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Earth’s Layered Structure
Earth’s Layered Structure
 Earth’s interior consists of three major
zones defined by their chemical
composition—the crust, mantle, and core.
Density estimates for the layers
of the earth (in grams per cubic
centimeter):
Continental Crust: 2.7 to 3.0
Oceanic Crust:
3.0 to 3.3
Mantle (silicates): 3.3 to 5.7
(increasing with depth?)
Outer Core (liquid): 9.9 to 12.2
Inner Core (solid): 12.6 to 13.0
Earth’s Layered
Structure
The earth’s mantle is sub-divided
into two layers:
1. The upper (brittle layer)
2. The lower (liquid) layer
The earth’s upper mantle and
crust form a relatively cool
ridged shell called the
lithosphere.
Beneath the lithosphere is the
asthenosphere:
A ductile layer where rock is
at or near its melting temperature.
Earth’s Layered
Structure
The core is divided into
Two different zones:
1. Outer core = 3500 ºC
2. Inner core = 5000 ºC
The outer core is a liquid
because the temperatures
exceeds the melt point the
iron-nickel alloy that
makes up the outer core.
The inner core is much hotter but
remains a solid under pressure.
The inner core is also comprised of
a iron-nickel alloy.
The earth’s crust is
composed of 2 types
of crust:
Oceanic Crust:
Rock type: Basaltic
(mafic composition)
Thickness: 3-7 km
1. Oceanic Crust
2. Continental Crust
Continental Crust
Rock type: Granitic (felsic)
Thickness: 8-50 km
Plate Tectonics
Plate Boundaries
and Motion
Plate Tectonics
Plate tectonic theory is founded on
observation of crustal plate movement
And the internal structure of the earth.
3 Types of Plate Boundaries
• Divergent Boundary – moving _____
apart
• Convergent Boundary – moving ________
together
• Transform Fault Boundary – moving
________________________
sideways past each other
The thick continental plate, pulls-apart, thinning by
extensional forces, and fractured into a rift-shaped
structure.
The continental plate is arched upwards
from the convection current's pushing the
crust upward
Divergent Plate Boundary:
Continental
Divergent boundary
Divergent boundary of two continental plates pull apart.
East African Rift
rift valley
Creating a __________.
Example: _____________
Divergent Plate
Boundary - Oceanic:
Convergent boundary
Subduction
Convergent boundary of an oceanic plate and a
continental plate. Forms a _______
volcanic mountain range
trench Examples: Cascades
Andes Mts
and a ______.
_______ or _______
Oceanic Plates Convergent Boundary
Convergent boundary of
two oceanic plates.
island arc and
Creates an ________
trench Example: _____
Japan
a _____.
Convergent Boundary Continental Plates.
Convergent boundary
of two continental plates.
folded mountain
Forms a ______
range.
Appalachians
Examples: ___________,
Himalayas
Alps, ______________
Transform Plate Boundary
Transform-fault boundary where the North American
and Pacific plates are moving ____
past each other.
San Andreas Fault in California
Example: ________________
Transform boundary
Transform boundary
Plate Boundary Summary
Type of Boundary
Process Involved
Characteristic features
Examples
Divergent
Sea-floor spreading
Mid-ocean ridge
Rift valleys,
Earthquakes,
Volcanic Activity
Mid-Atlantic Ridge
East Pacific Rise
Convergent
Ocean-ocean
subduction
Deep sea trenches
Islands of Indonesia,
Mariana Islands
Ocean-continent
subduction
Volcano along coast
of continent
Continent-continent
High continental
collision
Transform
Plates sliding past
each other
West coast of S.
America
mountain chains
Himalayas
Earthquake activity
San Andreas Fault,
North Anatolian
Fault,
Fracture zones along
mid-ocean ridge
Plate Boundaries Review
• Places where plates move apart are called
divergent
_____________
boundaries.
rift valley
• When continental plates diverge a ___________
is
formed.
• When two oceanic plates converge what is created?
_________________
an
island arc and a trench
• The Appalachians formed mainly from continental
folded
plate collisions and therefore are a __________
mountain range.
Convection currents
• The force moving the plates is ____________
.
What drive Plate Movement?
Plates probably move as a result of a combination of the
driving mechanisms.
Plate separation may be initiated by mantle convection or a
rising mantle plume;
Plate Motions are classified into two categories;
A. Plate-generated movement.
B. Mantle-generated movement.
A. Plate-generated movement.
1. Slab pull.
Hypothesis that the weight of the cold slab descending into
the asthenosphere pulls the whole plate along. Normal faulting in the ocean crust
provides evidence for these plates experiencing tensional stresses.
2. Ridge push.
Hypothesis that topography of the elevated mid-ocean
spreading ridges drives the plates by gravity away from the ridge. Calculations
suggest that plates could move down the gentle slope formed by the thermal
profile of the lithosphere-asthenosphere boundary. However, during initial rifting,
plates begin to move without the help of an elevated ridge.
B. Mantle-generated movement.
1. Mantle convection cells.
Rising warm rock from the
mantle spreads laterally upon encountering the lithosphere, applying shear
stress and causing it to move.
a. Shallow convection model: only the asthenosphere convects, down to
a depth of 700 km.
b. Deep convection model: the whole mantle down to the core convects.
2. Thermal plumes.
Vertical columns of of upwelling mantle
100-250 km in diameter lift the overlying lithosphere and spread laterally,
which applies drag to the lithosphere. Many thermal plumes lie at
divergent plate margins. Iceland is an example.