© fall 2005, pflugerville isd, 7th grade 7th grade science

© Fall 2005, Pflugerville ISD, 7th Grade

7th Grade Science

Unit 3 : Earth Science© Fall 2005, Pflugerville ISD, 7th Grade

Unit 3: Earth Science

Chapter 15: Organization of the EnvironmentSection 1: The Natural EnvironmentSection 2: How Ecosystems Change

Chapter 16: ClimateSection 1: What is Climate?Section 2: Climates of the WorldSection 3: Changes in Climate

Chapter 24: Earth, Sun, and MoonSection 1: Days and Seasons on Earth



Chapter 17: The Earth’s EcosystemsSection 1: Land Ecosystems

Section 2: Marine Ecosystems

Section 3: Freshwater Ecosystems

Chapter 6: Energy ResourcesSection 1: Natural Resources

Section 2: Fossil Fuels

Section 3: Alternative Resources



Chapter 21: EarthquakesSection 1: What are Earthquakes?

Section 2: Earthquake Measurement

Chapter 22: VolcanoesSection 1: Volcanic Eruptions

Section 2: Volcanoes’ Effects on Earth

Section 3: What Causes Volcanoes?

Unit 3 : Chapter 15 : Section 1© Fall 2005, Pflugerville ISD, 7th Grade

Organization of the Environment

How do you think our environment is organized?

What Do You Think?



An environment is made up of 2 parts.

1. Biotic- All of the organisms and the matter they produce such as dead leaves and molten skin.



An environment is made up of 2 parts.2. Abiotic- All of the physical things-water, sunlight,

rocks- that affect organisms living in a certain area.



The environment is organized into 5 levels.

1. Organism

2. Population

3. Community

4. Ecosystem

5. Biosphere



Organism• This level contains the individual species of a

particular organism.



Population• Populations are groups of individuals of the

same species that live together in the same area at the same time.



Communities• Communities are made up of all of the

populations of different species that live and interact in an area.



Ecosystems• Ecosystems are made up of a community of

organisms and its abiotic environment.



Biosphere• A biosphere contains the whole area of the Earth

where life exists, including its abiotic factors.


Let’s Review!

- 1 -

Give 2 examples of biotic and abiotic factors in your science room.


Answer

• Biotic- students, plants, textbooks

• Abiotic- floors, air, metal desks


Let’s Review!

- 2 -

What do you think would happen to the other organisms in a small lake if all of the plants got a fungus and died?


Answer

• Many of the organisms depend directly or indirectly on the plants for food. Without the plants, these other organisms would probably die or move into other areas.



• Natureworks: Habitat



Why could fire be good for a forest?

What Do You Think?



How Ecosystems Change

• Ecological succession is defined as the changes an ecosystem goes through as it develops or regrows.

• There are 2 types of ecological succession.

1. Primary succession

2. Secondary succession



Primary Succession• Primary succession occurs in an area where

there were no living things.• No soil is present during primary succession.• Over a very long time, many organisms live and

die on the rocks. This eventually breaks the rocks down.

• The rock is slowly changed into soil, and a community of organisms eventually develops.



Secondary Succession• This succession occurs in an area where an

earlier community was disturbed by fire, landslides, floods, or plowing for crops.

• Soil is present at the beginning, so the time for secondary succession is shorter than primary succession.



• Ecological succession helps an ecosystem stay balanced because it allows the ecosystem to slowly recover from disturbances.

• Without succession, the disturbed ecosystem would not recover after a natural disaster, and would not reach equilibrium again.


Let’s Review

- 1 -

How does ecological succession maintain equilibrium in an ecosystem?


Answer

• Ecological succession maintains equilibrium be allowing an ecosystem to slowly recover from disturbances.



• Websites to see:

Natureworks: Ecosystems



Identify the following examples as either primary succession or secondary succession:

1. A rock face exposed by a scraping glacier.

2. A new shoreline in Hawaii created after a lava flow.

3. A once forested area cleared by a tornado.

4. An island appearing from the activity of an undersea volcano.

5. The lawn of an abandoned farmhouse.


Climate

Why do we have different seasons each year?

What Do You Think?


