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Chapter 2 STUDY GUIDE
For use with
textbook pages 33–36.
Planet Earth
This section focuses on what humans
know about the physical nature of our planet, Earth.
Chapter 2,
Section 1
Terms to Know
hydrosphere The part of
the earth made up of oceans, lakes, rivers, and other bodies of water (page 35)
lithosphere The surface land areas of the earth’s crust, including continents
and the ocean floor (page 35)
atmosphere The air that
surrounds the earth (page 35)
biosphere The part of
the earth where life exists (page 35)
continental shelf The part of
a continent that extends underwater (page 36)
Earth’s
Features
(page 33) Water,
land, and air form the physical environment of the earth.
1. What makes up the physical
environment of the earth?
Our Solar System (page 33) Our solar system is made up of the sun and all the
objects that revolve around it. The sun, the center of the solar system, is a
ball of burning gases. The huge amount of matter contained in the sun creates a
strong pull of gravity. This physical force keeps the earth and the other
objects revolving around the sun.
Planets are the largest objects in
the solar system, besides the sun. Each planet moves in its own orbit around
the sun. There are nine known planets in our solar system:
A. Mercury, a hot,
inner planet, is closest to the Sun. B. Venus is a hot, inner planet.
Mercury and Venus are the only planets without moons. C.
Earth is an inner planet and
the third from the sun. It is fifth in size among the planets. Earth is the
only planet with liquid water at the surface and able to support varieties of
life. D. Mars is a cold, barren desert. It is an inner planet. E. Jupiter is an
outer planet and the largest of all planets. F.
Saturn is an outer planet with
at least 18 moons. G. Uranus is an outer planet. H.
Neptune is an outer planet.
I. Pluto is an
outer planet. It is the smallest planet and is a ball of ice and rock.
All the planets, except Pluto, are
grouped into two types:
A. Terrestrial planets have solid,
rocky crusts. Mercury, Venus, Earth, and
Mars are terrestrial planets.
B. Gas giant planets are
larger, more gaseous, and less dense than terrestrial planets. Jupiter, Saturn,
Uranus, and Neptune are gas giant planets.
STUDY GUIDE Chapter 2, Section 1
Besides planets, other objects that
revolve around the sun include asteroids, comets, and meteoroids. Asteroids
are small, oddly shaped, planet like objects. Comets are made up of icy, dusty
particles and frozen gases. Meteoroids are large pieces of rock and
iron.
Getting to Know Earth (page 35): The surface of the earth is made up
of water and land. About 70 percent of
Earth’s surface is water. The earth’s hydrosphere consists
of bodies of water such as oceans, lakes, and rivers. About 30 percent of
Earth’s surface is land, or lithosphere. Earth’s atmosphere
is a layer of gases that extends about 1,000 miles above the
surface. The biosphere is the part of the earth where
people, plants, and animals live.
The natural features of the earth’s
surface are called landforms. Earth is made up of four major types of
landforms: mountains, hills, plateaus, and plains.
Landforms are found on the earth’s surface and underwater. The largest
landforms on Earth are the seven continents. The continents are: Australia, Antarctica, Europe, Asia, North
America, South America, and Africa. The continental
shelf is the part of the continent that
extends underwater.
The earth has great differences in
the heights and depths of its surface. Mount Everest is its highest point at
29,035 feet above sea level. The shore of the Dead Sea is the earth’s lowest
point at 1,349 feet below sea level.
(For use with
textbook pages 37–43.)
Forces of
Change
DRAWING FROM
EXPERIENCE
In the last section you read about
the features of Earth. This section focuses on the forces that change the
surface of earth.
Chapter 2,
Section 2
Terms to Know
mantle A thick layer
of hot, dense rock beneath the earth’s crust (page 38)
continental drift The slow
movement of continents across the earth (page 38)
magma Molten rock
(page 38) plate tectonics The movement of great slabs of
rock that make up the earth’s
crust (page 38)
subduction: A heavier sea plate diving under a lighter
continental plate (page 39)
accretion Pieces of
the earth’s crust coming together slowly as a sea plate slides under a
continental plate (page 40)
spreading Sea plates
pulling apart (page 40)
fold A bend in
layers of rock (page 40)
fault A crack in
the earth’s crust (page 40)
weathering The process
that breaks down rocks into smaller pieces (page 42)
erosion The wearing
away of the earth’s surface by wind, glaciers, and moving water (page 42) loess A fertile, yellow-gray soil
deposited by wind and water (page 42)
glacier Large body
of ice that slowly moves across the earth’s surface (page 42)
moraine Large piles
of rocks and debris caused by melting and moving glaciers (page 42)
Internal Forces/
External Forces
Introduction (page 37) Scientists have evidence that the center of the earth is
active with intense heat and pressure. Movements deep within the earth cause
changes to the earth’s surface.
Earth’s Structure (page
37) The earth is made up of three layers:
A. The core is the
center of the earth. The inner core is solid,
very hot, and under great pressure. It contains lead, iron and nickel. The outer core is liquid. It is made up of
melted iron and nickel.
B. The mantle is a
thick layer of hot, solid rock. It is made up of many elements.
C. The crust is a rocky shell that forms the
earth’s surface. The crust is broken
into several huge slabs of rock called plates.
Many scientists believe in continental
drift. This is a theory that the continents were once joined
and then slowly drifted apart. Many scientists also believe that the moving
plates created the earth’s largest features— continents, oceans, and mountains.
Plate movement is constant and very slow. As the plates move, they crash into
each other, spread apart, or grind and slide past each other. The movements of
plates are called plate tectonics. When
the plates spread apart, magma, or
melted rock, pushes up from the mantle.
