Jeff Brungard, age 10, of Williamsport, Pennsylvania, for his question:
Where does our air come from?
To us, the most important gas in the air is breathable oxygen. Yet we are using it up every moment so are all the plants and animals that enjoy life on the planet Earth. None of us could last more than a few minutes without the oxygen in the air. The air's gaseous water vapor is almost as important to us as oxygen. It provides our rainfall and without drinkable water we could last only a few days. However, the air is not likely to run out of either oxygen or moisture.
The round world, as we know, is wrapped in a filmy blanket of air that reaches hundreds of miles up above our heads. We call it the atmosphere. Its mixture of gases has been more or less the same for ages and ages.
Most experts agree that our planet began as a big ball of airy gases. If this was so, then the atmosphere arrived first. About four and a half billion years ago, most likely our world was nothing but a ball of airy gases. Scientists estimate that this original big ball of air was about 2,000 times wider than the present planet Earth. What's more, most of the airy mixture was made of the gases hydrogen and helium.
These gases hardly exist in our modern atmosphere. This, we are told, is because they are very light. Later, when the great nuclear furnace started up in the sun, the earth's lighter gases were blown away and lost in space. Meantime, most of the earth's original gaseous materials packed together and formed the solid globe. Inside a shell of gases, it shrank and shrank down to its present size.
For a long time the youthful atmosphere was very dense with dark clouds. As rain fell, the water turned to steamy vapor on the hot earth and rose back up to become more clouds. Finally, the ground became too cool to turn raindrops into steam.
The experts think that then the dense cloudy atmosphere poured down torrents of rain and the water stayed on the ground, gradually filling up the great ocean basins to the brim. This took most of the moisture from the original atmosphere. Meantime, the mixture of other airy gases settled down more or less as they are today.
The plant world adds countless tons of oxygen to the atmosphere every day and breezy winds waft it around the globe. So as long as the earth has enough green plants, we shall never run out of breathable oxygen. The sun evaporates moisture from the surface and the vapor becomes clouds that shed rain. So long as the sun shines and the earth spins, the air will drop drinkable rainwater onto our heads.