Earth Sciences
Standards
Preview
Standard Set 3. Earth Sciences
3. Water on Earth moves between the
oceans and land through the processes
of evaporation and condensation. As a
basis for understanding this concept:
3.a. Students know most of Earth’s
water is present as salt water in the
oceans, which cover most of Earth’s
surface.
3.b. Students know when liquid water
evaporates, it turns into water vapor
in the air and can reappear as a liquid
when cooled or as a solid if cooled
below the freezing point of water.

Genre

Nonfiction

Comprehension Skill

3.c. Students know water vapor in the
air moves from one place to another
and can form fog or clouds, which are
tiny droplets of water or ice, and can
fall to Earth as rain, hail, sleet,
or snow.
3.d. Students know that the amount

of fresh water located in rivers, lakes,
underground sources, and glaciers is
limited and that its availability can be
extended by recycling and decreasing
the use of water.
3.e. Students know the origin of water
used by their local communities.

Text Features

Main Idea and Details • Captions
• Diagrams
• Glossary

Science Content

Water on Earth

Scott Foresman Science 5.5

ISBN 0-328-23465-6

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by Ann Cambal


Vocabulary
aquifer
condensation

evaporation
precipitation
reservoir
salinity
sea level
sleet
water cycle
water table
watershed

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ISBN: 0-328-23465-6
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by Ann Cambal


Water on Earth

There could be no life on Earth without water. It is a vital
resource. We are used to having water easily available to us.
We depend on it and sometimes even take it for granted. Earth
is the only planet on which liquid water can be found. The
hydrosphere includes all of the water on Earth.
Three-quarters, or 75 percent, of Earth’s surface is covered
by water. Think about what that means! The water from rivers,
ponds, swamps, streams, lakes, and oceans covers three times as
much of Earth as the land does. You can also think about it this
way. If you walked four blocks, three of those blocks would be
underwater!
San Francisco Bay

2

Only about 3 percent of the water on Earth is in places
other than the oceans. This makes water a very limited resource.
Communities have to develop ways to clean water and move it
to areas where there are large numbers of people. The role of
hydrologists is to understand Earth’s various forms of water and
water systems. Hydrologists also help plan for and educate us
about water’s relation to the environment and to all forms of life.
This is a big job. In the end, we all must work together to make
sure there is enough water to drink.

Lake Michigan

Vernal Falls, Yosemite National Park

3



Oceans of the World
—72— ,
The world’s oceans alone cover about 72 percent, or 100
of Earth. The Pacific Ocean is the largest. Next in size are the
Atlantic, Indian, Southern, and Arctic oceans. The water in all of
the oceans is salty.
The Pacific Ocean is the largest and deepest ocean in the
world. Its depth averages about 4,000 meters. At its deepest,
the Pacific is more than 11,000 meters deep. That’s about 11
kilometers! Another measure used in talking about the oceans is
sea level. This is the level of the ocean’s surface. Like the other
properties of the oceans, sea level varies from ocean to ocean.

Temperatures of the Oceans
Ocean surface temperature varies from place to place. Near
the equator, ocean water is about 30°C. But at Earth’s poles, the
ocean water can be -2°C.
Ocean water near the mouth of
the Nile River has less salinity than
ocean water farther away.

4

Another thing that varies in the oceans is the level of
salinity, or the amount of salt in water. Areas where rivers meet
oceans have very low salt levels. Ocean water usually has a high
salinity. In warmer areas, ocean water evaporates, leaving behind
salt, so water there has higher salt levels.

If water has a high salinity and is cold, then it is heavier than
the same amount of water that is warmer or less salty. This helps
explain how water is different in oceans across the world.

Resources of the Oceans
If you’ve ever tasted salt water, you know it’s not good for
you to drink. Yet the ocean is a great source of many things we
use and eat. These include the fish and other seafood we eat
and the salt we use on our food. Although it is expensive to do,
ocean water can become drinking water once the salt and other
chemicals have been removed.
Salt is left behind when ocean
water in these shallow ponds
evaporates.

5


Fresh Water
3 , or 3 percent, of the hydrosphere is fresh water.
Only about 100
——
Most of the water on Earth is in the oceans. Earth has many
different sources of fresh water. Fresh water still contains some salt,
but not nearly the amount that’s in seawater. How far do you live
from the nearest fresh water? Where is fresh water found?
Almost all of the fresh water starts out as either rain or snow.
Some of this water sinks into the soil. Some collects in rivers,
ponds, lakes, swamps, or streams. Not all of the water remains
in liquid form. Some of it becomes frozen into sheets of ice and

glaciers. More than half of Earth’s fresh water is frozen in ice.
The ice and glaciers are too far from where it’s reasonable to try
and use them.