Climate

Seasons• In most places around the

US, the year has four seasons.

• Winter is cooler where we live, but this is not the case in all places.

• For example, areas near the equator have around the same temperature and same amount of daylight hours all year.


Climate

• This happens because of the Earth is tilted on its own axis at a 23.5° angle.

• The tilt of the Earth affects how much solar energy an area receives as it moves around the sun. This also affects how long our days are.


Climate


Climate

Click below to see about the change of seasons on Earth.

• NASA: Earth's Seasons

• Enchanted Learning: Earth's Seasons


Let’s Review

- 1 -

Describe how the tilt of the Earth affects the amount of daylight hours in the Northern

Hemisphere.


Answer

• As the Earth revolves around the sun, the tilt of the Earth’s axis causes the Northern Hemisphere to receive different amount of sun, depending on the time of year.

• During the winter, when the Northern Hemisphere is tilted away from the sun, there are fewer daylight hours.

• In the summer, there are more daylight hours.


Let’s Review!

- 2 -

How would season’s be different if the Earth did not tilt on its axis?


Answer

• If the Earth did not tilt on its own axis, there would be no seasons at all.

• The same amount of solar radiation would reach both hemispheres year-round.


Climate

Can polar bears live in Texas? Why or why not?

What Do You Think?


Climate

• A Biome us a large region characterized by a specific type of climate and the plants and animals that live there.

• Climate is the average weather conditions in an area over a long period of time.

• Different biomes support different organisms based on their climate.


Climate

• Tropical Rain Forest

Temperature Rainfall Soil

25°C to 28°C(77°F to 82°F)

200 cm or more each

year

thin and nutrient

poor


Climate

• Tropical Deserts


16°C to 50°C (61°F to 120°F)

0-25 cm per year

poor in organic matter


Climate

• Tropical Savannas


27°C to 32°C (80°F to 90°F)

around 100 cm per year

generally nutrient

poor


Climate

• Temperate Deciduous Forest


0°C to 28°C (32°F to 82°F)

76-250 cm per year

very fertile, organically

rich


Climate

• Temperate Grassland


-6°C to 26°C (21°F to 78°F)

38-76cm per year

most fertile of all biomes


Climate

• Chaparrals


11°C to 26°C (51°F to 78°F)

48-56 cm per year

rocky, nutrient poor


Climate

• Temperate Deserts


1°C to 50°C (34°F to 120°F)

0-25 cm per year

poor in organic matter


Climate

• Tundra


-27°C to 5°C (-17°F to 41°F)

0-25 cm per year

frozen


Climate

• Taiga


-10°C to 15°C (14°F to 59°F)

0-25 cm per year

frozen


Climate

• Plants that require a lot of water must live in climates with a lot of precipitation (rain).

• Animals that require the sun to keep them warm must live in a biome that has higher temperatures.


Let’s Review

- 1 -

What kinds of plants and animals would live in a tropical desert?


Answer

• The organisms that would live in a tropical desert must be adapted to hot, dry conditions.

• Cactuses, and lizards would be examples.


Let’s Review!

- 2 -

Describe how different biomes support different varieties of organisms.


Answer

• Cold, wet biomes support animals and plants that can survive in cold, wet conditions.

• Warm, dry biomes support animals that can survive in warm, dry conditions.

• The same applies for cold and dry biomes, and warm and wet biomes.


Climate

What is global warming, and how does it affect us?

What Do You Think?


Climate

• The greenhouse effect is the Earth’s natural heating process in which gases in the atmosphere trap thermal energy.

• Global warming is a rise in the average temperatures that can result from an increase in the greenhouse effect.


Climate

Global Warming• Our Earth acts just like a plant greenhouse.• It allows the sunlight to come in, but the glass (or

atmosphere) keeps the thermal energy (heat) from escaping.

• This makes our Earth warmer, just like a plant greenhouse.


Climate

Global Warming• Most scientists believe that the rise in global

temperatures is due to an increase in carbon dioxide, a greenhouse gas, as a result of human activity.


Climate

Global Warming• Increased amounts of carbon dioxide in the air is

caused by the burning of fossil fuels (oil, coal, and gasoline).

