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A German scientist named Alfred Wegener
proposed a hypothesis called the continental
drift. Alfred Wegener hypothesized that the
continents once were all together in one mass,
this was called the super continent. Over
millions of years his hypothesis became a
reality the super continent began breaking
away into smaller continents over a peroid of
200 million years and to this present day they
remain where they drifted many years ago.
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Alfred's Wegener's hypothesis was correct, he
reasoned that if the continents had once been joined
fossils, plants and animals would be found in the
areas where the continents were once connected.
Geologic evidence supported Wegener's hypothesis
of continental drift due to the ages and types of rocks
in coastal regions separated areas now, but once
combined which now are western Africa and eastern
south America.
Climate changes also had a reason to support his
hypothesis because where the continents use to be it
had glaciers now in Southern African and South
America its way to warm for glaciers
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Problems
Despite Alfred's evidence of all things that
supported his hypothesis . Alfred's ideas were
strongly opposed by other scientists. They rejected
the mechanism by which Wegener proposed about
the supercontinent moving. Before he could find any
more geologic evidence to support his hypothesis
Alfred Wegener died in 1930.
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The supercontinent Pangaea formed about 300 million years ago
during the Paleozoic era. About 200 million years ago Pangaea
began to break away into 2 continents a large rift split the
continent from east to west. As this rift went on that’s how north
Atlantic ocean was formed another rift was made and split which
formed the south Atlantic ocean. With the continents in there
present position as they started to collide it welded new crust onto
the continents this formed mountain ranges such as the rocky
mountains and the indies. This caused new oceans to open but
also to close some to scientist predict that in 250 million years the
continents will collide back together and become one.
When all the continents were the supercontinent long ago there
was one single large ocean called pathalassa that covered earths
surface but as the continents moved into there current positions
new oceans formed and pathalassa didn’t exist anymore.
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Accretion is where terranes become part of a
continent, terranes forms mountains, while
some will just add surface area to a continent
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One way a continent can change is by breaking
apart from each other this process is called
rifting. As a result of rifiting happening new
smaller continents may form through this
process.
Scientists believe that as heat from the mantle
builds up beneath the continent the lithosphere
becomes thinner and begins to weaken and
eventually a rift will form in that zone and they
will begin to break apart.
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Geologic evidence shows that there is a lot of
climate change in many continents that have
had continental drift over the past 200 million
years ago. An example of this would be Sahara
in Africa, today it is one of the hottest places on
earth,but when the continents were together it
was covered by a thick ice sheet but over time
as the continents seperated tempertures
changed and the ice melted.
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Lithosphere is the solid outer layer of earth that
consists of The crust and the rigid upper part of
the mantle.
Plate tectonics is the theory that explains how
large pieces of the lithosphere form the thin
outer shell on earth the plates move and
change shape over time.
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Asthenosphere is the solid plastic
layer of the mantle beneath the
lithosphere it is made of mantle rock
that flows very slowly, which allows
tectonic plates to move on top of it .
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Tectonic plates can move from earthquakes this
happens because two or more plates will meet
in the same area and will have sudden
movements, volcanoes can make plates more
due to magma that erupts on earth surface.
Near the pacific ocean they have a lot of
earthquakes zones and active volcanoes , that’s
how we know its surrounded by plate
boundaries
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The 3 types of plates boundaries are divergent
convergent and transform bounders.
A divergent boundary-is a boundary that is
between tectonic plates that are moving away from
each other most divergent boundaries are located
on the ocean floor.
A convergent boundary-is a boundary that forms
were 2 plates collide. There are 3 types of
convergent boundaries that can happen in a
process.
Transform boundaries-are boundaries between
tectonic plates that are sliding past each other
horizontally.
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Isostatsy- its when two forces are balanced in
the lithosphere and asthenosphere, this occurs
when parts of earth crust changes.
