The Earth’s AtmosphereThe Earth’s Atmosphere

What is our weather like now?

Is it the same every day of the year?

Do we have a cold climate in Georgia?

Do we have a dry climate in Georgia?

How would you describe our climate?

• thin layer of gases surrounding the Earth

• no well-defined upper boundary – just fewer and fewer atoms

• density decreases with altitude because number of atoms decrease

What is the atmosphere?

View of the atmosphere from the space shuttle

Air PressureAir Pressure

• atmosphere – exerts pressure

• Why? Because the atoms have weight.

• Gravity holds it on the Earth

•Pressure is higher near surface because more atoms pressing from above.

•sea level pressure = 15 lb/in2

Think about air pressure as being a stack of books.

Here at the surface of the earth, we have more air “stacked” on top of us. That means we feel more pressure than if we were higher in the atmosphere.

http://curriculum.calstatela.edu

Air pressure is measured using an instrument called a barometer.

http://www.dkimages.com/

Notice that it looks like a thermometer. But is does not measure temperature. It measures pressure in inches. (see page 510 in your book)

Also notice that there are words around the gauge. There must be a connection be weather and pressure!

Cold air is more dense (has more pressure) than warm air.

Dry air is more dense than wet air. Notice on the dial that rainy weather has a lower pressure!

Composition of AtmosphereComposition of Atmosphere

atmosphere is a mixture of gasessolid particles

water droplets

Small changes are always happening

N2: nitrogen 78%

O2: oxygen 21%

This means that most of what you breath is NOT oxygen!

• lesser amounts of other gases

Permanent Gases – they are always in the air!

• Water vapor (H20) – can change by the minute!

• Carbon Dioxide (CO2)

• Ozone (O3)

Variable Gases – This means the percents are always changing.

source of this gas: evaporation from Earth’s surface

• water cycle – moves water between oceans, land and atmosphere

• 75% Earth’s surface covered by some form of water

Water Vapor

This satellite image shows the relative amounts of water vapor: Dark – low water, white – high water vapor

•sources: respiration, organic decay, volcanoes, natural and man-made caused fires, burning of fossil fuels.

•important Greenhouse gas

•More Carbon dioxide means more heating of the Earth

Carbon Dioxide (CO2)

What do you think this graph is telling us about the amount of carbon dioxide in the air year by year?

OzoneOzone (O(O33))

• consists of 3 O atoms (O2 + O = O3 )

• highest concentration in stratosphere

•shields surface from UV radiation

•It is good for us up in the stratosphere but bad at the surface where we are.

Why? Because it forms smog – a type of air pollution.

Video clip on ozone

Solids in the atmosphere

• small solid particles put in the air by nature or humans• examples: volcanic ash, salt in sea spray, pollen from plants, and ash from burning vegetation or fossil fuels

Pollen

http://learningoasis.org/mrmc

Dust particles from combustion

Copyright © Michael Collier

We just discussed many of these. Some are natural and some are manmade.

Two common results of pollutants in our atmosphere arephotochemical smog and acid rain.

http://science.kennesaw.edu

It is formed by sunlight causing reactions between chemicals in the air. Most of those chemicals come out of our cars and busses.

Photo taken of Atlanta smog. Notice the brown haze in the sky. That is smog! In Georgia, it is usually caused by car exhaust.

New York smog

http://jmsoul.files.wordpress.com/

Video clip on smog

http://science.howstuffworks.com

Acid rain is caused by water vapor combining with chemicals in the air and forming acid.

The acid rain then changes the water in an area. It can kill trees and poison streams.

http://www.ohiocitizen.org

Video segment on acid rain

Structure of the Atmosphere

• no clearly defined upper limit

• density decreases with elevation

• We divide the atmosphere into layers based on:

Changes in temperature

Layers from Earth’s surface

1) Troposphere

3) Stratosphere

5) Mesosphere

7) Thermosphere

The thermosphere has two parts: ionosphere and exosphere.

Let’s learn a little about each layer!

• lowest layer; temperature decreases with altitude

• thinnest layer (8-16 km, avg. 11 km)

• where weather occurs, where we live

Troposphere

Troposphere – when a cloud reaches the top of this layer, they cannot go higher so they flatten out.

Picture taken by the space shuttle.

Stratosphere

• found above the troposphere

• temperature rises with elevation

• Ozone Layer located here. Remember what we learned about ozone already?

Without the ozone layer protecting us, we could not live on the surface of the Earth!

Mesosphere• above the stratosphere

• temperature decreases with altitude

• Meteorites and space dust burns up in this layer

Thermosphere• above the mesosphere

• temperature increases with altitude

• contains two parts – ionosphere and exosphere

Ionosphere

Quartz Lake State Park, Alaska (Curtis, 1996)

• contains ions: charged particles

• Visible light is given off when ions are hit by energy from the sun. This produces auroras. They are often called northern lights and are seen at night.

http://apod.nasa.gov

Exosphere

The exosphere is the outer part if the atmosphere. Fewer and fewer atoms are found as you get farther from the surface of the earth.

Because of this, there cannot be an actual point where you are no longer in the atmosphere.

Satellites orbit in the exosphere.

What do you know about these layers?

Summary video segment