A wrapper of air

Long ago, people believed that the sky was a shiny metal roof stretched over the earth ! Now, of course, we know what the sky really is. It's simply air - a covering of air around the earth. Air is wrapped around the earth somewhat like the skin of an orange is wrapped around the fruit inside. This wrapper of air around the earth is called the atmosphere.

The atmosphere touches the ground everywhere. Close to the ground, the air is thick. Farther away, the air gets thinner, just as smoke from a chimney gets thinner the higher it rises. Finally, the air just comes to an end. Where the air ends, outer space begins