6

Fresh water is not evenly spread all over Earth. Some areas
have more fresh water than other areas. Some areas have more
fresh water in some seasons than others. But the amount of fresh
water is limted everywhere. The water supply can be used wisely
if it is recycled or less water is used.
Scientists can help people use water wisely. The scientists
can give people information about the water’s quality. They
can also help reduce the amount of water a community needs
through technology.

This iceberg is floating in Disko Bay,
1
Greenland. Only —
10 of the iceberg floats
above the water.

7


Groundwater
Groundwater is the melted snow or rainwater that ends
up sinking into the ground. This water sinks until it reaches
something that it cannot move through. Sand, for example, lets
water pass more freely through it than a dense layer of clay. The

layer of rock and soil that groundwater moves through is called
an aquifer.
The water table is the top level of the groundwater in an
aquifer. Depending upon climate, rainfall, and other factors, the
level of any water table can change many times during a year.
People need to use groundwater wisely so that the water table
doesn’t fall faster than the water is replaced.

Surface water
Earth’s surface waters come from rainwater, groundwater,
and melting snow. Rivers, lakes, and streams are
examples of surface water. The water from small
creeks sometimes come together to
flow into larger rivers and streams.
Groundwater can also seep into
rivers. A watershed is the name for
an area whose waters drain into a
river. This area can be very large.
If there are chemicals on crops or
from industry in the area, they can
bring pollutants into the watershed.

Some water falling
on the ground seeps
into spaces in the
rocks and soil.

8

Lakes are formed when water flows into a lower area that is

blocked by a natural or artificial dam. A reservoir is much like
a lake. It, too, is a body of water that collects in a low spot. A
reservoir, however, is usually an artificial lake formed behind a dam.
The majority of fresh water on Earth is not in the lakes and
rivers you’ve read about. Seven-tenths of the Earth’s fresh water
is frozen in ice. It is far from people and hard to use. Most of the
ice on Earth is in ice sheets on Greenland and Antarctica. Ice
sheets can be almost a mile thick in places. The one at the North
Pole floats on the ocean with no land underneath it.
Glaciers are smaller areas of ice. They form valleys near high
mountains. Glaciers and ice sheets form over time. If more snow
falls than melts, then the new snow pushes down the layers
beneath it. When glaciers and ice sheets come in contact with
water, they can break off and form icebergs.
Pollution from the
surface can seep into
the groundwater.

The water
table is lower
in places where
people are using
groundwater
from an aquifer
faster than it can
be refilled.

9



Getting Water Where
It Is Needed
How does water get to your faucet at school and at home?
How do you know whether it’s safe to drink?
In the United States, groundwater and surface water are two
sources of water that people use in their homes. Water from
these sources, however, needs to be pumped, transported, and
“cleaned” before it is available for use at your home.
Screens keep out large
objects. Water and
chemicals are mixed.

10

Heavy pollutants fall
to the bottom of the
settling tank. Water is
filtered through sand.

Water treatment plants are found across the United States.
Indeed, they are found around the world. In U.S. plants, various
chemicals and pollutants that have made their way into the
water supply are removed. Water is treated in order to create a
supply of useable water that’s free from bacteria, looks sparkling
clean, and has no unpleasant taste or odor. Depending upon
the water supply, the water may be processed through several
treatments.

Water is pumped with
other chemicals to the

water tower. Water flows
down from the tank. It
then flows through pipes
to homes and businesses.

11


California’s Water Needs
Before the California gold rush in 1848, few people lived
there, and so the need for water was met. During and after the
gold rush, however, the population of California saw a steep
increase. By the early 1900s, large cities—such as San Francisco
and Los Angeles–heavily increased the need for water resources.
Because California has a very limited supply of fresh water,
the people there depend on aqueducts to bring them fresh water.
An aqueduct is a system of pipes that carries water from a river
or lake to the area where it is needed. Water flows through the
state in a network of aqueducts, tunnels, canals, and pipelines.
The Los Angeles Aqueduct supplies some of the fresh water
used by the city of Los Angeles. It carries water from the Owens
River of the Sierra Nevada to Los Angeles. The first part of the
system was built about 100 years ago. Later, more pipes were
added to get water from some streams that flowed into Mono
Lake. In 1970, a second aqueduct was added to the system.
The Colorado River Aqueduct supplies much of San Diego’s
fresh water. This aqueduct begins at Lake Havasu at the border
of Arizona and California. It carries water nearly 390 kilometers
to Lake Mathews in Riverside County before it heads south to
San Diego.

