What is the composition of Earth’s atmosphere?

Earth’s atmosphere, apart from water vapor and pollutants, is composed of 78 percent nitrogen, 21 percent oxygen, and less than 1 percent each of argon and carbon dioxide. There are also traces of hydrogen, neon, helium, krypton, xenon, methane, and ozone. Earth’s original atmosphere was probably composed of ammonia and methane; 20 million years ago the air started to contain a broader variety of elements. The atmosphere weighs approximately 5 million billion tons. It exerts an average of 14.7 pounds per square inch (PSI) of pressure on the surface of the planet.


This is a web preview of the "The Handy Science Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App