The Rock Cycle

Three Types of Rocks on Earth

Presented by, Jaclyn Memmott

Did you know that rocks are constantly being recycled? Recycle means to take something old and change it into something new. So some of these old rocks that have been around for more than four billion years are being changed into different rocks. Of course, that doesn't happen over night. It takes millions of years. To better understand how this happens, let's take a journey through the rock cycle.

First our journey begins within the earth…

Here we see some hot magma (molten rock) that is being pushed up towards the Earth’s crust. Some of this magma creeps into the cracks of the volcano; while, the rest is forced out the top through the crater cone. Once the magma is out of the volcano, it is called lava.

Igneous Rocks are coolAs the magma pushes towards the earth's surface, and turns to lava it cools into solid igneous rock. Magma that cools quickly forms one kind of Igneous rock (extrusive), while magma that cools slowly forms another (intrusive).

Weathering and Erosion Over time wind, rain,

and sun wear rocks down and break them apart. The resulting bits and pieces of material are called sediment. Sediment is then transported by wind and water, often ending up far from where it started. These processes of breakdown and transport due to exposure to the environment are called weathering and erosion.

Compacting and cementing

Over time, sediment is washed into oceans, lakes, and valleys and it starts to build up in layers, weighing down the other sediment that is beneath it.

This weight presses the sediment particles together, compacting them. Water passing through the spaces in between the particles and helps to cement them together. This process of compacting and cementing sediment forms…

Heat & Pressure Due to movements in the crust, rocks are frequently

pulled under the surface of the earth, where temperatures increase dramatically the farther the rocks descend. Below the earth's surface, temperatures are hot enough to melt most rocks. However, before the melting point is reached, a rock can change.

Heat and pressure work together to alter the rocks under the earth's surface. This kind of change, which results from both rising temperature and pressure, is

called metamorphism, and the resulting rock is a…

Metamorphic Rocks

Melting it takes a lot of heat to melt a rock. The high

temperatures required are generally found only deep within the earth. It takes temperatures between 1,100 and 2,400 degrees Fahrenheit to melt a rock, turning it into a substance called magma (molten rock).

The Rock Cycle can

Begin all over again!

References: http://www.learner.org/interactives/rockcycle/

change2.html

http://library.thinkquest.org/J002289/index.html