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.
Alfred Wegener first proposed Continental Drift.
In 1915, about 100 years ago.
1. Alfred Wegener observed that the
eastern coastline of South America
fit together with the western coastline
1. What large land animal and plant supported Continental Drift?
1. Examples are:
a.) Cape Fold Belt
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.
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.
Long narrow depression formed in between
the peaks along the mid-oceanic ridge.
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.
a. Rocks equal distances from either side of
the Mid Oceanic Ridge have the same
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.
a. Please Define Convergent Plate Boundary:
Boundary where two plates collide, and
produces either subduction zones or
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.
Japan is an example of an oceanic-oceanic
convergent plate boundary.
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.
1). Example of Continental-Continental Convergent Plate Boundary.
Indian plate collides with the Asian plate
to make the Himalaya Mountains in Asia.
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.
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.
a. Please Define Transform Plate Boundary:
Tectonic plate boundary in which plates slide horizontally past each other in opposite directions.
The San Andreas Fault in California is an
example of a transform plate boundary.
Earthquakes are common along transform
a. Please Define Convection:
Transfer of thermal energy in a fluid by the movement of warmer and cooler fluid from one place to another.
a. Please Define Slab Pull:
When subduction occurs along a convergent plate boundary, a force called slab pull helps to move the plates.
In contrast to slab pull, ridge push moves
plates along a mid-ocean ridge.
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.
Earthquakes occur at tectonic plate boundaries.
a. Where are Earthquakes shallow?
Earthquakes that occur along divergent and transform plate boundaries tend to be shallow, typically less than 70 km depth.
However, earthquakes that occur along convergent plate boundaries commonly occur at depths greater than 70 km.
a. Please Define Deformation:
A force applied to an object can cause the object to change its shape, or be deformed.
1.) Compression stress, in which an object is squeezed or shortened.
2.) Tension stress, in which an object is stretched or lengthened.
3.) Shear stress, in which different parts of an object are moved in opposite directions along a plane.
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.
a. Please Define Fault:
Crack in Earth’s crust along which rock has moved.
The sudden release of strain energy from rock as it moves along a fault.
1. Please Define Focus:
Point of origin for an earthquake, the point from which seismic waves originate.
The point of Earth’s surface directly above the focus of an earthquake.
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.
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.
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.
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.
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.
1. Earthquake Damage causes:
a.) Collapsed buildings
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.
than break during an earthquake.
A. Earth From the Inside-Out
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.
1.) Please Define Discontinuity:
Boundary between two layers of material that have different densities.
This discontinuity separates Earth’s crust and mantle. Seismic waves can change both speed and direction when they encounter this discontinuity.
a. Please Define Shadow Zones:
Area on Earth’s surface where no seismic waves from a given Earthquake are recorded.
1.) What is the composition of the solid Inner Core?
Iron, nickel, oxygen, and sulfur.
Silicates, aluminum, and calcium.
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.
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.
1. Convergent plate boundaries
a. Why are Volcanoes found along
Convergent Plate Boundaries?
They form where tectonic plates collide along subduction zones.
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.
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.
a. Please Define Lava:
Underground magma that erupts to the Earth’s surface.
A fluid’s resistance to flowing.
Chemical compound, silica dioxide (SiO2),
a common ingredient in most magma and much of Earth’s crust.
a. Please Define Pyroclastic Material:
Any solid material that erupts from
3. Volcanic cinders
4. Volcanic blocks
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.
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.
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.
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.
a. Please Define Shield Volcano:
Large, broad, flat volcano composed of layer upon layer of basaltic lava flows made up of thin mafic lava.
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.