The Cycling of Matter
4
Key Concept Over time, matter—such as rock, water,
carbon, and nitrogen—is transferred between organisms
and the physical environment.
What You Will Learn
rock cycle is the series of
• The
processes in which rock changes
•
•
from one form to another.
In the water cycle, water condenses,
precipitates, and evaporates through
the various spheres of Earth.
Nitrogen, carbon, and phosphorus
cycle between Earth’s spheres.
You probably know people who recycle paper, plastic, and
aluminum. But did you know that Earth also recycles? Very little
new matter enters the Earth system. So, existing matter must
cycle continuously for this planet to support life. Water, carbon,
nitrogen, phosphorus, and even rocks move through cycles. If
these materials did not cycle, Earth could not support life.
Why It Matters
The Changing Earth
The cycling of matter is important
to many Earth processes and to the
survival of organisms.
As matter cycles through the Earth system, the matter
changes. Earth’s surface also changes. Some of the processes
that cause change may take millions of years. For example,
mountains that are thousands of meters high form at rates
of only a few centimeters per year. Over time, this slow rate
of change adds up to big changes. Many changes have taken
place on Earth over a long period of time. As Figure 1 shows,
Earth’s history spans 4,600 million (4.6 billion) years!
Some changes happen very quickly. You may see them take
place in a single day. For example, the weather may change
from one hour to the next. Some cycles include steps that take
millions of years and steps that take days or hours. All of the
steps of all of these cycles constantly change Earth’s surface.
Ma ⫽ millions of years ago
-A
-A
Precambrian time (4,600 Ma to 542 Ma)
Cenozoic Era
Mesozoic Era
Paleozoic Era
The first crustal
rocks form.
The first known
life appears.
The first fungi
appear.
Earth’s atmosphere
starts to become
oxygen rich.
Earth’s surface
is cool enough for
liquid water.
Figure 1 It has taken 4.6 billion years
for Earth to become the way we know
it today. How many millions of years
ago did the first life appear?
104
Chapter 3
0RESENT
Outlining In your Science Journal,
create an outline of the section. Use
the headings from the section in your
outline.
-A
• rock cycle • carbon cycle
• water cycle • nitrogen cycle
-A
Vocabulary
Earth’s Systems and Cycles
The first shelled
organisms appear.
The Sierra Nevada
Mountains begin to
be uplifted.
Figure 2
The Rock Cycle
Sediment
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(EAT AND P
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-ELTIN
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Metamorphic
rock
Magma
Igneous
rock
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ERIN
Sedimentary
rock
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7EATHERING AND E
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-ELTIN
The Rock Cycle
One cycle that takes millions of years is the rock cycle. The
rock cycle consists of the processes by which rocks change from
one form to another. Several geologic processes can change rock
from one type to another. These processes include melting,
cooling, cementation, heat, pressure, weathering, and erosion.
Weathering is the process by which rock is broken down by
wind, water, and temperature changes. Erosion is the process
by which wind, water, ice, or gravity transport parts of the
weathered rock from one location to another. A diagram of
these processes is shown in Figure 2.
rock cycle (RAHK SIE kuhl) the
series of processes in which rock
forms, changes from one type to
another, is destroyed, and forms
again by geologic processes
Pathways in the Rock Cycle
Rocks may follow a number of pathways in the rock cycle.
For example, if it is exposed to weathering and erosion, igneous
rock may become sedimentary rock. But under intense pressure
and heat, igneous rock may become metamorphic rock. The
pathway that a rock follows in the rock cycle is determined
by the forces that act on the rock.
Forces That Change Rock
A rock’s location determines the forces that will act on the
rock. At Earth’s surface, rock exposed to agents of weathering
and erosion, such as wind and water, may become sedimentary
rock. But deep inside Earth, rock exposed to high heat and
pressure may become igneous rock or metamorphic rock.
Section 4
6.4.a Students know the sun is the major source of
energy for phenomena on Earth’s surface; it powers
winds, ocean currents, and the water cycle.
