Download Objective 8 - Reading Guide pages 150

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Objective 8 - Reading Guide pages 150-154
The Theory of Plate Tectonics
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2.
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4.
5.
Earth’s ____________________ , its solid outer shell, is not one unbroken layer. It is broken into pieces
separated by jagged __________________.
A Canadian scientist, _____________ ________________, observed that there are cracks in the
_________________________ similar to those on the ocean floor.
In ______________, Wilson proposed that the lithosphere is broken into separate sections called
____________________. The plates fit together along cracks in the ____________________.
Wilson combined what geologists knew about sea-floor spreading, Earth’s ___________, and
______________________ drift into a single theory.
A __________________ _________________ is a well-tested concept that explains a wide range of
______________________.
How Plates Move
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2.
3.
4.
5.
The theory of ______________ _________________ states that pieces of the Earth’s lithosphere are in
slow, constant motion, driven by ____________________ _____________________ in the mantle.
The theory of __________________ ______________________ explains the ______________________,
_______________________, and ____________________ of Earth’s plates.
________________________ think that movement of ___________________ currents in the mantle is the
major force that causes __________________ motion.
During ________________________, gravity pulls one edge of a plate down into the mantle and the rest of
the plate also moves. This ____________ movement is similar to what happens in a pot of soup when gravity
causes cooler, denser soup near the surface to sink.
As the plates move, the ____________, pull apart, or grind past each other, producing spectacular changes in
Earth’s surface. These changes include __________________, mountain ranges, and deep-ocean
_____________________.
Plate Boundaries
1.
The edges of Earth’s plates meet at plate ________________________. Plate ______________________
extend deep into the lithosphere.
2. ________________________ - breaks in the Earth’s crust where rocks have slipped past each other – form
along these _______________________________.
3. There are three kind of boundaries __________________________, ______________________, and
____________________________ boundaries. A ___________________ type of plate movement occurs
along each type of __________________.
4. Scientists have used instruments on _________________________ to measure plate motion very precisely.
The plates move at slow rates: from about ______ to 24 cm a year. The North American and
___________________ plates are moving at a rate of ________ cm per year.
Divergent Boundaries
1.
The place where two plates move apart, or __________________, is called a _____________________
boundary. Most ___________________ boundaries occur along the mid-ocean ridges where
___________________________________ spreading occurs.
2. Divergent boundaries also occur on _________________. When a divergent boundary develops on land, two
of Earth’s ___________________ slide ________________________.
3. A deep valley called a _________________ ________________________ forms along the divergent
boundary. For example, the Great Rift Valley in East ___________________.
Convergent Boundaries
1.
2.
3.
4.
5.
6.
The place where two plates come together, or ____________________, is called a ____________________
boundary.
When two plates converge, the result is called a _________________________. When two plates collide, the
_____________________ of the plates determine which one comes out on top.
________________________ crust becomes __________________ and denser as it spreads away from the
mid-ocean ridge. Where two plates carrying _________________ crust meet at a trench, the
____________________ that is more dense sinks under the other plate.
Sometimes a plate carrying ______________________ crust collides with continental crust.
__________________ crust is more dense than continental crust. The _______________ dense continental
crust can’t ____________ under the more dense _________________ crust. Instead,
________________________ occurs as the oceanic plate sinks beneath the __________________________
plate.
When _____________ plates carrying continental crust _______________, _________________ does not
take place. Neither piece of _______________ is dense enough to sink very far into the ________________.
Instead, the ____________________ squeezes the crust into mighty mountain ranges.
Transform Boundaries
1.
A _______________________ boundary is a place where two plates slip past each other, moving in
__________________ directions.
2. ______________________________ often occur along transform boundaries, but _______________ is
neither created nor destroyed.
Plate Motions Over Time
1.
The movement of _____________ plates has greatly changed Earth’s surface. Geologists have
____________________ that, before Pangaea existed, other supercontinents formed and __________ apart
over _____________________ of years.