Download Chapter 21 Guided Reading

Chapter 21 Guided Reading- Planet Earth
Section 1- Earth’s Interior and Plate Tectonics
What is Earth’s Interior Like?
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We live on the topmost layer of Earth – the _____________. Because the ____________ is relatively
cool, it is made up of ___________, _____________ rock. The crust beneath the ocean is called
______________________. ____________________ crust is less dense and thicker than oceanic crust.
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Beneath the crust lies the ________________, a layer of rock that is denser than the crust. The
_______________ makes up about ____________ of Earth’s volume. For the most part, the mantle is
_____________. The outermost part is _____________ like the crust. Deeper than a few hundred
Kilometers, however, it is extremely hot, and said to be plastic—soft and easily deformed, like a piece
of ___________.
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The center of the Earth, the ____________ is believed to be composed mainly of _____________ and
________________. It has __________ layers. The _________________, which is solid metal, is
surrounded by the liquid metal ___________________.
Plate Tectonics
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Around 1915, a German scientist named ___________________________ noticed that the eastern coast
of South America and the western coast of Africa appeared to fit together like pieces of a
_____________. Wegener found that several other continents’ coastlines also seemed to fit together.
He pieced all the continents together to form a ________________________ that he called
_______________________.
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Using __________________ evidence, Wegener showed that ____________________ years ago the
same kinds of animals lived on continents that are now oceans apart. He argued that animals could not
have evolved on separate continents.
Evidence for Wegener’s ideas came later
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The evidence for _____________________ or the theory that Earths surface is made up of large moving
plates, was compelling. However, scientists did not have an explanation of how continents could move.
Wegener’s theory was ignored until the mid-1960s, when structures discovered on the ______________
floor gave evidence of a mechanism for the slow movement of the continents, or continental drift.
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In the 1960s, evidence was discovered in the middle of the ________________ that helping explain the
mechanisms of __________________________. New technology provided images of “bands” of
______________ on the ocean floor with alternating ________________ polarities.
Alignment of oceanic rock supports the theory of moving plates
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As molten ____________ pours out onto the ocean floor, iron minerals such as magnetite align
themselves parallel to Earth’s __________________________, just as compass needles do. The result
is a permanent record of Earth’s magnetic field as it was just before the rocks cooled.
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So, why are there differently oriented magnetic bands of rock? Earth’s magnetic field has ___________
direction many times during its history, with the _______________ magnetic pole become the ________
magnetic pole and the ____________ magnetic pole become the ____________ magnetic pole. This
occurs on average once every ___________________ years. This process is recorded in the rocks as
_______________. These magnetic bands are symmetrical on either side of the
____________________________. The rocks are ____________________ near the center of the ride.
The farther away from the ridge you go, the ________________ the rocks appear. This suggests that the
crust was moving ________________ from the plate boundary.
Earth has plates that move over the mantle
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The ____________________ is approximately __________ thick and is made up of the
______________ and the upper portion of the ________________. The lithosphere is made up of about
_____________ large pieces (and several ____________ pieces) called _________________________.
The theory describing the movement of plates is called _______________________________.
Plate Boundaries
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The theory of plate tectonics helps scientists study and sometimes predict ________________________
and has provided information on ________________________. Volcanoes and earthquakes often occur
where ________________________ come together. At these ________________________, many other
dramatic geological features, such as ___________________ and ___________________ can occur.
Mid-oceanic ridges result from divergent boundaries
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A _____________________________ occurs where two plates move ______________, creating a gap
between them. When this happens, hot rock rises from the asthenosphere and cools, forming new
lithospheric rock.
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Mid-oceanic ridges are __________________________ at divergent boundaries in the oceanic crust.
Unlike most mountains on land, which are formed by _________________ and _______________ of
continental crust, mid-oceanic ridges are mountain ranges created by _____________ rising to Earth’s
surface and cooling. As the plates move apart, magma rises from between the diverging plates and fills
the gap. The new oceanic crust forms a large valley, called a ______________________, surrounded by
high mountains.
Oceanic plates dive beneath continental plates at convergent boundaries
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Knowing that lithosphere is being created, you may wonder why Earth isn’t expanding. The reason is
that while new lithosphere is formed at _______________ boundaries, older lithosphere is destroyed at
_____________________ boundaries. The Andes Mountains, formed along a ____________________
boundary between an ______________ plate and the South American ____________________ plate.
The oceanic plate, which is _______________, dives beneath the _______________________ plate and
drags the oceanic crust along with it. This process is called _______________________. Ocean
trenches, mountains, and volcanoes are formed at _______________________ zones.
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Ocean _______________ form along the boundary between two _____________ plates or between an
_________________ plate and a ___________________ plate. These trenches can be very deep. The
deepest is the
_________________ trench in
the Pacific Ocean.
Subduction of ocean crust
generates volcanoes
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Chains of often-explosive
volcanic mountains form on
the overriding plate at
___________________ zoneswhere _______________ crust meets ______________________ crust.
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Volcanic mountains also form at ________________________ boundaries.
