Download World Geography Main Idea 2

World Geography
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.
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World Geography
Chapter 2
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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World Geography
Chapter 2
Rotation and Revolution
Rotation
Revolution
•
•
Earth follows an orbit, or path, around the
sun.
•
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.
Earth spins on its axis—an imaginary line
that runs through the center of the planet
around which it turns.
•
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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World Geography
Chapter 2
Tilt and Latitude
Tilt
Latitude
• 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.
• 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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Latitude is the distance north or south of
Earth’s equator.
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World Geography
Chapter 2
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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World Geography
Chapter 2
The Seasons
Winter and Summer
Spring and Fall
Rainfall and Seasons
•
• In spring, Earth begins to
tilt toward sun, solar energy
increases, temperatures
rise, and days grow longer.
• In fall, the opposite occurs.
•
In the tropics, regions
close to the equator,
seasons are marked by
rainfall rather than
temperature.
•
At certain times of year,
winds bring either dry or
moist air to the tropics,
creating wet and dry
seasons.
•
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.
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World Geography
Chapter 2
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.
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World Geography
Chapter 2
Main Idea 1: Salt water and freshwater make up Earth’s water supply.
Earth’s Water
•
Water covers some two-thirds of the planet.
Salt Water
•
About 97 percent of the Earth’s water
•
Unsafe to drink because of high levels of salt
•
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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World Geography
Chapter 2
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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World Geography
Chapter 2
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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World Geography
Chapter 2
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.
• Flooding can damage property and threaten
lives.
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• Important source of energy
• Provides us with recreation, including
swimming, fishing, surfing, and sailing
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World Geography
Chapter 2
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.
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World Geography
Chapter 2
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
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World Geography
Chapter 2
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 slowmoving 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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World Geography
Chapter 2
Plates Collide, Separate, and Slide
Plates Collide
Plates Separate
Plates Slide
•
Two ocean plates: one
pushes under the other,
creating ocean trenches, or
deep valleys in ocean floor
•
As plates move apart, gaps
between plates allow
magma to rise to Earth’s
crust.
•
•
Ocean and continental plate:
ocean plate drops beneath
continental plate, forcing
land above to crumple and
form mountain range
•
Lava, magma that reaches
the Earth’s surface,
emerges from the gap.
As plates pass by each
other, they sometimes
grind together, producing
earthquakes, sudden,
violent movements of
Earth’s crust.
•
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.
•
Two continental plates:
land pushes up to form
mountains
•
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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World Geography
Chapter 2
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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World Geography
Chapter 2
Types of Erosion
Wind Erosion
Glacial Erosion
Water Erosion
•
Winds lift sediment into air
and carry it across great
distances .
•
•
•
On beaches and in deserts,
deposits can form dunes.
Waves and flowing water
can cut through rock, carry
sediment, and deposit
sediment in new locations.
•
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.
•
Blowing sand can wear
down rock.
•
Glaciers, or large, slowmoving sheets of ice,
erode the land by carving
valleys and mountain
peaks.
Crush rock into sediment
and move it great
distances to form islands.
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World Geography
Chapter 2
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.
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World Geography
Chapter 2
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