1. Unit 4 The Restless Earth Part I Lessons 1, 2, & 3
The Big Idea: The movement of tectonic plates accounts for important features of Earth’s surface and for major geologic events.

2. Unit 4 Lesson 1 Earth’s Layers
Peeling the layers
Crust-outermost solid layer of Earth. (composed of O, Si & Al)
Continental
Oceanic-denser; contains 2x Fe, Ca & Mg
Mantle-region of hot, slowing flowing solid rock (composed of more Mg & less Al & Si)
Core- densest layer, mostly Fe & some Ni. Makes up about 1/3 of Earth’s mass.
Earth is made of several layers.
Each layer has its own characteristic properties.
Scientists think about Earth’s layers in two ways—in terms of chemical composition and in terms of physical properties.
Earth can be divided into three layers based on chemical composition: the crust, the mantle, and the core.
Both types of crust are made mostly of oxygen, silicon, and aluminum.
Oceanic crust is denser than continental crust because it contains almost twice as much iron, calcium, and magnesium.
The mantle is located between the crust and the core.
The core extends from below the mantle to the center of Earth.
Scientists think the core is made mostly of iron and some nickel.
The core is the densest layer and makes up about one-third of Earth’s mass.

3. Unit 4 Lesson 1 Earth’s Layers
Heat it up!
Convection -movement of matter that results from differences in density caused by variations in temperature.
Convection in the mantle causes cooler rock to sink and warmer rock to rise.
Scientists have proposed three mechanisms to explain how tectonic plates move: mantle convection, ridge push, and slab pull.
Hotter parts of the mantle rise as cooler, denser parts sink. This kind of movement of material due to differences in density is called convection.
Mantle convection drags the overlying tectonic plates.

4. Earth’s 5 physical layers
Unit 4 Lesson 1 Earth’s Layers
Earth’s 5 physical layers
Lithosphere—outermost layer, made of crust & the rigid part of the mantle divided into pieces called tectonic plates
Asthenosphere-layer of weak/soft mantle made of rock that moves very slowly.
Mesosphere-strong, lower part of mantle, rock flows more slowly than the rocks above.
Earth is also divided into layers based on physical properties, such as whether the layer is solid or liquid.
The five physical layers are the lithosphere, asthenosphere, mesosphere, outer core, and inner core.
The outermost, rigid layer of Earth is the lithosphere.
The lithosphere is made of the crust and the rigid, upper part of the mantle.
The asthenosphere is located below the lithosphere.
The strong, lower part of the mantle is called the mesosphere.
Rock in the mesosphere flows more slowly than rock in the asthenosphere.

5. Physical layers continued
Unit 4 Lesson 1 Earth’s Layers
Physical layers continued
Outer core-liquid layer of Earth’s core
Inner core-the solid, dense center of our planet
Open to
pg. 198
cut out Earth’s
layers &
glue into notes
The outer core is the liquid layer of Earth’s core.
The outer core lies beneath the mantle and surrounds the inner core.
The inner core is the solid, dense center of our planet.
The inner core extends from the bottom of the outer core to the center of Earth.

6. Unit 4 Lesson 2 Plate Tectonics
Puzzling Evidence
Alfred Wegener- proposed continental drift; the continents once formed a single landmass, broke up, & drifted.
Pangaea-single landmass formed about 245 mya
Evidence
Fossils
Locations of Mtn ranges
Rock types
Ancient climatic conditions
In the late 1800s, Alfred Wegener proposed his hypothesis of continental drift.
Several lines of evidence support Wegener’s hypothesis.
Fossils of the same species are found on continents on separate sides of the Atlantic Ocean.
The locations of mountain ranges and rock formations and evidence of ancient climatic conditions also support Wegener’s hypothesis.

7. Unit 4 Lesson 2 Plate Tectonics
About 200 million years ago, a large rift formed and Pangaea began to break into two continents, Laurasia and Gondwana.
Then, Laurasia began to drift northward, and a new rift separated Laurasia into the continents of North America and Eurasia.
At the same time, Gondwana also broke into two continents.
One continent contained land that is now the continents of South America and Africa.
The other continent contained land that is now Antarctica, Australia, and India.
Unit 4 Lesson 2 Plate Tectonics

8. Modern day proof Mid-ocean ridges- underwater mtn ranges
Unit 4 Lesson 2 Plate Tectonics
Modern day proof
Mid-ocean ridges- underwater mtn ranges
Youngest rock closest to ridge
Oldest rock further away
Sea-floor spreading-molten rock from inside Earth rises at the ridges & forms new oceanic crust. Older crust is pushed away from the ridge, & the sea floor slowly spreads apart.
Ocean trench-oceanic crust sinks into asthenosphere.
For many years, scientists did not accept Wegener’s ideas because they could not determine how continents moved.
In the mid-1900s, scientists began mapping the sea floor and discovered huge, underwater mountain ranges called mid-ocean ridges.
The discovery of mid-ocean ridges eventually led to the theory of plate tectonics, which built on some of Wegener’s ideas.
Rock samples from the sea floor revealed that the youngest rock is closest to the ridge, while the oldest rock is farthest away.
Even the oldest oceanic crust is young compared to continental crust.
Also, sea-floor rock contains magnetic patterns.
To explain the age and magnetic patterns of sea-floor rocks, scientists proposed a process called sea-floor spreading.
In this process, molten rock from inside Earth rises at the ridges and forms new oceanic crust.
Older crust is pushed away from the ridge, and the sea floor slowly spreads apart.
Scientists also discovered huge trenches in the sea floor where oceanic crust sinks into the asthenosphere.
Older crust is thus being destroyed at the ocean trenches at the same rate as new crust is forming at the ridges.
In this manner, Earth remains the same size.

