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Earth and the Sun’s Energy
The Big Idea
Earth’s movement and the sun’s energy interact to create
day and night, temperature changes, and the seasons.
Main Ideas
• Earth’s movement affects the amount of energy we
receive from the sun.
• Earth’s seasons are caused by the planet’s tilt.
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Main Idea 1:
Earth’s movement affects the amount of
energy we receive from the sun.
• All life on Earth requires solar energy, or
energy from the sun, to survive.
– Amount of solar energy received changes
constantly
– Earth’s rotation, revolution, tilt, and latitude all
affect the amount of solar energy Earth receives.
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Rotation and Revolution
Rotation
Revolution
• Earth spins on its axis—
an imaginary line that
runs through the center
of the planet around
which it turns.
• Earth follows an orbit, or
path, around the sun.
• It takes Earth 24 hours
to make one rotation,
or complete spin on its
axis.
• As Earth spins, different
parts of the planet face
the sun, thus causing
the changes from day to
night.
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• Orbit is not a perfect
circle.
• It takes Earth 365¼
days to complete one
revolution, or trip
around the sun.
• Our calendar year is
based on the time it
takes Earth to complete
its orbit.
Tilt and Latitude
Tilt
Latitude
• Earth’s axis is tilted at
an angle of 23½
degrees from vertical.
• Latitude is the distance
north or south of Earth’s
equator.
• At any give time of
year, some places on
Earth tilt toward the
sun, and others tilt
away.
• Low-latitude areas,
those nearest the
equator, receive direct
rays from the sun all
year.
• Places tilting toward the
sun receive more solar
energy and have
warmer temperatures
than those that tilt
away.
• High-latitude areas,
those farther from the
equator, receive indirect
rays from the sun and
have colder
temperatures.
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Main Idea 2:
Earth’s seasons are caused by the
planet’s tilt.
• Seasons are periods during the year that are
known for a particular type of weather.
– Many places experience four seasons—winter,
spring, summer, and fall.
– In some parts of the world, seasons are based on
the amount of rainfall
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The Seasons
Winter and
Summer
Spring and Fall
Rainfall and
Seasons
• Earth tilts away
from sun in
winter and
towards the sun
in summer.
• In spring, Earth
begins to tilt
toward sun,
solar energy
increases,
temperatures
rise, and days
grow longer.
• In the tropics,
regions close to
the equator,
seasons are
marked by
rainfall rather
than
temperature.
• In fall, the
opposite occurs.
• At certain times
of year, winds
bring either dry
or moist air to
the tropics,
creating wet
and dry
seasons.
• Because of the
Earth’s tilt, the
Northern and
Southern
hemispheres
experience
opposite
seasons.
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Water on Earth
The Big Idea
Water is a dominant feature on Earth’s surface and is
essential for life.
Main Ideas
• Salt water and freshwater make up Earth’s water supply.
• In the water cycle, water circulates from Earth’s surface to
the atmosphere and back again.
• Water plays an important role in people’s lives.
Holt McDougal,
Main Idea 1:
Salt water and freshwater make up Earth’s
water supply.
Earth’s Water • Water covers some two-thirds of the planet.
• About 97 percent of the Earth’s water
• Unsafe to drink because of high levels of salt
Salt Water • In general, found in Earth’s oceans, which
cover some 71 percent of the planet’s surface
• Also found in some of Earth’s lakes
Freshwater
• Water without salt
• Makes up only 3 percent of our water supply
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Freshwater
• Much of Earth’s freshwater is locked in glaciers, large areas of
slow moving ice, and in the ice of the Arctic and Antarctic
regions.
• Surface water is water that is found in Earth’s streams, rivers,
and lakes.
– Less than one percent of Earth’s water supply
– Streams, rivers, and lakes are common sources.
• Precipitation is water that falls to Earth’s surface as rain, snow,
sleet, or hail.
– Streams form when precipitation collects in a narrow channel and
flows toward the ocean.
• Most available freshwater is groundwater, water found below
Earth’s surface.
– Some naturally bubbles from the ground to the surface as a spring.
– Most obtained by digging wells
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Main Idea 2:
In the water cycle, water circulates from
Earth’s surface to the atmosphere
and back again.
•
Water is the only substance on Earth that occurs naturally as a
solid, a liquid, and a gas, or water vapor.
•
The water cycle is the movement of water from Earth’s
surface to the atmosphere and back ; it is driven by the sun’s
energy.
–
Evaporation—water turns from liquid to gas.
–
Condensation—the rising gas cools and condenses, or changes from
a vapor into tiny liquid droplets, to form clouds.
