New York State High School Regents Exam Prep
Earth Science

The Layers of the Earth

Seismic waves have been used by scientests to study the interior of the earth. The diagram below shows the different layers of the earth. Remember that the density of each layer increases as you go deeper into the earth.

Interior of the Earth

The Crust. Outermost layer, thickness varies from 5 km under the oceans to about 60 km under some mountain ranges. The composition of the crust varies from the continents to the ocean. Most continents are made up of thin layers of sedimetary rock that covers mostly granitelike rocks. The ocean crust is mostly basalt rock covered with layers of sediments.

The Mantle. It is divided into two parts. The upper portion, which is called the Asthenosphere, is a plastic like fluid. This is where the mantle convection currents occur. The rest of the mantle is made up of dense rock. The mantle is the thickest layer. Approximately 2900 km thick.

The Outer Core. This layer is thought to be a liquid composed of iron and nickel. S-waves do not pass through this layer and that's how scientists have inferred it is a liquid. You can also tell this layer is a liquid by looking on page 10 in your reference tables. Find the outer core in the diagram. Now go all the way down to the temperature graph at the bottom of the page. Notice the actual temperature line is above the melting point line. This means that the layer is a liquid. Approximately 1900 km thick.

The Inner Core. This is a solid that is composed of iron and nickle. This information is based on the study of meteorites. This layer of the earth has the greatest density. Approximately 1500 km thick.

The information on page 10 of your reference tables will help you answer questions about the earth's interior. Scientists know so much about the earth's interior because they study how the earthquake waves travel through the earth. The wave's velocity and direction are changed as they travel through different density material. The diagram below shows how the P and S-waves travel through the earth. The area called the shadow zone occurs with every earthquake. This happens because the P and S-waves are refracted or bent away from this area and no earthquake waves are received. The location on the opposite side of the epicenter only receives P-waves.

New York State High School Regents Exam Prep Center: Earth Science