Chris Sanville, age 10, of Covington,.Georgia, for his question:
How big is the atmosphere?
When we watch the smokey fumes from a factory chimney, we see for ourselves that they rise up, up and away. Perhaps we wonder how far they can spread. There is no doubt that air pollution can spread miles and miles. Then we wonder whether it can spread up to the very top of the atmosphere. However, this is not likely because the size of our atmosphere is so enormous.
The airy atmosphere takes up more room than the solid globe, including all the oceans and continents. We know that its lowest layer must cover 196,940,40 0 square miles because this is the area of the surface on which it sits. As it gets higher above the ground, it takes up more and more space, just as a big ball takes up more space than a smaller one.
Another surprise is the amount of gases in the atmosphere. The air around us seems like an airy nothing. Actually the air that fills an empty drinking glass weighs as much as an aspirin tablet which you may need to recover from the following figures. It is estimated that the total atmosphere contains about ten billion billion pounds of assorted gases. This equals five quadrillion tons, which you can write as figure five with a tail of 15 zeros.
All this filmy air, of course, is spread very thin. And to weigh so many tons, it must occupy an enormous space. The next question is where does it end. And this is a bit of a problem. The air gets thinner and thinner on the way to the top of the atmosphere. Finally the last few molecules get lost in space.
Way up there near the top, the air is so thin that the molecules of gas are hard to find. For this reason we cannot pinpoint just how high our atmosphere reaches. At 300 miles above the ground, the air is hardly worth mentioning. But a few stray molecules reach higher and still higher.
Most scientists suspect that the atmosphere reaches up a thousand miles. This is where the last few molecules get lost in space. Our messy air pollution may be wafted higher than the highest mountains. But little or none of it is likely to reach the top of the atmosphere and spread on out into space.
The earth's gravity hugs the air to the surface of the globe. And gravity grows weaker as it extends out. Near the surface, it is strong enough to hold down the thickest layer of air. About half the gases in the atmosphere are packed into the bottom layer, which reaches from the ground up to about 20 miles. All the remaining five billion billion pounds are spread outward and upward to 1,000 miles