Plate Tectonics
Continental Drift –
1. The first theory of continental drift was suggested by the German meteorologist
Alfred Wegener in 1912 (1906/1915).
2. The hypothesis stated that the continents consist of _______________ rocks that
rest on heavier crustal material—similar to the manner in which icebergs
________________ on water. Wegener contended that the positions of the
continents are not always in the same position but are slowly_______________—at
a rate of about one meter per century.
3. The theory of continental drift states that Earth’s continents were joined in a
single large landmass (called Pangaea) that broke________________, and that the
continents have drifted to their positions that they have today.
What Evidence Did Alfred Wegener Have For The Theory of Continental
Drift?
1. Shape of the Continents – The shape of the continents look like they should fit
together like _______________ pieces.
2, Fossil Evidence - Wegener found that identical fossils, that could not
________________ or ____________ across 3,000 miles of ocean, were located
directly opposite on widely separated continents. This had been realized previously
but the idea of "land bridges" was the most widely accepted solution. Wegener
found _________________ to be convincing evidence that a supercontinent had
existed in the past.
Example: Mesosaurus
3. Rock Type and Structural Similarities - We find similar _____________ types
on continents on opposite sides of the Atlantic Ocean. Similar age, structure and
rock types are found in the Appalachian Mountains in North America and
mountains in Scotland and Scandinavia.
When the continents are reassembled or put back together, the mountain chains
from a continuous belt — having the same rock types, structures and rock
_______________.
4. Climatic (climate) Evidence – Cold areas show evidence of once having been
____________ while hot areas show evidence of once being _______________.
For example, coal needs a ____________ humid climate to form. It does not form
in areas of extreme________________. Although Antarctica is extremely cold, it
has huge ______________ deposits. Also warm-climate
_______________________ plants and animals have been found in Antarctica and
also the cold Arctic areas of North America. This indicates that at one time in the
past, Antarctica and the Arctic areas of North America must have been physically
closer to the_____________________.
5. Glacial Evidence - Glacial evidence was left behind in the form of glacial
grooves which are deep scratches in rocks made as the glaciers moved across land
and rock deposits left behind as the glaciers melted away called glacial till. These
grooves (scratches) and till were found in parts of Africa, South America, Australia,
and India. Currently these areas are too warm to have glaciers.
Wegener's idea of continental drift was not generally accepted because no one could
come up with a reasonable mechanism (way) for the movement of the continents
(How did the continents ___________________?). It was not until the 1960's that
further data led to the development of the theory of plate tectonics that could
explain the ___________________ of continents.
The Theory of Plate Tectonics
Plate Tectonic Theory – The Earth’s surface is composed of Lithospheric plates
that “______________” atop the Asthenosphere and are in
constant__________________.
Lithosphere - The rigid and solid area that includes the ____________ and the
uppermost portion of the______________.
Asthenoshere - The lower part of the upper mantle that exhibits _______________
and plastic (flowing) properties.
 This is a far-reaching theory that has become the basis for understanding
many geologic processes such as mountain_______________,
_________________, and___________________.
 There are 12 major plates and many smaller plates which move in
different__________________. Plates move slowly but continuously on the
order of a few cm/year.
 This plate motion causes them to_________________, pull_______________,
or scrape against each_________________.
Plate Boundaries
There are 3 distinct types of boundaries:
1. divergent — plates move _________________ from one another
2. convergent — plates _____________________ into one another (collision)
3. transform — plate grind ____________________ one another
Each plate is bounded by a variety of plate boundaries.
New plates can be created by forces that split plates apart such as at the East
African Rift Valleys.
Two plates may come ________________________ to form one plate such as may
happen with the Himalayans.
2. http://www.youtube.com/watch?v=mB2pzhWUaiU&feature=related – 8min all types
3. http://www.youtube.com/watch?v=nfziy_860GU - convergent plates 4min
2a http://www.youtube.com/watch?v=0mWQs1_L3fA all types –
1. http://www.teachersdomain.org/resource/ess05.sci.ess.earthsys.lp_platetectonics/ used first intro and
further evidence and scientist
What Forces Cause The Plates to Move?
At the boundary of any moving plate earthquakes are formed.
Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
These plates in the lithosphere are made of rock that is lightweight compared with
the_______________, hot, fluid layer underneath (________________________).
This allows plates to ride and ____________________ on top of hot, denser,
flowing rock. Plates move because ________________ is being released from deep
inside the earth. Convection currents causes hot material to ______________ and
expand (plates diverge –move apart) and _____________________ material to sink
and contract (plates converge - move into each other). The plates move very
_________________ on the surface, about 5cm per year. Convection currents are
movements of fluids (________________and ____________) by unequal heating.
Hot fluids ______________ and cold fluids_________________.
In summary the asthenosphere is heated by the Earth’s ________ causing
convection currents. These convection currents cause the _______________ of the
plates. Where hot magma rises it causes the plates to diverge (move __________
from each other) and where ____________ magma sinks it causes the plates to
converge (______________ into each other).
What Geological Features do the Moving Plates Produce?
Convergent Boundary – This forms when plates_____________. The pressure and
violence at convergent boundaries produce folded or fault-block ______________,
bands of________________, ________________activity, and ___________
(Japan). The movement of one plate under another is called subduction.
