All Study Guides Earth Systems Science Unit 8
🌈 Earth Systems Science Unit 8 – Atmosphere: Composition and StructureThe atmosphere is Earth's protective blanket, a mix of gases held by gravity. It's mostly nitrogen and oxygen, with trace gases like CO2. This gaseous envelope shields us from harmful radiation, regulates temperature, and enables life-sustaining processes like the water cycle.
The atmosphere has distinct layers, each with unique properties. From the weather-filled troposphere to the auroral thermosphere, these layers play crucial roles in Earth's systems. Understanding the atmosphere's composition, structure, and functions is vital for grasping climate change and environmental challenges.
What's the Atmosphere?
Gaseous envelope surrounding Earth held in place by gravity
Composed of various gases including nitrogen (~78%), oxygen (~21%), and trace gases (argon, carbon dioxide, water vapor)
Extends from Earth's surface to the exosphere, gradually thinning with increasing altitude
Protects life on Earth by absorbing harmful ultraviolet radiation from the sun
Plays a crucial role in regulating Earth's temperature through the greenhouse effect
Enables the water cycle by storing and transporting water vapor
Provides oxygen for respiration and carbon dioxide for photosynthesis
Influences weather patterns and climate through atmospheric circulation
Layers of the Atmosphere
Troposphere: lowest layer, contains ~80% of atmospheric mass, where most weather phenomena occur
Extends from Earth's surface to an average height of ~12 km
Temperature decreases with altitude at a rate of ~6.5°C/km (lapse rate)
Stratosphere: layer above the troposphere, contains the ozone layer
Extends from the tropopause to an altitude of ~50 km
Temperature increases with altitude due to absorption of UV radiation by ozone
Mesosphere: layer above the stratosphere, where meteors burn up
Extends from the stratopause to an altitude of ~85 km
Temperature decreases with altitude, reaching the coldest point in the atmosphere at the mesopause
Thermosphere: layer above the mesosphere, where auroras occur
Extends from the mesopause to an altitude of ~600 km
Temperature increases with altitude due to absorption of high-energy radiation
Exosphere: outermost layer, gradually merges with outer space
Extends from the thermopause to ~10,000 km above Earth's surface
Extremely low density, composed mainly of hydrogen and helium atoms
Key Atmospheric Components
Nitrogen (N2): most abundant gas, essential for life as a component of amino acids and proteins
Oxygen (O2): second most abundant gas, crucial for respiration in many organisms
Produced by photosynthesis in plants and some microorganisms
Ozone (O3), a form of oxygen, absorbs harmful UV radiation in the stratosphere
Argon (Ar): third most abundant gas, an inert noble gas
Carbon dioxide (CO2): a greenhouse gas that absorbs and re-emits infrared radiation, contributing to Earth's warming
Concentration has increased due to human activities (fossil fuel combustion, deforestation)
Water vapor (H2O): a greenhouse gas that varies in concentration, influences weather and climate
Trace gases: gases present in small amounts (e.g., neon, helium, methane, krypton, xenon)
Some trace gases, such as methane and nitrous oxide, are potent greenhouse gases
Early Earth's atmosphere was composed mainly of hydrogen and helium, which escaped due to the planet's weak gravity and high temperature
Volcanic outgassing released gases (water vapor, carbon dioxide, nitrogen, sulfur dioxide) that formed the secondary atmosphere
Water vapor condensed to form oceans as Earth cooled
Carbon dioxide dissolved in oceans and was stored in carbonate rocks
Photosynthesis by early microorganisms (cyanobacteria) began producing oxygen ~2.4 billion years ago
Oxygen accumulated in the atmosphere, leading to the Great Oxidation Event
Ozone layer formed in the stratosphere, shielding Earth from harmful UV radiation
Nitrogen became the most abundant atmospheric gas due to its stability and low reactivity
Atmospheric composition has continued to evolve over time due to biological and geological processes
Atmospheric Pressure and Density
Atmospheric pressure is the force exerted by the weight of the atmosphere per unit area
Decreases with increasing altitude as the amount of air above decreases
Standard atmospheric pressure at sea level is ~1013.25 hPa (hectopascals) or 1 atm (atmosphere)
Density of the atmosphere decreases with increasing altitude
Caused by the compressibility of gases under the weight of the overlying atmosphere
About half of the atmospheric mass is contained within the lowest ~5.5 km
Pressure and density variations influence atmospheric circulation patterns
High-pressure areas have descending air, while low-pressure areas have ascending air
Wind flows from high-pressure to low-pressure areas, deflected by the Coriolis effect
Temperature Variations in the Atmosphere
Temperature changes with altitude, primarily due to variations in solar radiation absorption and heat transfer mechanisms
Troposphere: temperature decreases with altitude (negative lapse rate) due to adiabatic cooling of rising air
Lapse rate is influenced by moisture content, with moist air having a lower lapse rate than dry air
Stratosphere: temperature increases with altitude (positive lapse rate) due to absorption of UV radiation by ozone
Ozone layer is crucial for protecting life on Earth from harmful UV radiation
Mesosphere: temperature decreases with altitude, reaching the coldest point in the atmosphere at the mesopause
Meteors burn up in this layer due to friction with atmospheric gases
Thermosphere: temperature increases with altitude due to absorption of high-energy radiation (X-rays and UV)
Auroras occur in this layer when charged particles from the sun interact with Earth's magnetic field
Atmosphere's Role in Earth Systems
Regulates Earth's temperature through the greenhouse effect
Greenhouse gases absorb and re-emit infrared radiation, warming the planet's surface
Without the greenhouse effect, Earth's average temperature would be ~33°C colder
Enables the water cycle by storing and transporting water vapor
Evaporation from oceans and land surfaces adds water vapor to the atmosphere
Condensation of water vapor forms clouds and precipitation, redistributing water across the planet
Influences weather patterns and climate through atmospheric circulation
Uneven heating of Earth's surface creates pressure gradients and wind systems
Hadley, Ferrel, and Polar cells transport heat and moisture between the equator and poles
Interacts with the biosphere by providing gases for photosynthesis and respiration
Plants and other photosynthetic organisms absorb CO2 and release O2
Animals and other respiring organisms consume O2 and release CO2
Plays a role in the carbon cycle by storing and exchanging carbon with the biosphere and oceans
Atmospheric CO2 is absorbed by oceans and converted into carbonate rocks
Weathering of carbonate rocks and volcanic outgassing return CO2 to the atmosphere
Current Issues and Future Challenges
Climate change: increasing atmospheric greenhouse gas concentrations due to human activities
Burning of fossil fuels, deforestation, and land-use changes contribute to rising CO2 levels
Warmer global temperatures lead to changes in weather patterns, sea-level rise, and ecosystem disruptions
Air pollution: emission of harmful substances into the atmosphere from human activities
Particulate matter, nitrogen oxides, sulfur dioxide, and volatile organic compounds can impact human health and the environment
Acid rain, smog, and respiratory issues are some consequences of air pollution
Ozone depletion: thinning of the ozone layer due to the release of ozone-depleting substances (e.g., CFCs)
Montreal Protocol has helped reduce the production and emission of these substances
Recovery of the ozone layer is expected to take several decades
Geoengineering proposals: intentional, large-scale interventions to counteract climate change
Examples include solar radiation management (e.g., stratospheric aerosol injection) and carbon dioxide removal (e.g., direct air capture)
Potential risks and unintended consequences need to be carefully considered
Improving atmospheric monitoring and modeling to better understand and predict future changes
Satellite observations, weather balloons, and ground-based instruments provide valuable data
Climate models simulate the complex interactions between the atmosphere and other Earth systems