of the sun expands the rock - it contracts at night causing it to crack. If water enters and freezes it will crack more. With water and wind bits of rock knock into each other, breaking them. Chemical weathering is when rain which is slightly acidic dissolves some minerals in the rock. Biological weathering happens as lichens and then roots of plants grow on the rocks forcing their grains apart. Weathered rock forms the soil, but it is also eroded – that means it is transported, either by wind, or more usually by water, to the sea – erosion. After weathering the grains are carried to the sea where the harder quartz settles, as in the jar of soil, forming sand. The feldspar settles more slowly forming rich beds of clay – containing most of the trace metals plants need to grow. During the movement of the great tectonic plates the rocks get folded, and squashed, often ending up high in the air as new mountains form. If rocks are heated and compressed enough they change their form, and are called meta-morphic rocks. From sand stone we get quartzite, and from clay we get first shale, then slate. Sedimentary and metamorphic rocks get weathered and eroded too. Tectonics carry the rocks down into the earth’s hot mantle where they melt and emerge once again as igneous rocks, completing the rock cycle. We must also mention chalk and limestone, made of calcium carbonate, which are sedimentary rocks formed in the sea from the shells of dead sea creatures. Under heat and pressure they form the metamorphic rock, marble. Another rock formed by living things is coal, and the related fossil fuels. Peat is formed as vegetation in bog land is unable to rot. Under heat and pressure the peat metamorphises into coal.