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Isostatic adjustments is where movements of
the lithosphere to reach isostatsy as the isostatic
adjustments occur in areas of the crust are bent
up and down this bending causes rock in that
area deform.
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Stress-is the amount of force per unit area that
acts on a rock, as the earths lithosphere moves
the rock in the crust it squeezed stressed and
twisted , these actions exert force on the rock,
there are three types of stresses one is
compression , tension and the last one is shear
stress.
Sea-floor Spreading
 As divergent boundaries magma, from the
astherosphere rises to the surface as the plates
move apart. A mid-ocean ridge is the rock that
will sit higher than the sea floor because it will
be less dense. The Red Sea is an example of
this.
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An example of this would be the red sea which
occupies a big rift valley formed by the separation of
the African and Arabian plates
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Magnetic reversals
Geologic evidence says that the earth’s magnetic
field was not always pointing north. There are
rocks that are normal polarity and reversed
polarity. The rocks that the point north and in the
same time period are normal polarity. The rocks
that point south and fall into specific time periods
are reversed polarity. When scientists put the
periods of normal and reverse polarity in
chronological order, it made a pattern. This pattern
is called the geomagnetic reversal time scale.
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Magnetic symmetry-is a magnetic patterns on
the ocean floor. Scientists geomagnetic reversal
time scale to help them unravel the mystery of
these magnetic patterns.
They found rocks on the ocean floor that were
symmetrical the rocks in the center were the
youngest , and the oldest were on the ridges.
The fact is new rocks form at the center then as
they grow older the move away to the ridges.
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Normal fault-is a fault in which the hanging
wall moves downward relative to the footwall,
normal faults are commonly form at divergent
boundaries, where the crust is being pulled
apart by tension . Normal faults go up down
and side to side.
An example of normal fault is the great rift valley of
east Africa which was formed by large-scale normal
faulting.
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SUBDIVISION ZONE
Continental + Oceanic crust-the oceanic
lithosphere is dense so it will sink under
the continental lithosphere. As oceanic
plate sub ducts, it will heat up and
release fluids in the mantle above it all.
These fluids cause a material to melt
which will form magma.
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An example of this landform is volcanic mountains.
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Despite the high temperature in the mantle,
most of this zone remains solid because of the
large amount of pressure from the surrounding
rock. Sometimes however solid mantle and
crust melt to from magma or liquid rock that
forms under earths surface.
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Magma can form under three conditions . First
if the temperature of rocks above the melting
point of the minerals the rock is composed of
the rock will melt, second if enough pressure is
removed from the rock the melting point will
decrease and the rock will melt. Third the
addition of fluids such as water may decrease
the melting point of some minerals in the rock
and cause the rock to melt.
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When magma erupts onto earths surface the
magma is called lava. As lava flows from an
opening or vent the material may build up as a
cone of material that may eventually form a
mountain.
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The vent in earths surface through which
magma and gases are expelled is called a
volcano.
Volcanos occur near both convergent and
divergent boundaries of tectonic plates.
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The Pacific Ring of Fire (or just The Ring of Fire) is an area where a
large number of earthquakes and volcanic eruptions occur in the basin
of the Pacific Ocean. In a 40,000 km (25,000 mi) horseshoe shape, it is
associated with a nearly continuous series of oceanic trenches volcanic
arc, and volcanic belts and/or plate movements. The Ring of Fire has
452 volcanoes and is home to over 75% of the world's active and
dormant volcanoes. It is sometimes called the circum Pacific belt or the
circum Pacific seismic belt.
Eruption of Mount St. Helens on July 22, 1980.
About 90%of the world's earthquakes and 81% of the world's largest
earthquakes occur along the Ring of Fire. The next most seismic region
(5–6% of earthquakes and 17% of the world's largest earthquakes) is the
Alpide belt, which extends from Java to Sumatra through the
Himalayas the Mediterranean and out into the Atlantic. The MidAtlantic Ridge is the third most prominent earthquake belt.