• Deforestation, or the process of clearing forests, also adds carbon dioxide to the air.


Climate

Global Warming• There are many theories as to what will happen

if we continue to increase the greenhouse gases.1. The ice caps could melt, and flooding could occur.2. Areas that receive little rain, like deserts, might receive less because of increased evaporation.


Climate

Volcanic Eruptions• Many natural factors can affect global

warming. Volcanic eruptions can influence climate.


Climate

• A volcanic eruption would send large amounts of dust, smoke, and ash particles into the atmosphere.

• The dust, smoke, and ash particles act as a shield.

• They would block out so much of the sun’s rays that the Earth would cool.

• This could affect the balance of the gases in the atmosphere.


Let’s Review!

- 1 -

Explain how the greenhouse effect warms the Earth.


Answer

• Greenhouse gases allow sunlight to pass through the atmosphere, where it is absorbed by the Earth’s surface as heat.


Let’s Review!

- 2 -

What impact could a volcanic eruption have on the Earth?


Answer

• A large volcanic eruption could send enormous amounts of dust and ash into the atmosphere. These materials will block the sun’s rays and make the Earth cooler.


Climate

• Websites to Visit

Ozone Facts

Climate Changes

Global Warming

Volcanic Effects on Global Warming


Earth, Sun, and Moon

What causes daylight and night?

What Do You Think?



• Revolution is the motion of a body as it orbits another body in space.

- It takes 1 year, or 365 ¼ days for the Earth to revolve around the sun.



• Rotation is the spin of an object in space.

- The Earth rotates once on its own axis in 23 hours and 56 minutes.

- The Earth’s rotation is a direct cause of day and night.



• See Chapter 16, Section 1 for how the tilt and movement of the Earth causes changes in seasons and the length of the day.

Click here to return to the information on Seasons.



• Earth, Sun, and Moon Demo


The Earth’s Ecosystems

What are the main differences between a desert and a rain

forest?

What Do You Think?



• We learned in Chapter 16 that different climates of biomes support a variety of organisms.

• There are 4 main ecosystems that support different types of plants and animals.



Forests• Forest ecosystems develop in places where the

temperatures are mild and there is plenty of rain.• The 3 main types of forest ecosystems are

temperate deciduous forests, coniferous forests, and tropical rain forests.



• Temperate Deciduous Forest

Go.hrw.com



• Coniferous Forest (Taiga)

Go.hrw.com



• Tropical Rain Forest

Go.hrw.com



Grasslands• Grasslands are areas where grasses are the

main plants.• They are found between forests and deserts.• Most grasslands are flat or have gently rolling

hills.



• Temperate Grasslands



• Tropical Savanna



Deserts• Deserts are areas that are very dry and usually

very hot.• Organisms have developed special ways to live

in a hot, dry climate.• What is an example of a plant adaptation in the

desert?• What is an example of an animal adaptation in

the desert?



•Deserts

Go.hrw.com



Tundra• Areas with very cold temperatures and little

rainfall are called tundra ecosystems.• It is so cold here that trees don’t even grow!



• Arctic Tundra- The ground remains frozen almost all of the time.- This frozen layer is called permafrost.- The layer of soil above the permafrost is too shallow for plants with deep roots.- Grasses and shrubs live here.- Animals that feed on grasses and shrubs, such as the musk oxen, wolves, and caribou live here.



• Alpine Tundra- This is very similar to the artic tundra, but it’s found at the tops of tall mountains.

- Trees are not able to grow here.



• Natureworks: Land Ecosystems

• Enchanted Learning: Land Biomes



What is the difference between marine and freshwater

ecosystems?

What Do You Think?



Marine Ecosystems• Marine ecosystems are in the oceans of

the world. They contain a wide variety of plant and animal species.

• There are 4 main parts, or zones, in the ocean. Each zone has different plants and animals.



Part 1: The Intertidal Zone• The intertidal zone is the place where the ocean

meets the land.• Animals and plants that live here must adapt to

the tide moving in and out each day.• The animals and plants must be able to live in

and out of water.• Most of the animals have shells that protect

them from drying out. Other animals bury themselves in the sand for protection.



