CONTINENTAL DRIFT, LAYERS
OF THE EARTH, PLATE
TECTONICS
SI
I. Earth’s Interior
A. Layers of the Earth
1. Crust: thin and solid outermost layer of Earth
above the mantle.
a. Continental crust is less
dense and thicker than
oceanic crust.
layer of rock between the Earth’s
crust and core
a. Denser than the crust
b. Outermost part is solid and rigid, but as
you move closer to the core, the mantle
becomes soft and
easily deformed
(like gum)
2. Mantle:
c. Crust and uppermost solid
mantle called the lithosphere
d. Soft part of the mantle is called
the asthenosphere
3. Outer Core: Liquid metal composed
mainly of iron and nickel
4. Inner Core: Solid metal composed
mainly of iron and nickel
B. As you travel from crust into the core, the
temperature increases from 375oC at the
crust to over 6000oC in the inner core
C. Thermal Energy Transfer
1. Material and energy moves within the
Earth as a result of convection
currents(hot material rises and
cool material sinks
back to the core)
II. Continental Drift
A. Theory that Earth’s surface is made of
large movable plates
1. Alfred Wegener was a German scientist
who first proposed the idea that the
continents of the Earth were once one large
supercontinent
a. Called this supercontinent Pangaea
B. Early evidence for Continental Drift
1. Fossils: Mesosaurus fossil found in Brazil and
western Africa
a. Not likely to have swam between continents
2. Shape of continents :seemed to fit together like
a puzzle
3. Glacial deposits: same deposits in United States
are also found in Greenland and Western Europe
4. Rock structures : similar ones are found on
different continents
5. Migration patterns of animals have not changed
since it was supercontinent
C. Recent evidence for Continental Drift (Sea-floor
spreading)
1. Magnetic polarity bands near mid-ocean ridge
a. Alternating magnetic bands, on new ocean floor
2. Age of rocks relative to the mid-ocean ridge: the farther
away from the mid-ocean ridge, the older the rock
Plate Tectonics
• Theory that the Earth’s lithosphere is broken into plates
that move over the asthenosphere
• Replaced the theory of Continental Drift
Plate Tectonics continues
• Lithosphere is divided into 7 major
plates and several smaller plates
called tectonic plates
• How do tectonic plates move?
Types of Boundaries
1. Divergent
•Plates are moving apart
•New crust is created
•Magma is coming to the surface
Continental crust forms rift valley
Oceanic crust forms mid-ocean ridge
Sea-Floor Spreading – (Divergent)
Types of Boundaries
2. Convergent
•plates are coming together
•crust is being destroyed in the
mantle
2 oceanic plates or oceanic +
continental  subduction
2 continental plates  mountain range
(forms ocean trench)
Types of Boundaries
3. Transform
•plates are slipping past each
other
•crust is not created or
destroyed
Stress builds up
Stress is released earthquake
Common Events at Plate Boundaries:
Volcanoes
• Do not occur at convergent
boundaries of continental to
continental crust or transform
boundaries
• Geysers – water heated by magma
that comes to the Earth’s surface
Volcanoes-”Ring of Fire”
Where 80% of the world’s Earthquakes occur
Common Events at Plate Boundaries:
Earthquakes
Earthquake Effects: Tsunami
A tsunami is a giant wave or sequence of waves produced by
large water displacements. These are most commonly caused
by underwater earthquakes.
Tsunamis can be destructive long distances from their
sources.
Then how can there be volcanoes that are
not on plate boundaries?
= Volcano
?
Hot Spots
•A hot spot is an area of persistent volcanic activity
that comes from unusually hot areas of the mantlecore boundary.
•Hawaii, Iceland,
and Yellowstone
(geysers) are
examples of hot
spots.
V. Earthquakes
A. As plates move past each other, pressure builds up and
eventually the stress becomes so great it causes the rock
to crack
1. Focus: exact point inside Earth when an earthquake
originates
2. Epicenter: point on Earth’s surface directly above an
earthquake’s focus
B. Energy is transferred by waves
1. Longitudinal waves (P Waves):
Move faster through rock, so first
waves to reach recording stations
2. Transverse waves (S Waves): Move
more slowly, so arrive second to the
recording station
3. Surface waves: seismic waves that
can only move through solids
C. Seismograph: machine that records the movements
produced by an earthquake
1. Use seismographs to investigate the Earth’s interior
2. Differences in velocities of the waves indicate the type
of material the waves travel through
a. Scientists constructed the model of Earth [Fig.
19, p.712]
D. Richter Scale: a scale that expresses the
magnitude of an earthquake
1. Range from 2.0 to 10.0 magnitude
2. No earthquakes have ever been
recorded at 9.0 or 10.0