14. More
on the Plates
Expedition Menu
Let's now review and put it all together....first make a close examination of a portion of the pie-shaped slice through the interior of the earth that we examined previously.
The tectonic plates, or just plates, are composed of rigid, strong rocks in a layer called the lithosphere. The lithosphere contains all of the crust and the uppermost, solid portion of the mantle. The lithosphere varies from very thin under the mid-ocean ridges to more than 200 kilometers thick under the continents (even thicker in some regions).
The plates of lithosphere float on a weak, more mobile layer of the mantle called the asthenosphere. The asthenosphere is undergoing convection as a result of the intense heat in the interior of the Earth.
Think of the behavior of the lithosphere and asthenosphere as being similar to sheets of strong, but thin ice on a pond during winter -- the ice pieces move around over top of the waters below.
The rigid lithosphere, on the surface of the Earth, moves very slowly -- about as fast as your fingernails grow -- only a few inches per year.
Now that we have examined the plates and the process by which they form (seafloor spreading), in the next expedition, you will examine the processes at the boundaries between the plates.
Created By:
Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on
Sept. 22, 2008
Congratulations! You are done!!!
In order to receive credit for completing this expedition and access to answer key, go to Desire2Learn Email and send “Bye Don”
Remember to e-mail Bye Don at!!!!!
Put “End Expedition 6” in Subject Line.
Include "Bye Don" in body of email,
The completion word for this expedition are "seafloor spreading"