INTRODUCING…THE ATMOSPHERE!

We live at the bottom of a deep ocean, an ocean of air we call the atmosphere.  It’s about 50 miles thick and it covers the entire surface of the Earth.  That’s a lot of air, but the gaseous ocean above us makes up a very small part of our planet.  If Earth were the size of an apple, our atmosphere would only be as thick as the apple’s skin!
If you’re like most people, you probably don’t think about the atmosphere very often.  And why should you?  Air is just the stuff rockets travel through to see really interesting things, right?

Not so.  The Earth’s atmosphere is a complex shield that nourishes and protects all the life on this planet.  It’s also the strangest atmosphere in the Solar System.  Oxygen gas makes up about a fifth of the material in our air.  Since fires cannot burn without oxygen, ours is the only planet where you can light a match.

Another unique feature of our atmosphere is the water it contains.  Gaseous water – water vapor – accounts for only 10% of the water on the surface of our planet.  But the air is so filled with it that slight changes in temperature can force water vapor to condense into drops and form clouds.  As stargazers know all too well, the sky can fill with clouds in a matter of minutes.  Deep down in the atmosphere, where all life exists, the air is always in motion, always rearranging itself.  This constant activity is what we call “weather.”  When you consider all this, our atmosphere deserves a closer look. 

SLICING UP THE ATMOSPHERE

Scientists split the atmosphere into several layers.  The two most important ones are called the troposphere (TROHP-oh-sfear) and the stratosphere (STRAT-oh-sfear).  The lowest layer and the one most important to us is the troposphere.  About 8 miles thick, this bottom layer holds most of the air in our atmosphere.  Earth’s gravity pulls on the atmosphere and keeps it from leaking away into space.  Because the pull of gravity is strongest near the Earth’s surface, air is thickest at the bottom.  All of the weather on Earth occurs in the dense troposphere.

The stratosphere starts at the top of the troposphere and ends at the height of about 30 miles.  What happens in the stratosphere is very important.  You already know that ozone is produces (and destroyed) in this layer.  It’s also the home of the jet streams that affect the weather farther down.  Beyond the stratosphere the air is so thin that you’re practically in space.

Making a scale drawing of the atmosphere is a good way to remember how it’s put together.

Materials:  tape, 5 sheets of 8 ½ X 11 inch paper, a ruler, colored pencils or crayons, and a pencil

Make one long sheet of drawing paper by taping the 5 sheets together end to end.  Choose one end of the sheet to be the Earth’s surface.  Draw a straight line across the page about an inch from the bottom.  This represents sea level, so write “Sea Level” just above the line.

A convenient scale for your drawing is 1 mile to the inch.  Write at the bottom of your page “Scale:  1 inch = 1 mile.  This means that each inch upward from sea level on your drawing represents 1 mile of altitude in the real atmosphere.  For example, the tallest mountain in the world, Mt. Everest, is 5 ½ miles high.  On one edge of your paper, measure 5 ½ inches straight up from sea level and make a mark.  That mark is the peak or top of Mt. Everest.  Draw in the rest of the mountain.  Here are some other things you’ll want to include in your chart of the atmosphere.  As you drew in each item, make sure you label it so other people can tell what it is.  Remember:  The object’s height in miles is its height in inches above the line you called sea level.

Thunderstorms

A giant thunderstorm cloud can be several miles high.  Rain falls from its flat base, about 1 ¼ miles up.  The cloud towers up to 7 miles, where it flattens out to give the cloud its anvil shape.  Draw a thunderstorm cloud starting with the base at 1 ¼ inches and towering to 7 inches up your page.

Airplanes

Passenger jets usually cruise at an altitude of about 6 ½ miles.  Draw an airplane 6 ½ inches above sea level.

Half Above             

Half Below

At a height of just 3 ½ miles, you’re already above half the weight of the atmosphere.  That’s how much gravity compresses the air!  Make a line across your page at 3 ½ miles.

Welcome to the Stratosphere

Make another line across your page at 8 miles.  That’s the end of the troposphere – and the beginning of the stratosphere.

Mare’s Tails

Wispy cirrus (SEER-us) clouds, or “mare’s tails,” are very high up – between about 6 and 8 miles.   Unlike lumpy cumulus (CUE-mue-luss) clouds, which are built up from droplets of water, these clouds are composed of ice crystals.

Jet Stream

The jet streams are wavy ribbons of fast-moving air.  They usually occur between 10 and 15 miles up.  Speeds of over 300 miles per hour have been recorded in jet streams, but usually the winds are around 100 miles per hour.  Jet streams affect Earth’s weather, and are often associated with storms and tornadoes.

Ozone

The layer of ozone gas that protects us from the Sun’s harmful ultraviolet light lies between 15 ½ and 22 miles up.  Use a different color to represent this region.

Home of the Meteors

Draw a straight line across the page at 30 miles.  That’s the end of the stratosphere, and the beginning of the mesosphere (MEZ-oh-sfear).  The mesosphere is the home of meteors – the bright streaks you can often see at night.  These “shooting stars” actually are small particles from space that have entered the atmosphere.  They usually burn up between 35 and 45 miles up.

Goodbye air, Hello space

At 50 miles, draw another straight line across the page – you’ve reached the end of the mesosphere.  The layer above the mesosphere is called the ionosphere (eye-ON-oh-sfear).  By the time you get this high up there isn’t enough air around to bother counting it.  The lower boundary of space is usually set at 50 miles, so draw a small shuttle or astronaut above your line.  (Actually, the shuttle orbits about 170 miles up – you’d have to add 7 sheets of paper to your chart to put it in the right place!