ChapD1.1

Earth’s Atmosphere

The Air You Breathe

• atmosphere: the layer of air that surrounds our planet – atmosphere looks like a thin blanket surrounding

the entire planet– formed when gases from erupting volcanoes

collected around the planet millions of years ago• gases would have poisoned people but bacteria and other

living things used these gases and released new gases• the gas mixture changed slowly over time until it became

the atmosphere we have now

• atmosphere made of billions and billions of gas particles– about 4/5 of these gas particles are nitrogen (N)– 1/5 are oxygen (O)

• oxygen: a gas that your body uses in its life processes

– carbon dioxide (CO2) and water vapor make up the rest of the atmosphere

• plants use CO2 during photosynthesis• plants give off O as photosynthesis occurs• CO2 absorbs heat energy from the sun and Earth’s

surface– this helps keep the planet warm

• water vapor can absorb heat energy– amount of water vapor in the air varies

from place to place– air over bodies of water have more water

vapor– high in the air water vapor changes to

clouds

• properties of air– takes up space– has weight– air pressure: all the particles if air pressing

down on the surface• changes as you go higher in the atmosphere• at the surface particles are close - the further

you to into the atmosphere the farther apart the particles are

• less air pressure the higher the atmosphere

Atmosphere Layers

• atmosphere divided into 4 layers– troposphere: closest to Earth

• we live in the troposphere and breathe air• almost all weather can happen here• air temp goes down as you go up

– stratosphere: contains most of the atmosphere’s ozone, kind of O

• airplanes travel in the stratosphere to avoid bad weather

• ozone protects us from suns harmful rays• temps increase w/ height

– mesosphere• temp decreases w/

height• coldest layer

– thermosphere • hot, outermost layer• temp increases

quickly w/ height– can reach

thousands of degrees Celsius

Summary

• thin blanket of air surrounding Earth is the atmosphere

• atmosphere divided into 4 layers based on temp changes

• starting with closest to Earth the layers are: troposphere, stratosphere, mesosphere, and thermosphere