1. The Theory of Plate Tectonics

2. Background Information
The lithosphere (Earth’s Crust and Upper Mantle) is made of plates. When magma rises from an ocean ridge (sea floor spreading) the magma produces new crust, which pushes plates apart.
As these plates are pushed apart, other plates are pushed together.
Movement along any plate boundary results in changes at other boundaries.

3. Major Plates of the Lithosphere

4. Types of Plate Boundaries
Convergent Boundary – plates move toward each other and collide
Divergent Boundary – plates move away from each other
Transform Boundary - plates that slide past one another. This causes many of the features found on the Earth.

5. Continental Drift – No More
The theory of continental drift was no longer appropriate as scientists discovered how plates were moving do a new name was given.
Theory of Plate Tectonics – proposes that the plates of Earth’s lithosphere interact with each other.
Tectonics – is the study of the movement of large-scale structural features of Earth’s crust.

6. Convergent Boundaries
are areas where the plates meet and collide. Earth’s crust is subducted into the mantle at these boundaries. ie India converged into the Eurasian plate and formed the Himalayas.
The area where a plate thrusts downward under another is known as a subduction zone.

7. 3 Types of Convergent Boundaries
1. Oceanic-Continental Convergence – When an oceanic plate converges with a continental plate, the oceanic plate sinks under the continental plate. Subduction zones along an oceanic-continental boundary create a deep-sea trench – a long, narrow, deep depression in the sea floor.
Many of the trenches occur around the margin of the Pacific Ocean because of subduction. High temperatures cause rock to melt around the oceanic plate as it goes under the continental plate. The newly formed magma is forced upward through the upper plate, forming volcanoes.

8. 3 Types of Convergent Boundaries
2. Oceanic-Oceanic Convergence – when an oceanic plate meets another oceanic plate, the older, colder, denser plate bends and sinks into the mantle. New crust is then formed as the magma rises to make volcanoes. Oceanic-oceanic convergence also makes deep sea trenches. The island of Japan and the Japan Trench were formed by oceanic plates converging.

9. 3 Types of Convergent Boundaries
3. Continental-Continental Convergence – When two plates of continental crust collide and crumple up, tall mountain ranges may form. Earthquakes are common at these convergent boundaries. Volcanoes do not form, however, because there is little or no subduction when two continental plates collide.

10. Convergent Boundary

11. Divergent Boundaries
Occurs when plates move away from each other. Sea floor spreading occurs along a divergent boundary. The Mid-Atlantic Ridge in the Atlantic Ocean is an example of a divergent boundary.

12. Divergent Boundary

13. Transform Boundary
Transform boundaries occur where two plates slide past one another. The plates move in opposite directions or in the same direction at different rates. When one plate slips past another plate suddenly, an earthquake occurs.

14. Transform Boundary

15. How do we measure Plate Movement?
Earthquakes, volcanoes and mountain ranges are evidence of plate movement.
The theory of plate tectonics suggests that convection currents inside Earth can affect the crust differently in different locations. You have seen how the plates have moved since Pangaea separated.
Scientists now use satellites and laser technology to measure the exact movements of the plates, to the nearest centimeter. Laser pulses are shot from the ground to a satellite to determine an exact location on the ground. New data confirm that parts of the crust are moving from 1 – 12 centimeters each year.
Scientists are also using GPS by repeatedly measuring distances between specific points.