Ch 17 Section 1 Earth’s Atmosphere

Atmospheric Composition Air is comprised of 78% Nitrogen, 21% Oxygen and trace amounts of CO 2, Argon, and water vapor. The remaining gases are called trace gases because there is such a small amount of them present.

Biological Processes Organisms produce CO 2 and water vapor when they respire (breath). Photosynthetic organisms take in CO 2 and release O 2 during photosynthesis. Microorganisms produce N 2 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 O 2.

Atmospheric Structure The 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 Structure Above 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 Atmosphere As the earth is heated by the sun it emits infrared radiation (heat). The CO 2 and H 2 O 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 Atmosphere As 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 large Growth occurs when droplets collide and combine. Warm rain-when droplets combine Cold rain- when droplets combine with ice crystals high in atmosphere.

Global Water Cycle Precipitation, runoff, storage, and evaporation make up the global water cycle. Plants affect absorption and runoff.