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Physical Science 22Characteristics of the
Atmosphere
Objectives
• Identify the primary layers of the atmosphere
• Describe how the atmosphere has evolved over time
• Describe how the oxygen-carbon dioxide cycle works, and explain its importance to living organisms
• Discuss the recent changes in Earth’s atmosphere
Layers of the atmosphere
• Earth’s atmosphere consists of two main gases:
• Nitrogen 78%
• Oxygen 21%
• Trace elements~ 1%
The atmosphere has several different layers
• The layers differ in:
temperature
density
amount of gases present
• Turn to page 742 in your text book
• Copy figure 1 in your notebook
Be sure to note the different atmosphere layers, location, temperature, altitude, pressure, and special characteristics
Almost all weather occurs in the troposphere
• Troposphere-the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases
• This is the densest of the layers due to the weight of all other layers
The troposphere gets cooler with increasing altitude
• At the top of the troposphere the temperature stops decreasing
• This region, the tropopause, at (-55°C) keeps the water vapor and clouds.
Cold air can be trapped beneath warm air
• Temperature inversion- the atmospheric condition in which warm air traps cooler air near Earth’s surface
• This occurrence can trap pollution in areas surrounded by mountains
Stratosphere
• Stratosphere- the upper layer of the atmosphere, which lies immediately above the troposphere and extends from 10 km to about 50 km above Earth’s surface
• Ozone-a gas molecule that is made up of three oxygen atoms
• The stratosphere is a cold, low-pressure layer
• Key differences:– Little water vapor– No weather or clouds– Increase in temperature with increased
altitude (ozone layer-absorbs much of the sun’s ultraviolet radiation)
The mesosphere and thermosphere exhibit extremes of
temperature• Mesosphere- the coldest layer of the
atmosphere, between the stratosphere and the mesosphere (-80°C °F? )
• Thermosphere- the upper-most layer of the atmosphere, in which temperature increases as altitude increases
(980°C °F? )
Ionosphere is used in radio communication
• Ionosphere- area in which solar energy is absorbed in the lower thermosphere and upper mesosphere
(creating electrically charged ions)
• Electrons in the ionosphere reflect radio waves, allowing them to be received over long distances
Auroras
• Auroras- colorful light displays in the ionosphere that encircle Earth’s magnetic poles
• Form when energetic ions from the sun hit atoms and molecules causing photons of light to be emitted– Aurora borealis– Aurora australis
Changing in Earth’s Atmosphere
• Early in Earth’s existence, the atmosphere contained mostly carbon dioxide, nitrogen, and a few other trace gases
( H2, water vapor, H20, NH3, CH4, CO, CO2, but no O2)
This was due to outgassing from volcanoes
Photosynthetic plants contribute oxygen to the atmosphere
• Around 2.5 billion years some cells evolved a method of capturing energy from the sun and converting it to sugar that can be used as a food source
• Photosynthesis produces oxygen as a byproduct
Animals produce carbon dioxide necessary for photosynthesis
• In the oxygen-carbon dioxide cycle, plants produce oxygen, which is used by animals for respiration
• Animals produce carbon dioxide, which is used by plants for photosynthesis
Man-made chemicals can deplete the ozone layer
• Remember the ozone layer is in the stratosphere!!!
• O3 molecules absorb much of the sun’s damaging ultraviolet radiation
• Without the ozone layer UV rays would cause serious cellular damage
Ozone destruction
• Ozone destruction is caused by chlorofluorocarbons (CFCs)
• CFCs were widely used as refrigerants and in aerosol spray cans
• CFC use was banned Jan 1st 1996
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
• The greenhouse effect is a process in which atmospheric gases trap some of the energy from the sun in the troposphere
• A. Solar radiation warms Earth’s surface and is radiated back into the atmosphere as heat radiation
• B. Greenhouse gases, CO2 and H2O receive this heat radiation and radiate some back to Earth’s surface
• C. CO2 is added to the air in the burning of fossil fuels and in forest fires, possibly causing global warming!
Increased levels of carbon dioxide may lead to global warming
• Without the greenhouse effect, Earth would have a colder average temperature
• If too much heat is trapped, the global temperature will rise
• Global warming could cause the icecaps to melt, ocean levels to rise, and droughts to occur in some areas!
Sources of carbon dioxide
• Burning of coal, oil, and gas for power plants, machinery, and cars
Cause of global warming and what to do about it is highly debatable
Assignment
• Work on Earth Science Review Packet