Earth's Atmosphere Module 4

Module Four: Earth's Atmosphere

Earth’s Early Atmosphere

  • Not rich in oxygen and nitrogen.

  • Resembled the current atmospheres of Venus and Mars, high in Carbon Dioxide (CO2).

  • Over time, Carbon Dioxide was absorbed by oceans and converted to carbonate rock.

  • Enriched with oxygen over time by photosynthetic organisms.

Current Composition of the Atmosphere

  • Air Composition: Mixture of gases, liquids, and solids.

  • Varies from place to place.

  • Oxygen & Nitrogen: 99% of the atmospheric composition.

Carbon Dioxide (CO2)

  • Constitutes 0.04% or 400ppm of the atmosphere.

  • Although a small percentage, it plays an important role.

  • Usage: 60% is consumed by plants or becomes water.

  • Contributes to warming of Earth and has increased historically since 1960.

  • Major contributor to global warming and climate change.

Humidity

  • Definition: The amount of water vapor in the air.

  • Variation: Ranges from 0% to 4%.

  • Source of all clouds and precipitation.

Aerosols

  • Tiny liquid and solid particles present in the atmosphere:

    • Sea salt

    • Soil

    • Smoke

    • Pollen

    • Microorganisms

    • Ash

    • Dust

  • Aid in cloud formation by providing surfaces for condensation and contribute to the colors of sunsets.

Ozone (O3)

  • Present in small amounts: 3ppm.

  • Located in the stratosphere at a height of 10-50km (6-31mi).

  • Some chemicals like CFCs can break down ozone and cause ozone depletion.

  • Ozone depletion is most severe over the South Pole.

  • Health effects of ozone depletion:

    • Increased risk of skin cancer.

    • Reduced immune system functionality.

    • Potential for blindness.

Vertical Structure of Earth’s Atmosphere

  • Atmospheric Pressure: The weight of the air above.

  • 50% of the atmosphere exists below 6km (3.5mi).

  • 90% exists below 16km (10mi).

Troposphere

  • Description: Bottom layer of the atmosphere where humans live.

  • Temperature decreases with elevation.

  • This layer acts as a mixing zone with an environmental lapse rate of 6.5°C/km (3.5°F/1000ft).

  • Average height of the troposphere is approximately 12km (7.5mi).

  • Often referred to as the weather sphere.

Stratosphere and Mesosphere

  • Stratosphere:

    • Contains the ozone layer.

    • Temperature increases with height up to 50km (30mi).

    • Stratopause marks the boundary between the stratosphere and mesosphere.

  • Mesosphere:

    • Temperature decreases with height, coldest temperatures occur here.

    • Reaches a height of 80km (50mi).

    • Mesopause marks the boundary with the thermosphere.

Thermosphere and Exosphere

  • Thermosphere:

    • Lacks a well-defined upper limit.

    • Experiences the highest temperatures due to direct heating by the sun. Measured by exposure to UV radiation.

  • Exosphere:

    • Extends from 80-400km (50-250mi).

    • Contains charged ions.

    • Has no significant impact on human daily lives, but is known for phenomena like the Northern and Southern lights.

Heat Transfer in Earth’s Atmosphere

  • Main Mechanism: Convection is the primary method of heat transfer in the atmosphere.

  • Heat is transferred via movement and circulation of substances (air and water).

  • The sun's energy warms the Earth's surface, subsequently warming the atmosphere.

  • Warm air rises, creating thermal currents, with advection describing the horizontal component (winds) of this flow.

The Greenhouse Effect of Earth’s Atmosphere

  • Definition: A natural phenomenon where Earth's atmosphere traps some outgoing radiation.

  • Critical for maintaining life; without it, temperatures would plummet.

  • Carbon dioxide and water vapor absorb longwave radiation, elevating air temperature.

  • The greenhouse effect is distinct from global warming.

Ozone Hole in Earth’s Atmosphere

  • Ozone depletion was anticipated in the 1970s.

  • The “ozone hole” was discovered in the early 1980s due to CFCs damaging the ozone layer.

  • Efforts to reduce CFC production began in the 1990s; progress has been noted.

  • It is projected the ozone layer will recover by 2050-2070.

Temperature Changes in Earth’s Atmosphere

  • Extensive evidence supporting the warming of the Earth.

  • Since pre-industrial times, global average temperatures have risen about 1°C (1.8°F) due to human activities.

  • The rate of temperature increase is currently exceeding 0.2°C (0.36°F) per decade.

  • Trends show an unprecedented rate of warming over millennia.

Global Warming in Earth’s Atmosphere

  • Defined as the long-term heating of Earth's surface since the pre-industrial period (1850-1900).

  • Largely attributed to human efforts, particularly from fossil fuel combustion, which raises greenhouse gas levels in the atmosphere.

Magnetosphere

  • Description: Region around Earth characterized by charged particles originating from the solar wind.

  • These particles are confined in areas known as Van Allen Belts, spiraling around magnetic field lines.

Auroras

  • Occur near the poles where the Van Allen belts interface with the atmosphere.

  • Escaping charged particles produce glowing lights, commonly referred to as auroras:

    • Northern Hemisphere: Aurora Borealis.

    • Southern Hemisphere: Aurora Australis.