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Unit 4
Chapter 10
Plate Tectonics
Section 1 Continental Drift
Wegener’s Hypothesis
____________________________________________________________
____________________. He stated that the continents seemed to fit
together and have since moved away from each other. According to
Wegener, the super continent started breaking up about 200 million years
ago.
Fossil Evidence
Wegener found similarities in the coastlines of the continents, and he found
other evidence as well. He found identical fossils of the ____________ that
were located on the coasts of Eastern South America and Western Africa.
This animal did not swim across the ocean.
Evidence from Rock Formations
Along with fossil evidence, rock evidence pointed to the lands being joined
at one time. The_____________________ extend Northward along Eastern
Coast of North America are the same age and structure of the mountains
found in _______________________________________.
Climatic Evidence
Ancient ______________ was found in Southern Africa and South America.
Missing mechanisms
Wegener could not come up with the “how” part of the hypothesis. He died
in _____before anyone would discover the actual answer.
Mid Ocean Ridges
In 1947 Scientists set out to map the Mid-Atlantic Ridge, which was part of
the underground mountain ranges. They discovered two surprising trends.
1.
_____________________________________________________
_____________________________________________________
__
2.
_____________________________________________________
_____________________________________________________
2
__
Sea-Floor Spreading
In the late 1950’s geologist ___________came up with a new hypothesis.
He proposed that the center valley was actually a ridge where molten rock
would come to the surface and fill the cracks and push the land away.
_____________renamed the process as “Sea Floor Spreading”. Hess’s
hypothesizes were proven with more evidence discovered in the mid 1960’s.
The evidence was discovered through paleomagnetism which is the study
of the magnetic properties of rocks.
Paleomagnetism
Paleomagnetism_______________________________________________
____________________________
_______________________
It has been discovered that Earth’s magnetic properties have changed
orientation. Since the rocks magnetism goes along with the magnetic field,
Scientists have discovered a pattern of normal (points north) and reversal
(points south) magnetic orientations in rocks along the mid ocean ridge. The
pattern it created is called the geomagnetic reversal time scale.
___________________________
Scientists discovered that our form the center of the mid ocean ridge to the
edges of the continents a pattern of normal and reversed polarity formed.
These patterns were mirror images on either side of the ridge. They also
discovered the youngest rocks were on either side of the ridge with the
oldest rocks by the continents.
The symmetry of both the magnetic patterns and the rock ages supports
Hess’s theory.
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Wegener Redeemed
Another group of scientists discovered the reversal pattern on land was
similar to the one in the ocean. This added to the support of the continental
drift theory. They also suggested that the mechanics involved was similar to
a conveyor belt moving on both sides of the mid ocean ridge.
Section 2 The Theory of Plate Tectonics
____________, the evidence supporting the continental drift theory and sea
floor spreading lead to a new theory called Plate Tectonics.
Plate Tectonics - _____________________________________________
__________________________________________________
How continents Move
Lithosphere - solid layer of crust & uppermost part of the mantle
-Similar composition (100 kms)
Two types of crust
Continental – ________________________________________________
Oceanic – ___________________________________________________
Asthenosphere - lower part of the lithosphere similar composition but much
hotter almost melted - the rock flows in CONVECTION CURRENTS
which allows the rigid upper crust to move.
Tectonic Plates
There are approximately 15 major plates that fit together on the earth’s
surface like a jigsaw puzzle.
http://www.p12.nysed.gov/osa/reftable/earthscience-rt/esrt2010-engw.pdf
Earthquakes
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_______________________________________________________
Volcanoes
____________________________________________________________
____________________________________________________________
__
Types of Boundaries
Boundaries are areas on Earth’s surface where volcanic and earthquake
activity occurs.
Diverging Boundaries
Convergent
Boundaries
_________________________________________
-
Subduction Boundary - __________________________________________
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Collision Boundary - _________________________________________
____________________________________________________________
Transform
Boundaries
__________________________________________
____________________________________________________________
_
Fault crack in the earth's crust where movement has occurred
San Andrea's Fault moves 5cm/year
Thin Skin Thrusting - pushing of thin rock layers at continental margins
over long distance (Appalachian Mountains)
Causes of Plate Motion
Mantle convection is the driving force of the plates.
movement of heated material.
