McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams

Home » Teaching Plate Tectonics » Earth's Internal Structure

Earth's Internal Structure
Crust - Mantle - Core

Teaching
Plate
Tectonics


Three Parts of Earth's Interior

A knowledge of earth's interior is essential for understanding plate tectonics. A good analogy for teaching about earth's interior is a piece of fruit with a large pit such as a peach or a plum. Most students are familiar with these fruits and have seen them cut in half. In addition the size of the features are very similar.

If we cut a piece of fruit in half we will see that it is composed of three parts: 1) a very thin skin, 2) a seed of significant size located in the center, and 3) most of the mass of the fruit being contained within the flesh. Cutting the earth we would see: 1) a very thin crust on the outside, 2) a core of significant size in the center, and 3) most of the mass of the Earth contained in the mantle.
 


Earth's Crust

There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. These two different types of crust are made up of different types of rock. The thin oceanic crust is composed of primarily of basalt and the thicker continental crust is composed primarily of granite. The low density of the thick continental crust allows it to "float" in high relief on the much higher density mantle below.  


Earth's Mantle

Earth's mantle is thought to be composed mainly of olivine-rich rock. It has different temperatures at different depths. The temperature is lowest immediately beneath the crust and increases with depth. The highest temperatures occur where the mantle material is in contact with the heat-producing core. This steady increase of temperature with depth is known as the geothermal gradient. The geothermal gradient is responsible for different rock behaviors and the different rock behaviors are used to divide the mantle into two different zones. Rocks in the upper mantle are cool and brittle, while rocks in the lower mantle are hot and soft (but not molten). Rocks in the upper mantle are brittle enough to break under stress and produce earthquakes. However, rocks in the lower mantle are soft and flow when subjected to forces instead of breaking. The lower limit of brittle behavior is the boundary between the upper and lower mantle.  


Earth's Core

Earth's Core is thought to be composed mainly of an iron and nickel alloy. This composition is assumed based upon calculations of its density and upon the fact that many meteorites (which are thought to be portions of the interior of a planetary body) are iron-nickel alloys. The core is earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances.

The core is divided into two different zones. The outer core is a liquid because the temperatures there are adequate to melt the iron-nickel alloy. However, the inner core is a solid even though its temperature is higher than the outer core. Here, tremendous pressure, produced by the weight of the overlying rocks is strong enough to crowd the atoms tightly together and prevents the liquid state.
 

Contributor:


Teaching
Plate
Tectonics


Find it on Geology.com




More from Geology.com


gem photos
100+ Gems - Photos of over 100 beautiful gems ranging from the popular to the obscure.
Sand
Sand is a diverse material. This gallery includes photos of sand from around the world.
Types of Volcanic Eruptions
Types of Volcanic Eruptions: A description of the most common eruption types.
Emerald
Emerald is the most popular green gemstone in the United States and most of the world.
shale gas
Shale Gas is natural gas trapped within shale. It is a growing source of US supply.
Sunstone: Copper inclusions give this feldspar an aventurescent flash.
Salt Glaciers
Salt Glaciers are masses of salt that flow downslope under their own weight.
Land Below Sea Level
Land Below Sea Level: Did you know that dozens of land locations are below sea level?


 


© 2005-2015 Geology.com. All Rights Reserved.
Images, code and content of this website are property of Geology.com. Use without permission is prohibited. Pages on this site are protected by Copyscape.