ROCK CYCLE DIAGRAM
Did you know that rocks aren't stuck as they are forever? Yes that's right, they can change, metamorphosing from one type to another. The three major rock types are in fact related to each other as they transform from one type to another in a continuous cyclic manner, known as the rock cycle. The elements that rocks are composed of are never created or destroyed, instead they are recycled. Rocks change through various processes that are not quick, but are slow and in cases can take thousands of years or just a couple of weeks. As you very well know by now, rocks change on and underneath Earth's surface. So, how then can extrusive igneous rocks on Earth's surface transform into underground formed metamorphic rocks? Well, the answer is simple, the Earth pulls down and lifts up rocks. It has its own forces too! Forces inside the Earth bring rocks to the surface where they are weathered, eroded, compacted and cemented into sedimentary rocks and also cooled in the case of extrusive igneous rocks. On the other hand, forces on Earth's surface pull rocks down into Earth's crust where they are melted and cooled into intrusive igneous rocks and magma, and at other times heated and pressed into metamorphic rocks.
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THE FORCES AND FACTORS OF CHANGE
Rocks don't just spontaneously change from one type to another as there are forces that drive their metamorphosis. In the rock cycle diagram above the arrows represent these factors and how they turn a rock type to another. The forces and factors are listed below and explained.
Heat and Pressure & Melting:
High temperatures and pressure form metamorphic rocks from pre-existing rocks of any type. Temperatures increase the further rocks descend into Earth's crust. 100-200km below Earth's surface the temperatures are hot enough to melt most rocks. Temperatures between 600 and 1,300˚C can melt most rocks turning them into magma (molten rock). Before rocks melt they undergo significant changes in their chemical composition and physical appearance, transforming into metamorphic rocks due to the intense heat. This extremely high heat can partially melt rocks during the process of metamorphism. Pressure from the rocks above pressing down on the rock can also cause great changes. Heat and pressure usually work together altering rocks under Earth's surface into metamorphic rocks. |
Cooling:
Magma turns into solid rock when cooled, forming igneous rock. As you know, igneous rocks can form on Earth's surface and underneath it forming a different type of igneous rock. The cooling process is different in these separate locations as on Earth's surface lava emitted from a volcano cools at a much more rapid rate due to the cooler temperatures surrounding it. Underneath Earth's surface this is not possible as there is a natural high temperature, but still this can drop, cooling the magma at a slow rate taking hundreds, thousands, or even millions of years. |
Weathering & Erosion:
Objects exposed to the forces: wind, water, the sun, and temperature changes, erode and weather away. Rocks break down into smaller particles of rock, more commonly referred to as sediment. Due to its size, this sediment can easily be transported and deposited by wind and water Compacting & Cementing: Sediment accumulates in oceans, lakes, and valleys. It builds up into layers. The sediment above weighs down the material underneath, squeezing the particles together and compacting them. The water and minerals passing through the spaces in between the particles helps cement them together forming a sedimentary rock. |