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Water on Earth

Scott Foresman Science 5.5

StandardsPreview

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.

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.

ISBN 0-328-23464-8

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Vocabulary

aquifercondensationevaporationprecipitationreservoir salinitysea levelsleetwater cyclewater tablewatershed

Picture CreditsEvery effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.

ISBN: 0-328-23464-8

Copyright © Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to anyprohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic,mechanical, photocopying, recording, or likewise. For information regarding permission(s), write toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

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by Kristin Cashore

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How can the oceans be described?The Hydrosphere

Bodies of water, such as rivers, lakes, and oceans, are very important to us. We can travel and catch food on bodies of water. We can enjoy them for their natural beauty. What bodies of water are near you?

The hydrosphere is made up of all of the water on Earth. It covers three-fourths of Earth’s surface. Oceans, rivers, and lakes are all part of the hydrosphere. Only 3/100 of the hydrosphere is not in the ocean.

The Pacifi c Ocean is the biggest ocean. Next comes the Atlantic Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean. The oceans are all connected to each other.

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The Pacifi c Ocean is the biggest ocean. It is the deepest ocean too. Its average depth is about 4,000 meters. It is more than 11,000 meters deep at its deepest place.

Every ocean is different. Each ocean’s water is at different average depths. Some have more storms than others do. They have different temperatures and different amounts of salt. Even sea level, the level of the ocean’s surface, is slightly different from ocean to ocean.

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Earth’s OceansOcean water is salty. Rivers make the oceans salty. Rain

falls on the oceans and the land. Rain can dissolve salts and other minerals when it falls on land. Rivers then carry these salts and minerals into the oceans. Water evaporates from the surface of the ocean, but the salts are left behind in the water.

Salinity is a measure of the amount of salt in water. Some parts of the ocean have less salt than others. Places where fresh water from rivers fl ows into the ocean have low salinity. In warm, dry places ocean water evaporates fast. This leaves salt behind, so the ocean has a higher salinity.

Cold water with high salinity weighs more than the same amount of water that is warmer. It also weighs more than the same amount of water with lower salinity. The blue-colored water below is warmer and has lower salinity than the clear water. The blue water fl oats on the clear water because of this.

The blue water is at room temperature and has one-half of a spoonful of salt. The red water is warm and has no salt. The blue layer fl oats on top of the clear water, which is cold and has more salt.

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Ocean TemperaturesNot all ocean water is at the same temperature. Ocean

water near the equator is about 30°C. Ocean water near the poles can be as cold as a –2°C.

Currents in the ocean move water back and forth. Some currents carry warm water toward the poles. The Gulf Stream is one current that does this. It brings warm water from the Carribean Sea to the North Atlantic Ocean. Other currents carry cold water toward the equator. The California Current runs along the west coast of the United States. It brings cold water toward the south.

Ocean ResourcesThe oceans are very important to our Earth. People get

food and other materials from the ocean. A lot of the salt we use for food is from the ocean. People who process salt let ocean water fl ow into shallow ponds. When the water evaporates, salt is left behind.

When ocean water in these ponds evaporates, salt is left behind.

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Where is fresh water found?

Drinking water is also called fresh water. Fresh water has much less salt than seawater. Almost all fresh water begins as rain or snow. Some sinks into the ground. Some collects in rivers and lakes. Some freezes into ice sheets and glaciers.

Some places have much more fresh water than others. But fresh water around the world is limited. People should try to use less water. They should recycle water if they can.

GroundwaterGroundwater is rain or melted snow that sinks into the

ground. Groundwater fi lls spaces between pieces of rock and soil. It sinks until it reaches a layer of rock or clay it cannot move through. Water can fl ow over these layers.

The layer of rock and soil that groundwater fl ows through is called an aquifer. The top level of groundwater in an aquifer is the water table. The level of the water table depends on how much it rains or snows. People can use up the water in an aquifer if they are not careful.

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RiversRivers, streams, and lakes are all surface waters. Creeks

run downhill, full of rainwater and melted snow. The creeks join to form streams and rivers. Groundwater also seeps into rivers. Most rivers fl ow into the ocean. A watershed is the area from which water drains into a river.

A watershed can have a big effect on a river. If chemicals are dropped in a watershed, they can be carried by water to rivers. This can change river ecosystems.

