2 (h) Atmosphere
Composition of the Atmosphere: 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 is the most abundant gas in the atmosphere.
Nitrogen: Nitrogen is considered an element, because it is made of the same kinds of atoms (nitrogen atoms). Nitrogen is the most abundant gas in the atmosphere. It makes up a little more than three fourths of the air we breathe. Each nitrogen molecule consists of two nitrogen atoms.
An element is a pure substance that cannot be broken down into any other substances by chemical or physical means. Elements are the simplest substances. With each breath, you inhale the elements oxygen and nitrogen, which make up 99 percent of Earth’s atmosphere. Elements are often represented by one- or two-letter symbols, such as C for carbon, O for oxygen, and H for hydrogen.
Nitrogen is considered an element, because it is made of the same kinds of atoms (nitrogen atoms). Nitrogen is the most abundant gas in the atmosphere.
Nitrogen: Nitrogen is considered an element, because it is made of the same kinds of atoms (nitrogen atoms). Nitrogen is the most abundant gas in the atmosphere. It makes up a little more than three fourths of the air we breathe. Each nitrogen molecule consists of two nitrogen atoms.
An element is a pure substance that cannot be broken down into any other substances by chemical or physical means. Elements are the simplest substances. With each breath, you inhale the elements oxygen and nitrogen, which make up 99 percent of Earth’s atmosphere. Elements are often represented by one- or two-letter symbols, such as C for carbon, O for oxygen, and H for hydrogen.
Nitrogen is considered an element, because it is made of the same kinds of atoms (nitrogen atoms). Nitrogen is the most abundant gas in the atmosphere.
Notes #4: Earth's Atmospher
Oxygen
Oxygen is called an element, because it is made of the same kinds of atoms (oxygen atoms). Almost all of our oxygen in our atmosphere was made by producers through a process called photosynthesis.
Oxygen
Even though oxygen is the second most abundant gas in the atmosphere, it makes up less than one fourth of the volume.
Plants and animals take oxygen directly from the air and use it to release energy from their food.
Oxygen is also involved in many other important processes. Any fuel you can think of, from the gasoline in a car to the candles on a birthday cake, uses oxygen as it burns. Without oxygen, a fire will go out. Burning uses oxygen rapidly. During other processes, oxygen is used slowly. For example, steel in cars and other objects reacts slowly with oxygen to form iron oxide, or rust.
Chemical change
A change in matter that produces one or more new substances is a chemical change, or a chemical reaction.
In other chemical changes, two or more substances combine to form different substances. For example, iron metal combines with oxygen from the air to form the substance iron oxide, which you call rust. Unlike a physical change, a chemical change produces new substances with properties different from those of the original substances. The chemical change that occurs when fuels such as natural gas, wood, candle wax, and gasoline burn in air is called combustion.
Most oxygen molecules have two oxygen atoms. Ozone is a form of oxygen that has three oxygen atoms in each molecule instead of the usual two. Have you ever noticed a pungent smell in the air after a thunderstorm? This is the odor of ozone, which forms when lightning interacts with oxygen in the air.
If you have ever had a sunburn, you have experienced the painful effects of the sun’s ultraviolet radiation. But did you know that such burns would be even worse without the protection of the ozone layer? The ozone layer is a layer of the upper atmosphere about 30 kilometers above Earth’s surface Yet even the small amount of ozone in the ozone layer protects people from the effects of too much ultraviolet radiation. These effects include sunburn, eye diseases, and skin cancer. Ozone in the stratosphere filters out much of the harmful ultraviolet radiation from the sun The stratosphere is the second layer of the atmosphere and contains the ozone layer. The ozone layer is also important because it protects Earth’s living things from dangerous ultraviolet radiation from the sun.
Carbon Dioxide makes up less than 1 percent of the Earth’s atmosphere. Carbon dioxide is not an element like oxygen and nitrogen. It is a compound because it is made of a carbon atom and two oxygen atoms. The carbon and oxygen are chemically bonded in a 2-1 ratio. Compounds cannot be separated by physical means. However compounds can by broken down through a chemical change. Photosynthesis is a chemical change where plants break down carbon dioxide. Sugar and oxygen are new substance in this reaction.
