The Rock Cycle
There are several Earth cycles occurring simultaneously such as the water cycle, nitrogen cycle, carbon cycle, and others. And as with all of Earth's cycles, they are never-ending and the order of the steps in each cycle is not always the same, and this includes the rock cycle.
The rock cycle is the process by which rocks of one kind change into rocks of another kind. It is the journey rocks take as they change, and the changes can take millions of years. It is important to remember that rocks do not stay in one place forever.
Rocks move but not like living things. Rocks move several ways as they go through the rock cycle, rushing water may move them from one place to another, landslides position rocks in new places, and parts of rocks may be break and wind moves the sediments to other areas.
The three rock types include igneous, sedimentary, and metamorphic. Igneous is hardened magma or liquid rock and can form above or below ground. Sedimentary rocks are formed from compacted sediment which can come from the other types of rocks that have eroded and can be the remains of living things. Metamorphic rocks are the least common and have been formed from igneous and sedimentary rocks that have been transformed under extreme heat and pressure.
There are several steps in the rock cycle, and the steps have no special order. First, magma cools and crystallizes beneath the crust, and forms intrusive igneous rocks. With time, pressure causes uplift, the rocks end up on the surface. Next, molten magma flows to the surface as lava by volcanic activity. It causes extrusive igneous rocks as they harden and crystallize. Third, weathering, erosion, and movement of the rock on the surface carries sediments of rocks to low-lying places and water bodies.
Fourth, sedimentary rocks are formed as the sediments pile up and compaction and cementation take place. Then after a long time of pressure & heat, the igneous & sedimentary rocks buried in the crust change to metamorphic rocks. Finally, some of the metamorphic rocks melt as they get close to molten magma, some are uplifted to the surface, and if they melt, they get released again through volcanic activity.
The steps are numbered, but the cycle occurs simultaneously with each step taking place at any time, over a period of thousands or millions of years. In some places, the weathering and erosion may occur more often, and the three types of weathering that break down the rocks include physical, chemical, and biological weathering.
The three types of weathering include physical which involves temperature changes as rocks heat up and cool off leading to expansion and contraction and the cracking of the rocks. The layers of rock wear off during a process called exfoliation. It also includes weathering by wind, water, and waves.
Chemical weathering involves the reaction of some chemicals on rocks that are more prone to chemicals breaking down the substances. Rainwater can be acidic and cause the rock to weather and break apart, which includes air pollution.
The third type of weathering, biological, may occur when animals burrow into a crack in a rock, the crack widens, and the rock breaks apart. Algae, bacteria, and mosses grow on rock surfaces producing weak acids breaking apart rocks, plant roots get into cracks, and construction by humans leads to weathering.
Finally, erosion is also an important factor in the rock cycle. It involves the movement of the weathered rock from one place to another by wind, ice, water, and gravity. The natural elements move pebbles, sand, and soil that have been weathered to other places.
New rocks are always forming, and old rocks are always changing. The rock cycle and the different processes never stop and will continue to do so for millions and millions of years.
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