Name Date Class. This section describes Earth s atmosphere, or the layer of gases that surrounds the planet.

Transcription

1 The Atmosphere Name Date Class The Atmosphere Guided Reading and Study The Air Around You This section describes Earth s atmosphere, or the layer of gases that surrounds the planet. Use Target Reading Skills As you preview the section headings, write what you know about the atmosphere in the box What You Know. As you read the section, complete the What You Learned box. I. The atmosphere contains oxygen. What You Know I. What You Learned 2. 3.

2 Name Date Class The Atmosphere Guided Reading and Study The Air Around You (continued) Introduction 1. The condition of Earth s atmosphere at a particular time and place is called. 2. What is Earth s atmosphere? Composition of the Atmosphere 3. Label the two larger pieces of the graph with the gases they represent. Gases in Dry Air a. b. 78% 21% 1% All other gases c. Use the graph to estimate how many times more nitrogen than oxygen makes up air. d. What percentage of air is made of nitrogen and oxygen together? 4. Circle the letter of each sentence that is true about nitrogen. a. Humans do not breathe in nitrogen. b. A nitrogen molecule has two nitrogen atoms. c. Nitrogen is a gas. d. Nitrogen makes up more of the air than any other gas. 5. Circle the letter of each sentence that is true about oxygen. a. It is needed by animals but not plants. b. It is needed to release energy from food. c. It is released by fuels when they burn. d. It may form ozone when it interacts with lightning.

3 The Atmosphere Name Date Class The Atmosphere Guided Reading and Study 6. Circle the letter of each sentence that is true about carbon dioxide. a. It is essential to life. b. It is given off by plants and animals as a waste product. c. It is used by animals to digest food. d. It is needed by fuels to burn. 7. Is the following sentence true or false? Carbon dioxide alone makes up almost 1 percent of dry air. 8. What particles does air contain? 9. Water in the form of a gas is called. 10. Is the following sentence true or false? Water vapor is the same as steam. 11. What role does water vapor play in Earth s weather? Importance of the Atmosphere 12. How does Earth s atmosphere make conditions on Earth suitable for living things?

4 Name Date Class The Atmosphere Section Summary The Air Around You Key Concepts What is the composition of Earth s atmosphere? How is the atmosphere important to living things? Weather is the condition of Earth s atmosphere at a particular time and place. Earth s atmosphere is the envelope of gases that surrounds the planet. Earth s atmosphere is made up of nitrogen, oxygen, carbon dioxide, water vapor, and many other gases, as well as particles of liquids and solids. Nitrogen makes up about three fourths of the air. Oxygen is the second most abundant gas in air. Plants and animals take oxygen directly from air and use it to release energy from food. Oxygen also is needed for fire to burn. Most oxygen molecules have two oxygen atoms. A form of oxygen called ozone, which contains three oxygen atoms in each molecule instead of the usual two, is sometimes found in air. It forms when lightning interacts with oxygen in the air. Carbon dioxide is very important because plants need it to survive. Plants and animals give off carbon dioxide as a waste product when they break down food to produce energy. The burning of fuels such as gasoline and coal also produces carbon dioxide. Water vapor is invisible it is water in the form of a gas. The amount of water vapor in the air may vary greatly. Water vapor is important in weather. It produces clouds and precipitation. Pure air contains only gases. In the real world, air also contains tiny solid and liquid particles of dust, smoke, salt, and other chemicals. Earth s atmosphere makes conditions on Earth suitable for living things. The atmosphere contains oxygen and other gases that living things need. The atmosphere also traps energy from the sun, which keeps Earth s surface warm and Earth s water in liquid form, another requirement of living things. In addition, the atmosphere protects Earth from dangerous radiation from the sun and from meteoroids, which are chunks of rock from outer space.

5 Name Date Class The Atmosphere Review and Reinforce The Air Around You Understanding Main Ideas Fill in the blanks in the table below. Gases in Dry Air Percent by Volume Argon Nitrogen Answer the following questions on a separate sheet of paper. 5. Besides the gases shown in the table, what else is found in Earth s atmosphere? 6. What are two sources of carbon dioxide in air? 7. What are trace gases? 8. How does the atmosphere make conditions on Earth suitable for living things? 9. What are two processes that use oxygen? 10. Is the atmosphere always the same? Explain why or why not. Building Vocabulary Match each term with its definition by writing the letter of the correct definition on the line beside the term. 11. weather 12. atmosphere 13. ozone 14. water vapor a. the envelope of gases that surrounds Earth b. a form of oxygen that has three oxygen atoms in each molecule instead of the usual two c. water in the form of a gas d. the condition of Earth s atmosphere at a particular time and place

6 The Atmosphere Name Date Class The Atmosphere Enrich How Earth s Atmosphere Got Its Oxygen When Earth s atmosphere first formed, it contained little, if any, oxygen. How, then, did our oxygen-rich atmosphere come about? The answer is life, which first appeared on Earth in the form of bacteria about 3.5 billion years ago. By about 2.5 billion years ago, oxygen-producing organisms, called cyanobacteria, had evolved. Evolution is the process by which organisms change to give rise to new organisms over time. The cyanobacteria took in carbon dioxide and water and produced oxygen as a waste product. Over time, the oxygen they produced accumulated in the atmosphere. Some of the oxygen was converted to ozone by the sun s energy. This was important later for the development of life on land because as ozone increased, it protected Earth s surface from too much ultraviolet radiation. By 700 million years ago, the oxygen concentration had reached about ten percent of the current level, and organisms made up of many cells had evolved. By 450 million years ago, the ozone level was getting close to its present value, and soon after that land plants evolved. They were followed by land animals at about 380 million years ago. Both oxygen and ozone levels reached their current levels about 300 million years ago. By then there were many different kinds of complex land plants and animals living on Earth. Oxygen or ozone concentration (% of present level) 100% 10% 1.0% % 3,500 2,500 Ozone organisms 1, Date (millions of years ago) Flowering plants Mammals d animals Land plants 100 Answer the following questions on a separate sheet of paper. 1. How did life on Earth influence the development of Earth s atmosphere? 2. What role did ozone play in the evolution of life on Earth? 3. What do you think Earth s atmosphere would be like today if life had not evolved on Earth?