Plate Tectonic - Plate Tectonics (4)
Pre Lab 

  • Exploring the meaning of Plate Tectonics.
  • Distinguishing the different layers of the Earth.
  • converging
  • crust
  • diverging
  • inner core
  • mantle
  • outer core
  • plate tectonics
  • transform

Students calculate the thickness of the Earth’s internal layers.


Geologists have distinguished three main internal subdivisions of the Earth, based on the behavior of seismic waves and laboratory experiments. These divisions are based on the composition of each layer. The outermost layer is the crust. The Earth has two types of crust. Continental crust underlies much of the Earth’s land surface and is what we live on. The ocean floors are underlain by oceanic crust. These materials are composed of different kinds of minerals. The continental crust is like the igneous rock granite, and the oceanic crust is like basalt, another igneous rock.

Underlying the crust is the second layer, the mantle. It comprises the largest portion of the Earth. Like the crust, it is also composed of silicate minerals. The innermost portion of the Earth is the core. It is composed of metallic elements, primarily iron and nickel. The core is subdivided into two parts. The outer core is liquid metal, while the inner core is solid.

The plates are composed of the crust and the uppermost part of the mantle. These two layers are often called the lithosphere because they are both composed of solid rock. The underlying, partially molten part of the mantle, on which the plates slide, is called the asthenosphere. In contrast to the crust–mantle-core division, which was based on composition, the lithosphere and asthenosphere are separated based on strength. The lithosphere is strong, rigid rock, while the asthenosphere is a weaker, very viscous fluid. 

Students have learned that the locations of earthquakes and volcanoes provide clues (or data) that help understand plate tectonics. The causes of these movements are complicated, but at this level students should begin to recognize that some of the stresses come from within the Earth. In particular, one reason for the movement of the plates may be convection currents within the upper part of the mantle. Convection is the heat-driven circulation of a fluid. In the mantle, heat from deeper in the Earth causes the overlying mantle to circulate. The upper mantle can circulate because it contains a little magma (molten rock) and behaves like a very hot mush. Mantle convection currents move very, very, slowly. It is possible that as the mantle convects, it drags the overlying plates along with it. It is possible that as the mantle convects, it drags the overlying plates along with it. Where convection currents come together, a converging plate boundary is present. Where they move apart, a diverging plate boundary forms.

  1. Show students how geologists divide the interior of the Earth. Make sure you go over the vocabulary and contrast lithosphere and asthenosphere with the crust, mantle and core. Draw a picture on the board of the different divisions.
  2. On the worksheet, have the students label and color in each layer of the Earth. Next, instruct students to measure the thickness of each of the unit in millimeters and record their answers. Finally, have them calculate the approximate thickness of each layer.
    ANSWERS (Please note that these figures are simplified. The amount calculated by scientists is written in parenthesis.) 1. crust: 1mm/82 km (71 km); 2. mantle: 37mm/3034 km (2900 km); 3. outer core: 26mm/2132 km (2300 km); 4. inner core: 14mm/1148 km (1200 km).

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