Part 2: The Neritic Zone• As you keep walking into the ocean you reach

the neritic zone.• This area is warm and sunny.• Water in this area is less than 200 m deep.• Most animals and plants live in this zone.• The large amount of sunlight makes it possible

for a lot of plankton to grow. The plankton feeds many fish, which provide food for birds and marine mammals.



Part 3: The Oceanic Zone• This zone is past the continental shelf where

the ocean floor drops sharply.• Since there is not much sunlight, animals must

get their energy from food that has drifted down from the surface.

• Many of the larger mammals that live in the neritic zone also live in the upper parts of the oceanic zone. There is a lot of space to swim in this area.



Part 4: The Benthic Zone• This zone is the ocean floor. (From 200m-6000m

deep)• Very unusual organisms live here. Some get their

food from chemicals found near thermal vents.• A thermal vent is a place in the ocean floor where

heat and chemicals escape from a crack in the Earth’s crust.

• There is no sunlight here, so plants cannot produce food.

• This area is extremely cold, except in areas near thermal vents.


Let’s Review!

- 1 -

Describe how different marine environments support different varieties of

organisms.


Answer

• Different marine environments provide different combinations of light, salt concentration, temperature, and nutrients. These different combinations provide a variety of conditions, each of which supports organisms adapted to those conditions.


Let’s Review!

- 2 -

Determine which areas of the ocean each of the following animals would live in:

1. Dolphins

2. Starfish

3. Tube worms


Answers

1. Dolphins live in the neritic zone, or the upper part of the oceanic zone.

2. Starfish live in the intertidal zone.

3. Tube worms live near hot water vents in the benthic zone called black smokers.



• Natureworks: Marine Ecosystems

• Natureworks: Estuaries

• Natureworks: Intertidal Zone

• Natureworks: Oceanic Zone

• Natureworks: Benthic Zone



Name as many freshwater ecosystems as you can.

What Do You Think?



Freshwater Ecosystems• Freshwater Ecosystems include all of the plant

and animals, along with the abiotic factors, that are in fresh (no salt) water.

• They are usually separated on how fast the water is moving.



• Moving Water Ecosystems– Include brooks, streams, and rivers

• Fast Moving Water- many streams and some rivers have water that moves fast.

1. This type of water is full of life.

2. Organisms that live here need ways to keep from being washed away.



•Moving Water Ecosystems cont…• Slow Moving Water- eventually rivers grow

wider and slower

1. Many insects live in the slow moving rivers and marshes.

2. They eventually empty into a lake or an ocean.



Still Waters• Include ponds and lakes.• These still water ecosystems are divided into 3

parts:– Littoral Zone– Open-Water Zone– Deep-Water Zone



Littoral Zone• This zone is closest to the edge of the land.• Many plants an animals live here.• Examples of plants include cattails and water

lilies.• Animals include frogs, snakes, and various types

of fish.



Open Water Zone• This zone extends from the littoral zone across

the top of the open water.• The open water zone only goes as deep as the

light can reach.• This zone is home to bass, lake trout, blue gills,

and many plankton.



Deep Water Zone• This is an area below the open water zone.• No light reaches here.• Catfish, carp, bacteria, fungi, and worms feed on

pieces of dead organisms that fall from above.



Wetlands• A wetland is an area of land where the water

level is near or above the surface of the ground for most of the year.

• Wetlands have a variety of plants and animals.• They also play an important role in flood control.

During heavy rains, or spring snow melt, wetlands soak up large amounts of water that replenish the underground water supplies.



• There are 2 types of wetlands:1. A marsh is a treeless wetland.

• They are often found in shallow waters along the shores of lakes, ponds, rivers, and streams.

2. A swamp is a wetland where trees and vines grow.

• Swamps occur in low lying areas and beside slow moving rivers.

• Most swamps are flooded only part of the year, depending on rainfall.


Let’s Review!

- 1 -

Compare and contrast the littoral zone with the open-water zone of a lake.


Answer

Littoral Open Water

•Edge of lake

•Large number of plants and animals

•Both have light

•Both contain fish

•Both are in still water

•In the middle of a lake or pond

•Home to larger fish

•Contains many plankton


Let’s Review!

