chapter 18 the atmosphere. earth’s atmosphere made of a mixture of lots of gases 79% 21%

Chapter 18

The Atmosphere

Earth’s Atmosphere

• Made of a mixture of lots of gases

79%

21%

• Pressure– Decrease

as you go up

• Density– Decrease

as you go up

Layers of the Atmosphere

• Troposphere– Layer closest to surface (0 to 10 miles)

• 50% of all gases found below 3.5 miles

– Most dense layer of air– Where weather occurs– Gets cooler as you go up

• Temperature inversion can happen– Cooler air gets trapped under hot air

– Traps the pollutants causing smog


• Stratosphere– Second layer of the atmosphere (10 to 30 miles)

• 99% of all gases below 19 miles

– Ozone is located here• Shields life from the dangerous UV rays

– Absorbs the UV rays given off by the sun

– Makes this layer warm

– Temperature increases as you go up


• Mesosphere– Third layer of the atmosphere– Layer with the coldest temperatures

• Thermosphere– Last layer of the atmosphere– Very hot temperatures– Gases very spread apart

• Some escape into space


• Original atmosphere– Mostly hydrogen, water vapor, ammonia,

methane, carbon monoxide, carbon dioxide, and nitrogen

Earth’s Atmosphere• Gases keep the Earth warm

– Carbon dioxide and water trap heat– Known as the

greenhouse effect• Must have it to

keep Earth suitable for life


• Plant’s evolved by using water vapor and carbon dioxide– Used photosynthesis (oxygen-carbon

dioxide cycle)

Plants use carbon dioxide

Plants produce oxygen

Animals breath oxygen

Animals exhale carbon dioxide

Changes to the Atmosphere

• Photosynthesis– Plants use carbon dioxide to make oxygen– Puts more oxygen in the air

• Respiration– Animals use oxygen to make carbon

dioxide– Puts more carbon dioxide in the air

• Need a balance of carbon dioxide and oxygen to keep the atmosphere the way it is

Changes in the Atmosphere

• Human changes– Appliances add chlorofluorocarbons (CFC)

• CFC destroy ozone

– Cut down trees and other plants– Burning fossil fuels

• Drive cars, heat buildings, manufacturing

Water Cycle and Atmosphere


• Water evaporates from the surface into the atmosphere– Warmer temperature = more evaporation =

more water vapor in atmosphere– Humidity

• Amount of water vapor in the atmosphere


• Dew Point– Temperature where water vapor

condenses– Depends on humidity

• Higher humidity leads to higher dew point


• Water vapor condenses in air– Forms tiny drops of liquid water and ice

• Known as Clouds

• Clouds get very full and very heavy– Water will begin to fall because of the

weight and gravity• Known as precipitation

– Rain, snow, hail, sleet

Types of Clouds

Cirrus Clouds

Cumulus Clouds

Stratus CloudsFog - Very Low Clouds

Pressure and Atmosphere

• Air pressure is read with a barometer– Weight of all atmosphere pushing down– Cool air has higher pressure– Drops in pressure indicate stormy weather

• High pressure = fair weather• Low pressure = clouds and precipitation

Pressure and Atmosphere

• Difference in air pressure creates wind– Air moves from high pressure to low

pressure• Larger difference = stronger winds

– Areas of equal pressure are connected by isobars on a weather map

• Close bars = strong winds

Coriolis Effect

Close isobars = high winds

Fronts and Weather

• Air Masses– Body of air with the same temperature and

humidity

• Front– Boundary between different air masses– Three main types

• Cold• Warm• Stationary

Fronts and Weather

• Warm Front– Warm air mass moves toward and over

cold air mass– Clouds usually form

• Start as high cirrus clouds• Later form heavy stratus clouds that release

precipitation for a few days

Weather Map Symbol

Fronts and Weather

• Cold Front– Cold air mass moves under a warm air

mass– Very steep edge so cumulus clouds form

quickly and are very heavy– High winds, thunderstorms, tornadoes

occur here

Weather Map Symbol

Fronts and Weather

• Stationary Front– Two different air masses sit along side

each other– Act similar to a warm front– Weather usually stays the same for a few

days

Weather Map Symbol

Fronts and Weather

• Thunderstorms– Precipitation storms with lightning and

thunder• Lightning = sparks that jump between clouds

and ground because of a difference in electric charge

• Thunder = sound of lightning moving through the air

Fronts and Weather

• Tornadoes– High speed, rotating winds that extend out

of thunderclouds– Most common in Midwest region of the US

from April until June– Watches are set when conditions are right– Warnings are set when one has been

spotted

Fronts and Weather

• Hurricanes– Similar to tornadoes, but they form over

water • Water powers the hurricane so the longer it is

over water, the worse it can be

– Usually occur in late summer to early fall– Also called cyclones and typhoons in other

parts of the world

Weather and Climate

• Climate– The average weather patterns of a certain

area over many, many years– Depends on location on Earth and surface

features in the area

Weather and Climate

• Temperatures are hotter closer to the equator because of more direct sunlight

Weather and Climate

• Seasons occur because Earth tilts and it moves around the sun

Weather and Climate

• Surface features of Earth– Mountains cause air to rise, cooling it,

forming clouds– Oceans currents cause air to cool down – Bodies of water cause air to be more

humid– Flat lands don’t stop air from flowing so lots

of winds

chapter 18 the atmosphere. earth’s atmosphere made of a mixture of lots of gases 79% 21%

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