–
Precipitation—if the droplets in clouds become heavy enough, they
fall back to Earth as rain, snow, sleet, or hail.
–
Runoff—excess water that isn’t absorbed as groundwater flows over
land and collects in streams, rivers, and oceans.
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Main Idea 3:
Water plays an important role in
people’s lives.
Water Problems
Water Benefits
• Lack of available
freshwater, which
can be caused by
droughts or overuse
• Provides us with food to
eat
• Contaminated, or
polluted, water can
harm humans,
plants, and animals.
• Provides us with
recreation, including
swimming, fishing,
surfing, and sailing
• Flooding can
damage property
and threaten lives.
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• Important source of
energy
The Land
The Big Idea
Processes below and on Earth’s surface shape the planet’s
physical features.
Main Ideas
• Earth’s surface is covered by many different landforms.
• Forces below Earth’s surface build up our landforms.
• Forces on the planet’s surface shape Earth’s landforms.
• Landforms influence people’s lives and culture.
Holt McDougal,
Main Idea 1:
Earth’s surface is covered by many different
landforms.
• Landforms, or shapes on the planet’s surface, make up
the landscapes that surround us.
• Earth’s surface is covered with landforms of many
different shapes and sizes.
– Mountains, land that rises higher than 2,000 feet
– Valleys, areas of low land located between mountains or hills
– Plains, stretches of mostly flat land
– Islands, areas of land completely surrounded by water
– Peninsulas, land surrounded by water on three sides
Holt McDougal,
Main Idea 2:
Forces below Earth’s surface build up our
landforms.
Earth’s Plates
• The planet’s continents, or large landmasses, are part of Earth’s
crust—the solid outer layer of the planet.
• Theory of plate tectonics suggests that Earth’s surface is divided
into a dozen or so slow-moving plates, or pieces of Earth’s crust.
Movement of Continents
• The idea that continents have traveled great distances over millions
of years is known as continental drift.
• Theory, developed by Alfred Wegener, states that the continents were
once united in a single supercontinent and over time, slowly
separated and moved to their present positions.
• As plates collide, separate, and slide, they shape Earth’s landforms
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Plates Collide, Separate, and Slide
Plates Collide
• Two ocean plates:
one pushes under
the other, creating
ocean trenches, or
deep valleys in
ocean floor
• Ocean and
continental plate:
ocean plate drops
beneath continental
plate, forcing land
above to crumple
and form mountain
range
• Two continental
plates:
land pushes up to
form mountains
Plates Separate
Plates Slide
• As plates move
apart, gaps between
plates allow magma
to rise to Earth’s
crust.
• As plates pass by
each other, they
sometimes grind
together, producing
earthquakes,
sudden, violent
movements of
Earth’s crust.
• Lava, magma that
reaches the Earth’s
surface, emerges
from the gap.
• As lava cools, it
builds a mid-ocean
range, or
underwater
mountain, that can
rise above the
surface of the ocean
to form islands.
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• Earthquakes often
take place along
faults, or breaks in
Earth’s crust where
movement occurs.
• The region around
the Pacific plate,
called the Ring of
Fire, is home to
most of the world’s
earthquakes and
volcanoes.
Main Idea 3:
Forces on the planet’s surface shape
Earth’s landforms.
• Weather, water, and other forces change Earth’s
landforms by wearing them away or reshaping them.
• Weathering is the process by which rock is broken down
into smaller pieces called sediment.
– Heating and cooling can cause rocks to crack.
– Expansion of water as it freezes can cause cracks to expand.
– Roots of trees can pry rocks apart.
• Erosion is the movement of sediment from one location
to another.
– Can wear away or build up landforms
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Types of Erosion
Wind Erosion
• Winds lift sediment
into air and carry it
across great
distances .
• On beaches and in
deserts, deposits
can form dunes.
• Blowing sand can
wear down rock.
Glacial Erosion
Water Erosion
• Glaciers, or large,
slow-moving sheets
of ice, erode the
land by carving
valleys and
mountain peaks.
• Waves and flowing
water can cut
through rock, carry
sediment, and
deposit sediment in
new locations.
• Crush rock into
sediment and move
it great distances
• Floodplains are
created when rivers
flood their banks
and deposit
sediment.
• Sediment carried by
a river all the way
to the sea creates a
delta.
Holt McDougal,
Main Idea 4:
Landforms influence people’s lives and
culture.
Landforms can influence where people settle.
Landforms often influence what jobs are available in a region.
Landforms can affect language.
People sometimes change landforms to suit their needs.
Holt McDougal,