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PLATE TECTONICS
The Earth is divided
into layers by
density.
As the Earth solidified during the formation of
the solar system elements with higher density
were drawn toward the center of the Earth by
gravity.
EARTH’S CRUST

Oceanic crust is comprised mainly of the rock
basalt
EARTH’S CRUST

Continental crust makes up the land masses.
This thicker, less dense material allows the
continents to rise above sea level and remain
dry for very long periods Continental crust is
made primarily of the rock granite
As the very hot core heats the material in the
Mantle it causes the material to move in a
circular pattern. The mantle material heats up
and rises and then cools and sinks. This
circular pattern of movement within the mantle
(called a convection current) pushes the
lithospheric plates as they float. The
movement and interaction of these plates
causes most of the large scale changes on
Earth's surface.
CONTINENTAL DRIFT

Alfred Wegener a German scientist was the first
to propose this theory to the scientific
community in the early 1900’s
CONTINENTAL DRIFT

Pangea was the name for this supercontinent
that began to break up about 200 million years
ago
CONTINENTAL DRIFT

Wegener’s theories were not accepted at the
time because his explanations were not
supported by physicists
CONTINENTAL DRIFT

His explanation for movement was that the
continents plowed through the seafloor crust
like moving islands
CONTINENTAL DRIFT

His explanation for the reason why the
continents moved was the spinning of the earth
EVIDENCE OF CONTINENTAL DRIFT

Although his explanations for the reason the
continents drifted were incorrect there was still
convincing evidence that they were indeed
once together.
EVIDENCE OF CONTINENTAL DRIFT

Rock formations in the Appalachian Mountains
matched up with ones in Greenland.
EVIDENCE OF CONTINENTAL DRIFT

Fossil evidence found in South America and
Africa were especially strong
EVIDENCE OF CONTINENTAL DRIFT

Bones from the Mesosaurus and
Kannemeyerid were found in the same rock
formations in Brazil and Chad
EVIDENCE OF CONTINENTAL DRIFT

Even glacial striations from ancient Ice ages
were found to match perfectly
EVIDENCE OF CONTINENTAL DRIFT

Climatic evidence found that there were coal
deposits in Antarctica suggesting that continent
was at one time much closer to the equator
SEA FLOOR SPREADING

In the early 1960’s new evidence revealed the
process on how the continents could indeed
move
SEA FLOOR SPREADING

Advances in sonar technology in the 1940’s
and 50’s allowed us to begin to accurately map
the seafloor
SEA FLOOR SPREADING

This evidence proved that the seafloor was not
flat and featureless as once thought. Vast
underwater mountain chains and deep
trenches were discovered.
SEA FLOOR SPREADING

Earthquakes and volcanic activity was
prevalent in certain parts and missing in others
SEA FLOOR SPREADING

The ocean floor was found to be much younger
than the continental crust
SEA FLOOR SPREADING

The thickness of the layers of sediments
increased with the distance on either side of
the ocean ridges
PALEOMAGNETISM

Once scientists were able to bring sea floor
samples to the surface they were able to
determine that a record of the seafloor was
being kept by Earth’s magnetic field
PALEOMAGNETISM

Paleomagnetism is the study of this magnetic
record using data gathered from iron-bearing
minerals
PALEOMAGNETISM

The magnetic records for the seafloor on either
side of the mid-ocean ridges matched perfectly
showing that the seafloor was growing outward
from the ridges in both directions
THE THEORY OF PLATE TECTONICS

Theory of Plate Tectonics states that the Earth’s
crust and rigid upper mantle are broken into
enormous slabs called plates.
THE THEORY OF PLATE TECTONICS

There are 17 known plates
THE THEORY OF PLATE TECTONICS

The plates do not remain still. They slide
across the partially molten mantle material of
the asthenosphere as a result of convection
currents deep in the Earth’s interior.
PLATE BOUNDARIES

Tectonic plates interact at places called plate
boundaries.
PLATE BOUNDARIES

Typically, since the Earth is spherical the plate
boundaries would appear as the threads of a
baseball weaving through the mid-ocean rifts
and around the smaller plates.
PLATE BOUNDARIES

Notice that ALL of the major plates include both
continental and oceanic crust
PLATE MOTIONS

Some plates move towards each other, some
move away, and some slide horizontally past
each other. Each interaction results in geologic
process and characteristics that we can now
associate with it.
PLATE MOTIONS

Divergent boundaries are places where tectonic
plates are moving apart
PLATE MOTIONS

Most divergent boundaries are found on the
seafloor where they form mid-ocean ridges
PLATE MOTIONS

Iceland is a continuation of the Atlantic midocean ridge
PLATE MOTIONS

The Arabian Peninsula is an example of a newly
formed divergent boundary as it separates from
the rest of Africa
PLATE MOTIONS

Convergent boundaries are where plates move
toward each other.