If you were to plot the locations of the volcanoes
that have erupted in the past 50 years, you would
see that the locations form a pattern across earths
surface. Like earthquakes most active volcanoes
occur in zones near both convergent and
divergent boundaries.
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Consists of fragments of rock that form during
a volcanic eruption. When a volcano erupts the
dissolved gases within the lava escape and
send molten and solid particles shooting into
the air. So felsic lava tends to explode and
throw pyroclastic material into the air.
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Viscosity is a measure of the resistance of a fluid which is being
deformed by either shear stress or tensile stress. In everyday terms
(and for fluids only), viscosity is "thickness" or "internal friction".
Thus, water is thin having a lower viscosity, while honey is
"thick", having a higher viscosity. Put simply, the less viscous the
fluid is, the greater its ease of movement fluidity. Viscosity
describes a fluid's internal resistance to flow and may be thought
of as a measure of fluid friction. For example, high-viscosity
magma will create a tall, steep stratovolcano, because it cannot
flow far before it cools, while low-viscosity mafic lava will create a
wide, shallow-sloped shield volcano.
With the exception of superfluids, all real fluids have some
resistance to stress and therefore are viscous. A fluid which has no
resistance to shear stress is known as an ideal fluid or inviscid
fluid. In common usage, a liquid with the viscosity less than water
is known as a mobile liquid, while a substance with a viscosity
substantially greater than water is simply called a viscous liquid.
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Unlike the fluid lava produces by oceanic
volcanoes , the felsic lavas of continental
volcanoes such as mount St. Helens tend to be
cooler and stickier. Felsic lavas also contain
large amounts of trapped gases such as water
vapor and carbon dioxide.
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The first type of volcanoes is shield volcanoes , there
volcanic cones that are broad at the base and have gently
sloping sides. A shield volcano covers a wide area and
generally forms from quiet eruptions. Layers of hot lava
flow out around the vent.
The seconded type is a cinder cone, a type of volcano that
has very steep slopes. The slop angles od the cinder cone
can be close to 40 degree and the slopes are rarely more then
a few hundred meters high.
The third is a composite volcano , composite volcano are
made of alternating layers of hardened lava flows and
pyroclastic material. During a quiet eruption lava flows
cover the sides of the cone. Then when an explosive
eruption occurs large amounts of pyroclastic material are
deposited around the vent.
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Composite
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Cinder
Shield
caldera
When a magma chamber below a volcano
empties, the volcanic cone may collapse and leave
a large , basin-shaped depression. It erupts that
discharge large amounts of magma can also cause
a caldera to form . Krakatau a volcanic island in
indonesia .
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This collision happens by one plate that sub ducts
under the other plate. When this happens a deepocean trench is formed fluids are released from the
sub ducted plate which causes mantle rock to melt.
Which will form magma, Then the magma will rise
to the top and form an island arc. An island arc is
also a chain of volcanic islands.
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An example of landforms is japan.
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Continental + Continental Crust-in this collision the
continental lithosphere collide , but neither of them
sub duct because of the plates are not dense enough
to sub duct under the other plates
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The himalayas are an example.
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When colliding the edges crumple and thicken
which will cause up lifts that form large
mountain ranges.
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Reverse faults- a reverse fault if formed when
compression causes the hanging wall to move
upward relative to the footwall. A thrust fault is a
special type of reserve fault. This fault plane is at a
low angle of nearly horizontal, because of the low
angle, the rock on the hanging wall is pushed up and
over the rock of the footwall. You will find reverse
faults in the Rockies and the Alps.
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strike-slip fault happens when a fault plane slides
horizontal. This happens form chear stress
sometimes they can be vertical. This types of faults
commonly happen at transform boundaries. This is
where tectonic plates grind as they move in opposite
directions. These motions plates edges. Strike-slip
faults occur as groups of smaller faults.
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The stress that stretches and pulls a body apart
would be called tension. The rocks become
thinner when they are pulled apart by tension.
