Movements of the Earth’s Crust
Continental Drift
 Alfred
Wegener proposed the hypothesis
of continental drift
 The idea the continents were all together
at one point and drifted to their present
locations
 Pangaea: Name of all land masses
 Panthalassa: Water surrounding Pangaea
Pangaea
What is the Evidence?
Similarities of the coastlines
 Fossils of plants and animals in parts of
Pangaea that had been joined
 Types of rocks and rock layers on the
coastal region of formerly adjoined parts
 Changes in climate patterns


Glacier Records
Fossil Evidence
Rock Similarities
Coastline Similarities
Theory of Plate Tectonics
Plate Tectonics
 There
are two types of crust- oceanic and
continental
 There are 30 plates on the earth’s surface
 The plates are chunks of lithosphere that
float on the asthenosphere


Lithosphere: Crust and the upper mantle
Asthenosphere: Layer of plastic rock
Rules of Plate Tectonics
1. Continental crust is less dense, or lighter, than
Oceanic crust so it doesn't sink. It is never
destroyed and is permanent.
2. Oceanic crust is heavier so it can sink below
Continental crust. It is constantly being formed
and destroyed at ocean ridges and trenches.
3. Continental crust can carry on beyond the
edges of the land and finally end far below the
sea. This explains why the edges of all the
continents don't have deep trenches right up
against their coastlines.
4. Plates can never overlap. This means that they
must either collide and both be pushed up to
form mountains, or one of the plates must be
pushed down into the mantle and be destroyed.
Rules of Plate Tectonics
Continued…
5. There can never be gaps between
plates, so if two plates move apart, as in
the middle of the Atlantic, new rock will
be formed to fill the space.
6. We know the Earth isn't getting bigger or
smaller, so the amount of new crust being
formed must be the same as the amount
being destroyed.
7. Plate movement is very slow. This is partly
why Wegener's original ideas were
ignored. Nobody could 'see' the
continents moving. When the plates make
a sudden movement we call it an
Plates of the World
Types of Crust
 Crust:
very thin outer layer of the earth
 Oceanic crust is more dense, heavier,
and younger than continental crust
Types of Plate Boundaries
*Draw these
pictures in
your notes*
Diverging Plate Boundary
• In most cases, there is seafloor spreading
occurring at this type. Two plates moving
away from each other,


Molten Rock, from the asthenosphere,
move up to fill the gaps between the 2
plates and form new crust.
Rift Valley: Narrow valley formed when
plates are separating
Diverging Boundary
Seafloor Spreading
Rift Valley
Convergent Plate Boundaries
• Two plates colliding and one is being subducted
under another.
–Subduction Zone: one plate moving under
another
–Ocean Trench: generally forms along a
subduction zone
–Mountain Ranges
–Island Arc: chain of volcanic islands
Converging Boundary
Oceanic-Oceanic
Converging
Oceanic-Continental
Converging
Continental-Continental
Converging
Transform Plate Boundary
• Two plates grinding past each other.
Earthquakes occur here.
Transform Plate Boundary
What Causes Plate Motion?
 Most
think that the major reason for plate
movement is due to convection.
 Convection Current: formed by hot rock
formed in the asthenosphere rising and
the cold material at the surface falling to
replace the rising material.
 Plates float along this heated flowable
material.
Convection Currents
Compositional Layers of the
Earth
 Crust
 Mantle
 Outer
Core
 Inner Core
Mechanical Layers of the
Earth
 Lithosphere
 Asthenosphere
 Mesosphere
 Outer
Core
 Inner Core
Earthquakes
A.
B.
C.
D.
When rock fragments move, they release
energy in the form of seismic waves.
The point where the earthquake occurs is
called the focus.
The point on the surface that is directly above
the focus is the epicenter.
Most earthquakes have a shallow focus
because other focuses loose energy before it
reaches the surface.
ANSS Recent Earthquakes in the
US
Three major earthquake
zones
Pacific Ring of Fire

West coast of north/south
America

Along here, most plates are
being subducted or scrape
past each other.
Mid-Oceanic Ridge


Spreading motion creates stress in
the rocks along the mid-oceanic
ridges.
Seafloor spreading
–Mid-Atlantic Ridge: under sea
mountain range with a steep
narrow valley running down the
center.
–Part of a mid-oceanic ridge that
winds its way around earth.
–New rock is forming at the
oceanic ridges and is called
seafloor spreading.
Eurasian-Melanesian Belt:

Formed with the collision of Eurasian and
Africa and Indian plates.

