Forces Driving the Rock Cycle

FOCUS QUESTION: What are the forces that drive (or power) the rock cycle? 

water_cycle

EXTERNAL FORCES: the sun, the water cycle, weathering and erosion.

Water (and the water cycle) is the main agent in weathering and erosion.  Water breaks down material on the surface of the Earth in many ways and carries it and deposits it to new places. Years after years these sediments build up, are compacted and cemented, and over hundreds of thousands and even millions of years sedimentary rocks are formed.

“The driving force for the hydrologic cycle is the sun, which provides the energy needed for evaporation just as the flame of a gas stove provides the energy necessary to boil water and create steam.” (From VisionLearning.com)

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INTERNAL FORCES: Convection currents and the movement of the Earth’s plates.   Image Link

627a59344aa66c199aeb11e4d8b057751d829a33Internal processes driven by heat from Earth’s interior are responsible for forming both igneous and metamorphic rocks, as well as how they reach the surface and then form sedimentary rocks.

 

How does it happen? 

The crust of the Earth is broken into plates. These plates move because of convection currents in the mantle of the Earth. When these plates move it causes changes in our Earth’s surface, impacting the formation of all three types of rocks.  How fast or how much the plates move impacts how much each type of rock is created or transformed.

Metamorphic rocks: Metamorphic rocks are mostly formed where plates push together (convergent plate boundaries) and there is great pressure and compression of rocks. They are formed mainly in the lithosphere, wherever there is high pressure and high temperature. If the pressure and temperature are too high, metamorphic rock will melt and become magma.

Igneous rocks:  Igneous rocks can form where there is sea floor spreading and plates move apart. There magma comes up between the plates, cools, and forms new crust (or rock).

They can also form due to volcanic activity or the cooling of magma beneath the Earth’s crust.

Sedimentary rocks:  But how do rocks get to the surface to be weathered? This happens through uplift. “Uplift occurs when areas of the crust move up due to plate tectonic movements.” Once rocks reach the surface they can be weathered and eroded by nature’s external forces.

Information Resource: Windows to the Universe

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