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EARTH’S INTERNAL PROCESSES. Chapter 25. THE PLATE TECTONICS THEORY – 25.1 A. Continental Drift 1. Please Define Continental Drift:

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A. Continental Drift

1. Please Define Continental Drift:

Two hundred million years ago the supercontinent, called Pangaea, separated into pieces that drifted over the surface of the Earth like rafts on water.


Who first proposed Continental Drift?

Alfred Wegener first proposed Continental Drift.


When was Continental Drift first proposed?

In 1915, about 100 years ago.


Evidence for continental drift

a. Coastlines

1. Alfred Wegener observed that the

eastern coastline of South America

fit together with the western coastline

of Africa.



1. What large land animal and plant supported Continental Drift?

a.) Cynognathus


Rocks and mountains

1. Examples are:

a.) Cape Fold Belt


The controversy

Wegener, however, could not explain how

the continents drifted. He suggested that

Earth’s rotation, the gravitational pull of the

Sun and the Moon, and the centrifugal

force moved the continents. Physicists quickly concluded that these forces were unable to explain continental drift.


Seafloor Spreading Hypothesis

1. Please Define Mid-Ocean Ridge:

A system of mountain ranges with a rift valley between them that extends around Earth on the seafloor; formed where oceanic plates spread apart due to magma rising from Earth’s mantle.


Please Define Rift Valley:

Long narrow depression formed in between

the peaks along the mid-oceanic ridge.


Rocks and sediments on the seafloor

a. Where are the oldest rocks found on Planet Earth?

The oldest rocks are on the Continents and the

youngest rocks on the Seafloor. The difference in age can only be explained if rocks on the Seafloor

are continually being created at a mid-ocean ridge.


Where are the youngest rocks found on Planet Earth?

The youngest rocks are found on the ocean

seafloor which are being created at a mid-ocean ridge.


Magnetic polarity of rocks

a. Rocks equal distances from either side of

the Mid Oceanic Ridge have the same

magnetic polarity.


The Plate Tectonics Theory

1. Please Define Continental Plate:

The Earth’s surface is made of separate

slabs of rigid rock called plates that move

slowly over Earth’s upper mantle.


Convergent plate boundaries

a. Please Define Convergent Plate Boundary:

Boundary where two plates collide, and

produces either subduction zones or

continental collisions.


Subduction zones

1.) Please Define Subduction:

The movement of a dense oceanic plate under a buoyant continental plate.


2.) Example of a Continental-Oceanic Convergent Plate Boundary.

The Andes Mountains in South America are an example of a continental- oceanic convergent plate boundary.


3.) Example of an Oceanic-Oceanic Convergent

Plate Boundary.

Japan is an example of an oceanic-oceanic

convergent plate boundary.


c. Continental collision

1.) Example of Continental-Continental

Convergent Plate Boundary.

Along some convergent plate boundaries, two continental plates of equal density collide and do not subduct. Because no subduction occurs, the plates collide and buckle upward to form a high range of folded mountains. Volcanic activity is absent and there is no deep-sea trench. The Himalaya Mountains in Asia are an example of a continental-continental convergent plate boundary.


c. Continental collision

1). Example of Continental-Continental Convergent Plate Boundary.


Continental collision

Indian plate collides with the Asian plate

to make the Himalaya Mountains in Asia.


Divergent plate boundaries

a. Please Define Divergent Plate Boundary:

The boundary between two plates that

are moving apart. The magma rises between the plates, erupts from a rift valley as lava, and then cools to form new crust.


3. Divergent plate boundaries

A mid-ocean ridge is one example of a divergent plate boundary. In some places, such as the East African Rift, divergent plate boundaries create intraplate rift valleys that form in the middle of a continent.


4. Transform plate boundaries

a. Please Define Transform Plate Boundary:

Tectonic plate boundary in which plates slide horizontally past each other in opposite directions.


4. Example of Transform plate Boundary:

The San Andreas Fault in California is an

example of a transform plate boundary.

Earthquakes are common along transform

plate boundaries.


