The AtmosphereChapter 17

Composition – What’s in the air?• Earths atmosphere is a mixture of gases that has changed over time• The atmosphere did not contain a significant amount of oxygen until 2.5

billion years ago

• The atmosphere continuously exchanges gases and particles with the oceans and with earths surface

Composition – What’s in the air?• Major components of the atmosphere are about the same

everywhere on earth• Air is mostly nitrogen and oxygen (99%)• The remaining 1% is argon• 0.04% is carbon dioxide (CO2)

Composition – What’s in the air?• Variable components change from place to place• Dust - from smoke, ash, soil, and sea salt• Ozone – protects life on Earth by absorbing harmful UV radiation• Water vapor – the source of all clouds and precipitation. Absorbs heat from

the earth and from the sun• Pollution – particles and gases that are harmful to living things

Structure of the atmosphere• Air is concentrated near Earths

surface and thins as you travel away from Earth until the molecules are too spread out to detect. • Air is a form of matter, so it exerts

pressure on the Earth• Air pressure decreases as you go

higher in altitude

Structure of the Atmosphere• The atmosphere is divided into

4 layers based on temperature

Terms:Altitude - describes the height of something above the groundvs. Elevation – the height of a landform

Structure of the atmosphereTroposphere : 0 – 10 km above Earth• All major weather events happen in the troposphere• The troposphere has the most air particles• The temperature of the air decreases as altitude increases• The troposphere ends at the tropopause

Structure of the atmosphereStratosphere: 10 – 50 km above Earth• The ozone layer is located in the stratosphere• Commercial airplanes travel in the stratosphere• Temperatures increase as the altitude increases in the stratosphere• This is because the ozone layer absorbs solar radiation

• The stratosphere ends at the stratopause

Structure of the atmosphereMesosphere: 50 - 80 km above Earth• Meteors entering Earth’s atmosphere usually burn up in the

mesosphere• Temperatures decrease as altitude increases in the mesosphere• The mesosphere ends at the mesopause

Structure of the atmosphereThermosphere: 80 – 140 km above Earth• Aurora Borealis (The Northern Lights) occur in the thermosphere• The thermosphere has the least amount of air particles• Temperature increases as altitude increases in the thermosphere

What causes the northern lights?