1. Plate Tectonics

2. Lithosphere
The lithosphere is broken into a number of large pieces called plates that completely cover the earth’s surface including the oceans’ floor.
The plates make up both continental and oceanic crust.

3. Each plate includes a piece of the earth’s crust and some of the upper rigid or rocky mantle below it. Together these are called the lithosphere.

4. Earth’s Moving Plates
The plates move very slowly, only a few centimeters per year or about the rate that your fingernails grow.
The earth’s continents move with these plates (known as the idea of “continental drift”.

5. the continents appeared to fit together like a jigsaw puzzle
Alfred Wegener hypothesized “continental drift” in the early 1900’s. His hypothesis was based on:
the continents appeared to fit together like a jigsaw puzzle
Past continents from millions of years ago collided, forming a single large “super continent” that he called Pangaea
Millions of years later it broke apart forming our current continents.
fossils found in Africa and South America

7. The Theory of Plate Tectonics
The theory of plate tectonics states:
Earth’s plates are in constant slow motion
Explains how the plates form and move
How plates interact to produce volcanoes, earthquakes, mountain ranges, and structures of the ocean floor

8. Tectonic Plate Movement
Scientists believe plate movement is caused by the slow convection currents of the molten material in the upper mantle (an area called the asthenosphere).

9. Effects of Plate Movement
Plate Boundaries are located at the cracks between the plates of the lithosphere. At plate boundaries, plates can
Move together (Convergent Plate Boundary)
Pull apart (Divergent Plate Boundary) or
Slide past each other (Transform Plate Boundary)

10. These plate movements can cause extreme changes in the earth’s crust such as volcanoes, earthquakes, and mountain formation.

12. Major Concepts
The theory of plate tectonics explains the major structural features of the Earth as a result of a series of moving lithospheric plates.
Where plates move apart, hot material from the mantle wells up to fill the void and creates new lithosphere. The major features formed where plates spread apart are continental rifts, oceanic ridges, basaltic volcanism, and new ocean basins.
Where plates converge, one slides beneath the other and plunges down into the mantle. The major features formed at converging plate margins are (a) folded mountain ranges, (b) volcanic arcs, and (c) deep-sea trenches.
The Earth's lithosphere floats on the denser, plastic, asthenosphere beneath, and it rises and sinks in attempts to maintain isostatic equilibrium.
The crust and upper part of the mantle form the lithosphere, about 100 km thick, that overlies hotter and more plastic mantle of the asthenosphere, above which horizontal lithospheric displacement can take place.
Copyright Ó 1999, Pat Hayhurst Home Page URL: Last Updated: Saturday, March 13, 1999