Transcript Document 7203888

Phyllis Butler
NOTES Isostasy Forces Pangaea
ISOSTASY Theory = less dense floats on more dense
Crust is consist of continents and seafloor
Continents made of less dense Granite & seafloor is
made of more dense Basalt
Crust is lighter than the molten magma and floats on Mantle
FORCES that give the energy to create plate movement
Compression, Tension and Shear
PANGAEA “all land” all continents joined
Theory of Continental Drift proposed by Alfred Wegener
in 1915
Proofs
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Layered Earth - Isostatic Equilibrium
Think for a moment about the lithosphere. Why doesn’t it sink
into the asthenosphere? How are features such as mountains
supported?
The concept of buoyancy is illustrated by a ship on the ocean.
The ship sinks until it displaces a volume of water equal to the
weight of the ship and its contents.
Earth’s lithosphere is supported on the asthenosphere in a
similar manner, with a few important differences. Instead of
buoyancy, the term isostatic equilibrium describes the way the
lithosphere is supported on the asthenosphere.
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NOTES Lithosphere Asthenosphere Convection Cells
PLATE Tectonics Theory moving plates on crust
Proposed by Harry Hess of Princeton in 1960
Convection Cells in mantle provide Energy for plate
movement
Heat moves in circles powered from radioactive core
Creates movement and breaking of Earth’s plates
Proof of Continental Drift
Dynamic Earth areas that form our planet are the;
Lithosphere = crust and upper mantle (puzzle pieces)
Is brittle and moves above the
Asthenosphere = lower mantle of molten magma that
carries the Lithosphereic pieces above it.
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Plate Tectonics
An overview of the tectonic system.
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Types of plate movement
Convergence Divergence and Lateral Movement
DIVERGENCE = plates move apart (separate)
Creates volcanic activity mainly on the seafloor
Known as Mid-ocean ridges in middle of all oceans
Only divergence on land at African Rift Valley
CONVERGENCE = plates move together ( combine)
Oceanic-Oceanic makes island arcs ( Hawaii)
Continental-Continental makes mountains (Rockies)
Oceanic-Continental makes subduction, trenches, mts.
LATERAL = plates move beside each other = faults
Example is San Andreas fault;
Hot spots are prolonged volcanic areas by Mid-ocean ridge
Magnetic reversals where N and S polarity change by ridge
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Evidence for Plate Tectonics
Seafloor Spreading 1969
Ring of Fire
Magnetic Reversals
Similar findings on different continents of
Fossils
Coal Deposits
Glaciers
Plants
Animals
Rocks - Mountains
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Layered Earth
Evidence Of Earth’s Layers
BLANK
What evidence supports the idea that Earth has layers?
The behavior of seismic waves generated by earthquakes give scientists
some of the best evidence about the structure of Earth.
(above-left) S waves cannot penetrate Earth’s liquid core.
(above-right) P waves are bent as they pass through the liquid outer core.
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Layered Earth
A cross section of Earth
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How old is Earth?
The age of Earth has been subject to debate.
Scientists now use an age of 4.6 billion years.
The principle of uniformitarianism was
introduced in 1788. This principle states that
the forces which shaped Earth are identical to
forces working today.
Catastrophism is the thought that Earth is very
young, and events described in the Bible are
responsible for the appearance of Earth’s
features.
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New Evidence Supports
Alfred Wegener’s Theory of
Continental Drift
Wegener’s theory of continental drift was out of favor with
the scientific community until new technology provided
evidence to support his ideas.
• Seismographs revealed a pattern of volcanoes and
earthquakes
• Radiometric dating of rocks revealed a surprisingly
young oceanic crust.
• Echo sounders revealed the shape of the Mid-Atlantic
Ridge
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Pangaea
Pangaea
PANGAEA
The fit of the
continents at
a water depth
of 137
meters.
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Through the great
expanse of
geologic time, this
slow movement
remakes the
surface of Earth,
expands and splits
continents, and
forms and destroys
ocean basins.
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Lithospheric Plates
* Earth is composed of layers. These layers have
different chemical and physical properties.
* Researchers have learned about Earth’s layers
by studying waves generated by earthquakes.
• Plate tectonic theory suggests that Earth’s
surface is divided into segments called
lithospheric plates, which move, collide, and
slide past one another.
