Earth's atmosphere is a complex system of layers and gases that shape our planet's climate. From the weather-filled troposphere to the auroras in the thermosphere , each layer plays a unique role in protecting and regulating life on Earth.
The atmosphere interacts with other Earth systems to maintain a delicate balance. Through processes like the greenhouse effect , albedo , and atmospheric circulation , it regulates temperature and distributes heat and moisture around the globe, creating our diverse climates.
Atmospheric Structure and Composition
Structure of Earth's atmosphere
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Layers of the atmosphere
Troposphere
Lowest layer contains about 75% of the atmosphere's mass (air, water vapor, aerosols)
Weather phenomena occur here (clouds, precipitation , storms)
Temperature decreases with height at a rate of about 6.5℃ per km (lapse rate)
Stratosphere
Above the troposphere separated by the tropopause boundary
Contains the ozone layer which absorbs harmful UV radiation from the Sun
Temperature increases with height due to ozone absorbing UV
Mesosphere
Above the stratosphere separated by the stratopause boundary
Temperature decreases with height reaching as low as -90℃ at the mesopause
Meteors burn up here due to friction with the thin air (meteor showers)
Thermosphere
Above the mesosphere separated by the mesopause boundary
Temperature increases with height reaching up to 1,500℃ due to absorption of intense solar radiation
Auroras occur here when charged particles from the Sun interact with Earth's magnetic field (northern/southern lights)
Exosphere
Uppermost layer merges gradually with the vacuum of outer space
Extremely low density so gas molecules rarely collide and can escape Earth's gravity (helium, hydrogen)
Composition of the atmosphere
Nitrogen (N 2 N_2 N 2 ): 78%, most abundant gas but chemically inert
Oxygen (O 2 O_2 O 2 ): 21%, second most abundant gas essential for aerobic life
Argon (Ar): 0.93%, third most abundant gas but chemically inert
Carbon dioxide (C O 2 CO_2 C O 2 ): 0.04%, small amount but important greenhouse gas
Water vapor (H 2 O H_2O H 2 O ): 0-4%, highly variable amounts act as a powerful greenhouse gas (clouds, humidity)
Trace gases: methane (C H 4 CH_4 C H 4 ) from wetlands/livestock, nitrous oxide (N 2 O N_2O N 2 O ) from fertilizers/natural sources, ozone (O 3 O_3 O 3 ) in the stratosphere
Atmospheric Interactions and Climate
Atmosphere's role in climate regulation
Greenhouse effect
Greenhouse gases (C O 2 CO_2 C O 2 , H 2 O H_2O H 2 O , C H 4 CH_4 C H 4 ) absorb and re-emit infrared radiation emitted by Earth's surface
Traps heat in the lower atmosphere warming Earth to a habitable average of 15℃ (without it Earth would be -18℃)
Albedo
Fraction of incoming solar radiation reflected back to space by Earth's surface (snow, ice, deserts) and atmosphere (clouds, aerosols)
Higher albedo means more solar energy is reflected so Earth absorbs less heat (ice ages)
Atmospheric circulation
Hadley, Ferrel and Polar cells form as warm air rises at the equator and cold air sinks at the poles redistributing heat
Jet streams, trade winds and westerlies steer weather systems and transport heat/moisture affecting regional climates (monsoons, hurricanes)
Cloud formation and precipitation
Clouds reflect incoming sunlight cooling Earth (albedo) but also absorb outgoing infrared warming Earth (greenhouse effect)
Precipitation releases latent heat when water vapor condenses warming the air (thunderstorms, tropical cyclones)
Atmospheric interactions with Earth systems
Hydrosphere
Evaporation from oceans, lakes and rivers adds water vapor (humidity) to the atmosphere
Precipitation (rain, snow) returns water to the surface recharging rivers, lakes and groundwater (water cycle )
Cryosphere
Ice and snow cover have a high albedo cooling Earth by reflecting sunlight
Melting of glaciers and ice sheets due to warming raises sea levels and alters ocean circulation patterns (sea ice, permafrost)
Biosphere
Photosynthesis by plants removes C O 2 CO_2 C O 2 from the air and releases O 2 O_2 O 2 (carbon cycle )
Respiration by plants and animals releases C O 2 CO_2 C O 2 back into the atmosphere
Changes in vegetation (deforestation, agriculture) alter regional albedo, evapotranspiration and carbon storage affecting local climates
Human impact on atmospheric system
Greenhouse gas emissions
Burning fossil fuels (coal, oil, gas) and deforestation have increased atmospheric C O 2 CO_2 C O 2 by 50% since the industrial revolution
Enhanced greenhouse effect leads to global warming, rising sea levels, more extreme weather, shifting climates (climate change)
Air pollution
Emissions of pollutants like sulfur dioxide (S O 2 SO_2 S O 2 ) and nitrogen oxides (N O x NO_x N O x ) from industries and vehicles react to form acid rain harming ecosystems
Photochemical smog containing ground-level ozone irritates lungs and damages crops (Los Angeles, Beijing)
Stratospheric ozone depletion
Chlorofluorocarbons (CFCs) once used as refrigerants and propellants break down ozone in the stratosphere creating the 'ozone hole'
Increases risk of skin cancer, cataracts and immune disorders in humans and damages phytoplankton and crops (Montreal Protocol)
Land use changes
Deforestation and urbanization alter local albedo, evapotranspiration and roughness affecting regional temperature and rainfall patterns
Expansion of agriculture (irrigation, fertilizers) changes evapotranspiration and releases greenhouse gases (N 2 O N_2O N 2 O )