6.5.a Students know energy entering ecosystems
as sunlight is transferred by producers into chemical
energy through photosynthesis and then from
organism to organism through food webs.
6.5.b Students know matter is transferred over time
from one organism to others in the food web and
between organisms and the physical environment.
The Cycling of Matter
105
Classes of Rocks
Modeling the Rock Cycle
At home, you can use ordinary clay to model the steps
of the rock cycle. Flatten two
pieces of blue clay and two
pieces of red clay. All four
pieces should be the same
size and as flat as pancakes.
Lay the four pieces of clay on
top of one another. Be sure
to alternate the colors. Gently press the pieces together
without changing their shape.
Now, you have a model of
sedimentary rock. Next, apply
pressure to your sedimentary
rock by twisting and squeezing the rock. What class of
rock did you just model?
Which process of the rock
cycle did you model to form
this class of rock?
Geologists place all rocks into three major classes. These
classes are based on how the rocks form. The three major
classes of rocks are sedimentary, igneous, and metamorphic.
Sedimentary rocks form when rocks break into smaller pieces
and those pieces become cemented together. Igneous rocks form
when hot, liquid rock—called magma—cools and becomes solid.
Metamorphic rocks form when rock is changed because of chemical processes or changes in temperature and pressure. Figure 3
shows examples of the three major classes of rocks. Each class
of rock can be further classified into rock types based on composition and texture.
Sedimentary Rocks
Sedimentary rocks are divided into three types: clastic, chemical, and organic. Clastic sedimentary rocks are made of fragments of rock or minerals. Before they are cemented together,
these fragments of rock or minerals are called sediment. Clastic
sedimentary rocks form when sediments are buried, put under
pressure, and cemented by minerals such as calcite and quartz.
Chemical sedimentary rocks form when minerals crystallize
from a solution, such as ocean water. The minerals are buried,
put under pressure, and cemented together. Organic sedimentary rocks form when the shells and skeletons of dead marine
animals are buried and cemented by calcite or quartz.
Figure 3
Classes of Rocks
Sedimentary rock
Sandstone
Halite
106
Chapter 3
Earth’s Systems and Cycles
Coquina
Igneous Rocks
Igneous rocks are divided into groups based on the texture
of the rock, or the size of the crystals in the rock. Magma that
slowly cools deep inside Earth forms coarse-grained rocks made
of large crystals. Lava that erupts at Earth’s surface and quickly
cools forms fine-grained rocks made of very small crystals.
Igneous rock can also be classified by its chemical composition. The chemical composition of an igneous rock is determined by the type of rock that initially melts to form magma.
Magma from melted crustal material tends to form light-colored
igneous rocks, such as granite. Magma from Earth’s mantle
forms dark-colored igneous rocks, such as basalt.
Rock Brochure
Watch out, world. Here
come some new rock stars!
Create a brochure that
classifies “rock stars.” Go to
go.hrw.com, and type in the
keyword HY7MINW.
Metamorphic Rocks
Metamorphic rock is rock that forms from other rocks as a
result of intense heat, pressure, or chemical processes. Most metamorphic changes happen deep within Earth’s crust at depths
greater than 2 km. At these depths, pressure can be many times
greater than it is at Earth’s surface. Temperature is also much
higher at these depths than it is at Earth’s surface.
There are two types of metamorphic rocks. The minerals
of foliated metamorphic rock, such as gneiss, are arranged in
planes or bands. The minerals of nonfoliated metamorphic rock,
such as marble, are not arranged in planes or bands.
Igneous rock
Metamorphic rock
Gneiss
Granite
Basalt
Marble
Section 4
The Cycling of Matter
107
The Water Cycle
Quick Lab
Modeling the
Water Cycle
6.4.a
1. Start with a large, sealable, plastic freezer bag.
Be sure that the bag is
clean and dry and has no
leaks. Place a small, darkcolored bowl inside the
bag. Position the bag so that
the opening is at the top.