LakesLakes form when water collects in a low spot. Lakes

may be surrounded by higher land or blocked by a dam. A reservoir is usually an artifi cial lake that forms behind a dam.

A lake, pond, stream, or swamp forms where the water table meets the surface.

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IceAbout seven-tenths of Earth’s fresh water is frozen!

This makes it hard for people to use. In Greenland and Antarctica, big ice sheets cover most of the land. The sheets can be several kilometers thick. These places are where much of Earth’s ice is found.

GlaciersSmaller sheets of ice are called glaciers. Valley glaciers

sit in the valleys of high mountains. They move slowly downhill. As they move, they cut into the rock and move it. This changes the shape of the valley.

Glaciers and ice sheets form when the amount of snowfall is greater than the amount of snow that melts. Over time, the snow underneath is pressed into ice by the snow on top. Large pieces of glaciers and ice sheets can break off into the ocean. These pieces are called icebergs.

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Getting Water to HomesIn the United States, some towns get water from

groundwater or surface water. But sometimes this water has harmful bacteria or is polluted with chemicals. Water must fi rst be treated before it is safe to use.

Water is treated at a treatment plant. First, water is pumped from a river or lake through screens to a tank. Then, chemicals are added to the water. These chemicals make small particles stick together. The larger particles that are formed then sink to the bottom of the tank. Next, the water passes through fi lters made of sand and gravel. The fi lters take out smaller particles. Finally, even more chemicals are added to the water. Chemicals such as chlorine kill harmful bacteria. After the water is treated, it is stored in a water tower.

Now you know that a lot must happen before water gets to your home. This is why it is very important not to waste water.

This iceberg is in Greenland. Only 1/10 of the iceberg fl oats above the water. You cannot see the 9/10 that is underwater.

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What are some California water sources?Too Much or Not Enough?

Some parts of California get a lot of rain. Other parts are very dry. The northern coastal region of California gets about 250 centimeters of rain every year. But the deserts of southeastern California get only about 10 centimeters of rain every year. Because of this, the supply of fresh water in southern California is limited. However, southern California uses about two-thirds of the fresh water used in the state!

A lot of California’s water comes from winter snow. When the snow melts, its fresh water runs from the mountains into streams and lakes. This water is collected and sent all over the state.

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Transporting Water Throughout California

Aqueducts help to carry water throughout California. An aqueduct is a system of pipes that carries water from one place to another. Aqueducts carry water from rivers and lakes to where it is needed.

There are many aqueducts in California. The California Aqueduct brings water from the mouth of the Sacramento River to communities more than 400 kilometers away. The Los Angeles Aqueduct carries water from a number of sources to Los Angeles. The Colorado River Aqueduct carries water from the Arizona border to Riverside County. That is a distance of almost 390 kilometers! From there it travels south to San Diego.

Melted snow runs out of the Sierra Nevada. It provides drinking water to many Californians.

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This farm uses reclaimed water for watering crops to help save water.

Local Water SourcesDid you know that everyone lives in a watershed? The

amount of water in the watershed determines how much water an area has to use. Water from rain and snow falls in streams, rivers, and lakes. Water also sinks into the soil and becomes groundwater. Both surface water and groundwater are available for people to use.

The way land in a watershed is used affects how clean the water is. Chemicals that are use in cities and on farms can be carried in water that runs off streets and farms. Soil that is being disturbed by construction can also get into water. The land must be used wisely to help keep water safe. This is why there are laws to keep water safe.

Conservation is using a resource such as water wisely so that it lasts longer. Taking shorter showers and fi xing leaky faucets and toilets are some of the ways people can conserve water.

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ReclamationWater can be recycled and used again. This is called reclamation. In reclamation, wastewater is carried to a treatment plant. After being treated, the water can be used for things other than drinking. For example, it can be used to water lawns or crops.

Finding Out About Local Water SourcesSome places get their fresh water from nearby water

sources. Other places use aqueducts to get water from far away.

The amount of water in these lakes and rivers depends on how much rain and snow falls there. It also depends on how people use the water.

Where does your water come from? Try contacting your local water company or going to the library-media center to fi nd out.