The California Aqueduct carries fresh water from the
Sacramento River to people living more than 400 kilometers to
the south.

12

Aqueduct systems like the California
Aqueduct carry fresh water from
rivers and lakes to people living many
kilometers away.

13


California’s Water Sources
California has many natural water resources. The northern
part of the state gets a large amount from rainfall and runoff
from mountain snow. Most of the population of the state lives,
however, in Southern California. The central region contains the
most farmland. There are regional water projects, but even those
need additional water to meet the needs of the residents.
California is the number one agricultural-producing state in
the country. Some of its crops require a great quantity of water.
Agriculture has become more efficient in its use of water over
time. Yet great quantities are still needed to support this multibillion dollar industry.

Thinking about the different climates in California can help
you understand the need for a system that can supply water
from one region to another. California has many climates. They
vary from snow-peaked mountains to hot, arid deserts. From

season to season and year to year, the amount of rainfall varies.
Sometimes there are floods in the same years as droughts.

California Watersheds

Sacramento River

San Joaquin River
San
Francisco
Bay
Colorado River

Tulare Lake

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15


The Water Cycle
The water cycle is a complex process. It provides us with
the water that we drink, use to water our gardens, and bathe in.
It also makes the different weather patterns around the world.
In the hydrologic (water) cycle, Earth’s water mainly moves
through the air. The steps of the water cycle are affected by
temperature and pressure.

The Sun drives the water cycle. It heats water, causing some
of it to evaporate. Evaporation means that water changes

from a liquid into a vapor in the air. Snow and ice can turn into
water vapor by sublimation, or when ice changes to water vapor
without first melting into a lquid. When air cools, condensation
can occur. Condensation is the changing of water vapor back
into liquid. When condensation occurs, clouds form.

As water vapor rises, it may
form a cloud.

Some rain or melted
snow becomes
groundwater.

Water runs off the land
and evaporates from
plants.

Groundwater slowly
moves through
aquifers into rivers,
lakes, and the ocean.

16

Because salts are left
behind when water
evaporates, the oceans
remain salty.

17



Cloud Formation
Clouds are an important part of the water cycle. They form
when water vapor condenses onto dust or other particles. When
this happens, tiny droplets or ice crystals form. Precipitation
occurs when the water droplets or ice crystals grow large
enough to fall from clouds as rain, hail, sleet, or snow.

Kinds of Precipitation
Rain

Freezing Rain

Sleet

Snow

Temperature and Pressure
The temperature determines what a cloud is made from.
Clouds high in the sky often have a lower temperature than ones
near the surface of Earth.
Air pressure affects the formation of clouds. As air rises,
the pressure decreases. With less air pressure, the air cools
and expands. If the air cools enough, it can form ice crystals.
This may be a surprise to you, but in the United States most
precipitation begins as snow. The ice crystals that form in those
clouds may stick together and start to form snowflakes. If the
temperature of the air between the ground and the cloud is
below freezing, then it snows!

If the air is warm between the cloud and the ground,
then the crystals will melt to form rain. As the rain falls, it
can refreeze and become sleet, or frozen raindrops. You may
experience this when the temperature near the ground is cold.

Hail Formation
Hailstones can form in clouds when strong winds blow
upward in them. If raindrops blow up into freezing air, they will
freeze into ice and become heavier. As they fall to Earth, winds
blow them up again where they gain another layer of ice.

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19


Glossary
aquifer

the layer of rock and soil that groundwater
flows through

condensation

the process by which particles leave a gas
and become a liquid

evaporation

the process by which particles leave a liquid

and become a gas

precipitation

water that falls from clouds as rain, hail, sleet,
or snow

reservoir

usually an artificial lake that forms behind
a dam

salinity

a measure of the amount of salt in water

sea level

the level of the surface of an ocean

sleet

frozen raindrops that fall as precipitation

water cycle

the repeated movement of water through the
environment in different forms; also called
the hydrologic cycle


water table

the top level of the groundwater in an aquifer

watershed

the area from which water drains into a river

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What did you learn?
1. What are the three main steps of the water cycle?
2. What is the main purpose of a water treatment plant?
3. How does groundwater become part of an aquifer?
4.

Write a paragraph about the use and
importance of water resources in your community. Explain how
people’s lives, homes, and businesses are affected. Read your
paragraph. Write your paragraph again. Give more details to show
what you’ve learned about the importance of water. Use words
from the book as you write.

5.

Main Idea and Details How do the farms and various large
cities in California impact the state’s water needs?