2. Fill the bowl halfway with
water. Place a three drops
of red food coloring in the
water. Seal the bag.
3. Place the bowl and bag
under a strong and warm
light source, such as a
lamp or direct sunlight.
4. Leave the bag in the light
for one hour. Observe the
bag at regular intervals.
5. How does this activity
model the sun’s role in the
water cycle?
The water cycle is the continuous movement of water
between the atmosphere, the land, and the oceans, as shown
in Figure 4. The sun is the major source of energy that powers the water cycle. Energy from the sun heats the water on
Earth. This heating of water causes water to change states. For
example, liquid water changes to water vapor.
Steps of the Water Cycle
Evaporation is the process in which liquid water changes
into gaseous water vapor. Water vapor is also released into
the air through pores on the leaves of plants. This process is
known as transpiration. If air that contains water vapor cools,
the water vapor turns into liquid water droplets and forms
clouds. The change from a gas to a liquid is called condensation. When water droplets become large enough, they fall back
to Earth as precipitation, such as rain.
Pathways of the Water Cycle
Most precipitation falls directly into the ocean and never
reaches the land surface. Precipitation that does reach the land
surface may fill lakes, streams, and rivers and eventually return
to the ocean. Water moving over the land surface is called
runoff. Gravity may move the water downward through spaces
in rock or soil, where the water becomes groundwater.
What is the major source of energy for the water
20 min
cycle?
6.4.a
0RECIPITATION
#ONDENSATION
Figure 4 Water cycles
from the ocean, into the
air, onto land, and back
into the ocean in the
water cycle.
2UNOFF
4RANSPIRATION
'ROUNDWATER
108
Chapter 3
Earth’s Systems and Cycles
%VAPORATION
Figure 5 Carbon cycles through
the Earth system in both rapid
and slow processes.
!TMOSPHERIC
CARBON DIOXIDE
#/
0HOTOSYNTHESIS
2ESPIRATION
#OMBUSTION
$ECOMPOSITION
%ROSION
%XTRACTION
#OAL
#/ DISSOLVED
IN WATER
/IL
,IMESTONE
"URIAL
.ATURAL GAS
0LANT AND ANIMAL
REMAINS
0LANT AND ANIMAL REMAINS
The Carbon Cycle
Carbon is an important element that cycles through the
Earth system. Carbon is part of the proteins, fats, and carbohydrates in living things. But carbon is not only in living things.
Carbon is also in the atmosphere, the water, the land, and the
remains of living things. The cycling of carbon between Earth’s
spheres is called the carbon cycle, as shown in Figure 5.
Short-Term Processes
Parts of the carbon cycle are relatively rapid processes. To
build plant material, plants use energy from the sun; from
carbon dioxide, CO2; and from water. When animals eat the
plants, the energy in the plants is transferred to the animals.
When the animals break down food to release energy, carbon is
returned to the air as CO2. Then, the CO2 is reused by plants.
When a living thing dies, other organisms break down the
remains. This process, called decomposition, releases the carbon
from the dead organism back into the cycle.
water cycle (WAWT uhr SIE kuhl)
the continuous movement of water
between the atmosphere, the land,
and the oceans
carbon cycle (KAHR buhn SIE kuhl)
the movement of carbon from the
nonliving environment into living
things and back
Long-Term Processes
Other parts of the carbon cycle are much slower processes.
In some cases, dead organisms are buried before they decompose. Their bodies chemically change as they are compacted for
millions of years. This process forms rock, such as limestone,
or fossil fuels, such as coal, gas, and oil. When humans burn
these fuels, carbon returns to the atmosphere as carbon dioxide.
This process of burning fuel is called combustion.
Section 4
The Cycling of Matter
109
Nitrogen in plants is
consumed by animals.
Bacteria in soil change
nitrogen into N2.
Bacteria in soil change
N2 into nitrogen plants
can use.