• This plate movement explains Earth formations
and explains the youth of the seafloor.
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Confirmation of the Theory of
Plate Tectonics
Age and distribution of ocean sediments: The
sediment in the ocean is thinner and younger than
the age of the ocean indicates it should be.
The Oceanic ridges: Oceanic ridges are clear
indicators of past events.
Terranes: Oceanic plateaus that form by uplifting
and mountain building as they strike a continent.
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Confirmation of the Theory of
Plate Tectonics
Evidence supporting the
theory of plate tectonics:
Apparent Polar wandering:
plate movement causes the
apparent position of the
magnetic poles to have shifted.
The paleomagnetic fields in the
rocks would indicate a single
pole until the continents drift
apart.
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Confirmation of the Theory of
Plate Tectonics
Hot Spots: Surface expression of plumes of magma.
Volcanic Island Chain
A volcanic island chain can form when a plate passes
over a hot spot and a stationary mantle plume.
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Confirmation of Plate Tectonics Theory
Paleomagnetism: strips of alternating magnetic polarity at spreading
regions.
The patterns of paleomagnetism support plate tectonic theory.
The molten rocks at the spreading center take on the polarity of
the planet while they are cooling. When Earth’s polarity
reverses, the polarity of newly formed rock changes.
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Confirmation of Plate Tectonics Theory
Atolls and Guyots
Atolls and Guyots: Coral formations and submerged volcanic
mountains.
Guyots were once volcanic peaks above sea level. They were
eroded by wave action as they sank beneath the surface of the
water.
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Layered Earth
Chemical Properties
Chemical Properties of Earth’s Layers
Layer
Chemical Properties
Continental Crust
Composed primarily of granite
density = 2.7 g/cm3
Oceanic Crust
Composed primarily of basalt
density = 2.9 g/cm3
Mantle
Composed of silicon, oxygen, iron and magnesium
density = 4.5 g/cm3
Core
Composed mainly of iron
Density = 13 g/cm3
Note that Earth is density stratified, that is, each
deeper layer is denser than the layer above.
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Layered Earth
Physical Properties
Layer
Lithosphere
Asthenosphere
Mantle
Outer Core
Inner Core
Physical Properties of Earth’s Layers
Physical Properties
The cool, rigid outer layer
Hot, partially melted layer which flows slowly
Denser and more slowly flowing than the
asthenosphere
Dense, viscous liquid layer, extremely hot
Solid, very dense and extremely hot
So, when we examine the chemical and physical properties of
Earth’s layers, we see that a cool, rigid, less dense layer (the
lithosphere) floats on a hot, slowly-flowing, more dense layer (the
asthenosphere).
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Convection Cells - Internal Heat
Where does the heat within Earth’s layers come
from?
Heat from within Earth keeps the asthenosphere
flowing. This allows the lithosphere to keep moving.
The source of this heat is radioactive decay, given
off when the nuclei of unstable forms of elements
break apart.
This heat travels in convection currents in the
mantle.
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Tying It All Together - The Theory
Of Plate Tectonics
The ideas of continental drift and seafloor
spreading were tied together in the theory of plate
tectonics.
• Earth’s outer layer is divided into lithospheric
plates
• Earth’s plates float on the inner layer of
molten magma called the asthenosphere
• Plate movement is powered by convection
currents in the asthenosphere seafloor
spreading, and the downward pull of a
descending plate’s leading edge.
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The Major Lithospheric Plates
BL6ANK
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Plate Tectonics, Earthquakes and Volcanoes
Convergent Plate Boundaries
Convergent Plate Boundaries - Regions where plates are pushing
together can be further classified as:
Oceanic crust toward continental crust - for example, the west coast of
South America
Oceanic crust toward oceanic crust - occurring in the northern Pacific
Continental crust toward continental crust – one example is the
Himalayas
(right)
Compression
at convergent
boundaries
produces
buckling and
shortening.
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Island Formation
Hot spots/weaknesses
Subduction animation
Subduction
This refers to the process in which one plate goes underneath (or
subducts) the other. It occurs when two oceanic of when one oceanic
and one continental plates converge. (When two continental plates
meet, they buckle and form mountain ranges. See When the plate
subducts, an oceanic trench is created. Aleutian Island Trench
Mountain Formation
Converging animation
Mountainous volcanoes
Effects of movement
Divergent Plate Boundaries
The lithospheric plates interact with the neighboring plates in
several ways.
