Earths Interior
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Geology: the study of planet Earth
Geologists study the processes that
create Earth’s features and search for
clues about Earth’s history
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Geologists have to make predictions about what the
Earth’s interior is made of by making indirect
observations of seismic waves
Forces beneath the Earth’s surface change the Earth’s
appearance. There are two types of forces:
Constructive: forces that
build up mountains and
landmasses
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Destructive: forces that
destroy mountains and
other features of land
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Continents: the seven
great landmasses
surrounded by oceans

the seven
continents:
 1. North America
 2. South America
 3. Africa
 4. Europe
 5. Asia
 6. Australia
 7. Antarctica
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Use seismic waves:
vibrations that travels
through Earth,
carrying the energy
released during an
earthquake
determine the speed
and path of these
waves to reveal the
inner Earth’s structure
Crust: Layer of rock that forms Earth’s outer
skin (made of Oxygen, Silicon, Aluminum,
Calcium, Iron, Sodium, Potassium and
Magnesium)
 Includes soil and water
 8-40 km thick

Oceanic Crust: crust beneath the ocean
Thin layer of crust
Made of- basalt: dark dense rock with a fine
texture

Continental Crust: crust that forms the
continents
Thicker layer of crust
Made mainly of granite, which then weathers
and redeposits into many sedimentary and
metamorphic rocks
Mantle: a layer of hot rock under the Earth’s crust
(made of a material called peridotite which is high in
iron and magnesium)
 Lithosphere: a rigid layer made up of the
uppermost part of the mantle and the crust; about
100km thick- (tectonic plates)
Under the Lithosphere is a layer of hot rock
 Temperature and pressure in the mantle increase with
depth
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Asthenosphere: thick, soft material that flows in
the mantle; about 3,000km thick; moves in a
convection current
Core: innermost layer of Earth; consists of 2 parts
(made of iron and nickel)
3. Outer Core
layer of molten metal that surround the inner core
Behaves like a thick liquid
Is under enormous pressure
4. Inner Core
Dense ball of solid metal (mostly iron)
Extreme pressure makes it a solid
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The Earth has a magnetic field that is caused by the
inner core spinning within the outer
What is this magnetic field called?
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The crust is a very thin
layer compared to the
others.
We already know that over time, the Earth’s
crust cooled. The crust is thin, relatively,
varying from a few tens of kilometers thick
beneath the continents to less than 10 km
thick beneath the oceans.
The crust and upper mantle together constitute
the lithosphere, which is typically 50-100 km
thick and is broken into large plates. These
plates sit on the asthenosphere.
The asthenosphere is kept plastic largely
through heat generated by radioactive decay.
This heat source is relatively small, but
nevertheless, because of the insulating
properties of the Earth's rocks at the surface,
this is sufficient to keep the asthenosphere
plastic in consistency.
Heat Sources in the Earth
1. Heat from the early accretion and
differentiation of the Earth

still slowly reaching surface
2. Heat released by the radioactive
breakdown of unstable nuclides
Heat Transfer
1. Radiation
2. Conduction
3. Convection
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If you look at a map of the world, you may notice that some of the
continents could fit together like pieces of a puzzle.
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The Earth’s crust is divided into 12 major
plates which are moved in various directions.
This plate motion causes them to collide, pull
apart, or scrape against each other.
Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
The word, tectonic, refers to the deformation
of the crust as a consequence of plate
interaction.
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Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
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“Plates” of lithosphere are moved around
by the underlying hot mantle convection
cells
Three types of plate
boundaries
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Divergent
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Convergent
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Transform
Divergent Boundaries
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Spreading ridges
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As plates move apart new material is erupted to
fill the gap
Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
Iceland: An example of continental rifting
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Iceland has a divergent
plate boundary running
through its middle
Convergent Boundaries
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There are three styles of convergent plate
boundaries
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Continent-continent collision
Continent-oceanic crust collision
Ocean-ocean collision
Continent-Continent Collision
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Forms mountains, e.g. European Alps,
Himalayas
Himalayas
Continent-Oceanic Crust Collision
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Called SUBDUCTION
Subduction
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Oceanic lithosphere
subducts underneath the
continental lithosphere
Oceanic lithosphere heats
and dehydrates as it
subsides
The melt rises forming
volcanism
E.g. The Andes
Ocean-Ocean Plate Collision
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When two oceanic plates collide, one runs over the
other which causes it to sink into the mantle forming a
subduction zone.
The subducting plate is bent downward to form a very
deep depression in the ocean floor called a trench.
The worlds deepest parts of the ocean are found along
trenches.
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E.g. The Mariana Trench is 11 km deep!
Transform Boundaries
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Where plates slide past each other
Above: View of the San Andreas
transform fault