THE EARTHS ATMOSPHERE

• Earth’s atmosphere consists of a variety of gases.
• The two main gases are nitrogen (71%) and oxygen (16%).
• Earth’s atmosphere has several layers.
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• The Troposphere the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases
• Almost all weather occurs in the troposphere.
• The troposphere is the atmospheric layer closest to Earth’s surface.
• The troposphere is the densest layer.
• 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 from leaving the troposphere.
• Cold air can become trapped beneath warm air.
• Temperature inversion the atmospheric condition in which 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 for people to exercise outside.
• The stratosphere gets warmer with increasing altitude.
• 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.
• At about 25 km, the temperature begins to increase with altitude until it reaches about 0° C.
• Mesosphere the coldest layer of the atmosphere, between the stratosphere and the mesopause

The mesosphere and thermosphere exhibit extremes of temperature.

• Temperatures in the mesosphere decrease with increasing altitude, to about -80º C.
• Thermosphere the uppermost layer of the atmosphere, in which temperature increases as altitude increases
• Temperatures in the thermosphere are extremely hot, absorbing intense solar radiation.

The ionosphere is used in radio communication and is located in the lower section of the Thermosphere.

• Solar energy absorbed in the lower thermosphere and upper mesosphere forms charged ions.
• This layer is often called the ionosphere.
• Electrons in the ionosphere reflect radio waves.
• The ionosphere is where auroras take place.
• Auroras are colorful displays of light formed when energetic ions from the sun hit atoms and molecules in the ionosphere, causing photons to be emitted.

• When Earth began to solidify, about 4.4 billion years ago, volcanic eruptions released gases.
• The process of releasing gases during volcanic eruptions is called outgassing.
• The gases released by volcanoes did not include oxygen.
• Photosynthetic plants contribute oxygen to the atmosphere.
• Organisms evolved that used sunlight as an energy source in a process called photosynthesis.
• Photosynthesis produces oxygen as a waste product.
• Gradually the oxygen content increased to what it is today.
• 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.
• Man-made chemicals can deplete the ozone layer.
• Ozone is formed when the sun’s ultraviolet radiation strikes oxygen molecules.
• Ozone absorbs much of the sun’s harmful ultraviolet radiation.
• Without the ozone layer, ultraviolet radiation would damage living cells.
• Chlorofluorocarbons are chemicals that damage the ozone layer, but are now banned in most countries.
• The greenhouse effect keeps Earth warm.
• Greenhouse effect the warming of the surface and lower atmosphere of Earth that occur 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.
• Increased levels of carbon dioxide may lead to global warming.
• If too much heat is trapped the global temperature will rise.
• Global warming is the gradual increase in temperature on Earth due to an increase in greenhouse gases
• Global warming could cause problems, such as the melting of ice caps, rising of ocean levels, and drought in some areas.