Download The Rock Cycle

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

Mudrock wikipedia , lookup

Igneous rock wikipedia , lookup

Sedimentary rock wikipedia , lookup

Transcript
1
The Rock Cycle
1
Overview
You know that paper, plastic, and aluminum can be
recycled. But did you know that the Earth also recycles?
And one of the things that Earth recycles is rock.
READI NG WARM-U P
This section introduces the
rock cycle and the processes
that shape the surface of the
Earth. The processes of weathering, erosion, deposition, uplift,
melting, cooling, and metamorphism are explained, in
the context of the rock cycle.
Objectives
•
•
•
Describe two ways rocks have been
used by humans.
Describe four processes that shape
Earth’s features.
Describe how each type of rock
changes into another type as it
moves through the rock cycle.
List two characteristics of rock that
are used to help classify it.
•
Bellringer
Terms to Learn
rock cycle
rock
erosion
Pose the following questions
to students:
• How can rock be recycled?
deposition
composition
texture
READI NG STRATEGY
• How long would recycling a
rock take?
Reading Organizer As you read this
section, make a flowchart of the steps
of the rock cycle.
• What would the rock look
like before, during, and after
the process of recycling?
Scientists define rock as a naturally occurring solid mixture of
one or more minerals and organic matter. It may be hard to
believe, but rocks are always changing. The continual process
by which new rock forms from old rock material is called
the rock cycle.
The Value of Rock
Rock has been an important natural resource as long as humans
have existed. Early humans used rocks as hammers to make
other tools. They discovered that they could make arrowheads,
spear points, knives, and scrapers by carefully shaping rocks
such as chert and obsidian.
Rock has also been used for centuries to make buildings,
monuments, and roads. Figure 1 shows how rock has been
used as a construction material by both ancient and modern civilizations. Buildings have been made out of granite,
limestone, marble, sandstone, slate, and other rocks. Modern
buildings also contain concrete and plaster, in which rock is
an important ingredient.
✓Reading Check
Name some types of rock that have been used
to construct buildings. (See the Appendix for answers to Reading Checks.)
Discussion ----------------------------------g
Geologic Time Some students
may not realize how long
changes in the rock cycle take.
The processes that shape rock
can take millions to tens of
millions of years. Discuss the
geologic time scale with students
to give them a perspective of
how long the Earth has existed
and how long these processes
have been affecting the Earth.
Figure 1 The ancient
Egyptians used a sedimentary rock called
limestone to construct
the pyramids at Giza (left).
Granite, an igneous rock,
was used to construct the
Texas state capitol building
in Austin (right).
l Logical
CHAPTER RESOURCES
Chapter Resource File
CRF
• Lesson Plan
• Directed Reading A b
• Directed Reading B s
Technology
Transparencies
• Bellringer
90
Chapter 4 • Rocks: Mineral Mixtures
Answer to Reading Check
Types of rock that have been used by humans
to construct buildings include granite, limestone, marble, sandstone, and slate.
Processes That Shape the Earth
Certain geological processes make and destroy rock. These
processes shape the features of our planet. These processes
also influence the type of rock that is found in a certain area
of Earth’s surface.
Weathering, Erosion, and Deposition
Group
rock a naturally occurring solid
mixture of one or more minerals
or organic matter
rock cycle the series of processes
The process in which water, wind, ice, and heat break down rock
is called weathering. Weathering is important because it breaks
down rock into fragments. These rock and mineral fragments
are the sediment of which much sedimentary rock is made.
The process by which sediment is removed from its source
is called erosion. Water, wind, ice, and gravity can erode and
move sediments and cause them to collect. Figure 2 shows an
example of the way land looks after weathering and erosion.
The process in which sediment moved by erosion is dropped
and comes to rest is called deposition. Sediment is deposited
in bodies of water and other low-lying areas. In those places,
sediment may be pressed and cemented together by minerals
dissolved in water to form sedimentary rock.
in which a rock forms, changes
from one type to another, is
destroyed, and forms again by
geological processes
erosion the process by which wind,
water, ice, or gravity transports soil
and sediment from one location to
another
deposition the process in which
material is laid down
Heat and Pressure
Sedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of
sediment. If the temperature and pressure are high enough at
the bottom of the sediment, the rock can change into metamorphic rock. In some cases, the rock gets hot enough to
melt. This melting creates the magma that eventually cools
to form igneous rock.
How the Cycle Continues
Buried rock is exposed at the Earth’s surface by a combination
of uplift and erosion. Uplift is movement within the Earth that
causes rocks inside the Earth to be moved to the Earth’s surface.