D. Plates in Motion

1. Convection

a. Please Define Convection:

Transfer of thermal energy in a fluid by the movement of warmer and cooler fluid from one place to another.


2. Slab pull, ridge push, and friction

a. Please Define Slab Pull:

When subduction occurs along a convergent plate boundary, a force called slab pull helps to move the plates.


Please Define Ridge Push:

In contrast to slab pull, ridge push moves

plates along a mid-ocean ridge.


c. Please Define Friction as it pertains to Plate Motion:

Friction between a plate and the mantle also has an affect on plate motion. For example, plates that drag continental material along with them are slower than those that drag oceanic material.



A. Earthquake Distribution

1. Please Define Earthquake:

Sudden movement or vibration of ground that occurs when rocks slip and slide along enormous cracks in Earth’s crust.


2. Where do Earthquakes occur?

Earthquakes occur at tectonic plate boundaries.


Earthquakes depth

a. Where are Earthquakes shallow?

Earthquakes that occur along divergent and transform plate boundaries tend to be shallow, typically less than 70 km depth.


b. Where are Earthquakes deep?

However, earthquakes that occur along convergent plate boundaries commonly occur at depths greater than 70 km.


Causes of Earthquakes

1. Deformation

a. Please Define Deformation:

A force applied to an object can cause the object to change its shape, or be deformed.


b. What are the four main types of stress that

causes Earthquakes?

1.) Compression stress, in which an object is squeezed or shortened.


3.) Shear stress, in which different parts of an object are moved in opposite directions along a plane.


Types of deformation

1. What are the different types of Deformation?

a.) Elastic deformation occurs when a material, such as rock, deforms as stress is applied but snaps back into its original shape when the stress is removed.


b.) Plastic deformation occurs when a material changes shape as a stress is applied and remains in the new shape when the stress is removed.


Energy release

a. Please Define Fault:

Crack in Earth’s crust along which rock has moved.


Please Define Elastic Rebound:

The sudden release of strain energy from rock as it moves along a fault.


Seismic Waves

1. Please Define Focus:

Point of origin for an earthquake, the point from which seismic waves originate.


Please Define Epicenter:

The point of Earth’s surface directly above the focus of an earthquake.


Primary waves

a. Please Define Primary wave:

Primary waves are also called P-waves are similar to waves that travel along a coiled spring. Primary waves cause particles inside the Earth to move back and forth in the same direction that the wave is traveling. P-waves are faster seismic waves and can travel through Earth’s interior with speeds between 5 km/s and 7 km/s. P-waves travel through both solids and liquids.


4. Secondary waves

a. Please Define Secondary waves:

Secondary waves, or S-waves, are another type of body wave. Secondary waves are like Transverse waves in which the wave moves right angles to the direction of the wave. S-waves travel more slowly than P-waves. Unlike P-waves, S-waves can travel only through solids.


5. Surface waves

a. Please Define Surface waves:

Surface waves only travel on Earth’s surface. They move in a more complex manner, rolling like ocean waves. Buildings, roads, and power lines are often damaged by the side-to-side rocking motion that results from surface waves.


D. Earthquake Measurement

1. Logarithmic scale

a. Please Define the Richter Scale:

The Richter Scale measures the energy released during the earthquake. It is a logarithmic scale that represents a 10-fold increase in wave amplitude from one magnitude to another.


b. Please Define the Mercalli Scale:

This scale ranges from 1 to 12. A rank of 1 on

the scale represents an earthquake that is rarely felt by anyone. A rank of 12 reflects earthquakes that cause the most severe damage.


Earthquake Damage

1. Earthquake Damage causes:

a.) Collapsed buildings

b.) Landslides

c.) Fires

d.) Tsunamis


Earthquake-safe structures

a. How are buildings made safe during Earthquakes?

1.) Design a system that allows the whole structure to move as a unit. Base isolated systems use bearings that separate the building from the ground.


2.) By using building materials that bend rather

than break during an earthquake.



A. Earth From the Inside-Out

1. Refraction

a. How does Refraction show the interior of our Planet?

