Chapter 15 Section 1The Earth’s Atmosphere Notes Guide
Importance of the Atmosphere • Earth’s atmosphere is a thin layer of air that forms a protective covering around the planet. • The atmosphere maintains a balance between the amount of heat absorbed from the sun and the amount of heat that escapes back into space. • It also protects s from the Sun’s harmful rays.
Makeup of the Atmosphere • The atmosphere is a mixture of gases, solids, and liquids. • Earth’s early atmosphere contained nitrogen and carbon dioxide, but little oxygen. • A layer rich in ozone developed, which protects the earth from the Sun’s harmful rays. • This layer allowed green plants to grow all over the Earth, which increased the amount of oxygen in the atmosphere. • Today nitrogen is the most abundant gase in the atmosphere, making up 78%.
Makeup of the atmosphere • Oxygen makes up 21% of the atmosphere. • Other gases in the atmosphere include argon and carbon dioxide. • The atmosphere also contains solids and liquids such as dust, salt, pollen, and water droplets.
Lower Layers of the Atmosphere • There are 5 layers of the atmosphere. • The lowest of the layers is the troposphere, and it extends from the Earth’s surface up to 10 km. -It contains 99% of the water vapor and 75% of atmospheric gases. -Rain, snow, and clouds occur in the troposphere. • The layer directly above the troposphere is the stratosphere, which extends from 10km above the Earth’s surface to 50 km. -This layer contains the ozone layer.
Upper Layers of the Atmopshere • The mesosphere extends from the top of the stratosphere to about 85 km above Earth. -This is the layer in which meteors are visible. • The next layer is the thermosphere, found 85 km and 500 km above Earth. -This is the thickest layer and it has very high temperatures. • The ionosphere is found within the mesosphere and thermosphere. This is a layer of electrically charged particles that allows radio waves to travel across the country. • The exosphere is the last layer, where the space shuttle orbits. • Beyond the exosphere is space.
Atmospheric Pressure • Atmospheric molecule have mass. • As Earth’s gravity pulls the gases towards the surface, the weight of the gases presses down on the air below. • Because of this, molecules nearer the Earth’s, surface are closer together. This dense air exerts more force than the less dense air at the top of the atmosphere. • Force exerted on an area is called pressure. • Air pressure is the greatest Earth’s surface, and it decreases as you go up.
Temperature Changes with Atmospheric Layers • Temperature varies in the atmospheric layers because some layers contain gases that easily absorb the Sun’s energy, while other layers do not. • In the troposphere, the sun warms the Earth’s surface, which then warms the air above it. Temperature decreases as altitude increases. • In the stratosphere, molecules of ozone absorb the Sun’s energy, so that temperature decreases with increasing altitude. • The mesosphere is like the troposphere, in which temperature decreases with increasing altitude. • The thermosphere and exosphere are the first two layers to receive the Sun’s rays, and temperatures here are very high.
The Ozone Layer • Ozone is made up of three oxygen atoms bonded together. • Ozone absorbs most of the ultraviolet radiation that enters the atmosphere. • Ultraviolet radiation is energy that comes to Earth from the Sun, and too much exposure to it can cause skin damage and cancer. • Chlorofluorocarbons (CFCs) are chemical compounds that destory ozone. They are found in refrigerators, air conditioners, aerosol sprays, and foam packaging. -They enter the atmosphere through leaks or imporper discarding of products. The chlorine atoms in CFCs break apart the ozone molecules. • The destruction of ozone has resulted in the ozone hole, over Antarctica, which occurs seasonally. • The ban on production and use of CFCs has helped to decrease their amounts in the atmosphere.