- 2 -

How are a swamp and a marsh different?


Answer

• A marsh is a wetland with trees, and a swamp is a wetland without trees.

• Because they lack trees, marshes support plants and animals that thrive in sunlight.

• Since swamps have trees, they provide a better environment for organisms that can live in shade.



• Natureworks: Freshwater Ecosystems


Energy Resources

Why is recycling so important?

What Do You Think?


Energy Resources

Earth’s Resources• The Earth provides almost everything needed for

life!• A natural resource is any natural substance,

organism, or energy form that living things use.• We use natural resources to help make our lives

easier.• What would be a natural resource that you are

using right now that makes your life easier?


Energy Resources

There are 2 types of Natural Resources.

1. Renewable Resources

2. Nonrenewable Resources


Energy Resources

Renewable Resources• A renewable resource is a natural resource that

can be used and replaced over a short period of time.

• Examples include trees and freshwater.• Humans often use renewable resources more

quickly than they can be replaced.


Energy Resources


Energy Resources

Nonrenewable Resources• A nonrenewable resource is a natural resource

that cannot be replaced, or can only be replaced over thousands or millions of years.

• The amount available on Earth is fixed, once they are used up, they are gone forever.

• Examples are coal, oil, and natural gas.


Energy Resources


Energy Resources

Label the following as renewable or nonrenewable resources:

1. Trees

2. Gasoline

3. Petroleum

4. Water

5. Sunlight


Energy Resources

How can natural resources be conserved?

• use them only when we have to.

• recycle (newpapers, cans, plastic)

• carpool / ride your bike instead of driving.


Let’s Review!

- 1 -

List 2 ways humans use natural resources.


Answer

• Lumber from trees for paper

• Gasoline for cars, lawnmowers, etc…

• Sun, wind, and water to create energy


Let’s Review!

- 1 -

What is the difference between renewable and nonrenewable resources?


Answer

• Renewable resources can be replaced over a relatively short period of time.

• Nonrenewable resources cannot be replaced pr can only be replaced over thousands or millions of years.


Energy Resources

Why do you think the term fossil fuels has the word fossil in it?

What Do You Think?


Energy Resources

• Energy resources are natural resources that humans use to produce energy.

• Fossil fuels are defined as nonrenewable energy resources that form in the Earth’s crust over millions of years.

• Fossil fuels form from the buried remains of once-living organisms.


Energy Resources

Fossil Fuels• Fossil fuels release energy when they are

burned.

• We rely on fossil fuels to provide us the energy we need for many modern conveniences.

• Fossil fuels can be solids, liquids, or gases.


Energy Resources

Liquid Fossil Fuels• Composed of things such as gasoline, jet

fuel, kerosene, diesel fuel, and oil.

• Petroleum, also known as crude oil, is a mixture of oily compounds.

• Petroleum is separated in a refinery.


Energy Resources


Energy Resources

Solid Fossil Fuels• Humans most use coal.• Coal is a source of energy formed underground

from buried, decomposed plant materials.• Coal used to be the leading source of energy in

the US, but it has been replaced by things that create less pollution and are more affordable.


Energy Resources


Energy Resources

Gaseous Fossil Fuels• Gaseous fossil fuels are also called natural gas.• Natural gases are often used for heating and

generating electrical energy.• Examples of natural gases include methane,

butane (camp stoves), and propane (outdoor grills).

• The use of vehicles powered by natural gases is increasing. Why?


Energy Resources


Energy Resources

• There are many problems associated with using fossil fuels.

1. When coal is burned, sulfur dioxide is produced. When mixed with air, sulfur dioxide causes acid precipitation. This harms wildlife, plants, buildings, and statues.


Energy Resources

Fossil Fuel Problems continued….2. The mining of coal can also cause

environmental problems. Strip mining removes soil which plants need for growth, and some animals need for shelter.


Energy Resources

Fossil Fuel Problems continued….3. Transporting petroleum can also cause

environmental problems. In 1989, Exxon Valdez had a tanker spill 257,000 barrels of crude oil into the ocean off the coast of Alaska. Thousand of plants and animals were killed by the oil.


