Upload
others
View
8
Download
0
Embed Size (px)
Citation preview
100 LESSON 1 Plate Tectonics
Did you ever wonder how mountains were formed or why theyare located where they are? Why do earthquakes happen?
The earth’s surface is not the same everywhere, and it keepschanging. One cause of these changes has to do with what’s hap-pening inside the earth.
Inside the EarthLook at Figure 3-1. It shows that the earth is made up of three
layers—the core, the mantle, and the crust. The core is locatedabout 4,000 miles (6,430 km) below the earth’s surface. It is madeup of iron and nickel. The middle layer is the mantle. This is alayer of hot, molten rock. The outer layer is the earth’s crust. Thislayer of rock ranges from about 2 miles (3 km) thick under theoceans to about 75 miles (121 km) thick under mountains.
The crust is broken into more than a dozen great slabs of rockcalled tectonic plates. These plates float on a partially meltedlayer of the mantle. The plates carry the earth’s continents andoceans. Map 3-1 shows the earth’s major tectonic plates and theirboundaries.
Plate TectonicsWhat You Will Learn
To explain how Earth’s majorphysical features were formed
Reading Strategy
Create a diagram like the one below.In the left box, write “platemovements.” In the right box,describe the effect this force has onthe earth.
Terms to Know
core, mantle, crust, tectonic plate,plate tectonics, divergent boundary,magma, transform boundary,convergent boundary
Lesson 11
Figure 3-1 Inside the Earth
How Do the Tectonic Plates Move?The theory of plate tectonics explains how most of the major
features of the earth’s surface were formed. According to this the-ory, tectonic plates have been moving and shaping the surface ofthe earth for 2.5 to 4 billion years. Map 3-1 shows the direction inwhich the plates are moving. Most of the time, plate movement isso gradual—only about 4 inches (10 cm) a year—that it cannot be
cause effect
Mantle
Crust
Inner Core
Outer Core
LESSON 1 Plate Tectonics 101
plates. Look at Map 3-1. Find the North AmericanPlate and the Pacific Plate. The North AmericanPlate moves in a northwest direction. The PacificPlate moves in a westward direction. The SanAndreas Fault in California is a boundary betweenthe two plates. Many earthquakes occur alongthis boundary.
At convergent boundaries, two tectonic platesmove toward each other and collide. One plate isoften forced below the other. When an ocean platecollides with a continental plate, the ocean plateslides under the continental plate and forms a deepocean trench. The Mariana Trench in the northPacific Ocean is an example of such activity. Whencontinental plates collide, they form major moun-tain ranges, such as the Himalaya. Look at Map 3-1.What two plates collided to form the Himalaya?
Sometimes a plate that is forced beneathanother reaches into the deeper regions of theearth where it is hot enough to melt part of theplate. The melted rock, or lava, rises back towardthe surface where it forms volcanoes and islands.The Hawaiian Islands were formed in this way.
felt. The way the plates move determines thekinds of landforms that are formed. It also deter-mines where earthquakes occur.
There are three kinds of movement that happenat the boundaries between the plates. At diver-gent boundaries, tectonic plates move apart, orrift, from each other. When a rift occurs on a con-tinent, it creates a gap into which water flows.This creates lakes and when the gap continues towiden, it creates seas. The Red Sea, for example,was formed when a rift occurred between theAfrican and Indo-Australian tectonic plates.
When a rift occurs in the ocean, liquefied rock,called magma, rises up to fill the gap between theseparating plates. The magma creates new cruston the edges of the two plates. The separation ofthe plates and the new crust helps to enlarge theocean floor. The built-up crust forms long under-water mountain ranges called ocean ridges.
At transform boundaries, plates slide pasteach other along what are called faults. Thismovement does not create landforms, but it doescreate earthquakes along the boundary of the two
Map 3-1 Plates and Plate Movement
N
S
EW
N
S
EW
Convergent BoundariesDivergent BoundariesPlate Movement
Earth's Tectonic Plates
EURASIAN PLATE
AFRICAN PLATE
CARIBBEANPLATE
NORTH AMERICANPLATEJUAN DE FUCA
PLATE
COCOS PLATE
NAZCA PLATE
PACIFIC PLATE
SOUTH AMERICANPLATE
SCOTIAPLATE
ANTARCTIC PLATE
ARABIANPLATE
INDO-AUSTRALIANPLATE
FIJIPLATE
PACIFICPLATEPHILIPPINE
PLATE
EURASIAN PLATE
AFRICAN PLATE
CARIBBEANPLATE
NORTH AMERICANPLATEJUAN DE FUCA
PLATE
COCOS PLATE
NAZCA PLATE
PACIFIC PLATE
SOUTH AMERICANPLATE
SCOTIAPLATE
ANTARCTIC PLATE
ARABIANPLATE
INDO-AUSTRALIANPLATE
FIJIPLATE
PACIFICPLATEPHILIPPINE
PLATE
Reviewing Key Terms
Match each term with its meaning. Draw a line from each term to itsdefinition.
1. tectonic plates
2. mantle
3. divergent boundaries
4. transform boundaries
5. convergent boundaries
6. crust
7. magma
8. core
Recalling Facts
Fill in the blanks to correctly complete the following sentences.
1. The earth’s is made up of iron and nickel.
2. According to the theory of plate tectonics, plates have been moving for
years.
3. The way that move determines the kindsof landforms that are created on the earth’s surface.
4. The Himalaya were formed at a boundaryof two tectonic plates.
5. Earthquakes in California often occur at the
boundary of two tectonic plates.
6. The Red Sea was formed at the boundaryof two tectonic plates.
7. When a rift occurs in the ocean, rises upto fill in the gap between the two plates.
8. The was formed at a convergent bound-ary of a continental plate and an ocean plate.
Mariana Trench
magma
divergent
transform
convergent
tectonic plates
2.5 to 4 billion
core
Using Your Skills
102 LESSON 1 Plate Tectonics
a. boundaries where tectonic plates move toward each other
b. a layer of hot, dense rock inside the earth
c. boundaries where tectonic plates slide past each other
d. slabs of rock that are part of the earth’s crust
e. boundaries where tectonic plates move away from each other
f. innermost layer of the earth
g. outer layer of the earth
h. liquefied rock
Practicing Map Skills
Use Map 3-1 on page 101 to answer the following questions.
1. On which tectonic plate is the United States located?
the American Plate
2. On which tectonic plate is Panama located?
the Caribbean Plate
3. On which tectonic plate is India located?
the Indo-Australian Plate
4. Which two plates make up a convergent boundary near South America?
the American Plate and the Nazca Plate
5. Which two plates make up a convergent boundary near Southeast Asia?
the Eurasian Plate and the Indo-Australian Plate
6. Which three plates make up a divergent boundary near the AtlanticOcean?
the American, Eurasian, and African Plates
7. Which two plates are responsible for the creation of the Himalayamountain ranges?
the Eurasian Plate and the Indo-Australian Plate
8. Which two plates are responsible for the creation of the Andes moun-tain ranges?
the American Plate and the Nazca Plate
LESSON 1 Plate Tectonics 103