what are the four gases that make up the atmosphere?

Question

Im studing for my test but i dont know the awnser to this one

Answer 1

Nitrogen 78%
Oxygen 20.95%
Argon 0.93%
Carbon Dioxide 0.038%

According to Wikipedia: http://en.wikipedia.org/wiki/Air
"Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor. "

Trace gases can include hydrogen, methane, krypton, helium, radon and other gases given off by the planet.

Notice the carbon dioxide level is pretty low so increasing that slightly can have a big effect.