The Atmosphere I. The Earth’s Atmosphere is a layer of air surrounding the Earth that supports and protects life by: 1. Absorbing harmful radiation 2. Maintaining the Earth’s temperature 3. Providing elements essential for life A. Our atmosphere is a mixture of gasses that is held around the planet by gravity. B. The atmosphere has both physical and chemical properties. 1. Density (physical property) - density of the atmosphere decreases with altitude 2. Composition (chemical property) - 78.08% Nitrogen - 20.94% Oxygen - 0.93% Argon - 0.04% Carbon Dioxide - 0.01% Other Elements - 0-4% Water Vapor II. Natural processes modify the atmosphere A. Carbon Cycle Plants take in carbon dioxide from the air and release oxygen during photosynthesis. During respiration, animals use oxygen and release carbon dioxide and water into the air. B. Nitrogen Cycle Nitrogen-fixing bacteria convert atmospheric nitrogen into solid forms and solutions. Living things use these forms of nitrogen, and when they decay, they release nitrogen back into the soil and eventually back into the air. C. Water Cycle Water is constantly circulated between Earth’s surface and the atmosphere by evaporation, condensation, and precipitation. III. Energy from the Sun heats the atmosphere. A. Most energy on Earth comes from the Sun in the form of visible light. B. Visible light is a form a radiation that moves in electromagnetic waves. - 30% of the sun’s radiation is reflected by clouds, the atmosphere, and Earth’s surface. - 70% of solar radiation is absorbed and becomes different forms of energy. IV. The atmosphere moves energy by radiation, conduction, and convection. A. Radiation 1. Energy in the form of electromagnetic waves 2. Energy hits a surface, it heats the surface 3. Causes the molecules to move faster you feel this as an increase in temperature 4. The energy on the surface is then transferred to the atmosphere B. Conduction 1. The transfer of thermal energy from one material to another by direct contact. 2. Thermal energy is always transferred from warm to cold objects 3. Warm land or water will heat the air on the surface C. Convection 1. The transfer of thermal energy by circulation or movement of a liquid or gas 2. Warm air is less dense and rises, Cool air is more dense and sinks 3. Cooler air is heated by the ground and rising air loses heat 4. This circular movement of the air is called a convection current V. The Atmosphere can be divided into 4 different layers. Layer 1 – Troposphere about 0-10 km (0-6 miles) above the Earth’s surface most clouds and weather located in this layer water vapor and dust can also be found in this layer WE live in this layer of the atmosphere this layer contains 80% of the total mass of the atmosphere in this layer, temperature decreases as altitude (height above the Earth’s surface) increases Layer 2 – Stratosphere about 10-50 km (6-31 miles) above the Earth’s surface hardly any water vapor or dust in this layer because there is very little mixing with the air below. the air is “thinner” here; it contains less molecules this layer contains the ozone layer because ozone absorbs the ultraviolet light from the sun, this layer gets warmer as the altitude increases Layer 3 – Mesosphere about 50-90 km (31-56 miles) above the Earth’s surface in this layer temperature falls as altitude increases this is the coldest part of the atmosphere temperatures recorded at -93C violent wind storms occur in this layer with winds reaching 320 km/h we have not had any aircraft reach this layer only very large helium balloons reach this high Layer 4 – Thermosphere about 90 km and up (50 miles and above) where nitrogen and oxygen absorb solar energy like x-rays and gamma rays temperature increasing gas particles become electrically charged and can radiate energy as light (ex. Aurora Borealis-northern lights and Aurora Australis-southern lights) this layer can reflect radio waves Some scientists describe a 5th layer as the Exosphere. Once we get above 180 miles above the surface of the Earth, the atmosphere gradually merges with the thin gasses of interplanetary space. Remember there is not a line or an edge to our atmosphere; it slowly ends and blends into space. VI. Gases in the atmosphere absorb radiation. A. Gasses can absorb and give off radiation. 1. In the stratosphere, ozone gas absorbs ultraviolet radiation. 2. In the troposphere, Carbon Dioxide, Methane, Water Vapor, and Nitrous Oxide absorb and emit infrared radiation. B. The ozone layer protects life from harmful radiation by absorbing ultraviolet (UV) rays. 1. Ozone is a gas made up of 3 bonded oxygen atoms – O3 2. UV rays can cause sunburn, skin cancer, & damaged eyesight. C. The greenhouse effect keeps the Earth warm. 1. Water vapor, carbon dioxide, methane, nitrous oxide, and some other gasses are known as green house gasses. 2. These gasses absorb and give off infrared radiation through a process called the Greenhouse Effect. GREENHOUSE EFFECT: Solar Radiation heats Earth’s surface, which grows warm and emits infrared radiation. Greenhouse gasses absorb some of this infrared radiation and allow the rest to pass into space. Greenhouse gasses then emit infrared radiation. Some is absorbed by the ground, while some is lost to space. VII. Human Activities affect the atmosphere. A. Human activity can cause air pollution. 1. Air Pollution consists of gases and particulates. a. Gases include: methane, ozone, carbon monoxide, sulfur oxides, & nitrogen oxides. b. Particulates include: dust, dirt, pollen, and sea salt. 2. Air pollution can be caused naturally (volcanoes) or by human activities (burning fossil fuels). B. Human activities are increasing greenhouse gasses. 1. When greenhouse gasses increase, global temperatures increase. 2. Increased greenhouse gasses may lead to global warming or global climate change. C. Human activities produce chemicals that destroy the ozone layer. 1. Chlorofluorocarbons (CFCs) are chemicals that were once used in cooling systems, spray cans, and foam packing that react with sunlight and destroy ozone molecules. Substitute chemicals that destroy ozone more slowly are now used. 2. Chemical reactions in the stratosphere that produce and destroy ozone depend on the weather. Much of the ozone over the South Pole is destroyed in certain seasons, resulting in the “Ozone Hole”.