Transcript MS1_PNT_Geologyppt_V01

Chapter 11
Pgs 11-4 to 11-29
Layers of the Earth
pgs 11-4 to 11-6
 The current theory is
that the Earth’s
interior consists of
multiple layers:
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Inner core
Outer core
Mantle
Crust
The inner core
 The center of the Earth
 Made up primarily of iron,
nickel, other heavy
elements
 It is theorized to be solid
due to enormous
pressure
The Outer Core
 Made of the same
elements as the inner
core, but with less
pressure, it is theorized
to be liquid
The Mantle
 Contains mostly silicon
and oxygen
 makes up nearly 80
percent of the Earth's
total volume.
 Consists of the upper
and lower mantle
 The upper mantle itself
is made of 2 layers
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Asthenosphere
Lithosphere
Lithosphere and Asthenosphere
 Lithosphere
includes the uppermost, rigid part
of the upper mantle and the crust.
 Asthenosphere
 Solid but flows slowly over time
 Hotter, less dense material
(magma) rises towards the surface
where it can eventually flow from a
volcano or other opening. At this
point the molten rock is lava.
 The flowing asthenosphere carries
the lithosphere of the Earth,
including the continents, on its
back.
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The Crust
 composed mainly of
oxygen, silicon,
magnesium, and
iron
 Varies in thickness
and is the outer
layer of the
lithosphere
11-7 to 11-8 Isostatic Equilibrium
 Even before the plate tectonics theory
emerged, scientists believed that the crust
floated on the denser mantle below
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Still believed today
 Continental crust (crust under the continents)
 Ocean crust (crust under the ocean basins)
 Oceanic crust is thinner and denser than
continental crust

Because the continental crust is made of
granite and the oceanic crust is made of basalt
rock
Interaction of Oceanic Crust and
Continental Crust
 With the crust resting on the mantle, there
must be a balance between the weight of the
crust and the upward force of buoyancy

