4.4: Earth’s atmosphere

Description of the Atmosphere

• 5 layers of gases held to the surface by gravity

  • Nitrogen – 78%

  • Oxygen – 21%

  • Remaining ~1% is Ar, CO₂, H₂O (varies with weather)

• Greenhouse gases: carbon dioxide and water vapor

Troposphere

• Densest layer (most O₂ H₂O etc)

  • Contains 99% of the atmosphere’s water vapor and clouds

• Layer of gases closest to earth. 

  • Contains the air we breathe.

• Circulation and mixing (convection)

• Where all weather/climate/climate change occurs.

• Temperature decreases with increasing altitude

  • Air density decrease with altitude

Stratosphere & Ozone Layer

• Less dense and drier than Troposphere.

• A thin band of ozone (O₃) exists in the lower half of the Stratosphere

• The Ozone traps the high-energy radiation of the sun, holding some of the heat and protecting the troposphere (& Earth’s surface) from the radiation.

• Contrast to Troposphere, gases are NOT mixed well 

  • Temperatures increase with distance from the Earth

Mesosphere

• Where meteors usually burn up. 

• Temps continue to decrease.

Thermosphere

• Colorful auroras take place

  • ionosphere, the ions of the solar wind collide with atoms of oxygen and nitrogen from Earth's atmosphere.

  • Dispersed throughout upper meso., thermo., and lower exo.

  • Regions of ionized gases that absorb charged particles from the sun.

Exosphere

• Upper limit is NOT definitively defined

• Concentration of gases is thinnest here

• Human-made satellites orbit here and in the upper thermosphere