The common name given to the atmospheric gases used in breathing and photosynthesis is air. By volume, dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases such as methane. Air also contains a variable amount of water vapor, on average around 1%. Although air content and atmospheric pressure vary at different layers, air suitable for the survival of terrestrial plants and terrestrial animals currently is only known to be found in Earth's troposphere and artificial atmospheres.
The Earth's Atmosphere is split into five layers. These are:
- Exosphere, which is almost eighty percent of the outer atmosphere: >700 km (>440 miles)
- Thermosphere, lower base of the Exosphere: 80 to 700 km (50 to 440 miles)
- Mesosphere, which houses the Northern Lights: 50 to 80 km (31 to 50 miles)
- Stratosphere, where meteors are seen: 12 to 50 km (7 to 31 miles)
- Troposphere, lowest layer where planes fly: 0 to 12 km (0 to 7 miles)