Oxygen is called an element, because it is made of the same kinds of atoms (oxygen atoms). Almost all of our oxygen in our atmosphere was made by producers through a process called photosynthesis.
Oxygen
Even though oxygen is the second most abundant gas in the atmosphere, it makes up less than one fourth of the volume.
Plants and animals take oxygen directly from the air and use it to release energy from their food.
Oxygen is also involved in many other important processes. Any fuel you can think of, from the gasoline in a car to the candles on a birthday cake, uses oxygen as it burns. Without oxygen, a fire will go out. Burning uses oxygen rapidly. During other processes, oxygen is used slowly. For example, steel in cars and other objects reacts slowly with oxygen to form iron oxide, or rust.
Chemical change
A change in matter that produces one or more new substances is a chemical change, or a chemical reaction.
In other chemical changes, two or more substances combine to form different substances. For example, iron metal combines with oxygen from the air to form the substance iron oxide, which you call rust. Unlike a physical change, a chemical change produces new substances with properties different from those of the original substances. The chemical change that occurs when fuels such as natural gas, wood, candle wax, and gasoline burn in air is called combustion.
Most oxygen molecules have two oxygen atoms. Ozone is a form of oxygen that has three oxygen atoms in each molecule instead of the usual two. Have you ever noticed a pungent smell in the air after a thunderstorm? This is the odor of ozone, which forms when lightning interacts with oxygen in the air.
If you have ever had a sunburn, you have experienced the painful effects of the sun’s ultraviolet radiation. But did you know that such burns would be even worse without the protection of the ozone layer? The ozone layer is a layer of the upper atmosphere about 30 kilometers above Earth’s surface Yet even the small amount of ozone in the ozone layer protects people from the effects of too much ultraviolet radiation. These effects include sunburn, eye diseases, and skin cancer. Ozone in the stratosphere filters out much of the harmful ultraviolet radiation from the sun The stratosphere is the second layer of the atmosphere and contains the ozone layer. The ozone layer is also important because it protects Earth’s living things from dangerous ultraviolet radiation from the sun.
Carbon Dioxide makes up less than 1 percent of the Earth’s atmosphere. Carbon dioxide is not an element like oxygen and nitrogen. It is a compound because it is made of a carbon atom and two oxygen atoms. The carbon and oxygen are chemically bonded in a 2-1 ratio. Compounds cannot be separated by physical means. However compounds can by broken down through a chemical change. Photosynthesis is a chemical change where plants break down carbon dioxide. Sugar and oxygen are new substance in this reaction.
Carbon Dioxide Each molecule of carbon dioxide has one atom of carbon and two atoms of oxygen. Carbon dioxide is essential to life. Plants must have carbon dioxide to produce food. When the cells of plants and animals break down food to produce energy, they give off carbon dioxide as a waste product.
When fuels such as coal and gasoline are burned, they release carbon dioxide. Burning these fuels increases the amount of carbon dioxide in the atmosphere.
All matter is made of elements, but most elements in nature are found combined with other elements. A compound is a pure substance made of two or more elements chemically combined in a set ratio. A compound may be represented by a chemical formula, which shows the elements in the compound and the ratio of atoms. For example, part of the gas you exhale is carbon dioxide. Its chemical formula is CO2. The number 2 below the symbol for oxygen tells you that the ratio of carbon to oxygen is 1 to 2. (If there is no number after the element’s symbol, the number 1 is understood.)
When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements. Table sugar (C12H22O11) is a compound made of the elements carbon, hydrogen, and oxygen. The sugar crystals do not resemble the gases oxygen and hydrogen or the black carbon you see in charcoal.
Recall that gases in Earth’s atmosphere hold in heat from the sun, keeping the atmosphere at a comfortable temperature for living things. The process by which gases in Earth’s atmosphere trap this energy is called the greenhouse effect. Notice that sunlight does not heat the air in the greenhouse directly. Instead, sunlight first heats the soil, benches, and pots. Then infrared radiation from these surfaces heats the air in the greenhouse. The greenhouse effect in Earth’s atmosphere is similar in some ways.
Gases in the atmosphere that trap energy are called greenhouse gases. Carbon dioxide, water vapor, and methane are some of the greenhouse gases. Many scientists have hypothesized that human activities that add greenhouse gases to the atmosphere may be warming Earth’s atmosphere.
