What is the earths atmosphere composed of?

~75% nitrogen. ~25% oxygen. + tiny fraction of other stuff

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• Nitrogen . . . 78.1%
• Oxygen . . . 20.9%
• Argon . . . 0.93%
• Carbon dioxide . . . 0.04%
• Neon . . . 0.002%
• Helium . . . 0.001%

Less than 0.001% :

• Methane
• Krypton
• Hydrogen

Less than 0.0001%

• Nitrous oxide
• Carbon monoxide

Less than 0.00001%

• Xenon
• Ozone
• Nitrogen dioxide
• Iodine
• Ammonia

Water vapor . . .

• about 0.4% in the whole atmosphere
• typically 1% to 4% at the surface