'''Earth's atmosphere''' is a layer of [[gas]]es 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 in the Earth's atmosphere|carbon dioxide]], trace amounts of [[#Composition|other gases]], and a variable amount (average around 1%) of [[water vapor]]. This mixture of gases is commonly known as '''air'''. The atmosphere protects [[organism|life on Earth]] by absorbing [[ultraviolet]] [[solar radiation]] and reducing [[temperature]] extremes between day and night. | '''Earth's atmosphere''' is a layer of [[gas]]es 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 in the Earth's atmosphere|carbon dioxide]], trace amounts of [[#Composition|other gases]], and a variable amount (average around 1%) of [[water vapor]]. This mixture of gases is commonly known as '''air'''. The atmosphere protects [[organism|life on Earth]] by absorbing [[ultraviolet]] [[solar radiation]] and reducing [[temperature]] extremes between day and night. |