When tectonic plates pull apart it is tension.
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Shear stress distorts the body. This is caused by
the body being pulled in opposite directions.
When rocks are sheared they bend and break
apart or twist when sliding past each other.
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An example of reverse fault is the Rocky's and alps.
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Elastic rebound- scientists believe that elastic
rebound is a result of earthquakes. It is a
sudden return of elastically deformed rock it its
undeformed shape. The rocks on each side of a
fault rock move very slowly. If the fault is
locked , stress in the rocks increase. When the
rocks are stressed past the point at which they
can maintain their integrity, they fracture. The
rocks then separate at their weakest point and
rebound.
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Many scientists study earthquakes because
earthquakes are the best tool earth scientists
have for investigating earths internal structure
and dynamics. These scientists have developed
special sensing equipment to record locate and
measure earthquakes. Seismology is the study
of earthquakes and seismic waves.
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Seismograph is vibrations in the ground that
can be detected and recorded by using and
instrument.
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A modern 3 component seismograph consists of 3
sensing devices. One device records horizontal
motion one from eat to west motion and the other
for north to south motion. Seismographs record
motion into electronic signals.
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The location within earths along a fault at
which the first motion of an earthquake occurs
is called the focus.
Although the focus depths of earthquakes vary
about 90% of continental earthquakes have a
shallow focus. Earthquakes that have foci take
place within 70km of earths surface
earthquakes that have an immediate foci occur
at depths between 70km to 300km
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The point of the earths surface directly above an
earthquakes starting point or focus.
As rocks along a fault slip into new positions, the
rocks release energy in the form of vibrations.
These waves travel outward in all directions from
the focus through the surrounding rock
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Body waves can be put into two main
categories S waves and P waves also called as
primary waves or compression waves
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P waves cause particles of rock to move in a
back and forth direction that is parallel to the
direction in which the waves are traveling. P
waves can move through solids liquids and
gases.
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S waves are called secondary waves or shear
waves are the second fastest seismic waves and
arrive at detection sites after p waves. S waves
cause particles of rock to move in a side to side
direction that is perpendicular to the direction
in which the waves are traveling .
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Surface waves form from motion along a
shallow fault or from the conversation of
energy when P waving and S waves reach
earths surface . Although surface waves are the
slowest moving waves they may cause the
greatest damage during an earthquake.
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Seismic waves are useful to scientists in
exploring earths interior. The compostion
material through the P waves and S waves
travel affects the speed and direction of the
waves. P waves travel fastest through materials
that are very rigid and are not easily
compressed.
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Not all earthquakes result from movement along plate boundaries. The
most widely felt series of earthquakes in the history of the united states
did not occur near an active plate boundary. Instead these earth quakes
occurred in the middle of the continent near New Madrid , Missouri, in
1811 and 1812. The vibrations from the earthquakes that rocked New
Madrid were so strong that they caused damage as far away as South
Carolina.
The measure of the strength of an earthquake is
called magnitude. Magnitude is determined by
measuring the amount of ground motion caused
by an earthquake. Seismologists express
magnitude by using a magnitude scale.
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Before the development of magnitude scales
the size of an earthquake was determined
based on the earthquakes effects. A measure of
the effects of an earthquake is the earthquakes
intensity.
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It expresses intensity in roman numerals from 1
to 12 and provides a description of the effect of
each earthquake intensity.
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An earthquake whose epicenter is on the ocean floor may cause a
giant ocean wave .
Tsunami cause serious destruction if it crashes into land. A
tsunami may begin to form when a sudden drop or rise in the
ocean floor occurs because of faulting associated with undersea
earthquakes.
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An example of hot spots are Hawaiian Islands. Hot
spots are volcanically active areas that lie far from
tectonic plate boundaries.
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An example of a dome mountain is the black
hills of south Dakota and the Adirondack
mountains of New York. Dome mountains
form when tectonic forces gently uplift rock
layers.