Download 14.4 Resources from the Seafloor

HSES_1eTE_C14.qxd 5/16/04 1:00 PM Page 410
Section 14.4
14.4 Resources from the Seafloor
1 FOCUS
Section Objectives
14.10
14.11
14.12
Identify ocean resources used
for energy production.
Explain how gas hydrates
are formed.
List other types of ocean
resources.
Key Concepts
Which ocean resources are
used for energy
production?
Vocabulary
◆
◆
gas hydrates
manganese nodule
Reading Strategy
Identifying Details Copy the concept map
below. As you read, complete it to identify
details about resources from the ocean.
How are gas hydrates
formed?
Sand and Gravel
What other resources are
derived from the ocean?
consist of
a.
?
are used for
b.
?
sometimes contain
c.
?
Reading Focus
Build Vocabulary
L2
Paraphrase Have students explain, in
their own words, the meanings of the
new vocabulary terms in this section,
plus the terms evaporative salts and
halite. Have students write their
definitions and share them.
Reading Strategy
T
he ocean floor is rich in mineral and organic resources. Recovering
them, however, involves technological challenges and high costs. As
technology improves we are able to access some of these resources more
efficiently. However, other resources, such as manganese nodules,
remain untouched.
L2
a. rock fragments and shells of marine
organisms
b. landfill, recreational beaches,
concrete
c. diamonds, tin, platinum, gold,
titanium
2 INSTRUCT
Energy Resources
Figure 13 Offshore drilling rigs
tap the oil and natural gas
reserves of the continental shelf.
These platforms are near Santa
Barbara, California.
Inferring What changes to the
marine environment may occur as
a result of drilling for oil?
Energy Resources
L2
Students may have the misconception
that sand contains only the mineral
silicon. However, the term sand refers
more to particle size (smaller than gravel
but larger than silt) than to mineral
content. Ask students to explain how
they think sand is formed. Guide them
to understand that sand particles are
made up of minerals that come
primarily from pulverized rocks, which
have varying compositions. Sand
particles can also come from pulverized
shells of marine organisms.
Logical
410 Chapter 14
410 Chapter 14
Most of the value of nonliving resources in the ocean comes from their
use as energy products.
Oil and natural gas are the main energy
products currently being obtained from the ocean floor. Other
resources have the potential to be used as a source of energy in the future.
Oil and Natural Gas The ancient remains of microscopic
organisms are the source of today’s deposits of oil and natural gas.
These organisms were buried within marine sediments before they
could decompose. After millions of years of exposure to heat from
Earth’s interior and pressure from overlying rock, the remains were
transformed into oil and natural gas. The percentage of world oil produced from offshore regions has increased from trace amounts in the
1930s to more than 30 percent today. Most of this increase is due to the
continual update of the technology used by offshore drilling platforms
such as the one shown in Figure 13.
Major offshore reserves exist in the Persian Gulf, in the Gulf of
Mexico, off the coast of southern California, in the North Sea, and in the
East Indies. Additional reserves are probably located off the north coast
of Alaska and in the Canadian Arctic, Asian seas, Africa, and Brazil. One
HSES_1eTE_C14.qxd 5/16/04 1:00 PM Page 411
L1
Use Visuals
A
B
environmental concern about offshore petroleum exploration is the possibility of oil spills caused by accidental leaks during the drilling process.
Gas Hydrates Gas hydrates are compact chemical structures
made of water and natural gas. The most common type of natural gas
is methane, which produces methane hydrate. Gas hydrates occur
beneath permafrost areas on land and under the ocean floor at depths
below 525 meters.
Most oceanic gas hydrates are created when bacteria break
down organic matter trapped in ocean-floor sediments. The bacteria
produce methane gas along with small amounts of ethane and propane.
These gases combine with water in deep-ocean sediments in such a way
that the gas is trapped inside a lattice-like cage of water molecules.
Vessels that have drilled into gas hydrates have brought up samples of mud mixed with chunks of gas hydrates like the one shown in
Figure 14A. These chunks evaporate quickly when they are exposed to
the relatively warm, low-pressure conditions at the ocean surface. Gas
hydrates resemble chunks of ice but ignite when lit by a flame, as
shown in Figure 14B. The hydrates burn because methane and other
flammable gases are released as gas hydrates evaporate.
An estimated 20 quadrillion cubic meters of methane are locked up
in sediments containing gas hydrates. This amount is double the
amount of Earth’s known coal, oil, and natural gas reserves combined.
One drawback to using gas hydrates as an energy source is that they
rapidly break down at surface temperatures and pressures. In the
future, however, these ocean-floor reserves of energy may help provide our energy needs.
What happens when gas hydrates are brought to
the surface?
Figure 14 Gas Hydrates
A A sample from the ocean floor
has layers of white, ice-like gas
hydrate mixed with mud.
B Gas hydrates evaporate when
exposed to surface conditions,
releasing natural gas that can be
burned.
