Unit 4 Study Guide Answer Key

Lesson 1: Earth’s Layers
1. What are the Earth’s compositional layers?
• The outermost solid layer of Earth is the crust.
• Mostly made of oxygen, silicon, and aluminum.
• Oceanic crust is thinner and denser than continental crust because it contains twice as much iron, calcium, and magnesium.
• The region of hot, slow-flowing, solid rock between the crust and core is called the mantle.
• Convection: movement of matter based on differences in density caused by temperature variation.
• Contains more magnesium and less aluminum than the crust.
• The mantle is denser than the ¬¬¬¬¬¬¬crust but less dense than the core.
• Scientists can study the mantle by looking at mantle rocks that rise to the surface and seismic waves that travel through the Earth during earthquakes.
• The core goes from below the mantle to the center of the Earth.
• It makes up 1/3 of the Earth’s mass.
• It is the densest layer.
• It is made of mostly iron and nickel
2. What are the Earth’s physical layers?
• Lithosphere: outermost rigid layer of Earth, including the crust and upper mantle.
• Asthenosphere: made of weak rock that flows slowly in the mantle
• Tectonic plates move on top of this layer.
• Mesosphere: strong lower part of the mantle that flows more slowly
• Outer core: liquid layer of Earth’s core between mesosphere and inner core.
• Inner core: solid, dense center of the Earth
Lesson 2: Plate Tectonics
3. What evidence do we have for Plate Tectonics?
• Shape of continents
• Mountain ranges that span continents (North America and Europe)
• Fossils found on both sides of the Atlantic Ocean, in both South America and Africa
4. What is Pangaea?
• Single large landmass that contained all of the present-day continents
• Pangaea began to break apart 200 million years ago
5. What evidence do we have for continental drift?
• Age and magnetic properties of sea floor
• Sea-floor spreading: molten rock moves up through cracks in oceanic crust, creating new crust at mid-ocean ridges and pushing the sea floor apart, moving continents.
• Ocean trenches: dense oceanic crust sinks back into the asthenosphere
• Old crust destroyed at similar rates to which new crust is created, so Earth stays the same size.
6. What is the theory of plate tectonics?
• Explains the large scale movement of Earth’s lithosphere which includes both continental and oceanic crust and the rigid, upper part of the mantle.
• Helps us understand how continents move.
7. What is a tectonic plate?
• Pieces of the lithosphere that move on top of the asthenosphere.
• Thicker continental crust displaces more of the asthenosphere than denser, thinner oceanic crust.
• Major tectonic plates include North American, Pacific, Nazca, South American, African, Eurasian, Indian, Australian, and Antarctic. Be able to find these on a map!

8. What are the three types of plate boundaries?
• Convergent boundaries: where two plates collide
• Form mountains on continental crust.
• Form trenches on oceanic crust.
• Form subduction zones where ocean crust meets less dense continental crust.
• Divergent boundaries: where two plates move away from each other.
• Form mid-ocean ridges in oceanic crust,
• Form rift valleys on continental crust.
• Transform boundaries: where two plates move past each other horizontally
• Unlike other boundaries, does not produce magma.
• One example is the San Andreas Fault in California.
9. What causes tectonic plates to move?
• Mantle convection: the hotter less dense rock rises up, while cooler, denser rock sinks
• Thought to be the weakest of the three forces
• Ridge push: newly formed warm, less dense crust in the ocean pushes the older, denser crust away from mid-ocean ridges
• Slab pull: at subduction zones dense ocean crust sinks under continental crust, pulling the rest of the plate along with it
• Now considered the strongest of the three forces
Lesson 3: Mountain Building
10. How can tectonic plate motion cause deformation?
• Stress is the amount of force per area
• Deformation is the process by which rocks change shape under stress
• Rocks under stress can bend or break
• Cold brittle rock is more likely to break, while hot rock is more likely to bend
11. What are two kinds of folds?
• Folding occurs when rocks bend under stress
• Synclines are folds shaped like a bowl, while anticlines are folds shaped like a dome
12. What are three kinds of faults?
• A fault occurs when large blocks of rock break and move past each other
• The block above the fault plane is the hanging wall
• The block below the fault plane is the foot wall
• Strike-Slip Faults: fault blocks move past each other horizontally
• Occur at transform boundaries like San Andreas in California
• Normal Faults: hanging wall moves down relative to foot wall
• Occur at divergent boundaries
• Result from tension or stress that stretches or pulls rocks apart
• Can also occur within a tectonic plate, like in the Southwestern United States
• Reverse Faults: hanging wall moves up relative to foot wall
• Occur most often at convergent boundaries
• Result from compression or stress that squeezes or pushes rock together
13. What are three kinds of mountains?
• Folded Mountains: rock layers squeezed together and pushed up
• Form at convergent boundaries
• Examples include the Appalachian Mountains in the United States and the Pyrenees Mountains in Europe.
• Volcanic Mountains: Form when melted rock erupts to the Earth’s surface
• Often found at convergent boundaries, like those found around the Pacific Ocean on the Ring of Fire, such as Alaska’s Mt. Griggs
• Fault-Block Mountains: form when tension breaks the lithosphere into many normal faults and the pieces left standing form mountains, like the Teton Mountains and Sierra Nevadas