9. Unit 4 Lesson 2 Plate Tectonics
A giant jigsaw
Plate tectonics- theory that describes large-scale movements of Earth’s lithosphere
Tectonic plates- lithosphere is divided into pieces which move around on TOP of the asthenosphere
Scientists began to form a new theory to explain continental drift, mid-ocean ridges, and sea-floor spreading.
It explains how and why features in Earth’s crust form and continents move.
The lithosphere is divided into pieces called tectonic plates, which move around on top of the asthenosphere.

10. Unit 4 Lesson 2 Plate Tectonics
Plate boundaries
Convergent boundaries - form where two plates collide. This can happen in three ways, depending on the types of crust involved. Divergent boundary - two plates move away from each other, and magma rises to form new lithosphere at mid-ocean ridges. Transform boundary -two plates move past each other horizontally. The motion of the two plates often produces earthquakes.
Plate boundaries may be on the ocean floor, around the edges of continents, or even within continents.
The three types of plate boundaries are convergent boundaries, divergent boundaries, and transform boundaries.
Each type is associated with characteristic landforms.
The mechanism called ridge push moves plates away from mid-ocean ridges as rock cools and becomes more dense.
Newly formed rock at a mid-ocean ridge is warm and less dense than older, adjacent rock, which slopes downward away from the ridge.
As the newer rock cools and becomes denser, it moves down the slope, pushing the rest of the plate away from the mid-ocean ridge.
In the mechanism called slab pull, a plate moves because it is pulled along when its denser edge sinks beneath Earth’s surface.
The leading edge of a sinking plate is colder and denser than the mantle, so it sinks. The rest of the plate follows.
Many scientists think slab pull is the most important mechanism driving plate motion.

12. Unit 4 Lesson 3 Mountain Building
Stressed out
Stress- amount of force per unit area that is placed on an object
Deformation- process by which rocks change shape when under stress.
Folding- when rock layers bend under stress
Syncline-A fold in rocks in which the rock layers dip inward or upward from both sides toward the axis. (like a bowl)
Anticline-A fold of rock layers that slope downward on both sides of a common crest.
The movement of tectonic plates causes stress on rock structures.
Stress is the amount of force per unit area that is placed on an object.
When a rock is placed under stress, it deforms, or changes shape.
When rocks bend, folds form; when rocks break, faults form.
Folding. The bends are called folds.
Scientists assume that all rock layers start out as horizontal layers deposited on top of each other over time.
A fold, or bend, in the rock layers means that deformation has happened.
Two common types of folds are synclines and anticlines.
In a syncline, the youngest layers of rock are at the core of the fold. The rock layers are usually arched upward, like a bowl.
In an anticline, the oldest layers of rock are at the core of the fold. The rock layers are usually arched downward.

13. Unit 4 Lesson 3 Mountain Building
faulted
Fault- a crack formed when large blocks of rock break & move past each other.
3 Main Kinds of Faults
strike-slip fault-fault blocks move past each other horizontally (common along transform boundaries)
Sometimes rock is under so much stress that it breaks.
The blocks of rock on either side of a fault are called fault blocks. The movement of faults can create mountains and other landforms.
The three main kinds of faults are strike-slip faults, normal faults, and reverse faults.
A fault plane is the location where two fault blocks meet.
For any fault except a perfectly vertical fault, the block above the fault plane is called the hanging wall. The block below the plane is the footwall.
In a strike-slip fault, the fault blocks move past each other horizontally.
Strike-slip faults form when rock is under shear stress, or stress that pushes rocks in parallel but opposite directions.
Strike-slip faults are common along transform boundaries, where tectonic plates move past each other.

14. Unit 4 Lesson 3 Mountain Building
Normal Fault- the hanging wall moves down relative to the footwall (Common along divergent boundaries)
Reverse Fault- then hanging wall moves up relative to the footwall. (Common along convergent boundaries)
In a normal fault, the hanging wall moves down relative to the footwall, in a way you would normally expect as a result of gravity.
Normal faults form when rock is under tension, which is stress that stretches or pulls rock apart.
Normal faults are common along divergent boundaries.
In a reverse fault, the hanging wall moves up relative to the footwall.
Reverse faults form when rocks undergo compression, which is stress that squeezes or pushes rock together.
Reverse faults are common along convergent boundaries, where two plates collide.

15. Formation of Mountains
Moving on up
Unit 4 Lesson 3 Mountain Building
Uplift-process that can cause land to rise, can also contribute to mountain building.
Formation of Mountains
Folding-rock layers are squeezed together & pushed upward (convergent boundaries)
Volcanism-melted rock erupts onto Earth’s surface
Faulting –tension makes
the lithosphere break into
many normal faults.
Because tectonic plates are always in motion, some mountains are constantly being uplifted.
Most folded mountains form at convergent boundaries where plates collide.
Many volcanic mountains are located at convergent boundaries.
Volcanic mountains can form on land or on the ocean floor.
Fault-block mountains form when tension makes the lithosphere break into many normal faults.
Along the faults, some pieces of the lithosphere drop down compared with other pieces.
The pieces left standing form fault-block mountains.