Figure 14 Have students examine the
photos of gas hydrates. Ask: Why do
you think the burning gas hydrate
does not burn the hands of the
person holding it? (Accept reasonable
hypotheses. This demonstration could be
done only with a large chunk of gas
hydrate. As the gas hydrate slowly
dissociates, it releases methane from all
surfaces. Methane is less dense than air,
so it quickly rises and tends to concentrate
above the sample. A combustible mix of
methane and air is reached just above the
upper surface, so the flame is confined to
that region. At the lower surface, there is
not enough methane to combust. The
person’s hands are contacting only the
lower portion of the hydrate, which
remains cool enough to handle. It would
be more prudent to wear asbestos gloves
or place the hydrate on a metal screen, as
there is always a risk of getting burned.)
Logical, Verbal
Build Science Skills
Inferring Remind students that when
water freezes, the molecules arrange
themselves in a lattice structure that
takes up more space than liquid water.
This lattice contains open spaces that
are large enough to hold methane
molecules. If methane molecules enter
those spaces during lattice formation, a
hydrate may be produced. The presence
of methane molecules inside the cavities
helps hold the hydrate crystal together.
Point out to students that methane is
produced by bacteria involved in the
decomposition of organic matter. Ask:
Why do gas hydrates form only
where there is plenty of decaying
organic matter? (Bacteria involved in
decomposition produce methane, which
is required for gas hydrate formation.)
Logical, Verbal
For: Links on ocean resources
Visit: www.SciLinks.org
Web Code: cjn-5144
The Ocean Floor
L2
411
Answer to . . .
Download a worksheet on ocean
resources for students to complete,
and find additional teacher support
from NSTA SciLinks.
Figure 13 Drilling platforms may
provide structure for some marine
organisms to live on; drilling may
disturb some organisms or destroy
habitats; an oil spill could be harmful
to organisms in the immediate area
Gas hydrates evaporate
quickly at surface
temperature and pressure.
The Ocean Floor 411
HSES_1eTE_C14.qxd 5/16/04 1:00 PM Page 412
Section 14.4 (continued)
Other Resources
Other Resources
L2
Students may not think that ordinary
tap water contains minerals that would
precipitate out during evaporation.
Guide students to understand that,
because water is the universal solvent,
there is virtually always something
dissolved in it. Heat tap water in a pan
with a black Teflon© coating. When the
water boils off, a white residue remains
of mineral salts. Explain that there are
a number of physical and chemical
processes that can be used to remove
non-water molecules and ions from a
sample of water. Have students look up
information about the effectiveness of
various water purification methods, such
as distillation, active carbon filtration,
and ozone treatment systems.
Logical, Verbal
Evaporative Salts
L2
Objective Students observe that any
salt dissolved in water is left behind
when the water evaporates.
Skills Focus Observing, Measuring,
Comparing, Drawing Conclusions,
Predicting
Prep time 10 minutes
Class Time 10–15 minutes to set up;
5 minutes to make final measurements
Expected Outcome Students find that
all of the salt they put into the water is
left behind when the water evaporates.
Analyze and Conclude
1. The masses should be equal.
2. It is left behind (precipitates out).
3. Certain areas with proper conditions
could be used to evaporate water and
collect solid salt.
Kinesthetic, Logical
For Enrichment
L3
Have students evaporate water taken
from a variety of sources (tap water,
rainwater, bottled water) to determine
if an evaporite is left behind. Students
could test any evaporite they obtain for
the presence of minerals.
412 Chapter 14
Figure 15 These manganese
nodules lie 5323 meters on the
Pacific Ocean floor south of the
island of Tahiti.
Applying Concepts How do
manganese nodules form?
Other major resources from the ocean floor include sand and
gravel, evaporative salts, and manganese nodules.
Sand and Gravel The offshore sand-and-gravel industry is
second in economic value only to the petroleum industry. Sand and
gravel, which include rock fragments that are washed out to sea and
shells of marine organisms, are mined by offshore barges using
suction devices. Sand and gravel are used for landfill, to fill in
recreational beaches, and to make concrete.
In some cases, materials of high economic value are associated with offshore sand and gravel deposits. Gem-quality
diamonds, for example, are recovered from gravels on the continental shelf offshore of South Africa and Australia. Sediments
rich in tin have been mined from some offshore areas of
Southeast Asia. Platinum and gold have been found in deposits
in gold-mining areas throughout the world. Some Florida beach
sands are rich in titanium.
Manganese Nodules As described earlier, manganese
nodules are hard lumps of manganese and other metals that precipitate around a smaller object. Figure 15 shows manganese
nodules on the deep-ocean floor. They contain high concentrations of manganese, iron, and smaller concentrations of copper,
Evaporative Salts
Materials
400 mL beaker, table salt, tablespoon, balance,
glass stirrer
4. When all of the water has evaporated, place
the beaker and its remaining contents on the
balance and record the measurement.
Procedure
Analyze and Conclude
1. Place the empty beaker on the balance and
add between 3 and 5 tablespoons of the salt.
Measure the combined mass of the balance
and the salt. Record the measurement and
remove the beaker from the balance.
1. Comparing How did the mass of the beaker
and salt before the water was added compare
to the mass of the beaker and salt after the
water evaporated?
