The AtmosphereSection 1 Section 1: Characteristics of the Atmosphere Preview Key Ideas Bellringer Layers of the Atmosphere Changes in Earth’s Atmosphere

The AtmosphereSection 1 Key Ideas 〉 What are the parts of Earth’s atmosphere? 〉 Where did Earth’s atmosphere come from?

The AtmosphereSection 1 Bellringer The phrase greenhouse effect refers to a process that keeps Earth warm. The greenhouse effect describes how Earth’s atmosphere traps energy from the sun. Write a paragraph describing what you think life on Earth would be like as a result of too much of the greenhouse effect and also not enough of the greenhouse effect. Include possible consequences for plant and animal life as well as for climate and Earth itself.

The AtmosphereSection 1 Layers of the Atmosphere 〉 What are the parts of Earth’s atmosphere? 〉 The atmosphere has several layers. These layers differ in temperature, in density, and in the relative amounts of the different gases that are present. –troposphere –stratosphere –mesosphere –thermosphere –The two main gases in the atmosphere are nitrogen and oxygen.

The AtmosphereSection 1 Layers of the Atmosphere, continued

The AtmosphereSection 1 Layers of the Atmosphere, continued Almost all weather occurs in the troposphere. The troposphere is the atmospheric layer closest to Earth’s surface. The troposphere is the densest layer. Troposphere: the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases

The AtmosphereSection 1 Layers of the Atmosphere, continued The troposphere gets cooler with increasing altitude. The temperature decreases by 6° C for every kilometer of altitude. At the top of the troposphere the temperature stops decreasing. –The boundary where this occurs is called the tropopause. –The temperature at the tropopause is -55 °C. The low temperature keeps water vapor in the troposphere.

The AtmosphereSection 1 Layers of the Atmosphere, continued Cold air can become trapped beneath warm air. A temperature inversion happens when warm air traps cooler air near Earth’s surface. –When a temperature inversion occurs, trapped air can become thick with pollution. –As long as a temperature inversion lasts, it is not healthy to exercise outside.

The AtmosphereSection 1 Visual Concept: Temperature Inversion

The AtmosphereSection 1 Layers of the Atmosphere, continued The stratosphere gets warmer with increasing altitude. stratosphere: the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer –At about 25 km, the temperature begins to increase with altitude until it reaches about 0° C. –The stratosphere contains few clouds and no storms. –The ozone layer shields living things on Earth’s surface from ultraviolet-radiation damage.

The AtmosphereSection 1 Layers of the Atmosphere, continued The mesosphere and thermosphere exhibit extremes of temperature. mesosphere: the coldest layer of the atmosphere, between the stratosphere and the thermosphere, in which temperature decreases as altitude decreases –Temperatures in the mesosphere decrease to about -80º C. thermosphere: the uppermost layer of the atmosphere, in which temperature increases as altitude increases –Temperatures average about 980 °C (1,796 °F) because the small amount of oxygen absorbs intense solar radiation.

The AtmosphereSection 1 Layers of the Atmosphere, continued The ionosphere is important to radio communication. –When solar energy is absorbed in the lower thermosphere and upper mesosphere, charged ions are formed. –This layer is often called the ionosphere. –Radio waves are reflected in the ionosphere. –Auroras take place in the ionosphere.

The AtmosphereSection 1 Changes in Earth’s Atmosphere 〉 Where did Earth’s atmosphere come from? 〉 When Earth began to solidify, about 4.4 billion years ago, volcanic eruptions released a variety of gases. The process of releasing gases during volcanic eruptions is called outgassing. The gases released by volcanoes did not include oxygen.

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued Photosynthetic plants contribute oxygen to the atmosphere. –Organisms evolved photosynthesis, a method of capturing energy from the sun. –Photosynthesis produces oxygen as a waste product. –Gradually the oxygen content increased to what it is today.

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued Animals produce carbon dioxide necessary for photosynthesis. –Oxygen breathing organisms evolved and released carbon dioxide as a waste product. –The oxygen-carbon dioxide cycle maintains a balance of atmospheric gases on Earth.

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued Human-made chemicals can deplete the ozone layer. –Ozone forms when the sun’s ultraviolet rays strike molecules of O 2. –Ozone absorbs much of the sun’s ultraviolet radiation. –Without the ozone layer, ultraviolet radiation would damage living cells. Chlorofluorocarbons, CFCs, are chemicals that destroy the ozone layer, but are now banned in most countries.

The AtmosphereSection 1 Visual Concept: Ozone and Ecosystems

The AtmosphereSection 1 Visual Concept: Ozone and Ozone Holes

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued The greenhouse effect keeps Earth warm. greenhouse effect: the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation –Greenhouse gases trap the sun’s heat and keep Earth’s surface warm.

The AtmosphereSection 1 Greenhouse Effect

The AtmosphereSection 1 Visual Concept: Greenhouse Effect

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued Too much carbon dioxide may cause global warming. –If too much energy is absorbed by the atmosphere, global temperatures will rise. –Global warming could cause problems, such as rising ocean levels, because of melting polar icecaps, and droughts. –Combustion of coal, oil, and gas has added more carbon dioxide to the air.

The AtmosphereSection 1 Changes in Earth’s Atmosphere, continued