Atmosphere

• The Ionosphere is a region within the mesosphere and thermosphere where ions and free electrons are present.
• Nitrogen is the most abundant gas in the atmosphere.
• The 2nd most abundant gas in the atmosphere is Oxygen.
• Methane is the major greenhouse gas.
• Ozone is good in stratosphere (protects from UV), bad near the surface (corrosive to lungs and more)
• Troposphere is the lowest atmosphere layer and is the closest to the earth's surface.
• The early atmosphere would have been similar to the Sun containing mainly hydrogen and helium
• Surface of earth as hell period is extremely hot, dry, with little water and no oxygen and no life in this period there are a lot of volcanoes.
• Carbon dioxide is one of the main greenhouse gases that contributes to global warming.
• Atmospheric Constituents:

  • CO2: a greenhouse gas, very effective absorber and emitter in the infrared
  • O3: good in the stratosphere (protects from UV), bad near the surface (corrosive to lungs)
  • SO2: emitted by volcanoes, contributes to atmospheric particles and acid rain
  • NO2: produced by combustion, contributes to acid rain and smog
  • Water vapor (~0 to 4%): critically important, plays a role in clouds and precipitation, major greenhouse gas
  • Methane (CH4): major greenhouse gas
• Non-Gas Constituents:

  • Hydrometeors: rain clouds, hail
  • Particulates and aerosols: aerosol is a liquid or solid dispersed in a gas, can absorb or scatter radiation, reduce visibility, impact human health
  • Particulates can be inorganic (soil, smoke, dirt, sea salt, volcanic dust, surface acid aerosol) or organic (seeds, spores, pollen, bacteria)
• The First Atmosphere:

  • Early atmosphere similar to the Sun, mainly hydrogen and helium
  • Lost quickly due to weak gravity and impact by a large object, resulting in the origin of the moon and loss of the early atmosphere
• Earth as Hell:

  • Surface extremely hot with numerous volcanoes
  • Constant bombardment by objects of varying sizes
  • Earth started to cool down and the second atmosphere began to form
• Earth's Second Atmosphere:

  • Established by outgassing of volcanoes
  • Mixture of gases similar to today's volcanoes, including water vapor, CO2, N2, and trace gases
  • Virtually no oxygen, leading to no ozone layer and high UV radiation
• The Rise of Oxygen and the Third Atmosphere:

  • Oxygen increased while CO2 decreased due to photosynthesis and chemical weathering
  • Sulfur compounds removed from the atmosphere as acid rain
  • N2 gas increased slowly, establishing the current composition of the atmosphere
• Changes Over Time:

  • Earth became more susceptible to ice ages with lower CO2 levels
  • Earth cooled down and became nearly entirely glaciated around 750-550 million years ago
  • Volcanic activity and reduced weathering led to an increase in CO2, warming the earth
• Last 500 Million Years:

  • Climate has not been constant, with warm periods interrupted by ice ages
  • Variability forced by changing solar radiation, orbital characteristics, tilt, and major volcanic eruptions
• Orbital Characteristics:

  • Earth's orbit varies from nearly circular to slightly elliptical due to gravity from Jupiter and Saturn
  • Eccentricity affects the distance between Earth and the Sun
  • Axial tilt angle affects the seasons, currently tilted at 23.4 degrees and slowly decreasing
  • Axial precession makes seasonal contrasts more extreme in one hemisphere and less extreme in the other