2. Add 100 mL of water to the beaker and stir
until the salt is dissolved.
3. Place the beaker in a warm, sunny area and
allow the water to evaporate.
2. Drawing Conclusions What happened to
the salt when the water evaporated?
3. Predicting How could the oceans be used as
a source of salt?
412 Chapter 14
Facts and Figures
In Earth’s geologic history, there have been
incidents in which an entire body of salt water
evaporated away. The evidence for this
includes extensive deposits of evaporite
minerals, including one in the Mediterranean
Sea. Evidence suggests that, about 6 million
years ago, the Mediterranean Sea was cut off
from the Atlantic Ocean at the Strait of
Gibraltar. The Mediterranean Sea almost
completely evaporated within a few thousand
years, leaving a thick deposit of evaporites on
the hot, dry basin floor. A half million years
later, water re-entered the Mediterranean Sea,
filling it with seawater again.
HSES_1eTE_C14.qxd 5/16/04 1:00 PM Page 413
nickel, and cobalt, all of which have a variety of economic uses.
Cobalt, for example, is important because it is required to produce strong alloys with other metals. These alloys are used in
high-speed cutting tools, powerful permanent magnets, and jet
engine parts. With current technology, mining the deep-ocean
floor for manganese nodules is possible but not economically
profitable.
Manganese nodules are widely distributed along the ocean
floor, but not all regions have the same potential for mining.
Good locations for mining must have a large amount of nodules
that contain an optimal mix of copper, nickel, and cobalt. Sites like this
are limited. In addition, it is difficult to establish mining rights far from
land. Also, there are environmental concerns about disturbing large
portions of the deep-ocean floor.
Use Community
Resources
Figure 16 Common table salt, or
halite, is harvested from the salt
left behind when ocean water
evaporates. About 30 percent of
the world’s salt is produced by
evaporating seawater.
Evaporative Salts When seawater evaporates, the salts increase
in concentration until they can no longer remain dissolved. When the
concentration becomes high enough, the salts precipitate out of solution and form salt deposits. These deposits can then be harvested, as
shown in Figure 16. The most economically important salt is halite—
common table salt. Halite is widely used for seasoning, curing, and
preserving foods. It is also used in agriculture, in the clothing industry for dying fabric, and to de-ice roads.
1.
2.
3.
4.
5.
6.
What are the main energy resources from
the ocean?
How are gas hydrates formed?
What drawbacks are associated with
harvesting ocean resources for energy use?
What other resources are derived from the
ocean?
What are the uses of evaporative salts?
What are manganese nodules? Why is it
difficult to recover them from the ocean?
Ask the owner or manager of a local
quarry to explain to the class how gravel
and sand are mined, their uses, and
their economic value. If possible, have
the presenter bring samples of different
types of sand and gravel for students to
examine. Ask the presenter to discuss
the differences between sand and gravel
from marine and terrestrial sources.
Interpersonal, Visual
3 ASSESS
Evaluate
Understanding
L2
Have students explain how gas hydrates
and evaporative salts are formed. Ask
students to write a short paragraph on
each.
L1
Reteach
On the board, write a skeleton of an
outline for the content of this section,
with Energy Resources as Roman
numeral I and Other Resources as
Roman numeral II. Have students copy
the skeleton and complete the outline
by adding the ocean resources discussed
in this section, along with details about
their uses and how they form.
Section 14.4 Assessment
Reviewing Concepts
L2
8. Inferring Near-shore mining of sand and
gravel can result in large amounts of
sediments being suspended in water. How
might this affect marine organisms living in
the area?
Sand and gravel are coarse sediments
that settle out more quickly than finegrained sediments. Sand and gravel are
terrigenous sediments.
Sand and Gravel Why are most sand
and gravel deposits found on the continental shelf? What type of sediment is
sand and gravel?
Critical Thinking
7. Making Generalizations How does
technology influence the availability of
resources from the ocean?
Answer to . . .
The Ocean Floor
Section 14.4
Assessment
1. oil and natural gas
2. Most oceanic gas hydrates are formed
when bacteria break down organic matter
trapped in seafloor sediments. The bacteria
produce methane gas along with small
amounts of ethane and propane. These gases
combine with water in deep-ocean sediments
in such a way that the gas is trapped inside
a lattice-like cage of water molecules.
413
3. possibility of oil spills, possible effects on
marine habitats, gas hydrates break down
quickly when brought to the surface
4. sand and gravel, evaporative salts,
manganese nodules
5. used to season, cure, and preserve foods;
used in agriculture, to dye fabric, and to deice roads
6. Manganese nodules are round, hard
lumps of manganese, iron, and other metals
that precipitate around an object, such as a
grain of sand.
Figure 15 Manganese nodules form
when metals such as manganese and
iron precipitate around an object, such
as a grain of sand.
7. As technology improves, people may be
able to retrieve resources more efficiently.
8. Suspended sediments can make water
cloudy, interfering with the amount of light
that penetrates water. This can affect organisms that need light for photosynthesis.
Suspended sediments can also affect filterfeeding organisms, preventing them from
feeding properly.
The Ocean Floor 413