Earth’s Atmosphere

The Origin of the Atmosphere

  • The gases that made up our early atmosphere likely came from volcanoes through the process of outgassing.
  • Large amounts of water vapor from these volcanoes eventually condensed to form the oceans.
  • The first life forms converted carbon dioxide into oxygen to form our modern atmosphere.

The Structure of the Atmosphere

  • The atmosphere is made up of four layers:
    Troposphere: the lowest layer, where all weather occurs and where most of the gases are found
  • Stratosphere: the second layer up, where the ozone layer is found • Mesosphere: the third layer up
  • Thermosphere: the fourth layer up
  • These layers are all separated by pauses (i.e. the tropopause, stratopause, etc.)
  • Selected Properties of the Earth’s Atmosphere” in the ESRTs will illustrate how temperature, air pressure, and water vapor concentration change as you travel up through these layers.
Changes in Air Temperature

  • Temperature changes are generally cyclic.
  • It is generally colder in the early morning and warmer in the afternoon
  • and It is generally colder in the winter and warmer in the summer (in the N. hemisphere)
  • Temperature is measured with an instrument called a thermometer.
  • The three temperature scales are Fahrenheit, Celsius, and Kelvin. Conversions between each scale can be made using the “Temperature” diagram in the ESRTs
  • Everything emits energy as long as it has a temperature above absolute zero (0°K), the temperature at which all molecular motion stops..
  • All types of energy (electromagnetic radiation) can be found on the “Electromagnetic Spectrum” in the ESRT’s.
How does Heat Energy Travel

  • The energy that heats the Earth comes from the Sun and is called insolation. 90% of insolation is in the form of visible light (short-wave)
  • Insolation travels from place to place in one of three ways:
    • Convection- heat transfer caused by differences in density (LIQUID/GAS)
    • Conduction- heat flow resulting from contact between two substances (SOLID)
    • Radiation- heat flow in the form of waves through space (NO MEDIUM REQUIRED)
  • Heat always flows from source (hot) to sink (cold)
  • Insolation reaches the Earth through radiation, It comes to the Earth as short-wave visible light is absorbed and then emitted back out as long- wave infrared.
  • Dark, rough surfaces absorb high amounts of energy.
  • Light, smooth surfaces reflect high amounts of energy.
  • As insolation travels through the Earth’s atmosphere, some passes through to the surface, some is reflected back to space, some is scattered throughout the atmosphere, and some is refracted, or bent.
  • The Earth’s atmosphere allows visible light to enter, but increasing levels of carbon dioxide are trapping the infrared causing global temperatures to rise. This is called the Greenhouse Effect.
Specific Heat

  • Specific heat is the amount of heat energy required to heat up a substance.
  • The higher the specific heat, the longer it takes to heat up and cool down.
  • The lower the specific heat, the faster it heats up and cools down.
  • Water has the highest specific of any substance on Earth which means it takes a lot of energy and a long time to raise it’s temperature. Additionally, it means that water will hold on to heat energy for a long time (it will cool slowly).
  • Oceans remain cooler in the summer and warmer in the winter which keeps coastal locations from having extreme climates.
  • Substances like metals generally have low specific heats meaning they will heat up quickly and cool off quickly.
  • The specific heats of common substances can be found on the cover of the ESRTs.
Phase Changes of Water

  • Water exists on Earth in three phases: solid, liquid, and gas.
  • Phase changes:
    • solid to liquid: melting
    • liquid to gas: evaporation
    • gas to liquid: condensation
    • liquid to solid: freezing
    • solid to gas: sublimation
  • Adding or removing energy from the water will result in a phase change. The amounts of energy involved can be found on the “Properties of Water” table on the cover of the reference tables.