We are surrounded by air, a gas layer held to the earth by gravity. The earth's gravity holds the air in an envelope around the planet that's about 6.5 miles (11 km) thick. This is called our atmosphere. The atmosphere is very important in protecting us from things in space. The moon is covered with craters from being bombarded by meteors because it has no atmosphere to protect it. Most meteors that might have hit the earth burn up in the atmosphere before reaching us. All we see is the streak of light as meteors burn up as shooting stars.

The atmosphere also protects us from the fierce ultraviolet light from the sun. It absorbs much of this light and lets just enough through to warm and nourish us. The atmosphere keeps us from getting too hot when our side of the planet faces the sun on a summer day or too cold when we are facing away from the sun on a winter night. It may sound like the atmosphere knows just what we need, but in truth, life on Earth evolved the way it did because our atmosphere provided the exact conditions we needed to live.

Environmental Experiment

Smog in a Jar

Create your own smog in a jar. All you need is one jar, an aluminum foil top, some ice cubes, some paper, matches, and an adult to help. Everything has to be done fast so be sure to have all the materials ready.

• Rinse the jar out, so the sides are coated with water.

• Form a lid with the foil and set it aside with the ice cubes on top to cool.

• Have your adult helper light the paper and drop it into the jar. Quickly put on the cold foil lid with the ice cubes on top.

• See how the smoke sits on the bottom of the jar? This is the way smog forms.

• Don't breathe it in when you release your smog outside. It's bad for you!

The earth's atmosphere is divided into five layers. The layers closest to the earth are the thickest and then get thinner and fade into space. A rocket leaving our atmosphere would have to go through each layer to get to space. When a rocket launches from Earth it starts in the first layer, the troposphere. It is in this level of the atmosphere where all our weather occurs. This is where clouds form, as well as lightning, high winds, hurricanes, tornadoes, snow, hail, and freezing rain. It's a busy, bumpy place!

Next a rocket would pass through the stratosphere where the air is calmer. This is where airplanes travel because the air is much less bouncy at this altitude. It is also where ultraviolet radiation from the sun reacts with oxygen to form ozone gas and the ozone layer. The ozone layer protects us from getting too much harmful radiation from the sun.

Next the rocket would fly through the atmosphere, the layer of the atmosphere that stops most meteors as they fly toward Earth. Then the rocket would reach the thermosphere. This is where the space shuttle orbits the earth. Then it would go through the exosphere, which is the outermost boundary of our atmosphere. This is where satellites orbit. From here a rocket would leave Earth's atmosphere and begin its journey into space.

OZONE-DEPLETING GASES: Ozone-depleting gases are CFCs found in refrigerants, aerosols, solvents, methyl bromide fumigant, and halon.

SMOG: Smog is ground level ozone and particulate matter formed by burning fuels on hot, sunny days. The word smog came from the combination of the words smoke and fog.