Download Chapter 17: Plate Tectonics

Chapter 17: Plate Tectonics
I. Continental Drift
A. Theory
1. the continents are continually moving around the Earth
2. Caused by forces deep within the Earth
B. Alfred Wegner
1. German born scientist
2. 1910 proposed the theory of continental drift
3. Is known as the “father” of plate tectonics.
4. Stated the continents were once on large super continent called
Pangaea
C. Wegner’s Evidence for Continental Drift
1. Continental Fit
a) continents appear to fit together like puzzle pieces
b) Wegner studied South America and Africa
2. Like fossils and minerals
a) similar plant fossils were found on the east coast of S. America
and the west coast of Africa
b) diamonds and other similar minerals are found on east coast of
S. America and the west coast of Africa
3. Evidence of past glaciers are found on both continents,
indicating that both continents were at a different latitude at
one time
II. Spreading Centers
A. Mid- Ocean Ridges
1. Areas where the ocean floor is spreading apart
2. Mid-Atlantic Ridge
a) World’s longest volcanic mountain range
b) almost completely underwater
B. Magnetic Reversals
1. Igneous rock records the magnetic polarity of the time when it turns
solid
a) recorded by the iron minerals in the liquid magma
b) each mineral acts like a miniature magnet
2. Reversed Polarity
a) Magnetic polarity is opposite of the direction it is today
b) Your compass would point to the south instead of north
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c) Has occurred many times in history and is recorded at the
Mid-Ocean ridges
C. Age of Igneous Rock
1. The ocean floor is made of basalt
2. The farther you travel from the ridge the older the basalt
a) new igneous basalt is constantly formed at the spreading center
3. Each side of the mid ocean ridge is like a mirror of the other side
a) see diagram of last page
D. Heat Flow
1. the highest measure of heat flow will be at the ridge
2. Heat flow decreases as you move away from the ridge
3. You can expect measurements for heat flow to be the same on each side
of the ridge at the same distance away from the ridge.
III. . Plate Tectonics
A. Modern Theory
1. The Earth is broken up into several sections called plates
2. explains how the plates move
a) lithosphere moves over the asthenosphere
B. Types of Plate Boundaries
1. Divergent plate boundary
a) area where two plates are moving away from each other
b) tension is pulling the plates apart
c) forms a normal fault
d) Ex.
e) The Mid-Atlantic Ridge is the most studied divergent boundary
2.Convergent boundaries
a) area where two plates are running into each other
b) Ocean-continent converging: the ocean plate always goes under
the continent. Ocean plates are more dense. The end of the ocean
plate melts and the rising magma forms volcanoes.
c)Ocean-ocean converging- the denser ocean plate goes underneath
the less dense ocean plate. The plate underneath melts and the
rising magma forms island arcs ( Ex. Japan)
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d) continent-continent converging- two continent plates crash into
each other. Neither plate will go underneath the other. Both plate
ends crumple and form mountains ( Ex, Himalayans, form as India
is crashing into Asia)
3.Transform (Sliding) Plate Boundaries
a) One plate is sliding past another
b) forms a transform fault
c) Ex. San Andreas Fault
III. Other Plate Tectonic Facts
A. How do plates move?
1. Movement is caused by huge convection currents
inside the Earth
B. Isostacy
1. The Crust is rising
a) rock material is eroded off the top of the crust
b) this decrease in weight allows the crust to rise
C. Crustal Thickness
1. Continental crust is thicker
a) is much less dense than ocean crust
b) will float on ocean crust
c) is mostly granite
2. Oceanic crust
a) is almost completely basalt
b) very dense
c) always sinks underneath continental crust
D. Hot Spot
1. An area in the middle of the crust with a high heat flow
a) magma is rising upward through the crust
2. Causes volcanoes and volcanic islands to form
a) Ex. Hawaii
3. The hot spot never moves
a) the plate moves over the hot spot causing old volcanoes to
become extinct and new volcanoes to form.
*You must also know your vocabulary
* The test will contain several application style questions.
*There will be some open-ended questions also for completion (these are worth more)
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