Refraction occurs when a change in speed causes a wave to bend and change direction. The refraction and change of speed of seismic waves as they pass through Earth provides evidence of Earth’s layered structure.


b. Speed and direction

1.) Please Define Discontinuity:

Boundary between two layers of material that have different densities.


2.) What is the Mohorovicic Discontinuity?

This discontinuity separates Earth’s crust and mantle. Seismic waves can change both speed and direction when they encounter this discontinuity.


Shadow zones

a. Please Define Shadow Zones:

Area on Earth’s surface where no seismic waves from a given Earthquake are recorded.


The inner and outer cores

1.) What is the composition of the solid Inner Core?

Iron, nickel, oxygen, and sulfur.


2.) What is the composition of the liquid Outer


Silicates, aluminum, and calcium.


Composition of Earth’s Layers

1. Please Define Lithosphere:

The layer of Earth made of rocky material broken up into tectonic plates, consists of Earth’s crust and uppermost mantle.


Please Define Asthenosphere:

The plastic-like layer of Earth made of partially-molten rock material directly beneath the tectonic plates.



A. Volcano Formation

1. Why is Magma forced upward from the Earth’s Asthenosphere or Upper Mantle?

Because magma is a liquid, it is less dense than the surrounding solid rock.


Plate Boundaries and Hot Spots

1. Convergent plate boundaries

a. Why are Volcanoes found along

Convergent Plate Boundaries?

They form where tectonic plates collide along subduction zones.


Divergent plate boundaries

a. Why are Volcanoes found along Divergent Plate Boundaries?

Most of this activity goes unnoticed because

it occurs under water at mid-ocean ridges. However, there are places where volcanic activity due to divergent plates occurs on land. An example of this the East African Rift Valley.


Hot spots

a. Why are Volcanoes found at Hot Spots?

Hot spots are areas of volcanic activity where magma moves toward Earth’s surface in large,

ballon-like plumes. Hot spots are stationary and the Hawaiian Islands are volcanic islands formed when the oceanic pacific plate moved over a hot spot.


C. Eruptive Products

1. Lava

a. Please Define Lava:

Underground magma that erupts to the Earth’s surface.


Please Define Viscosity:

A fluid’s resistance to flowing.


Please Define Silica:

Chemical compound, silica dioxide (SiO2),

a common ingredient in most magma and much of Earth’s crust.


Pyroclastic material

a. Please Define Pyroclastic Material:

Any solid material that erupts from

a volcano.


b. Pyroclastic Material described in terms of


1. Ash

2. Globules

3. Volcanic cinders

4. Volcanic blocks


3. Gases

a. What kind of Gases erupt from a Volcano?

1.) Water vapor- most abundant gas.

2.) Carbon dioxide-next most abundant gas.

3.) Sulfur dioxide-can combine with oxygen and water in the atmosphere to form droplets of sulfuric acid.


Eruptive Styles

1. What are Felsic Magmas?

Thick, cool, and sticky felsic magmas have high

viscosities and resist eruption, causing the pressure inside a volcano to increase. Consequently an explosive eruption occurs for this type of magma.


What are Mafic Magmas?

In contrast, running Mafic magmas have low

viscosities and they erupt quietly. These eruptions are characterized by fluid lava flows having a high temperature along divergent plate boundaries and hot spots.


Types of Volcanoes

1. Cinder cone volcanoes

a. Please Define Cinder Cone Volcano:

Small steep-sloped volcano with a short eruption cycle, composed of cinder, formed at vents in Earth’s crusts,

often around the central vent of a larger volcano.


Shield volcanoes

a. Please Define Shield Volcano:

Large, broad, flat volcano composed of layer upon layer of basaltic lava flows made up of thin mafic lava.


Composite volcanoes

a. Please Define Composite Volcano:

Large and steep-sided volcano composed of layers of thick flowing felsic lava and ash.



A. Please do Check Concepts 34-40 on page

802 in your Text.

B. Please do Standardized Test Practice 1-6

on page 804 in your Text.