Rock Cycle Examples

Students in school are very familiar with the water cycle, which explains the process of how water moves around the planet in solid and vaporous forms. The carbon dioxide cycle further explains the cyclical nature of gases in our atmosphere and how plants and animals use carbon dioxide and oxygen. But not many people understand the rock cycle, and how rocks are formed.

The rock cycle is geological concept that explains the changes over long periods of time that occur in igneous, metamorphic, and sedimentary rocks. Each of these kinds of rocks undergoes changes or destruction when its environment is out of balance. This kind of change in equilibrium can be caused by atmospheric changes, plate tectonic activity, the movement of bodies of water, and more.

The rock cycle has long interested geologists because it also demonstrates how three very different types of rock can be related to each other. It also gives researchers a clearer picture of how the processes involved in changing rocks differ with the type of rock involved.

1. Heat and Pressure Changes

Rocks are often shifted from one layer of the Earth's crust to the other due to changes in the crust itself. Below the surface, temperatures increase as the rocks go down. By the time a rock is between sixty and one hundred miles beneath the surface, the temperature can be high enough to melt rocks. Before that melting occurs, though, a rock would undergo a number of key changes from the heat.

But heat is only one factor beneath the crust's surface. Intense pressure from the layers of dirt and rock around it can also causes significant changes. When rocks are changed due to this combination of heat and pressure, metamorphic rock is formed.

2. Melting

As stated above, rocks can melt at high enough temperatures. Luckily for the animals on the surface, the temperatures required to melt rock only occur deep beneath the Earth's crust. As a rock is pulled downward by shifting of the crust, temperatures rise to as high as 2,400 Fahrenheit. At that temperature, the rock can melt and form a whole new substance.

3. Cooling

One other process in the rock cycle is the cooling phase, which occurs when rocks are taken out of the high heat and pressure environments that caused change. When magma cools and forms into solid rock, there are two different processes involved. If the magma erupts out of a volcano and cools rapidly on the Earth's surface, it forms what's known as extrusive igneous rock, from the word "extruded," just like icing being extruded out of a baker's decorating bag. But if the magma is slowly pushed up through the layers of the Earth's surface over hundreds of thousands or even millions years, it cools much more slowly and is called intrusive igneous rock.