Name:_____________________
Plate Tectonics
Inside Earth
Chapter 1 Study Guide
Answer key
Earth’s Interior
1) Compare constructive forces to destructive forces. Give an example of each.
 Constructive forces shape the surface by building up mountains and landmasses.
 Destructive forces are those that slowly wear away the mountains and, eventually, every other feature on
the surface.
2) List 2 facts about each of the layers of Earth.
1. The Crust- 5-40 kilometers thick
a. The crust is a layer of rock that forms Earth’s outer skin.
b. it includes both the dry land and the ocean floor
c. it is thinnest beneath the ocean and thickest under high mountains
d. The oceanic crust consists of mostly dense rock (basalt).
e. The continental crust, the crust that forms the continents, consists of less dense rock (granite).
f. The composition of the crust: oxygen silicon, aluminum, calcium, iron, sodium, potassium, and magnesium
2. The Mantle- 3000 kilometers thick
a. The mantle is the layer of hot solid material between the Earth’s crust and core.
b. The uppermost part of the mantle and the crust together form a very rigid layer called the lithosphere.
c. Temperature and pressure increase as the depth increases.
d. The heat and pressure make the part of the mantle just beneath the lithosphere less rigid than the rock
above. This part of the mantle is somewhat soft and can bend like plastic.
e. This soft layer is called the asthenosphere. Here, the material can flow slowly.
f. Beneath the asthenosphere, solid mantle material extends all the way to the Earth’s core.
g. The composition of the mantle: silicon, oxygen, iron, and magnesium
h. The temperature of the mantle: 870o - 2,000o Celsius
3. The Core – approximately 3500 km thick
a. The outer core is the liquid layer of molten metal that surrounds the inner core.
b. The inner core is a dense ball of solid metal with extreme pressure
c. The inner core and outer core together are almost the same size as the moon.
d. The composition of the core: iron and nickel
f. The temperature of the inner core: Celsius 5000o Celsius and above- outer core: 2,200o - 5000o.
3) How do temperature and pressure change as you move deeper into the Earth?
Temperature and pressure increase as the depth increases.
4) What do geologists do?
Geology is the study of the planet Earth.
Geologists are scientists who study the forces that make and shape the planet Earth.
5) What is the continental crust made up of? What is oceanic crust made up of?
Continental crust is made up of granite rock which is less dense.
Oceanic crust is made up of basalt which is more dense.
Convection Currents and the Mantle
Study the diagram on page 27 in your textbook and make sure you understand what is taking place.
The heat source for the convection current in the mantle is coming from the Earth’s core and the mantle itself. It
happens in the asthenosphere. Hot material is less dense so it rises up. It spreads out and pushes the cooler
materials out of the way when it reaches the top of the asthenosphere. Because of the gravity, the cooler material
which is more dense sinks down. In this way, the convection current forms.
6. What are the three types of heat transfer? Give an example of each.
Convection
Conduction
Radiation
Drifting Continents
7. What is the Theory of the Continental Drift and who developed it? Why it was not originally accepted?
A. Developed by a scientist named Alfred Wegener
1 His hypothesis was that all the continents has once been joined together as a single landmass and have
since drifted apart.
2. He named this supercontinent Pangaea.
3. The idea that the continents slowly moved over Earth’s surface became known as continental drift.
4. It was not originally accepted because he had no evidence that could explain the force that could move
the continents.
8. Where did evidence on Wegener theory come from? Give three examples.
Evidence on Wegener theory from Landforms, Fossils, and Climate
1. A mountain range running from east to west in South Africa lines up with a mountain range in
South America.
2. Glossopteris fossils have been found in rocks in Africa, South America, Australia, India, and
Antarctica.
3. Scratches from glaciers found in South Africa. (Also tropical plant fossils in the Arctic).
9) What was the name of the one supercontinent? Pangaea; What two continents did it break into? Gondwanaland
and Laurasia.