Figure 6 The nitrogen cycle
includes bacteria, plants, and
animals.
nitrogen cycle (NIE truh juhn
SIE kuhl) the process in which
nitrogen circulates among the air,
soil, water, plants, and animals in
an ecosystem
Decomposition releases
nitrogen into the soil.
The Nitrogen Cycle
The circulation of nitrogen among Earth’s spheres is called
the nitrogen cycle. This cycle is shown in Figure 6. Nitrogen is
an important nutrient for all living things. Certain bacteria in
soil change atmospheric nitrogen, N2, into forms of nitrogen
that plants can use. Other organisms get the nitrogen that
they need by eating plants. When organisms die, decomposers release nitrogen from the dead organisms back into the
soil. Then, plants use some of this nitrogen. Some bacteria in
soil change this nitrogen into atmospheric nitrogen, which
returns to the air.
The Phosphorus Cycle
Like carbon and nitrogen, phosphorus is found in living things. Phosphorus is also found in soil, rock, and water.
The roots of plants absorb phosphorus from the soil. Then,
animals obtain phosphorus when they eat the plants. When
the animals die, the phosphorus returns to the soil through
decomposition.
Other Cycles in Nature
Other forms of matter on Earth also pass through cycles.
Many of the minerals that living things need, such as the
mineral calcium, are cycled through the environment. When
a living thing dies, every substance in its body is recycled.
Each cycle is connected to other cycles in many ways. Some
forms of nitrogen and carbon are carried through the environment by water. Many nutrients pass from soil to plants to
animals and back. Living things play an important part in each
of the cycles and depend on the cycles for survival.
How is matter passed from one living thing to
another?
110
Chapter 3
6.5.b
Earth’s Systems and Cycles
Review
6.4.a, 6.5.a,
6.5.b
0 Analyzing Processes What is the importance
of gravity in the movement of water through the
water cycle?
Summary
processes that cycle matter in the Earth
• The
system can be relatively rapid or may take
millions of years.
rock cycle is the series of processes in
• The
which rock changes from one form to another
by geologic processes.
three major classes of rocks are sedimentary,
• The
igneous, and metamorphic.
moves continuously from the ocean, to
• Water
the atmosphere, to land, and back to the ocean
q Making Comparisons Compare the role of
decomposers with the role of plants in the
carbon cycle.
w Analyzing Processes How is combustion part
of the carbon cycle?
e Making Comparisons Compare combustion
and decomposition.
INTERPRETING GRAPHICS Use the diagram
below to answer the next two questions.
7i>Ì iÀˆ˜}
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through the water cycle.
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cycle, carbon cycle, and nitrogen cycle.
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1 Write an original definition for rock cycle, water
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of matter that are cycled through the
• Types
Earth system include carbon, phosphorus,
and nitrogen.
i«
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vÌ
In the carbon cycle, carbon is cycled in both
rapid processes and slow processes.
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iÌ>“œÀ« ˆV
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r Analyzing Processes Describe what needs
to happen in order for metamorphic rock to
change into igneous rock.
2 Describing Describe how igneous rock can
form into sedimentary rock.
3 Describing Describe the sun’s role in the
t Identifying Relationships What type of rock
forms when igneous rock is weathered and
eroded?
water cycle.
4 Describing Describe how sedimentary rock
can form into metamorphic rock.
5 Identifying Identify the steps in the water
cycle.
6 Identifying Identify the origin from which all
y Identifying Relationships Organisms get their
energy from eating other organisms. Where do
plants get their energy? What would happen to
all of the organisms on Earth if plants did not
have this source of energy?
living things on Earth get their energy.
7 Describing Explain the role that plants play in
the carbon cycle.
8 Summarizing How is matter transferred from
one organism to another?
9 Summarizing How is energy from the sun
Internet Resources
For a variety of links related to this
chapter, go to www.scilinks.org
Topic: Water Cycle; Cycles of Matter
SciLinks code: HY71626; HY70373
transferred from plants to animals?
111