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Condensation

What is the water cycle?Water in the Air

Did you know that the air around you has water in it? This water is not in a liquid form, like the water in a river. It is also not in a solid form, like the ice in a glacier. The water in the air is an invisible gas called water vapor.

Air always has some water vapor in it. Even desert air contains water vapor. Water vapor was liquid water at some time in the past. It may have been part of a river or an ocean, or may have even been inside a plant!

The particles of water vapor are like the particles of other gases. They are always moving.

Evaporation

Precipitation

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The Water CycleWater moves from the oceans to the land and back

again through a process called the water cycle. The water cycle is the repeated movement of water through the environment in different forms. It is also called the hydrologic cycle. The water cycle has many steps.

Evaporation is the changing of liquid water to water vapor. Liquid water changes into water vapor when it is heated by the Sun. Condensation happens when air cools water vapor. Condensation is the changing of water vapor back into a liquid, such as water droplets in clouds or fog. The droplets are so small that they hang in the air. In precipitation, the air cools the water droplets even more. The water droplets grow big and heavy, and fall as rain, hail, sleet, or snow. Water can go many different ways through the water cycle.

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Water runs off the land and evaporates from plants.

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

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Many Paths of the Water CycleThe water cycle is not as simple as it seems. Water is not

always in the nonliving part of the environment. Living things use water. During photosynthesis, plants break down water as they make sugar. Living things also release water. They do this during respiration.

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Because salt is left behind when water evaporates, the oceans remain salty.

As water vapor rises, it may form a cloud.

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Energy in the Water CycleThe energy of the Sun is very important to the water

cycle. Sunlight causes melting and evaporation. It also causes sublimation, or the changing of ice directly to water vapor. The energy to raise water vapor to the clouds comes from the Sun. The energy to move water vapor with winds also comes from the Sun.

When water vapor condenses into liquid water, it releases energy. This energy heats nearby air or water. When liquid water evaporates, it takes in heat energy.

This cools nearby air and water. This heating and cooling can affect weather patterns.

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How do clouds form?Temperature and Pressure

Clouds come in many shapes and sizes. They form when water vapor condenses. This forms water droplets or ice crystals. The condensation of water vapor to form clouds is an important part of the water cycle.

The temperature of the air is part of why a cloud is made of water droplets or ice crystals. It is much colder in the clouds than it is on the ground. Even on hot days, many clouds are made of ice crystals.

Air pressure also affects the way clouds form. Clouds often form when air rises into areas of lower air pressure. As air rises, the pressure goes down. With less pressure, the air expands and cools. If the air cools enough, water vapor will form droplets or ice crystals.

Cirrus clouds are high-altitude clouds that are thin, wispy, and white.

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Vertical clouds are sometimes called thunderheads because they often cause thunderstorms.

PrecipitationMost rain in the United States starts as snow. This is

because the temperature of the air up high is often below 0°C. Clouds made of ice crystals form. The crystals grow bigger until they fall as snowfl akes. If the temperature of the air between the cloud and the ground is less than 0°C, the ice crystals fall to the ground as snow.

Falling ice crystals may change as they pass through different layers of air. Ice crystals will melt if they go through air that is warmer than 0°C. Then they will fall as rain. If the air near the ground is very cold, the rain may freeze before it hits the ground. These frozen raindrops are sleet. Freezing rain forms when rain freezes right as it hits the ground.

Hail FormationHail forms when strong winds blow upward into a

cloud. The winds blow raindrops up into the freezing air at the top of the cloud. The raindrops freeze into pieces of ice. The winds blow the ice back up into the cloud many times. More layers of water freeze onto the ice. Hailstones fall when pieces of ice grow too heavy for the winds to lift.

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aquifer the layer of rock and soil that groundwater fl ows 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 artifi cial 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

water table the top level of the groundwater in an aquifer

watershed the area from which water drains into a river

Glossary

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What did you learn?1. What is likely to happen if a factory drops harmful chemicals on

the ground in the watershed of a river?

2. What part do plants and animals play in the water cycle? 3. How is hail formed?

4. You learned about the importance of

preserving and protecting our water. Write a story about a student who does something to protect the water in his or her watershed. Be sure to use a lot of description.

5. Main Idea and Details California has a limited supply of fresh water. List details that support this idea.

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