When uplifted rock reaches the Earth’s surface, weathering,
erosion, and deposition begin.
Figure 2 Bryce Canyon,
in Utah, is an excellent
example of how the processes
of weathering and erosion
shape the face of our planet.
v -------g
Rates of Weathering
Tombstones can be used to
determine rates of weathering.
In the 1960s, professor E. M.
Winkler calculated the weathering rate for a marble marker in
Indiana to be 1.5 mm in 43 y. In
1916, American geologist D. C.
Barton estimated the weathering
rate for granite monuments near
the Nile River to be only 1 to
2 mm per millennium! With
your students, visit a cemetery,
and measure weathering rates
of grave markers. Quartz veins
in marble markers do not erode
easily. Students can measure
how much the marble has
eroded relative to a quartz vein.
By dividing the amount that a
grave marker has eroded by the
number of years the stone has
been standing (the date of
death), students can calculate
the rate of weathering.
l Visual/Kinesthetic
Cultural
Awareness
g
Stone Cities Between
900 and 1400 CE, the
Anasazi Indians of the
American Southwest carved
small towns in cliff sides.
In what is now Cambodia,
a vast temple complex called
Angkor was carved from clay,
sandstone, and laterite in
the 12th century. In the
1300s, African traders built
the Great Zimbabwe, a walled
city guarded by huge monoliths. Have students write a
report or build a model of
one of these ancient sites.
Writing
MISCONCEPTION
ALERT
Weathering, Erosion, and Deposition
Some students may be confused by
weathering, erosion, and deposition.
Explain that weathering is the process
that actually breaks down rock, whereas
erosion is the removal and transport
of the sediment that is formed by
weathering. Deposition is the process by
which sediments are dropped in a new
location. The processes of weathering
and erosion are not easy to separate
because they happen simultaneously.
l Logical/Kinesthetic
Section 1 • The Rock Cycle
91
Illustrating the Rock Cycle
You have learned about various geological processes, such as
weathering, erosion, heat, and pressure, that create and destroy
rock. The diagram on these two pages illustrates one way that
sand grains can change as different geological processes act on
them. In the following steps, you will see how these processes
change the original sand grains into sedimentary rock, metamorphic rock, and igneous rock.
Using the Figure -----g
Diagramming the Rock
Cycle Ask students
to use the information in the
rock-cycle illustration to draw
a diagram of the rock cycle in
their science journal. The
first step in the illustration is
the formation of sedimentary
rock; ask students to begin their
rock cycle with a different step.
Encourage them to write a
descriptive caption for every
stage of the rock cycle. l Visual
PORTFOLIO
ion
Dep
osi
tio
n
Eros
MISCONCEPTION
ALERT
Rock Cycle Misconceptions
Rocks rarely undergo the
complete process shown
in the rock-cycle diagram.
Sedimentary rocks can
become igneous rocks,
and metamorphic rocks can
become sedimentary rocks.
Also, some students may not
realize the length of time it
takes for changes to occur in
the rock cycle. The process
shown in the diagram can
take millions to tens of
millions of years.
1
Sedimentary Rock Grains of sand and other
sediment are eroded from hills and mountains
and wash down a river to the ocean. Over
time, the sediment forms thick layers on the
ocean floor. Eventually, the grains of sediment
are compacted and cemented together to form
sedimentary rock.
Compaction and
cementation
2
Me
ta
m
or
phi
sm
Metamorphic Rock When
large pieces of the Earth’s
crust collide, some of the
rock is forced downward.
At great depths, intense
heat and pressure heat and
squeeze the sedimentary
rock to change it into
metamorphic rock.
INCLUSION
Strategies
• Learning Disabled
• Hearing Impaired
• Attention Deficit Disorder
Groups will use different foods to model
sedimentary, metamorphic, and igneous
rocks and minerals. Have real rock samples
available (enough for each group). Organize students into groups of three or four
students. Give students a chocolate-chip
cookie to model granite (igneous), a sugar
cube to model marble (metamorphic), a
brownie to model shale (sedimentary), a
92
Chapter 4 • Rocks: Mineral Mixtures
magnifying glass, a large sheet of paper, and
magic markers. Ask students to describe and
sketch their three samples. To describe each
sample, students should note the sample’s
texture, color, and composition. On the
board, compile descriptions for each “rock”
from each group. Pass real rock samples
to each group, and have the groups
match their samples to
e
the real rocks. l Visual
v------------------------------------------b
hering
Weat
5
Sediment Uplift and erosion
expose the igneous rock at the
Earth’s surface. The igneous rock
then weathers and wears away
into grains of sand and clay. These
grains of sediment are then transported and deposited elsewhere,
and the cycle begins again.
