Our Changing Earth – Read and highlight important information then take the quiz on the other side. Plate Tectonics
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.
The Earth's tectonic plates.
These plates, a part of the Earth called the lithosphere, are made of the crust & very top part of the mantle. They rest upon the deeper, hot, flowing asthenosphere which is the middle part of the mantle. This inner furnace of the Earth is the engine that powers the movement of the plates through convection. Some move apart, some slide parallel to each other, and some even collide and smash together. Three Types of Faults
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. What happens at a fault boundary depends, in part, on whether the plates next to it 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. A divergent fault occurs when two plates are moving away from each other. These cause rift valleys on land or ridges if underwater .
When two plates come together, the result is a convergent fault. Continental crust plates colliding can form mountains.
A fault that occurs when. two plates slide past each other is known as a transform fault. An example is the San Andreas Fault along the western edge of California which causes earthquakes.
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.
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 (under the oceans) 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 (above water) averages about 2.3 BILLION years (geologic adult), with the oldest known rocks dating back 4 billion years (that’s 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. Let's all stick around to find out, okay? QUIZ Name______Class______
1. Where is the San Andreas fault located?
Ontario, Canada Texas, USA Tokyo, Japan California, USA
2. A convergent fault is where
two people are wrong. two plates collide. two roads join. two roads split.
3. Scientists think that a supercontinent existed
25 years ago. 150 million years ago. 225 million years ago. 2.3 billion years ago.
4. A divergent fault is formed
when two plates slide against each other, building up tension.
when magma pushes its way through one spot to the surface.
when the Atlantic Ocean shrinks to a sea again.
when magma pushes two plates apart.
5. The massive supercontinent that scientists believe existed in the past was given what name?
Alison Athena Pangaea Demeter
6. What type of fault line movement is making the Himalayan Mountains?
converging plates diverging plates transform boundries sliding plates
7. Continental crust is ______than oceanic crust.
less dense smarter heavier thinner
8. Long ridges of land underwater can be built by ______.
piles of dirt a Continent-Continent collision Transform boundries diverging plates
9. What can happen when a transform fault suddenly releases its energy?
A flood A tornado An earthquake A hurricane