called isostatic equilibrium
 As material adds to the oceanic crust from
sedimentation, glaciers and volcanic activity
or from the continental crust from erosion, this
balance becomes disrupted. This is one
theorized cause of earthquakes.
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To restore equilibrium, landmasses will sink or
rise slightly along a weak area called a fault.
 The accepted theory of plate tectonics
suggests that the continents move in
horizontal directions and that earthquakes
also result from that movement.
The Theory of Continental Drift
11-10 to 11-13
 Proposed by Alfred Wegener
 All earth’s continents had been a single
continent that he called Pangaea
CONTINENTAL DRIFT
Pangaea broke up with part of the continent drifting north and part
south. 1) The northern part split to form the North Atlantic Ocean 208146 million years ago (mya). 2) The South Atlantic and Indian oceans
began to form 146-65 mya. 3) The continents continue to drift. Today
the oceans are still changing shape; the Atlantic Ocean gets wider by a
few inches each year.
 Surrounding Pangaea was a single large
ocean he called Panthalassa
 The theory that all of the continents were
once a single landmass that drifted apart (and
are still doing so) is called the theory of
continental drift
Evidence for Continental Drift
pgs 11-10 through 11-13
 Appeared that the continents fit together like
jigsaw puzzle pieces
 Fossils found in different locations
 Distribution of coal
 Glacial rock deposits
 Limestone deposits
 Salt deposits
Criticism of Continental Drift
 Wegener was a meteorologist, not a geologist
 Could not give an explanation of how the
continents could drift
 Jigsaw puzzle had gaps
Seafloor Spreading
pgs 11-14 to 11-18
 New technology- sonar
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Came about at the same time as the continental
drift theory and partly in response to the Titanic
disaster
The German Meteor mapped the contours and
depths of the South Atlantic in 1925 using sonar
 The ability to map the seafloor in greater
detail revealed important new features:
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Mid-ocean ridges are enormous mountain
ridges on the bottom of the ocean.
Rift valleys are deep valleys
running through the center of
mid-ocean ridges such as
the Atlantic Ridge.
Trenches are deep ravines
in the seafloor.
 The idea that the seafloor is in a constant state
of creation and destruction is called seafloor
spreading- an explanation proposed by Harry
Hess and Robert Dietz.
 New crust emerges from
the rift valley in a midocean ridge
 Magma from the
asthenosphere pushes up
through the rift and
solidifies into new crust
 As more magma pushes up
from below, it pushes new
crust away on each side of
the ridge
 New seafloor near the
ridge continuously pushes
old seafloor away from the
ridge
Evidence for Seafloor Spreading
11-17 to 11-18
 Ocean-bottom sediment samples
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Glomar Challenger- coring
 Radiometric dating
 Used to determine the
age of rocks
 Seafloor rocksignificantly younger
than rock in the center
of the continents
(theory states that
seafloor rock subsides
and continental rock
doesn’t).
 Magnetometer data
 measures the polar
orientation and
intensity of magnetism
of minerals
 Scientists towed
magnetometers
around the seafloor
beginning in 1950
 discovered that the
seafloor on either side
of the mid-ocean
ridges roughly mirrors
each other’s polar
orientation
Divergent, Convergent, & Transform
Plate Boundaries 11-22 to 11-25
 The theory of plate tectonics unites the
theories of continental drift and seafloor
spreading.
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Earth’s lithosphere consists of more than a
dozen separate plates
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rigid and float on the asthenosphere.
Divergent Boundaries
 At a spreading, or divergent boundary, two plates are
moving apart
 The crust pulls apart and forms valleys.
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Magma flows up through the rift valleys creating new crust
and widening the seafloor.
Mid-ocean ridges and rift valleys mark divergent
boundaries.
Hot Spots
 Stationary plume of
magma under a
moving plate
 Creates volcanic
islands in the
middle of plates
EX: Hawaiian Islands
and the Emperor
Seamount Chain
Convergent Boundaries
 At a colliding or convergent boundary, two
plates push together
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also called destructive boundaries because
movements along these destroy crust
 Subduction zones (convergent boundary).
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A trench forms as a more dense oceanic plate
moves under a less dense continental plate. As
subduction occurs, some of the material from the
melting oceanic plate rises upward to form
volcanoes on the continent.
Mountain formation at continental plate collision.
Transform Boundaries
 At a transform boundary or fault, two plates
slide past each other.
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Earthquakes result as rocks move when the
plates slide next to each other.
Ex: California’s San Andreas Fault
Ocean Floor Topography Vocabulary
 Continental Shelf: the part of the continent that
is under water. It is the biologically richest part of
the ocean. At times of low sea level the shelves
were exposed.
 Continental Slope: the edge of the continent.
Extends downward to the deep-sea floor.
 Continental Rise: a gentle slope or a rise on the
bottom of the ocean that is due to the sediments
being carried down the slope. The sediment is
carried downward by the turbidity current.
 Seamount: underwater volcanoes due to hotspots
and magma. Formed when magma below is
pushed upward and cooled and solidified.
 Mid-Ocean Ridge: the cracks in the bottom of the
ocean where the plates meet. Is called an
underwater mountain range.
 Rift Valley: a valley between 2 plates. Caused
when the 2 plates are pushed apart and the seabottom collapses forming a valley between the 2
ridges.
 Abyssal Plain: the almost perfectly flat area of the
ocean. Flat due to deposits of sediments and
erosion. Called the ocean desert because few life
forms exist here.
 Guyot: a flat-topped underwater mountain. It is flat
at the top due to erosion.
 Trench: a narrow depression on the sea floor.
Caused when 2 plates collide and one plate is
pushed under the other one and pulls the sea
bottom with it. The deepest trench is the Marianas
trench with a depth of 11,022 meters, or almost 7
miles.
 SONAR: uses echolocation or sound waves to
see the seafloor and make an accurate map of it.
SONAR is used to make accurate
maps of the ocean floor.
Sediments: 12-10 to 12-12
 Lithogenous sediments come from the land
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Mainly result from erosion by water, wind, and
ice carrying rock and mineral particles into the
sea.
Other lithogenous sediments enter the sea from
landslides and volcanic eruptions
Make up majority of sediments found near
continents and islands
Includes sand and clay
 Biogenous sediments: originate from organisms
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Particles in the sediment come from shells and
hard skeletons
Cover the largest area of sea floor.
The majority of biogenous sediment comes from
planktonic organisms that obtain siliceous and
calcareous compounds from seawater.
Under the right conditions, organic molecules in
the sediment form crude oil (petroleum) and
natural gas
 Hydrogenous sediment results from chemical
reactions within seawater
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Less than 1% of the seafloor sediments
Form slowly
 Cosmogenous sediments come from outer space
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Made up of small particles the size of sand or
smaller called cosmic dust.
Some thought to result from collisions between
objects in space
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Meteors: large, fast-moving objects that enter the
atmosphere
Meteorite: a meteor that strikes the ground
Least abundant of the sediments- a few parts per
million of marine sediment per year