Ch 17

Section 1

Earth’s Atmosphere

Atmospheric CompositionAir is comprised of 78% Nitrogen, 21% Oxygen

and trace amounts of CO2, Argon, and water vapor.

The remaining gases are called trace gases because there is such a small amount of them present.

Biological ProcessesOrganisms produce CO2 and water vapor when

they respire (breath).

Photosynthetic organisms take in CO2 and release O2 during photosynthesis.

Microorganisms produce N2 and Methane.

Microorganisms in some animal’s digestive tract can produce Methane.

Formation of the Atmosphere

Earth’s early atmosphere was made of Hydrogen and Helium.Was replaced by gases from volcanic eruptions.

Oxygen was converted to Ozone due to the sun’s radiation.

Ozone layer then shielded Earth from harmful ultraviolet light.This allowed more photosynthetic organisms to

prosper and produce more O2.

Atmospheric StructureThe atmosphere extends 1,000 km from Earth’s

surface.

Most of Earth’s weather takes place in the Troposphere.Extends 30 km above Earth’s surface.

Temperature normally decreases with height in the troposphere.

Atmospheric StructureAbove the troposphere is the Stratosphere.

Extremely dry and rich in Ozone.Temp always increases with height.The tropopause is where the temp inversion takes

place.

The Mesosphere is above the stratosphere

The Thermosphere is above the mesosphere.

The Exosphere is the upper most layer.

Heating the AtmosphereAs the earth is heated by the sun it emits

infrared radiation (heat).

The CO2 and H2O absorb some of the heat coming off Earth and re-emit it back to earth.Greenhouse Effect-refers to the re-emission of

heat by Ozone.

Latent heat is energy released by phase changes of water, like water evaporating or snow melting.

Water in AtmosphereAs hot air rises it brings water molecules with it and

as it cools in the atmosphere it forms clouds.Clouds are the first step in the precipitation process.

For participation to occur, droplets must grow largeGrowth occurs when droplets collide and combine.

Warm rain-when droplets combine

Cold rain- when droplets combine with ice crystals high in atmosphere.

Global Water CyclePrecipitation, runoff, storage, and evaporation

make up the global water cycle.

Plants affect absorption and runoff.