Divergent plate boundaries – Boundaries between plates
moving apart, further classified as:
Divergent oceanic crust – for example, the Mid-Atlantic Ridge
Divergent continental crust - for example, the Rift Valley of
East Africa.
Extension of divergent boundaries causes splitting and rifting.
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Seafloor Spreading - A Key Idea
Seafloor spreading
was proposed in 1960
to explain the
features of the ocean
floor.
It explained the
presence of the MidAtlantic Ridge.
Convection currents
in the mantle were
proposed as the
force that caused the
ocean to grow and
The Mid-Atlantic Ridge conforms to the
the continents to
shape of the adjacent continents.
move.
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Spreading
. When
the plates pull apart, something has to rise to fill in the hole. Magma from the mantle rises
upward from the crust to fill the gap. Then, it hardens, pulls away from the hole, and makes way
for more magma to ooze out. This occurs in the creation of ocean ridges (sea floor spreading).
These are just like mountains, only on the ocean floor. In fact, this process has created a 46,600
mile-long Mid-Ocean Ridge System. It is through these spreading centers that the sea floor
replenishes itself; new magma rises, forms a "plug", and, eventually, the youngest part of the sea
floor is born.
Mid Atlantic Ridge
Mid Atlantic Ridge
Mid Atlantic Ridge
Mid Atlantic Ridge
Transform Plate Boundaries
Transform plate boundaries - locations where
crustal plates move past one another, for
example, the San Andreas fault.
Plate Boundries illustrated
Translation at transform boundaries causes shear.
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Transform Fault
These are two plates that move sideways. You can find these
boundaries along fault lines where earthquakes occur. Because the
plates suddenly, violently pull apart in the opposite direction, the
ground is left unsettled and an earthquake results.
Alaskan Earthquake
Alaskan Earthquake
Mercalli Intensity Scale
I.
II.
III.
IV.
People do not feel any Earth movement.
A few people might notice movement.
Many people indoors feel movement. Hanging objects swing back and forth.
Most people indoors feel movement. Hanging objects swing. Dishes, windows, and doors
rattle. The earthquake feels like a heavy truck hitting the walls. Parked cars rock.
V.
Almost everyone feels movement. Sleeping people are awakened. Doors swing open or close.
Dishes are broken. Pictures on the wall move. Small objects move or are turned over.
VI.
Everyone feels movement. People have trouble walking. Objects fall from shelves. Damage is
slight in poorly built buildings.
VII. People have difficulty standing. Drivers feel their cars shaking. Some furniture breaks. Loose
bricks fall from buildings.
VIII. Drivers have trouble steering. Houses that are not bolted down might shift on their
foundations. Tall structures such as towers and chimneys might twist and fall. Well-built
buildings suffer slight damage.
IX.
Well-built buildings suffer considerable damage. Houses that are not bolted down move off
their foundations. Some underground pipes are broken. The ground cracks. Reservoirs suffer
serious damage.
X.
Most buildings and their foundations are destroyed. Some bridges are destroyed. Large
landslides occur.
XI.
Most buildings collapse. Some bridges are destroyed. Large cracks appear in the ground.
Underground pipelines are destroyed.
XII. Almost everything is destroyed. Objects are thrown into the air. The ground moves in waves or
ripples. Large amounts of rock may move.
Richter Scale
As a general rule, an increase of one magnitude unit corresponds to ten times greater
ground motion, an increase of two magnitude units corresponds to 100 times greater ground
motion, and so on in a logarithmic series.
Richter Earthquake Magnitudes Effects
Less than 3.5 Generally not felt, but recorded.
3.5-5.4 Often felt, but rarely causes damage.
Under 6.0 At most slight damage to well-designed buildings.
Can cause major damage to poorly constructed buildings over
small regions.
6.1-6.9 Can be destructive in areas up to about 100 kilometers
across where people live.
7.0-7.9 Major earthquake. Can cause serious damage over
larger areas.
8 or greater Great earthquake. Can cause serious damage in
areas several hundred kilometers across.
The End
Produced by Phyllis Butler