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_____________________.
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__________________.
Lithoshere - 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_________________.
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).
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).
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.
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.
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 midoceanic 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 midoceanic 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 ___________.