Energy Resources

Fossil Fuel Problems continued….4. Burning petroleum causes an

environmental problem called smog. Smog is a fog produced by the reaction of sunlight and air pollutants. It is a big problem in bigger cities such as Los Angeles and Houston.


Energy Resources

How do we help fossil fuel problems?1. Carpooling

2. Riding your bike

3. Walking

4. Ride the bus

5. Use alternative energy resources


Let’s Review!

- 1 -

Name 3 problems with fossil fuels.


Answer

1. Oil spills

2. Loss of soil from strip mining coal.

3. Production of smog.


Energy Resources

What is an alternative energy resource?

What Do You Think?


Energy Resources

Alternative Energy Resources• Alternative energy resources are needed to slow

the use fossil fuels.

• They include:

1. Nuclear energy 4. Hydroelectric energy

2. Solar energy 5. Plant energy

3. Wind energy 6. Geothermal energy


Energy Resources

Nuclear Energy• Nuclear energy is an alternative source of

energy that comes from the nuclei of atoms.• Fission is a process in which the nuclei of

radioactive atoms are split and energy is released.

• The energy from fission is used to produce steam to run electric generators in a power plant.


Energy Resources

Nuclear Energy continued…• Fusion is the joining of two or more nuclei with

small masses to form a larger, more massive nuclei. This process releases energy.

• So far, fusion reactions have only taken place in laboratory experiments.


Energy Resources

Pros Cons

No air pollutionRadioactive wastes are

produced.

More concentrated source of energy than fossil fuels.

Storage sites are hard to find.

Can be cheaper than obtaining fossil fuels.

High temperatures are required for fusion. No

materials can withstand the temperatures required.

Pros and Cons of Using Nuclear Energy


Energy Resources

Solar Energy• Solar energy is energy from the sun.• The sun is an inexhaustable resource because it

cannot be used up. The Earth always receives solar energy.


Energy Resources

Pros Cons

No air pollutionVery expensive to produce solar

cells.

Solar cells are dependable, quiet, and can last for

years with no maintenance.

Running electrical wires required to use solar cells is difficult and

costly.

Pros and Cons of using Solar Energy


Energy Resources

Wind Energy• Wind is created indirectly by solar energy

through the uneven heating of air.• Wind energy is the energy captured in wind.


Energy Resources

Pros Cons

No air pollution Wind turbines are costly.

Wind energy is inexhaustable along as solar energy is present. The wind does not blow strong

and steady in most places in the US, so wind energy is only beneficial in places with a lot of

wind, such as California.The land that has the wind

turbines on them can also be used for farming.

Pros and Cons of Using Wind Energy


Energy Resources

Hydroelectric Energy• Electrical energy generated by falling water is

called hyrdoelectric energy.


Energy Resources

Pros Cons

Little pollution is produced.Can only be produced where

large amounts of falling water can be harnessed.

Inexpensive to produce. Building the dams for hydroelectric power plants

destroys forests and wildlife habitats.

Water can be renewed because of the water

cycle.

Pros and Cons of Using Hydroelectric Energy


Energy Resources

Plant Energy• Plants are similar to solar collectors because

they store energy from the sun for later use in their leaves, wood, and stems.

• An organic matter that contains stored energy is called biomass.

• Most countries use animal dung or wood to heat their homes and cook their food.


Energy Resources

Plant Energy• Biomass can also be changed into liquid fuel.

Plants that contain sugar or starch can be used to produce ethanol. Ethanol can be burned, or mixed with gasoline to make a fuel mixture called gasohol.


Energy Resources

Pros Cons

Can be used in countries that are poor, and do not

have access to fossil fuels.

Produces a lot of air pollution when burned.

Always renewable.Requires a lot of biomass

to make a small amount of fuel.

Pros and Cons of Using Biomass for Energy


Energy Resources

Geothermal Energy• Geothermal energy is the energy resulting from

the heating of the Earth’s crust.• In some areas, rainwater enters porous rock

near a source of magma. Magma heats up water that is below the surface of the Earth.

• This water turns into steam, and it escapes through natural vents called geysers.


Energy Resources

Pros Cons

Geothermal energy is renewable.

