Download Land, Air, and Water • What forces shape the land? • What are the

Chapter 2 , Section 2
page 31
Land, Air, and Water
• What forces shape the land?
• What are the Earth’s major
landforms?
Chapter 2 , Section 2
Forces Inside the Earth
What is the Earth made of?
The Earth’s surface is made up of 75 percent water and 25
percent land.
Continents are unique, in part because of their landforms,
which include mountains, hills, plateaus, and plains.
Pangaea: The Supercontinent
Geographers theorize that millions of years ago the Earth
had only one huge landmass, which they call Pangaea.
They believe that 200 million years ago, some force made
Pangaea split into several pieces and begin to move apart,
forming separate continents.
The theory of plate tectonics explains why the continents
separated. Continents are part of plates that shift over time.
Chapter 2 , Section 2
The Movement of the Continents
When geographers first began to study world
maps, they realized that the continents look like
pieces of a jigsaw puzzle.
Chapter 2 , Section 2
Volcanoes,
Volcanoes, Earthquakes,
Earthquakes, and
and Shifting
Shifting Plate
Plate Forces
Forces on
on
the
the Earth's
Earth's Surface
Surface
The world’s plates move in different directions, causing a variety
of effects:
Ridges: In some places, plates move apart, and magma leaks
through the cracks in the crust. In the oceans, over time, the
cooling rock builds up to form lines of underwater mountains
called ridges.
Volcanoes: In other places, the plates push against one another,
forcing one plate under the other. Tremendous pressure and
heat builds up causing molten rock to explode on the
surface.
Earthquakes: Along plate boundaries, there are many weak
places in the Earth’s crust. When plates push against each
other, the crust cracks and splinters from pressure. These
cracks are called faults. When the crust moves along faults,
it releases great amounts of energy in the form of
earthquakes.
Chapter 2 , Section 2
Air and Water: Two Ingredients for Life
Air
• The thick layer of gases that surrounds the Earth is called the
atmosphere.
• It provides life-giving oxygen for people and animals and lifegiving carbon dioxide for plants.
• It also acts as a blanket, holding in enough heat from the sun
to make life possible.
• Winds distribute this heat around the globe.
Water
• Roughly 97 percent of Earth’s water is found in the oceans.
• The rest is fresh water, or water without salt. Most of that is
frozen at the poles.
• Fresh water comes from lakes, rivers, and rain. Much fresh
water, called groundwater, is stored in the soil.
• People need fresh water—the Earth has enough, but some
places have too much, and others have too little.
Chapter 2 , Section
Chapter 2 , Section 2
The World: Wind Patterns
Chapter 2 , Section 2
Land, Air, and Water–Assessment
Why are there earthquakes and volcanoes?
Weak places in the Earth’s crust crack and splinter from
pressure, causing earthquakes, or break apart, allowing liquid
rock from beneath the surface to rise as volcanoes.
What forces on the Earth’s surface break down rocks?
Wind, rain and ice
Why is the atmosphere important?
It makes it possible for life to exist on the Earth.