Download Plate Tectonics The Earth`s tectonic plates. Three

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.
. two plates slide past each
A fault that occurs when
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
9. What can happen when a transform fault suddenly releases its energy?
A flood
A tornado
An earthquake
A hurricane
diverging plates