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Chapter 2
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.
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.
Rotation
spins on its axis —
an imaginary line that
runs through the center
of the planet around
which it turns.
Earth
takes Earth 24 hours
to make one rotation,
or complete spin on its
axis.
It
As
Earth spins, different
parts of the planet
face the sun, thus
causing the changes
from day to night.
Revolution
follows an orbit,
or path, around the sun.
Earth
Orbit
is not a perfect
circle.
takes Earth 365¼ days
to complete one
revolution, or trip
around the sun.
It
calendar year is
based on the time it
takes Earth to complete
its orbit.
Our
Tilt
Tilt
Earth’s
axis is tilted at
an angle of 23½
degrees from vertical.
At
any give time of
year, some places on
Earth tilt toward the
sun, and others tilt
away.
Places
tilting toward
the sun receive more
solar energy and have
warmer temperatures
than those that tilt
away.
Latitude
 Latitude
is the
distance north or
south of Earth’s
equator.
 Low-latitude
areas,
those nearest the
equator, receive
direct rays from the
sun all year.
 High-latitude
areas,
those farther from
the equator,
receive indirect
rays from the sun
and have colder
temperatures.
Latitude
Questions of the Day
1.
What is solar
energy?
2.
How does the
Sun affect life on
Earth?
3.
What four things
affect the
amount of
sunlight we
receive?


Take the next 5
minutes in class to
answer these
questions.
Refer back to your
notes for help!

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
Earth’s seasons
are caused by
the planet’s
tilt.
Summer
 Earth
tilts towards the sun in summer.
Winter
 Earth
tilts away from sun in winter
Spring and Fall
• In
spring: tilt toward sun, solar energy
increases, temperatures rise, and days
grow longer.
• In
fall: tilts away from sun, solar energy
decreases, temperatures decrease,
days are shorter
Tropics
 Tropics:
seasons are
marked by rainfall
rather than
temperature.
 Monsoons,
winds bring
either dry or moist air to
the tropics, creating
wet and dry seasons.
The Seasons
Winter and
Summer
• Earth tilts
away from
sun in winter
and towards
the sun in
summer.
• Because of
the Earth’s tilt,
the Northern
and Southern
hemispheres
experience
opposite
seasons.
Spring and Fall
Rainfall and
Seasons
• In spring,
Earth begins
to tilt toward
sun, solar
energy
increases,
temperature
s 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.
Water on Earth
Water is a dominant feature on Earth’s surface and is
essential for life.
• 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.
Salt water and freshwater make
up Earth’s water supply.
Earth’s Water
Salt 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


Freshwater
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

Water without salt

Makes up only 3 percent of our water supply
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.

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
The Water Cycle


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.
Water plays an important role in
people’s lives.
Water Problems
 Lack
of available
freshwater, which
can be caused by
droughts or overuse
 Contaminated,
or
polluted, water can
harm humans,
plants, and animals.
 Flooding
can
damage property
and threaten lives.
Water Benefits
 Provides
eat
us with food to
 Important
energy
 Provides
source of
us with
recreation, including
swimming, fishing,
surfing, and sailing
The Land
Processes below and on Earth’s surface shape the planet’s
physical features.
• 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.
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
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
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.
• 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.
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
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.