Convection is the
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Mantle Convection
This is the heat transfer through the mantle where less dense, heated
material rises. The cooler denser material flows away from the hot
material and sinks back into the mantle to replace the rising material.
Moho – Real name Mohorovicic discontinuity
It is the boundary between the crust and the mantle where dense rock of the
mantle meets less dense rock of the crust. It is an average of 32 km
under the continents, and 8 km under the sea. This is where most of
the action occurs.
__________________________
This happens when the cooling lithosphere slides down the slope formed by
the elevation of the mid-ocean ridge. The force pushed the rest of the
plate away.
_______________________________
This happens when the leading edge of the subducting plate moves under
the upper plate. It pulls the plate back into the asthenosphere.
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Scientists believe that all three mechanisms together create the convecting
system that makes the Earth’s tectonic plates move constantly.
Section 3 The Changing Continents
The continents did not always look they way they do now and through time,
they will once again change shape and positions. Remember, we
are Dynamic.
Reshaping Earth’s Crust
Craton – ___________________________________________________
Shields – ___________________________________________________
Rifting and Continental Breakup
Rifting
_______________________________________________________
___________________________________________.It
s
the
pressure build up that causes the crust to break and move.
Terranes and Continental Growth
Terrane
It is a piece of lithosphere that has a unique geologic history
1. ________________________________________________
2. ________________________________________________
3. ________________________________________________
As oceanic crust subducts, a terrane is scraped off and becomes part of
the continental crust (accretion). It can also be continental crusts colliding.
The Himalaya Mountains formed this way 500 million years ago.
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Effects of Continental Change
When the continent moved, it changed the climate. The nearness of the
continent to the equator or the poles brought about a different
climate. The location by oceans and other continents plays an
important role too. When continents move, they also change the flow
of air round the globe.
Change in Climate
Geologic evidence shows ice once covered most of Earth’s surfaces.
Even
the
Sahara
had
ice.
This
occurred
about
_____________________ when all the land was located near the
South Pole.
Change in Life
The separating of the continents caused species to have to evolve into
different ones. Isolation of species also caused life to adapt to its
new environments.
The Supercontinent Cycle
When the continents are arranged as to create a large landmass called a
______________. These ________________break apart and can
form new and different ones. This is called the Supercontinent cycle.
Why Super Continents Form
Supercontinents form when convergent boundaries between two
continents collide, neither plate subducts, the boundaries become
inactive and a new supercontinent is formed. When the pressure
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builds up, the continent breaks apart.
Formation of Pangaea
Pangaea formed _____________________.
It also formed the
Appalachian Mountains and the Ural Mountains of Russia. The
Tethys Sea cut into Pangaea and the ocean that surrounded it was
later called Panthalassa.
Break up of Pangaea
_____________________during the Mesozoic Era, Pangaea broke up into
2 continents, Laurasia and Gondwanaland.
Laurasia drifted northward and rotated and then split into North America
and Eurasia with the North Atlantic Ocean between them. It also
shrank the Tethys Sea to become the Mediterranean Ocean.
Gondwanaland also changed, South America and Africa were formed.
Then about ___________ years ago a split began to happen
between South America and Africa opening up the South Atlantic
Ocean. The other chunk of Gondwanaland broke to form India,
Australia and the Antarctic. India started to move northward and at
about 50 million years ago, it collided with Eurasia to form the
Himalayan Mountains.
The Modern Continents
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As the continents continued to shift and collide, other features were
formed.
The
__________________________________________________were
all formed at this time.
Geology of the Future
Some Scientists believe in approximately 150 million years, Africa may
collide with Eurasia and the Mediterranean will close.
New
subductive zones will form by the East Coast of North and South
America and they will collide with Eurasia. The Atlantic Ocean will
disappear. Mexico’s Baja Peninsula will become part of Alaska. In
about 250 million years from now we will have another
supercontinent.