Changing Levels of Carbon Dioxide
Scientists think that an increase in carbon dioxide is a major factor in global warming. For example, the burning of wood, coal, oil, and natural gas adds carbon dioxide to the air. During the last 100 years, these activities have increased greatly in many different countries. The carbon dioxide in Venus’s atmosphere traps heat so well that Venus has the hottest surface of any planet. At 460°C, its average surface temperature is hot enough to melt lead. This trapping of heat by the atmosphere is called the greenhouse effect.
Other Gases Oxygen and nitrogen together make up 99 percent of dry air. Argon and carbon dioxide make up most of the other one percent. The remaining gases are called trace gases because only small amounts of them are present.
Water Vapor So far, we have discussed the composition of dry air. In reality, air is not dry because it contains water vapor. Water vapor is water in the form of a gas. Water vapor is invisible. It is not the same thing as steam, which is made up of tiny droplets of liquid water. Each water molecule contains two atoms of hydrogen and one atom of oxygen.
The amount of water vapor in the air varies greatly from place to place and from time to time. Water vapor plays an important role in Earth’s weather. Clouds form when water vapor condenses out of the air to form tiny droplets of liquid water or crystals of ice. If these droplets or crystals become heavy enough, they can fall as rain or snow.
Earth’s water is naturally recycled through the water cycle. The water cycle is the continuous process by which water moves from Earth’s surface to the atmosphere and back. In the water cycle, water moves from bodies of water, land, and living things on Earth’s surface to the atmosphere and back to Earth’s surface. The water cycle has three major steps—evaporation, condensation, and precipitation. The cycle itself has no real beginning or end. But it is driven by an energy source—the sun.
Water Evaporates As you learned earlier, evaporation is the process by which molecules at the surface of a liquid absorb enough energy to change to a gaseous state. Water is constantly evaporating from the surfaces of oceans and large lakes.
Condensation Forms Clouds What happens after a water molecule evaporates? Warm air carries the water molecule upward. At higher altitudes, air tends to become much colder. Cold air cannot hold as much water vapor as warm air can. As a result, some of the water vapor cools and condenses into liquid water. Condensed droplets of water clump together around tiny dust particles in the air, forming clouds.
Water Falls As Precipitation As more water vapor condenses, the water droplets in a cloud grow larger and larger. Eventually, they become so heavy that they fall back to Earth. Water that falls to Earth as rain, snow, hail, or sleet is called precipitation.
Most precipitation falls directly into the ocean. The precipitation that falls on land may evaporate immediately or run off the surface into rivers and lakes. From there, it may evaporate or flow back into the ocean. In addition, some water may trickle down into the ground. After a long time, this groundwater may reach a river, lake, or ocean and continue the cycle by evaporating again.
Precipitation is the source of all fresh water on and below Earth’s surface. The water cycle renews the usable supply of fresh water on Earth. For millions of years, the total amount of water on Earth has remained fairly constant—rates of evaporation and precipitation are balanced.
Most precipitation falls directly into the ocean. The precipitation that falls on land may evaporate immediately or run off the surface into rivers and lakes. From there, it may evaporate or flow back into the ocean. In addition, some water may trickle down into the ground. After a long time, this groundwater may reach a river, lake, or ocean and continue the cycle by evaporating again.
Precipitation is the source of all fresh water on and below Earth’s surface. The water cycle renews the usable supply of fresh water on Earth. For millions of years, the total amount of water on Earth has remained fairly constant—rates of evaporation and precipitation are balanced.
When fuels such as coal and gasoline are burned, they release carbon dioxide. Burning these fuels increases the amount of carbon dioxide in the atmosphere.
All matter is made of elements, but most elements in nature are found combined with other elements. A compound is a pure substance made of two or more elements chemically combined in a set ratio. A compound may be represented by a chemical formula, which shows the elements in the compound and the ratio of atoms. For example, part of the gas you exhale is carbon dioxide. Its chemical formula is CO2. The number 2 below the symbol for oxygen tells you that the ratio of carbon to oxygen is 1 to 2. (If there is no number after the element’s symbol, the number 1 is understood.)
When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements. Table sugar (C12H22O11) is a compound made of the elements carbon, hydrogen, and oxygen. The sugar crystals do not resemble the gases oxygen and hydrogen or the black carbon you see in charcoal.
