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Plate Tectonics header

Earth's continental landmasses, upon which we live, may be thought of as ships drifting upon a sea, propelled wherever the currents take them. This slow voyage of the continents has reshaped the face of the Earth throughout its history.

 

Scientists have investigated the theory of plate tectonics (which states that the Earth's crust is made of several plates, each moving independently of the others) for many years. Studies by NASA and radio astronomy sites around the world support this theory.

Plate Map

The Earth's tectonic plates.

These plates, a part of the Earth called the lithosphere, rest upon the deeper, hot, flowing asthenosphere. This inner furnace of the Earth is the engine that powers the movement of the plates, moving some apart, sliding some parallel to each other, and even forcing some plates to collide.

 

A fault is a fracture in the Earth's crust along which motion may occur. It marks the boundary between two plates. There are three main types of faults.

 

 

Divergent Plate Boundary

 A divergent fault occurs when two plates are moving away from each other.

When two plates come together, the result is a convergent fault.

 

Convergent Plate Boundary
 

Transform Plate Boundary

 A fault that occurs when two plates slide past each other is known as a transform fault.
 

What happens at a fault boundary depends, in part, on whether the adjacent plates are made of continental or oceanic crust. Continental crust makes up the landmasses we live on. It is lighter, less dense, and thicker than the oceanic crust that lies under the seas and oceans of the world.

 

 

 

 

 

Pangaea

 

The existence of tectonic plates tells us that the Earth is a very active planet. In fact, many millions of years ago, the face of the Earth was vastly different than it is today! There are currently seven continents, but scientists believe that 225 million years ago there may have been only one! They have named that supercontinent Pangaea.

Plate Movement Animation

The breakup of Pangaea formed today's continents.

 

 

 

What does all this mean?

 

 

We think we have a good understanding of how the plates have moved since Pangaea broke up, but the motion is less clear in the time before Pangaea.

How much time is involved? Oceanic crust has an average age of only 55 million years (pretty young, geologically speaking). It gets totally recycled into the Earth every 150 million years or so (geologic teenager).

On the other hand, continental crust averages about 2.3 BILLION years (geologic adult), with the oldest known rocks dating back 3.96 billion years (that's really old).

Scientists studying these rocks suspect that the Earth has had several supercontinents throughout time. These supercontinents all went through a cycle similar to pangaea's.

Maybe in another 200 million years there will be no need for a transoceanic trip from America to Europe.