These boundaries give us the most interesting
geologic features. There are three types of
convergent boundaries
PLATE MOTIONS

Oceanic crust to oceanic crust results in the
subduction of one of the two plates and an
island arc
PLATE MOTIONS

Subduction is the process of one plate
descending beneath the other
PLATE MOTIONS

The Phillippines are a noticeable example
PLATE MOTIONS

Oceanic to continental convergence also
results in the subduction of the oceanic crust
PLATE MOTIONS

A volcanic mountain range such as the western
portions of North and South America is the
result
PLATE MOTIONS

The oceanic crust always subducts because it
is denser than continental crust
PLATE MOTIONS

Continental to continental convergence results
in folded mountains
PLATE MOTIONS

The Himilayas are an active folded mountain
chain
PLATE MOTIONS

Transform boundaries occur where plates
slide horizontally past each other. They rarely
are seen on the continents however the San
Andreas Fault in California is an exception
EARTHQUAKES

Most earthquakes occur when rocks fracture
deep within the Earth
EARTHQUAKES

Compression decreases the volume of a
material
EARTHQUAKES

Tension pulls the material apart
EARTHQUAKES

Shear causes a material to twist
EARTHQUAKES WAVES

The vibrations in the ground during an
earthquake are called seismic waves
EARTHQUAKES WAVES

Primary Waves (P-waves) squeeze and pull
rocks in the same direction along which the
waves are traveling
EARTHQUAKES WAVES

P-waves travel the fastest and CAN travel
through liquids
EARTHQUAKES WAVES

Secondary Waves (S-waves) cause rocks to
move at right angles to the direction of travel
EARTHQUAKES WAVES

S-waves travel slower than P-waves and
CANNOT travel through liquids
EARTHQUAKES WAVES

Surface Waves (L-waves) travel only on the
surface in two directions causing an up-anddown and side-to side motion
EARTHQUAKES WAVES

Most of the damage we see on the surface
from earthquakes is caused by surface waves
EARTHQUAKES WAVES

Most of our knowledge of Earth’s interior
comes from the study of seismic waves. The
relationship between P-waves and S-waves
allows us to measure the size of the inner and
outer cores
MEASURING AND LOCATING
EARTHQUAKES

More than one million earthquakes occur each
year. More than 90 percent of these are not
even felt by humans.
MEASURING AND LOCATING
EARTHQUAKES

Magnitude is the amount of energy released by
an earthquake
MEASURING AND LOCATING
EARTHQUAKES

Richter Scale is the numerical scale to measure
magnitude based on the size of the largest
seismic waves generated
MEASURING AND LOCATING
EARTHQUAKES

Each number on the Richter scale represents
an increase in amplitude by a factor of 10
MEASURING AND LOCATING
EARTHQUAKES

8 is ten times the amplitude of 7
MEASURING AND LOCATING
EARTHQUAKES

Modified Mercalli Scale measures the amount
of damage done by the earthquake in Roman
numerals I - - X II
MEASURING AND LOCATING
EARTHQUAKES

Earthquakes are located by tracking the
seismic waves registered at different locations
and plotting circles based on the speed of the
waves and time elapsed
MEASURING AND LOCATING
EARTHQUAKES

Seismometers are sensitive instruments used
to detect and record even the slightest
vibrations of the earth’s surface
MEASURING AND LOCATING
EARTHQUAKES

Focus is the point of initial fault rupture and the
location where the earthquake originates
MEASURING AND LOCATING
EARTHQUAKES
Epicenter is the point on the surface directly
above the focus
 Focus is the point of initial fault rupture and
the location where the earthquake originates