Solidification
Rock Dictionary Have students prepare a Rock Dictionary.
Ask them to list the three types
of rock and the processes that
occur in the rock cycle. Ask students to record the dictionary
definition for each rock type or
rock-cycle process and then
define it in their own words.
Encourage students to make
up mnemonic devices, such
as jokes or rhymes, to help
them remember the meaning
of each term.
l Logical
4
Igneous Rock The sand grains from
step 1 have changed a lot, but they
will change more! Magma is usually
less dense than the surrounding rock,
so magma tends to rise to higher
levels of the Earth’s crust. Once there,
the magma cools and solidifies to
become igneous rock.
Cooling
CONNECTION v
Language Arts -----------------------------b
Passing Through
Ask students to imagine
being an ancient grain
of sand on a beach. Have them
write a letter describing their
lifetime in the rock cycle. The
grain of sand should pass
through several processes in
the rock cycle during its lifetime.
Students can share their letters
with the class.
Writing
l Intrapersonal
3
Mel
ting
Magma The hot liquid that forms when rock partially or completely melts is called magma. Where
the metamorphic rock comes into contact with
magma, the rock tends to melt. The material
that began as a collection of sand grains now
becomes part of the magma.
Is That a Fact!
Geologists can use the Earth’s magnetic
field to determine the approximate age
of rocks. They examine both igneous
and sedimentary rocks to determine
the pattern of magnetic reversals. When
these rocks form, the magnetic minerals
they contain orient with the direction
of the Earth’s magnetic field. The
pattern of magnetic reversals allows
scientists to date the rock layers.
CHAPTER RESOURCES
Technology
e
e
h -----------------------------g
Illustration Have students
make a poster that illustrates
the rock cycle. Encourage them
to cut out pictures from magazines of the different types of
rock and processes in the rock
cycle. For example, marble is a
metamorphic rock that could be
represented by a picture of a
marble statue.
l Visual
e
Transparencies
• The Rock Cycle
Section 1 • The Rock Cycle
93
Figure 3
Awareness
Sedimentary rock
g
g
in n
s io
W
an ea
d th
e
Igneous rock
Co
ol
in g
e r io n
s
ro
Avicenna The Persian
scholar Avicenna (980–1037)
contributed immensely to
our knowledge of medicine,
astronomy, mathematics,
and geology. In the Book of
Minerals, he described how
rivers and seas laid down sediment that eventually became
rock. Avicenna’s theories contributed to the foundations
of Western geology. Many
of his controversial ideas did
not gain acceptance in Europe
until the 1600s. Encourage
students to learn more about
Avicenna. Have them come
to class as Avicenna and act
out his life story. l Logical
He
pr e at a
ssu nd
re
W
a n d e at h
er er
o
Cultural
The Rock Cycle
in g
Metamorphic rock
Me
ltin
g
Magma
Round and Round It Goes
You have seen how different geological processes can change
rock. Each rock type can change into one of the three types of
rock. For example, igneous rock can change into sedimentary
rock, metamorphic rock, or even back into igneous rock. This
cycle, in which rock is changed by geological processes into
different types of rock, is known as the rock cycle.
Rocks may follow various pathways in the rock cycle. As
one rock type is changed to another type, several variables,
including time, heat, pressure, weathering, and erosion may
alter a rock’s identity. The location of a rock determines which
natural forces will have the biggest impact on the process of
change. For example, rock at the Earth’s surface is primarily
affected by forces of weathering and erosion, whereas deep
inside the Earth, rocks change because of extreme heat and
pressure. Figure 3 shows the different ways rock may change
when it goes through the rock cycle and the different forces
that affect rock during the cycle.
CONNECTION to
Environmental
Science -----------------------------------------------a
Cycles in Nature Many
important substances on Earth
follow cycles. Examples include
water, carbon, and rock. Use the
teaching transparency entitled
“The Water Cycle” to lead a
discussion about the ways that
the water cycle and the rock
cycle interact with each other.
l Visual
✓Reading Check What processes change rock deep within
the Earth?
CHAPTER RESOURCES
Technology
Transparencies
• LINK TO LIFE SCIENCE The Water Cycle
Workbooks
Math Skills for Science
• Percentages g
94
Chapter 4 • Rocks: Mineral Mixtures
Answer to Reading Check
Rock within the Earth is affected by
temperature and pressure.
