Earth's Atmosphere and Atmospheric Layers

• The atmosphere is the envelope of air surrounding Earth
• Air is a mixture of gases, consisting of about 78% nitrogen, 21% oxygen, 0.93% argon, 0.04% carbon dioxide, and 0.3% traces of other gases like methane, nitrous oxide, and ozone.
• Air also contains variable amounts of water vapor, which is an important component because without it, rainfall would not be possible.
• Water vapor forms when water on the ground evaporates and mixes with air.
• Sunlight assists in the formation of water vapor, making the molecules of water move faster and detach into the air.
• Water vapor condenses to form clouds, rain, dew, frost, snow, sleet, hail, or fog.
• Water vapor regulates air temperature by allowing sunlight to reach Earth and preventing radiation from escaping to space.

Atmospheric Layers

• The atmosphere is divided into the troposphere, stratosphere, mesosphere, and thermosphere.
• The atmosphere becomes less dense as one moves up from Earth's surface.

Troposphere

• Troposphere is the lowermost layer with the densest air
• Known as the "weather sphere" due to cloud formation and precipitation
• Temperature decreases as altitude increases because this layer is warmed from below by absorption and reemission of solar radiation
• The boundary separating the troposphere from the next layer is tropopause

Stratosphere

• The next layer of the atmosphere
• Temperature increases with altitude
• Temperature increases slowly in the lower stratosphere but rapidly in the upper layer due to ozone gas concentration
• Ozone absorbs ultraviolet (UV) rays and infrared radiation from Earth's surface.
• Stratosphere is ideal for flights due to good visibility and low air turbulence
• Since the air is thin, there is little resistance reducing fuel consumption
• The boundary between the stratosphere and the next layer is called the stratopause.

Mesosphere

• The third layer of the atmosphere
• Temperature decreases as altitude increases
• The average temperature reaches about -90°C because it does not absorb solar radiation, making it the coldest layer.
• Meteors burn up as they enter the atmosphere due to friction in the mesosphere
• The boundary between the mesosphere and the next layer is the mesopause.