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1 Standards Preview Earth Sciences 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. by Ann Cambal Genre Comprehension Skill Text Features Science Content Nonfiction Main Idea and Details Captions Diagrams Glossary Water on Earth Scott Foresman Science 5.5 ì<(sk$m)=cdegfd< +^-Ä-U-Ä-U ISBN

2 Vocabulary aquifer condensation evaporation precipitation reservoir salinity sea level sleet water cycle water table watershed by Ann Cambal Picture Credits Every 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. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). Opener: (TR) Danita Delimont, Agent, (BR) Index Stock Imagery; 3 (CL) Danita Delimont, Agent; 4 (CR) Danita Delimont, Agent, (C) Getty Images; 13 (C) Peter Arnold, Inc.; 14 (C) Index Stock Imagery ISBN: 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 any prohibited 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 to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois V

3 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 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 2 3

4 Oceans of the World The world s oceans alone cover about 72 percent, or 72 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. 100, Ocean water near the mouth of the Nile River has less salinity than ocean water farther away. 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. 4 5

5 Fresh Water Only about 3 100, or 3 percent, of the hydrosphere is fresh water. 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. 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, Greenland. Only 1 10 of the iceberg floats above the water. 6 7

6 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. 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. 8 9

7 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. 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. Screens keep out large objects. Water and chemicals are mixed. Heavy pollutants fall to the bottom of the settling tank. Water is filtered through sand. 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

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

9 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 14 15

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

11 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. 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. Kinds of Precipitation Rain Freezing Rain Sleet Snow 18 19

12 Glossary aquifer condensation evaporation precipitation reservoir the layer of rock and soil that groundwater flows through the process by which particles leave a gas and become a liquid the process by which particles leave a liquid and become a gas water that falls from clouds as rain, hail, sleet, or snow usually an artificial lake that forms behind a dam 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? salinity sea level sleet water cycle water table watershed a measure of the amount of salt in water the level of the surface of an ocean frozen raindrops that fall as precipitation the repeated movement of water through the environment in different forms; also called the hydrologic cycle the top level of the groundwater in an aquifer the area from which water drains into a river 20