Recall that gases in Earth’s atmosphere hold in heat from the sun, keeping the atmosphere at a comfortable temperature for living things. The process by which gases in Earth’s atmosphere trap this energy is called the greenhouse effect. Notice that sunlight does not heat the air in the greenhouse directly. Instead, sunlight first heats the soil, benches, and pots. Then infrared radiation from these surfaces heats the air in the greenhouse. The greenhouse effect in Earth’s atmosphere is similar in some ways.
Gases in the atmosphere that trap energy are called greenhouse gases. Carbon dioxide, water vapor, and methane are some of the greenhouse gases. Many scientists have hypothesized that human activities that add greenhouse gases to the atmosphere may be warming Earth’s atmosphere.
Changing Levels of Carbon Dioxide
Scientists think that an increase in carbon dioxide is a major factor in global warming. For example, the burning of wood, coal, oil, and natural gas adds carbon dioxide to the air. During the last 100 years, these activities have increased greatly in many different countries. The carbon dioxide in Venus’s atmosphere traps heat so well that Venus has the hottest surface of any planet. At 460°C, its average surface temperature is hot enough to melt lead. This trapping of heat by the atmosphere is called the greenhouse effect.
Other Gases Oxygen and nitrogen together make up 99 percent of dry air. Argon and carbon dioxide make up most of the other one percent. The remaining gases are called trace gases because only small amounts of them are present.
Water Vapor So far, we have discussed the composition of dry air. In reality, air is not dry because it contains water vapor. Water vapor is water in the form of a gas. Water vapor is invisible. It is not the same thing as steam, which is made up of tiny droplets of liquid water. Each water molecule contains two atoms of hydrogen and one atom of oxygen.
The amount of water vapor in the air varies greatly from place to place and from time to time. Water vapor plays an important role in Earth’s weather. Clouds form when water vapor condenses out of the air to form tiny droplets of liquid water or crystals of ice. If these droplets or crystals become heavy enough, they can fall as rain or snow.
Earth’s water is naturally recycled through the water cycle. The water cycle is the continuous process by which water moves from Earth’s surface to the atmosphere and back. In the water cycle, water moves from bodies of water, land, and living things on Earth’s surface to the atmosphere and back to Earth’s surface. The water cycle has three major steps—evaporation, condensation, and precipitation. The cycle itself has no real beginning or end. But it is driven by an energy source—the sun.
Water Evaporates As you learned earlier, evaporation is the process by which molecules at the surface of a liquid absorb enough energy to change to a gaseous state. Water is constantly evaporating from the surfaces of oceans and large lakes.
Condensation Forms Clouds What happens after a water molecule evaporates? Warm air carries the water molecule upward. At higher altitudes, air tends to become much colder. Cold air cannot hold as much water vapor as warm air can. As a result, some of the water vapor cools and condenses into liquid water. Condensed droplets of water clump together around tiny dust particles in the air, forming clouds.
Water Falls As Precipitation As more water vapor condenses, the water droplets in a cloud grow larger and larger. Eventually, they become so heavy that they fall back to Earth. Water that falls to Earth as rain, snow, hail, or sleet is called precipitation.
Most precipitation falls directly into the ocean. The precipitation that falls on land may evaporate immediately or run off the surface into rivers and lakes. From there, it may evaporate or flow back into the ocean. In addition, some water may trickle down into the ground. After a long time, this groundwater may reach a river, lake, or ocean and continue the cycle by evaporating again.
Precipitation is the source of all fresh water on and below Earth’s surface. The water cycle renews the usable supply of fresh water on Earth. For millions of years, the total amount of water on Earth has remained fairly constant—rates of evaporation and precipitation are balanced.
Most precipitation falls directly into the ocean. The precipitation that falls on land may evaporate immediately or run off the surface into rivers and lakes. From there, it may evaporate or flow back into the ocean. In addition, some water may trickle down into the ground. After a long time, this groundwater may reach a river, lake, or ocean and continue the cycle by evaporating again.
Precipitation is the source of all fresh water on and below Earth’s surface. The water cycle renews the usable supply of fresh water on Earth. For millions of years, the total amount of water on Earth has remained fairly constant—rates of evaporation and precipitation are balanced.
