Earth’s Atmosphere

Chapter 3, Section 2

•Describe the composition of the Earth’s atmosphere•Describe the layers of the Earth’s atmosphere•Explain 3 mechanisms of heat transfer in Earth’s atmosphere•Explain the greenhouse effect

General Description of Atmosphere

• Mixture of gases– Nitrogen– Oxygen– Carbon dioxide & others

• Addition/removal results in change– Living organisms (plants & animals)– Volcanic eruptions– Vehicles/industries

• Insulates Earth’s surface

Composition of Earth’s Atmosphere• Gases– 78% Nitrogen– 21% Oxygen– 1% other (Ar, CO2, CH4, H2O)

• Atmospheric Dust– Solid particles

• Soil, salt, ash fro fire & volcanic eruptions• Particulate matter (combustion, skin, hair,

clothing bits, pollen bacteria & viruses• Aerosols (tiny liquid droplets)

• Creates air pressure– Due to gravitational pull– Greatest near Earth’s surface

Earth’s Atmospheric Layers

(Ionosphere)

Earth’s Atmospheric Layers

• Divided into 4 layers based on– Temperature

changes– Pressure

changes

Location of Atmospheric Layers above Earth’s Surface

Troposphere• Nearest Earth’s surface (up to 18 km)• Makes up 75% of Earth’s atmospheric mass• Densest layer• Temperature & pressure decrease with altitude– Except tropopause – very top of layer– Stable temperature – called “cold trap”

• Wider at equator than poles• Location of weather occurrence– Uneven heating due to convection current & winds– Causes cloud formation (rising water vapor cooled)

• Related to Greenhouse effect

Stratosphere

• 2nd layer above Earth’s surface (32 km thick, 18-50 km above surface)

• Temperature increases with altitude

• Contains ozone layer– Reduces UV radiation– Thinning in Europe, Asia,

North America & Antarctica

Mesosphere

• 50-80 km above surface• Coldest layer– Temperature decreases

with increase in altitude– -30°C (-130°F)

• Slows, prevents meteors entering atmosphere

Thermosphere

• 80 – 1000 km above surface

• Very hot temperatures (200-2000°C or 360-3600°F)

• Ionization of gases – N2 & O2 absorb X-rays &

gamma rays– Radiate light (auroras)

• Reflect radio waves• Area where shuttles orbit

Energy Transfer in the Atmosphere• Radiation– Electromagnetic waves – absorbed & converted to

heat– Visible light, X-rays, UV, Gamma (from sun)

• Conduction– Transfer by contact between different matter

• Convection – Caused by temperature differences & changes in

densities of materials– Occurs only in fluids– Creates currents

Energy Transfer Diagram

Atmospheric Energy

• Reaches Earth as electromagnetic radiation– ½ entering atmosphere reaches surface– ½ absorbed or reflected by gases, clouds, dust

• Oceans & land radiate energy back into atmosphere– Prevents overheating of Earth’s surface

• Dark colors absorb more energy than lighter ones– More energy released by darker colors– Explains higher temperatures in cities than surrounding

country sides

Energy Movement in Atmosphere

• Result of convection currents– Air heated by Earth’s surface & rises into

atmosphere– Cools as it rises & becomes more dense & sinks– Continual process results in circular movement of

air (currents)– Occurs in troposphere, resulting in weather

occurrences (rain, wind, tornadoes, etc.)

Greenhouse Effect• Warming of Earth’s surface & lower atmosphere • Due to carbon dioxide, water vapor & other gases

(methane, nitrous oxide) absorbing & radiating infrared waves – Called “greenhouse gases”– Maintain temperatures that support life

• Excess amounts of carbon dioxide & methane result in increased heat retention– Caused by natural & industrial events– Cause abnormal increases in temperatures (heat) – Result in shifts in climatic zones, melting of polar ice

caps, increased ocean levels around the world

How is Earth’s atmosphere like glass in a car?

• Both allow solar energy to pass through

• Both can absorb and stop heat from escaping