Can only be used in places on the Earth where magma and rainwater are

avaliable in the same place.

Pros and Cons of Using Geothermal Energy


Let’s Review!

- 1 -

How could human activities affect inexhaustable resources?


Answer

• Although inexhaustable resources, such as sunlight, cannot be used up, the amount available to a specific area can be affected.

• The amount of solar energy in an area can be affected by air pollution from using other energy resources.


Let’s Review!

- 1 -

Explain why the use of gasohol could help to reduce the problems associated with the

use of fossil fuels.


Answer

• The use of gasohol would reduce the total amount of gasoline used. As the amount of gasoline used decreases, the problems with fossils fuels will also be reduced.


Energy Resources

Websites to Visit!• Energy Facts• Fossil Fuels


Earthquakes

Where do earthquakes happen, and what causes them?

What Do You Think?


Earthquakes

Where do Earthquakes happen?• Most earthquakes happen near boundaries

between tectonic plates.• Tectonic plates are giant pieces of Earth’s thin,

outermost layer.• Tectonic plates move around on a layer of softer

rock beneath.


Earthquakes

Where do Earthquakes happen?• Because of tectonic plate movements, the

Earth’s crust breaks in some places.• A fault is a break in the Earth’s crust along which

blocks of the crust slide past each other.


Earthquakes

What causes Earthquakes?• As the tectonic plates push against each other a

huge amount of potential energy is built up.• Potential energy is energy that an object has

because of its position or shape.• Potential energy does not cause the Earth to

move. It is energy built up along the fault.


Earthquakes

What causes Earthquakes?• When the rocks of the earth shift (along a fault

line), this potential energy changes to kinetic energy and the earth shakes.

• Kinetic energy is the energy of motion.• An earthquake is the kinetic energy that is finally

released after enough pressure builds up along a fault.


Let’s Review!

- 1 -

Explain how potential and kinetic energy act on rock to cause earthquakes.


Answer

• Most earthquakes occur because tectonic forces cause potential energy to build up in the rocks along a fault.

• When the stress becomes too great, the rocks shift and kinetic energy is released, causing an earthquake.


Earthquakes

Explain how earthquakes are detected.

What Do You Think?


Earthquakes

How are Earthquakes detected?• Seismologists use a device called a

seismograph to detect seismic waves.• The focus is the place on earth where the

earthquake originates.• The epicenter is the place on earth directly

above the focus.• The epicenter from several stations help

determine where an earthquake began.


Earthquakes

How strong are Earthquakes?•The Richter scale measures the strength of an earthquake.

•As magnitude increases, the amount of energy released by the earthquake increases.

Magnitude Effects

2Detected by a

seismograph

3 Felt at epicenter

4 Felt by most in area

5 Damage at epicenter

6 Widespread damage

7Great, widespread

damage.


Let’s Review!

- 1 -

Predict the impact of an earthquake with a magnitude of 5.0.


Answer

• If an earthquake with a magnitude of 5.0 happened in a small town, some buildings would be damaged, but only a few people would be hurt.


Earthquakes

Websites to visit

• Earthquake Seisomgraph

Unit 3 : Chapter 21 : Pre-AP© Fall 2005, Pflugerville ISD, 7th Grade

Pre-AP ExtensionEarthquakes

Transform plate

Plates slip back and forth

Moderate, shallow earthquake

Convergent plate

Plates come together

Strong, deep earthquake

Divergent plate

Plates pull apart Weak, shallow earthquake

3 Causes of Earthquakes



• Seismic waves are waves of energy that travel through the earth away from the earthquake in all directions.

• 2 types of seismic waves

1. Body Waves

2. Surface Waves

How do Earthquakes travel?


Body Waves• P (primary) waves

- move rock particles back and forth by first squeezing and then stretching the rock.

- first waves to arrive- travel through solids, liquids, and

gases




Body Waves continued…• S (shear) waves

-these waves move back and forth like a flag waving in the wind-1/2 as fast as p waves-only travel through solids



Surface Waves• Surface Waves are seismic waves that move the

ground up and down.• These do not affect deep layers of the earth.• Travel slower than body waves, but are more

destructive.