Subduction happens at converging plate boundaries. When a plate undergoes
subduction, the rocks in that plate are pushed deep into the _______________
where they are heated and changed into molten material called _____________ (A
temperature hot enough to melt lithosphere is about a thousand degrees!). This
molten material, which is under great_________________, can escape through
weak spots in Earth’s crust as an erupting___________________. Where colliding
ocean and continental plates occur deep ocean valleys called
___________________ are formed. These trenches are the deepest area of the
ocean (the Mariana Trench in the western Pacific Ocean 10924 meters deep). These
subduction zones occur when dense ______________ plates collide with less dense
________________ plates. The ___________ heavier oceanic plates are pushed and
forced down into the ___________________ and the _______ dense lighter
continental plates are pushed up forming folded and/or volcanic mountains.
When two less dense _______________ plates collide the two plates are both
pushed up forming folded __________________ such as the Himalayan Mountain
range in Asia.
Folded Mountains
Fault-Block Mountains
How colliding plates affect the rock cycle
This process affects the rock cycle producing new ____________rock or
___________________ rock. New igneous rocks are produced as the
________________ inside the Earth or ____________________ erupting from a
volcano cools to form rocks. Also the great ____________________ and
_____________ produced by the converging plates can cause rocks to be into
changed into metamorphic rocks (called contact metamorphism).
Divergent Plates – This forms when two plates diverge, or _____________ from
each other. Melted rock from the mantle can move to the surface at divergent
boundaries and form new _______________. Most divergent boundaries are in the
oceans (Atlantic Ocean has been forming for about 180 million years). Here, they
build undersea __________________ ranges called mid-oceanic ridges. Also
major ___________________ occur and where the molten rock pushes up above
the ocean ____________________ islands form (Iceland). When divergent plates
occur on _______ within a continent they can form continental rifts or enormous
splits in the Earth’s _________. Faults are created in the cold upper part of the
________ where large blocks of crust move downward creating __________
between ridges. The East African Rift is splitting ____________ into two parts at
the rate of 3-6 mm a year. In conclusion when plates diverge they can produce
mountains, volcanoes and earthquakes.
How plates moving apart affect the rock cycle
As the molted magma hardens under the surface or reaches the ocean floor as lava
new ________________ rock is formed. In conclusion when plates diverge they
can produce_____________, ______________, and _______________.
Transform Boundary – This forms where two plates slide ________________
each other. The sliding causes rocks along the boundary to grind past each other
from time to time, causing jolts that you feel as _____________________. In the
United States the San Andres Fault is an example of two plates sliding past each
other.
Volcanoes And Earthquakes Are Closely Linked To The Margins Of The
Tectonic Plates.
Anytime there is movement along a plate boundary _________________ occur.
The movements occur along faults, which are large ______________ in the Earth’s
crust. Rocks on either side of a fault are under great _________________ and get
locked together. When too much pressure builds up, the rocks suddenly slide past
each other and release the_________________. The longer the plates lock up
before releasing energy the ___________________ the earthquake.
Volcanoes occur when plates converge (come _____________) or diverge (move
________________) from each other.
Volcanoes that do not Form over Plates called Hot Spots
Not all volcanoes form on or near ____________ boundaries. ______________ in
the Hawaiian Islands are far from plates. Volcanoes not associated with
___________ boundaries are called hot spots. Scientists believe that rising
___________ currents deep within the Earth’s mantle cause hot _____________ to
rise. Where the hot ____________rises it is called a plume. A __________ forms
right above the rising magma caused by rising convection currents. As a plate
moves away from the hot spot the volcano attached to the plate will no longer be
directly over the rising magma. When this occurs the volcano becomes
_____________, or inactive. A new volcano will start to form over the hot spot
underneath the rising magma caused by rising _________________
______________.
Location of Plate Boundaries.
Location of Major Earthquakes
Locating of Major Volcanic Areas
What Evidence Exists For The Theory of Plate Tectonics?
1. The same evidence for __________________ _________ that was discussed
earlier.
2. As plates move apart new material is erupted out of __________________
and rock fissures to fill the gap. This is occurring at the mid-oceanic ridge.
This causes a slow steady movement of the sea-floor crust away from the
center. The movement is eastward toward Europe and Africa and westward
toward North and South America. Measurements of the age of sea-floor rocks
show very_______ rocks closest to the ridge and _____ rocks farther away
from the ridge. The composition of rocks is on both sides of the ridge is the
same.
oldest rock
oldest rock
The above diagram shows the spreading of rock at the mid-oceanic ridge
where the ______________ rocks are at the center and
___________________ at the edges.
3. Paleomagnetism - The Earth's _______________field produces invisible
lines of force that extend from one pole to the other. A compass needle aligns
itself with these lines of force — points toward the magnetic poles. When
igneous rocks containing magnetic _____________ minerals crystallize and
harden, the crystals in the rocks become __________________ in a direction
of the Earth’s magnetic field. Earth's magnetic field periodically reverses
polarity (direction of the _______________ and _______________ magnetic
pole) — the north and south poles switch.
Rocks crystallizing during one
of these periods of magnetic reversal will be magnetized with a polarity
opposite of __________________ that crystallize earlier.
These ______________ rocks provide evidence of the different locations of
the Earth’s magnetic poles at the time when the rocks were formed. An
example is at the mid-oceanic ridge ___________________ rocks formed new
patterns in two long bands on each side of the ridge where the rocks poured
out. The __________________ ______________ of the rock then points
toward the magnetic pole that existed when the rock formed. Scientists have
studied magnetic volcanic rocks at the mid-ocean ridge. The rocks magnetic
field acts as a "fossil compass." There is an exact copy of the direction of the
Earth’s magnetic field on both sides of the ___________.