Sea- Floor Spreading
Study the diagrams in your textbook (pgs 35, 37, & 38)
10) Explain, in detail, the cycle of sea-floor spreading. Be sure to include the word subduction.
11) How do scientists map the mid-ocean ridge? Explain how the device works.
Mapping the Mid-Ocean Ridge
1. A mid-ocean ridge is the undersea mountain chain where new ocean floor is produced.
2. Scientists mapped the mid-ocean ridge using sonar
a. Sonar is a device that bounces sound waves off underwater objects and then records the echoes
of these sound waves.
b. The time it takes for the echo to arrive indicates the distance to the object.
12) What are the three types of evidence of sea floor spreading? Explain each.
 Evidence form Molten Material
1. Scientists that went to the ocean floor in a submersible found that there was new material erupting along
the mid-ocean ridge.
a. The crew found strange rocks shaped like pillows
b. These rocks could only have formed like this when molten material hardens quickly after erupting
under water.
 Evidence from Magnetic Stripes
1. Found evidence that the Earth’s magnetic poles have reversed themselves.
a. This last happened 780,000 years ago
b. If this happened today, you would find your compass needle would point south
2. Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized
stripes.
3. They use sensitive instruments that record the magnetic memory of rocks on both sides of the midocean ridge.
 Evidence from Drilling Samples
1. The final proof of sea floor spreading came from rock samples obtained by drilling into the ocean floor.
a. The Glomar Challenger sent drilling pipes through water six kilometers deep to drill holes in the
ocean floor
b. They found that the farther away from the ridge the samples were taken, the older the rocks
were.
13) Where is the longest chain of mountains in the world?
Mid- ocean ridge in Atlantic ocean is the longest mountain range on earth.
14) Who is Harry Hess? What ideas did he come up with?
1. Harry Hess examined maps of the mid-ocean ridge and from his work realized that Wegener’s theory may
have been correct.
2. He also came up with the idea that the ocean floor moves like conveyor belts, carrying the continents
along with them.
3. At the mid-ocean ridge, molten material rises from the mantle and erupts. It then spreads out, pushing
older rock to both sides of the ridge.
4. Hess named the process that continually adds new material to the ocean floor sea-floor spreading.
15) How is it that the Atlantic Ocean is expanding? How is it that the Pacific Ocean is shrinking?
There are a lot of deep ocean trenches in Pacific Ocean. The subduction happens at the deep ocean trench. It
swallows more oceanic crust than the mid ocean ridge produces. That is why in the long term, the Pacific Ocean is
shrinking.
There are fewer deep ocean trenches in Atlantic Ocean. The spreading oceanic floor has nowhere to go. It will push
the continental crust away to make the oceanic floor extend.
The Theory of Plate Tectonics
16) What is a plate? A section of Earth’s lithosphere.
17) Describe each of the three types of plate boundaries and where they occur.
Transform boundaries: two plates slip past each other, moving in opposite directions. Earth quakes will happen.
Divergent boundaries: two plates move apart in opposite directions. Mid- ocean ridge, rift valley
Convergent boundaries: two plates move together. subduction zones and mountains
18) What happens when a plate carrying oceanic crust collides with a plate carrying continental crust?
Because the oceanic crust which is made of basalt is denser than the continental crust, it begins to sink and
plunges beneath the continental plate.
19) What happens when two plates carrying continental crust collide?
Because two continental crusts are less dense rocks, the subduction will not happen. The two plates will squeeze
together to form mountains.
20) What is a rift valley? Give an example of where one is located?
When continental plates pull apart at the divergent boundary on land, a rift valley forms. Example: The Great
Rift Valley in east Africa. (on land)
mid ocean ridge ( in ocean)
REVIEW ALL OF THE VOCABULARY WORDS! IF YOU KNOW AND UNDERSTAND THOSE WORDS, YOU
WILL DO A LOT BETTER ON THE TEST.