Volcanoes

How could potential and kinetic energy relate to volcanoes?

What Do You Think?


Volcanoes

• A volcano is a mountain that forms when molten rock, called magma, is forced to the Earth’s surface.

• Magma is commonly a mixture of hot, liquid rock, and solid mineral crystals below the surface of the Earth.

• Lava is molten rock at or above the surface of the Earth.


Volcanoes

Potential and Kinetic Energy in Volcanoes

• Just like earthquakes, potential energy builds up at tectonic plates where a volcano may occur.

• As the pressure from the magma builds up, the potential energy is changed to kinetic energy as the volcano erupts.


Volcanoes

Volcanoes as Systems• A volcano is a system of vents, magma, and

rock.• The system is in equilibrium when the force of

the magma pushing up equals the force of the rock pushing down.


Volcanoes

Volcanoes as Systems• When a volcano erupts, it is no longer in

equilibrium because the force of the magma is greater than the downward force of the rocks.

• After the eruption, the system returns to equilibrium, because the forces are equal again.


Volcanoes

Magma• The composition of the magma determines how

explosive a volcanic eruption will be.• Viscosity is a liquid’s resistance to flow.• If magma has a high viscosity, it flows slow, like

honey.• If magma has a low viscosity, it flows fast, like

water.


Volcanoes

• Magma with a high viscosity keeps water vapor and other gases from escaping easily. This can cause a huge buildup of pressure, causing a very explosive reaction.

• Magma with a low viscosity produces a nonexplosive, less violent reaction.


Let’s Review!

- 1 -

Describe how a volcanic system changes from a state of equilibrium to a state of

eruption and back.


Answer

• When in equilibrium, the force of the magma pushing up equals the force of the rocks pushing down.

• If more magma build up under the volcano, the forces are no longer equal and an eruption results.

• After the eruption, the forces of the rock and the magma are once again in equilibrium.


Volcanoes

What impact could volcanoes have on Earth?

What Do You Think?


Volcanoes

Impacts of Volcanoes• In the most violent eruptions, ash and gases are

blasted into the atmosphere.• These blasts can blow down trees and even

nearby buildings.• The volcanic ash can also stay in the

atmosphere, where it can block the sun for weeks. This can dramatically affect crops.


Let’s Review!

- 1 -

Explain why the ash from an eruption can be catastrophic.


Answer

• Volcanic ash is hazardous when it flows downhill, which chokes and burns living things, and when it smothers crops, it can result in food shortages.


Volcanoes

What methods do scientists use to predict volcanoes?

What Do You Think?


Volcanoes

Predicting Volcanoes• Scientists classify volcanoes based on their

eruption histories and on the likelihood that they will erupt again.– Extinct volcanoes are those that have not erupted in

recorded history, and probably never will again– Dormant volcanoes are those that are not now

erupting, but have erupted at some time in recorded history

– Active volcanoes are those that are now erupting or that show signs of erupting soon.


Volcanoes

Predicting Volcanoes• Small earthquakes, detected by a seismograph,

usually occur just before a volcanic eruption. Scientists can predict if a volcano will occur based on the small earthquake waves.


Volcanoes

Predicting Volcanoes• The movement of magma can also cause

changes in a volcano’s slope.• Scientists use a tiltmeter to measure small

changes in the angle of the volcano’s slope.• The tiltmeter can help scientists to predict a

volcanic eruption based on the movement of the magma below.


Volcanoes

Predicting Volcanoes• Scientists measure changes in the ratios of

certain volcanic gases to help predict eruptions.• If the ratios of certain gases change, the magma

is also changing, and a volcanic eruption could be near.


Volcanoes

Predicting Volcanoes• Using satellite images to predict volcanic

eruptions is a new technique used in science.• Infrared satellite images can see changes in the

temperature of a certain area.• If a volcano is getting hotter, the magma below

is probably rising.


Volcanoes

Websites to visit

• Volcanoes


Let’s Review!

- 1 -

What kind of technology do scientists use to predict volcanic eruptions?


Answer

• Seismographs

• Tiltmeters

• Infrared satellite images

© fall 2005, pflugerville isd, 7th grade 7th grade science

Documents