Internal Force of Change (page
39) There are six internal forces that change the surface of the
earth:
A. Mountains
can form when continental plates collide.
For example, the Himalaya ranges were formed when the Indian landmass
rammed into Asia. Mountains can also be formed in a process known as subduction, where
a sea plate dives beneath a continental plate.
The sea plate melts as it crashes into the mantle, and the resulting
magma bursts through the crust to form volcanic mountains.
Chapter 2, Section 2
In another process known as accretion, pieces
of the earth’s crust pile up slowly as a sea plate slides under the continental
plate. This accumulating debris causes
continents to rise.
B. Spreading is a
process in which sea plates pull apart. This
causes deep cracks in the ocean floor, releasing magma, which hardens into
undersea volcanic mountains or ridges.
C. Moving
plates sometimes squeeze the earth’s surface, causing folds or bends in layers of
rock.
D. Grinding
or sliding plates create cracks in the earth’s crust called faults.
E. Earthquakes are
caused by sudden, violent movements in plates along a fault line.
F. Volcanic eruptions can
occur when one plate plunges beneath another. Magma often blasts through the
surface of the earth as volcanoes. Volcanic
island chains can form from the molten rock.
External Force of Change (page
42) Wind and water change the earth’s surface:
A. Weathering is the
process that breaks down rocks on the earth’s surface into smaller pieces.
B. Erosion is the
wearing away of the earth’s surface by wind, glaciers, and moving water. It can
cause the loss of soil and lead to dust storms.
Wind erosion can also create deposits of mineral–rich soil called loess, a fertile, yellow-gray soil
found in China.
Glaciers are
large bodies of ice that slowly move across the earth’s surface, causing
erosion. As glaciers move, they pick up
rocks and soil and carve grooves in the landscape. When glaciers melt and withdraw, they leave
behind large piles of rock and debris called moraines. Water
erosion is mostly caused by fast-moving water in streams and rivers that wears
away soil and rock. The pounding waves
of oceans cause erosion along coasts.
(For use
with textbook pages 46–49.)
Earth’s Water
In the last section, you learned
about the forces that change the earth’s surface. This section focuses on the
earth’s water.
Chapter 2,
Section 3
Terms to Know
water cycle The movement
of water from the oceans to the air to the ground (page 47)
evaporation The changing
of liquid water into gas or vapor (page 47)
condensation A process in
which water vapor changes into liquid water (page 47)
precipitation Moisture
that falls to the earth in the form of rain, snow, or sleet (page 47)
desalination The process
of removing the salt from ocean water (page 48)
groundwater Fresh water
which lies beneath the earth’s surface (page 49)
aquifer An
underground rock layer saturated with water in the form of streams (page 49)
Earth’s Water: Fresh Water/Salt Water
(page 46) All
living things need water to survive. Water on Earth comes in three forms:
A. The liquid form of
water is in rivers, lakes, and oceans. B. The gas form
of water is held in the atmosphere. It is sometimes called water vapor. C. The frozen form of
water is in glaciers and ice sheets.
Where is the earth’s water found?
The Water Cycle (page 46) Almost
all of the hydrosphere is salt water found in oceans, seas, and salt- water
lakes. The rest is fresh water found in lakes, rivers, and springs.
The total amount of water on Earth
does not generally change. The water cycle is the constant movement of water
from the oceans, to the air, to the ground, and finally back to the oceans. The
water cycle has four main stages:
A. Evaporation is the
changing of liquid water into vapor, or gas.
The sun’s heat causes water vapor to rise from the oceans and other bodies
of water into the atmosphere.
B. Condensation is the
stage in which warm air cools and some of the water vapor changes back into
liquid water. Tiny droplets of water
come together to form clouds.
C. Precipitation is
rain, snow, or sleet, which falls from clouds that contain more water than they
can hold.
D. Surface
runoff is formed from the precipitation as it falls to the ground. This water collects in rivers, lakes, and
oceans.
Chapter 2, Section 3
Bodies of Salt Water (page 47)
About 70 percent of the earth’s
surface is water. Almost all of the earth’s water is salt water. There are four
main kinds of bodies of salt water— oceans, seas, gulfs, and bays. Oceans make
up about 97 percent of the earth’s water. There are four oceans—the Pacific,
the Atlantic, the Indian, and the Arctic. The Pacific is the largest and covers
more area than all the earth’s land combined. Seas, gulfs, and bays are much
smaller than oceans. These bodies of water are partially enclosed by land.
The water found in oceans is too
salty for drinking, farming, or manufacturing. A process is being developed,
called desalination, or obtaining freshwater
from oceans by removing the salt content.
Bodies of Freshwater (page 48) About
3 percent of Earth’s total water supply is freshwater. Most of this 3 percent
is not available to use. More than 2 percent of Earth’s total water supply is
frozen in glaciers and ice caps. About 0.5 percent is found beneath the earth’s
surface. Lakes, streams, and rivers contain less than 1 percent of the earth’s
water. This water is important to people because it meets their everyday needs.
For this reason, most large urban areas began as settlements along the shores
of lakes and rivers where people could have a constant supply of water.
Another source of freshwater is groundwater, which
lies beneath the earth’s surface and supplies wells and springs. Groundwater
comes from rain and melted snow that filter through the soil. It also comes
from water seeping into the ground from lakes and rivers. In areas with little
water, people sometimes depend on aquifers for
their water supply. An aquifer is an underground porous rock layer often filled
with water in the form of streams.
