Name:
PD.
Unit 3B – The Lithosphere
3.5 Plate Tectonics Notes
1.
2.
3.
4.
5.
Continental Drift
a. An idea before its time
i. Wegener’s ___________________________ hypothesis: continents had once been joint to form a single
supercontinent, ________________
1. Began to break apart _______ million years ago and starting forming present continents
b. Evidence
i. The continental puzzle – all of the continents fit together like the pieces of a puzzle
ii. Matching fossils:
1. ___________________: small reptile that swam in _______________ coastal waters. It could not
have crossed an ocean, yet its fossils are found in both South America and Africa.
2. ___________________: a land plant, is found in Africa, South America, Australia, India, and
Antarctica
iii. Rock Types and Structures
1. Rock evidence in form of ______________ belts that end at one coastline and reappear on a
landmass across the ocean  Appalachian system
2. Ancient _______________ (ex. Glacial deposits found in southern Africa and South America
c. Rejecting the hypothesis
i. Wegener could not provide a ___________________ for moving the continents
ii. He thought _____________ influence from the moon caused them to move (if true, it would stop the
rotation of Earth)
iii. Also thought continents _____________________ through the seafloor
Earth’s Magnetic Field
a. Magnetic field: invisible lines of _______________ that pass through Earth from one ____________ to another
b. A compass aligns with these lines and points toward the magnetic poles
c. Shown by a simple bar magnet
d. Earth’s Magnetic field every once in a while __________________ polarity
i. North magnetic pole becomes South magnetic pole, and vice versa
ii. Caused by movement heat around our molten iron core
Paleomagnetism
a. _________________ is the natural magnetism in rocks; this can be used to determine the location of the magnetic
poles at the time the rock became magnetized
b. Normal polarity - when rocks show the ____________ magnetism as the present-day magnetic field
c. Reverse polarity – when rocks show the ____________ magnetism as the present-day magnetic field
d. Magnetic striping on the Ocean Floor
i. The discovery of strips of alternating polarity, which lie as mirror images across ocean ridges, is among the
strongest evidence for ___________________________.
Seafloor Spreading
a. Seafloor spreading is the tectonic plates ____________________ from each other and making new ocean floor
material
b. Occur along ____________________ (large mountain ranges rising from the ocean floor)
c. These new developments led to a theory known as __________________________
i. Finally  Wegener’s missing mechanism!
d. Rates of spreading averages around _______ cm per year
i. Rapid enough so that all of Earth’s ocean basins are not older than ___________ million years old.
Layers of the Earth
a. Layers of the Earth are defined in two ways:
i. By composition (what each layer is made of)
ii. By physical properties (how each layer behaves)
b. Layers defined by composition
i. Three major zones defined by their chemical composition – the crust, _____________, and core
ii. Crust
1.
2.
3.
4.
6.
__________, rocky outer layer
Ocean crust (BASALTIC) is roughly _______ km thick, Continental crust (GRANITIC) averages
__________ km thick
Continental crust:
a. Dominant granitic composition
b. Average density is ________________
c. Up to ____________________ years old
Oceanic crust
a. Basaltic composition
b. Density is about ___________
c. _____________ (180 million years or less) than continental crust
iii. Mantle
1. Below crust and goes to a depth of ____________ kilometers
2. Composition of upper part is igneous rock _______________ (changes at greater depths)
iv. Core
1. Below the mantle
2. _____________ shape with a radius of 3,500 kilometers
3. Composed of __________________ alloy
4. Density of nearly 11 g/cm3
c. Layers Defined by Physical Properties
i. Lithosphere
1. Makes up crust and uppermost _________________ (about 100 km thick)
2. Cool, ____________, solid
ii. Asthenosphere
1. Beneath the lithosphere
2. Made of upper _____________
3. To a depth of about 660 kilometers
4. Soft, weak layer that is easily ________________ (think of as silly putty)
iii. Lower Mantle
1. 660-2900 km depth
2. More _____________ layer
3. Rocks are very __________ and capable of flow
iv. Outer core
1. ____________ layer
2. 2270 km thick
3. Heat flow of metallic iron makes Earth’s __________________________
v. Inner core
1. Sphere of radius 1216 km
2. Behaves like a ______________ (still the hottest part of Earth_  immense _________________
Plate Boundaries
a. The uppermost mantle, along with the crust above, behave as a strong, ____________ layer (lithosphere)
i. A ____________ is one of many rigid “parts” of lithosphere that move as a unit over the silly putty-like
Asthenosphere.
b. Divergent boundaries (also called spreading centers) are the places where two plates move __________________
c. Convergent boundaries form where two plates __________________ into each other
i. A ________________________ occurs where one OCEANIC PLATE is forced ____________ into the
mantle under another plate
ii. Ocean-continental convergence – less dense continental plate ______________ above and the denser
oceanic plate subducts, forming a CONTINENTAL ________________________ ARC.
iii. Ocean-ocean convergence – one oceanic plate subducts beneath another oceanic plate, forming a
VOLCANIC __________________ ARC.
iv. Continental-continental convergence - continental lithosphere CANNOT be subducted because it floats,
which forms ______________________ RANGES.
d.
7.
Transform boundaries are where two plates ________________ past each other, WITHOUT the production or
________________ of the lithosphere.
i. The grinding motion causes ________________________
1. Ex. San Andreas Fault off the coast of California
Future Plate Motions
a. The Atlantic Ocean will get ______________, but the Mediterranean Sea will ________________; as Africa collides
with Europe
b. Australia and Southeast Asia will JOIN, and California will move in the direction of ________________.
c. In 150 million years, further changes will have taken place
d. In 250 million years from now, another supercontinent _________________________ will appear
e. The Supercontinent Cycle
i. Several times in Earth history, the continents have joined to form one body, which later _____________
apart.
ii. The process seems cyclic; it shapes ______________ of a region and _______________, which influences
life on land.