Colliding tectonic plates create mountains
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The Himalayas are the tallest mountains. They formed during the collision between the
_____________________ tectonic plate containing ______________ and the Eurasian continental plate.
Transform fault boundaries can crack Earth
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Plate movement can cause breaks in the ________________________. Once a break occurs, rocks in
the lithosphere continue to move, scraping past nearby rock. The crack where rock moves is called a
_______________. Faults can occur is any area where forces are great enough to _____________ rock.
When rock moves horizontally at faults along plate boundaries, the boundary is called a
______________________________ boundary.
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Plate movement at transform fault boundaries is one cause of _____________________. Transform
fault boundaries occur in many places across Earth, including the ___________ floor.
Section 2- Earthquakes and Volcanoes
What are Earthquakes?
Compare the occurrence of earthquakes, shown as red dots in Figure 13 in your book, with the plate
boundaries marked by black lines. Each red dot marks the occurrence of an earthquake sometime between
1985 and 1995.
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You can see that earthquakes occur mostly at the boundaries of _______________________, where the
plates shift with respect to one another.
SKIP TO PAGE 716
Most volcanoes occur at convergent plate boundaries
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Like earthquakes, _______________________ are linked to plate movement. _________________ are
common all around the edges of the Pacific Ocean, where _______________ tectonic plates collide with
___________________________ plates. In fact, ____________ of the active volcanoes on Earth are
located in these areas. The volcanoes around the Pacific Ocean lie in a zone known as the
__________________________.
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As a plate ____________ at a convergent boundary, it causes ___________ in the mantle and
_________________ rises to the surface. The volcanoes that result form the edges of the
___________________________.
Underwater volcanoes occur at divergent plate boundaries
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As plates move ___________ at divergent boundaries, ___________ rises to fill the gap. This magma
creates the __________________________ that form the ridges around a central _____________ valley.
Volcanoes occur at hot spots
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Some volcanoes occur in the _______________ of plates. They occur because mushroom-shaped trails
of hot rock, called _______________________________, rise from deep inside the mantle, melt as they
rise, and erupt from volcanoes as _______________________ at the surface.
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When mantle plumes form below _________________________, lava and ash build up on the
______________ floor. If the resulting volcanoes grow large enough, they break through the water’s
surface and become ___________________. As the ____________________________ continues
moving, however, the ____________________ does not move along with it. The plume continues to
rise under the moving oceanic plate, and a new _______________ is formed at a different point. A
_______________ in the form of a _____________ of extinct volcanic islands is left behind.
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The _______________________________ lie in a line that roughly corresponds to the motion of the
_______________ plate. The island of ______________ is the most recently formed in the chain, and
contains the active volcanoes situated over the mantle plume.
Section 3- Minerals and Rocks
Structure and Origins of Rocks
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All rocks are composed of ______________________. Minerals are naturally occurring, nonliving
substances that have a composition that can be expressed by a _____________________ formula.
Molten rock cools to form igneous rock
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When molten rock cools and solidifies it forms _______________________.
Remains of older rocks and organisms form sedimentary rocks
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Even very hard rock with large crystals will break down over thousands of years. The process by which
rocks are broken down is called _______________________. Pieces of rock fall down hillsides due to
gravity or get washed down by ____________ and ____________. Rivers then carry the pieces down
into deltas, lakes, or the sea. Chemical processes also knock pieces of rock away. The action of
_________________ and ___________________ weathering eventually breaks the pieces into pebbles,
sand, and even smaller pieces.
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As pieces of rock accumulate, they can form another type of rock-- _________________________ rock.
Rocks that undergo pressure and heating without melting form metamorphic rock
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____________ and ____________________ within Earth cause changes in the ________________ and
______________________________ of rocks. These changes produce _______________________
rocks.
Old rocks in the rock cycle form new rocks
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The sequence of events in which rocks
can be weathered, melted, altered, and
formed is described by the
__________________.
How Old are Rocks?
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Rocks form and change over
__________________ of years. It is
difficult to know the exact time when a
rock formed. To determine the age of
rocks on a geologic time scale, several techniques have been developed.
The relative age of rocks can be determined using the principle of superposition
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Think about your hamper of dirty clothes at home. If you don’t
disturb the stack of clothes in the hamper, you can tell the relative
time the clothes were places in the hamper. In other words, you
may not know how long ago you placed a particular red shirt in the
hamper, but you can tell that the shirts above the red shirt were
placed there more recently. In a similar manner, the
_________________________ of rocks can be determined using the
_______________________________________. The principle of superposition states the following:
Assuming no ___________________ in the position of the __________ layers, the ____________ will
be on the bottom, and the _________________ will be on top.
Now answer these questions from your textbookPg 708 # 1-6
Pg 732 # 4,5,7,10,18,22,28,
Pg 717 # 3 and 5
Pg 734 # 1,2,6
Pg 724 # 1,2,3