Answer to Math Practice
Rock Classification
100% of rock (30% quartz ! 55%
feldspar) " 15% biotite mica
You have already learned that scientists divide all rock into
three main classes based on how the rock formed: igneous,
sedimentary, and metamorphic. But did you know that each
class of rock can be divided further? These divisions are also
based on differences in the way rocks form. For example, all
igneous rock forms when magma cools and solidifies. But
some igneous rocks form when magma cools on the Earth’s
surface, and others form when magma cools deep beneath the
surface. Therefore, igneous rock can be divided again based on
how and where it forms. Sedimentary and metamorphic rocks
are also divided into groups. How do scientists know how to
classify rocks? They study rocks in detail using two important
criteria—composition and texture.
What’s in It?
Assume that a granite sample
you are studying is made of
30% quartz and 55% feldspar
by volume. The rest is made
of biotite mica. What percentage of the sample is biotite
mica?
Composition
The minerals a rock contains determine the composition of that
rock, as shown in Figure 4. For example, a rock made of mostly
the mineral quartz will have a composition very similar to that
of quartz. But a rock made of 50% quartz and 50% feldspar
will have a very different composition than quartz does.
✓Reading Check
Figure 4
composition the chemical makeup
of a rock; describes either the minerals or other materials in the rock
Group
v -----------b
Describing Rocks Organize
the class into small groups.
Give each group samples of
sandstone, limestone, and conglomerate. Number the samples.
Provide a magnifying lens, a
mineral identification key, a
small dental pick, and paper
towels (to capture any pieces
of rock that break off during the
activity). Write the following
instructions on the board:
1. Describe the color and texture
of each rock.
What determines a rock’s composition?
2. Using your unaided eye,
examine the grains that make
up each rock. Describe what
you see.
Two Examples of Rock Composition
The composition of a rock depends on the
minerals the rock contains.
3. Using the magnifying lens,
Granite
Limestone
try to identify the mineral
composition of each rock.
99 A
010
10% Biotite mica
4. Use the dental pick to test
how well each rock is
cemented, and record what
you discover.
5. Classify each rock by grain
size as fine grained, medium
grained, or coarse grained.
95% Calcite
5% Aragonite
35% Quartz
55% Feldspar
After groups have analyzed the
rocks, have group members discuss their findings.
l Logical/Kinesthetic
CONNECTION to
Math ---------------------------------------------------------------------------g
Percentages A percentage is a ratio that
is expressed in terms of hundredths. When
analyzing pure substances, percentage composition remains the same at any mass.
For example, in terms of atomic mass, the
percentage of oxygen by weight in water is
88.8%, whether you are describing a single
raindrop or an entire ocean. l Logical
e
Answer to Reading Check
The minerals that a rock contains
determine a rock’s composition.
Section 1 • The Rock Cycle
95
Figure 5
Fine-grained
Reteaching -------------------------------------b
Diagramming the Rock Cycle
Have students create a diagram
of the processes that shape
Earth’s surface. The diagram
should be a simplified version
of the rock cycle. The diagram
should include the processes of
weathering, erosion, deposition,
and uplift. l Visual
Quiz ---------------------------------------------------------------------g
1. List four processes that
change rock from one type to
another. (weathering, changes
in pressure, melting, and cooling)
Three Examples of Sedimentary Rock Texture
Medium-grained
Siltstone
Sandstone
Conglomerate
Texture
texture the quality of a rock that is
based on the sizes, shapes, and positions of the rock’s grains
2. What are the three main
classes of rock? (igneous, sedimentary, and metamorphic)
3. How is a brick similar to a
metamorphic rock? (Bricks
are made from clay and then
baked to become strong and
resistant to weathering. Bricks
are “metamorphosed” by high
temperatures.)
The size, shape, and positions of the grains that make up a rock
determine a rock’s texture. Sedimentary rock can have a finegrained, medium-grained, or coarse-grained texture, depending
on the size of the grains that make up the rock. Three samples
of textures are shown in Figure 5. The texture of igneous rock
can be fine-grained or coarse-grained, depending on how much
time magma has to cool. Based on the degree of temperature
and pressure a rock is exposed to, metamorphic rock can also
have a fine-grained or coarse-grained texture.
The texture of a rock can provide clues as to how and
where the rock formed. Look at the rocks shown in Figure 6.