The mountains are being produced at
boundaries.
these
Potential Earthquakes in US
Recorded Earthquakes Around
The World
Earth/ Env Sci
 Please
get your notes out and something
to write with.
 You should ALL be in your seats, ready to
go when the bell rings.
 We have notes to take first, then a guided
worksheet, then our test review.
*TEST MONDAY!!!
Fault Zones
 Created
when the plates separate,
collide, subduct, and slide past each
other.
 Example: San Andres fault in California.
 Earthquakes can also occur along former
fault lines in the middle of current plates.
What is a Fault?
 Faults
are fractures in Earth's crust where
rocks on either side of the crack have slid
past each other
3 Types of Faults



Strike-slip faults indicate rocks are sliding past each
other, with little to no vertical movement. Both the
San Andreas and Anatolian Faults are strike-slip.
Normal faults create space. Two blocks of crust pull
apart, extending the crust. The Basin and Range
Province in North America and the East African Rift
Zone are two well-known regions where normal faults
are spreading apart Earth's crust.
Reverse faults, also called thrust faults, squeeze the
crust, pushing two blocks of crust on top of each
other. These faults are commonly found in mountain
ranges such as the Himalayas and the Rocky
Mountains.
Faults
Recording Earthquakes
 Earthquakes
are recorded by an
instrument called a seismograph
 Every earthquake is going to give off
three different seismic waves
 To find the location of an earthquake
readings from three different locations are
needed
Types of Seismic Waves
P
Waves: the fastest moving wave and
can travel through solids and liquids
 S Waves: Can only travel through solids
and are the second wave to arrive
 L Waves: Slowest moving seismic wave,
but causes the most damage
Richter Scale
 The
Richter scale measures magnitude of
an earthquake
 Magnitude is a measurement of the
energy released by an earthquake
 Each whole number increase in
magnitude is an increase of 31.7 times
more energy
Mercalli Scale
A
measurement of the intensity of an
earthquake
Parts of a Volcano
 Volcano:
vent and the lava material that
builds up around the vent
 Crater: Funnel shaped pit at the top of a
volcanic pit
 Caldera: Large basin shaped depression
at the top of a volcano. Usually due to a
violent eruption
Magma
 Volcanism:
Any activity that includes the
movement of magma toward or onto the
surface
 Magma: Liquid rock

Most magma is formed at a subduction
boundary
 Lava:
Magma that reaches the earth’s
surface
There Are Three Major
Volcanic Zones
 Subduction
Zones
 Mid-oceanic ridges
 Hot spots
Subduction Zones
 Plate
being subducted is turned into
magma
 Some magma will erupt to form
volcanoes
 EX. “The Pacific Ring of Fire”
Mid Oceanic Ridge
 Greatest
amount of magma surfaces
here
 Diverging boundary
 Emerging lava forms new ocean floor
 EX. Mid-Atlantic Ridge
Hot Spots
 Areas
of volcanism within a plate
 Generally hot spots are shield volcanoes
 Ex. Hawaii
There are Two Different
Types of Lava
 Mafic
lava is dark in color when cooled
and usually produced from oceanic crust
 Felsic lava is lighter in color and usually
produced from continental crust
There are Three Different
Types of Volcanoes
 Sheild
Cone- Broad base and gently
sloping sides
 Cinder Cone- Very steep slopes, not to tall
 Composite Cone- Develops into high
volcanic mountains
Composite Cone
Mt. Rainer