The rocks look different because they formed in very different ways. The texture of a rock can reveal the process that
formed it.
✓Reading Check
Give three examples of sedimentary rock
textures.
Figure 6
Alternative
Assessment ---------------------------g
Texture and Rock Formation
Basalt, a fine-grained igneous
rock, forms when lava that
erupts onto Earth’s surface
cools rapidly.
Rock Cycle Skit Have students
write a skit portraying the rock
cycle. Roles can include the
minerals that make up rock and
the forces that affect them. To
represent the forces—heat, pressure, erosion, and weathering—
suggest that students create
special costumes. l Kinesthetic
Answer to Reading Check
Fine-grained rocks are made of small grains,
such as silt or clay particles. Medium-grained
rocks are made of medium-sized grains, such
as sand. Coarse-grained rocks are made of
large grains, such as pebbles.
96
Coarse-grained
Chapter 4 • Rocks: Mineral Mixtures
Sandstone, a medium-grained
sedimentary rock, forms when
sand grains deposited in dunes,
on beaches, or on the ocean
floor are buried and cemented.
Answers to Section Review
Review
Summary
• Rock has been an important natural
•
resource for as long as humans have
existed. Early humans used rock to make
tools. Ancient and modern civilizations
have used rock as a construction material.
Weathering, erosion, deposition, and uplift
are all processes that shape the surface
features of the Earth.
• The rock cycle is the continual process
by which new rock forms from old rock
material.
• The sequence of events in the rock cycle
depends on processes, such as weathering,
erosion, deposition, pressure, and heat,
that change the rock material.
Composition and texture are two characteristics that scientists use to classify rocks.
•
• The composition of a rock is determined
by the minerals that make up the rock.
• The texture of a rock is determined by the
size, shape, and positions of the grains that
make up the rock.
Using Key Terms
Complete each of the following sentences by
choosing the correct term from the word bank.
rock
composition
rock cycle
texture
1. The minerals that a rock is made of determine
of that rock.
the
2.
is a naturally occurring, solid mixture of
crystals of one or more minerals.
Understanding Key Ideas
3. Sediments are transported or moved from their
original source by a process called
a. deposition.
b. erosion.
c. uplift.
d. weathering.
4. Describe two ways that rocks have been used
by humans.
Critical Thinking
8. Making Comparisons Explain the difference
between texture and composition.
9. Analyzing Processes Explain how rock is
continually recycled in the rock cycle.
Interpreting Graphics
10. Look at the table below. Sandstone is a type of
sedimentary rock. If you had a sample of sandstone that had an average particle size of 2 mm,
what texture would your sandstone have?
Classification of Clastic
Sedimentary Rocks
Texture
Particle size
coarse grained
> 2 mm
medium grained
0.06 to 2 mm
fine grained
< 0.06 mm
5. Name four processes that change rock inside
the Earth.
6. Describe four processes that shape Earth’s
surface.
7. Give an example of how texture can provide
clues as to how and where a rock formed.
For a variety of links related to this
chapter, go to www.scilinks.org
Topic: Composition of Rock
SciLinks code: HSM0327
CHAPTER RESOURCES
Chapter Resource File
CRF
• Section Quiz g
• Section Review g
• Vocabulary and Section Summary g
1. composition
2. Rock
3. b
4. Rocks have been used by
humans to make tools and
weapons and to construct
buildings.
5. Four processes that
change rock inside the Earth
are compaction and cementation, metamorphism, melting,
and cooling.
6. Weathering is the process
by which water, wind, ice,
and heat break down rock.
Erosion is the process by which
sediment is removed from its
source. Deposition is the process by which sediment moved
by erosion is laid down. Uplift
is the process by which rock
within the Earth moves to
Earth’s surface.
7. Answers may vary. Sample
answer: Fine grains in an
igneous rock indicate that
the rock cooled quickly, which
means it was likely to have
formed at Earth’s surface.
8. Composition is the percent
of elements that make up a
rock. Texture is a quality of
a rock that is based on the
size, shape, and position
of its grains.
9. Answers may vary. Sample
answer: Rock is continually
recycled by different processes
in the rock cycle. Melting of
sedimentary, metamorphic,
or igneous rock creates new
igneous rock. The weathering,
erosion, deposition, burial, compression, and cementation of
igneous, metamorphic, or sedimentary rock creates new
sedimentary rock. Igneous,
sedimentary, or metamorphic
rock that is subjected to
increased heat and pressure
can be metamorphosed.
10. a medium-grained texture
Section 1 • The Rock Cycle
97