Atmosphere and Oceans 

The atmosphere was initially formed through outgassing of crustal minerals which decomposed within heating. N₂ and CO₂ were possibly the main original constituents. Water vapor condensed to create the liquid oceans. O₂ is a extremely unusual constituent of our own atmosphere through comparison with other planets. Almost all of it comes from photosynthesis, the process through which green plants get their organic carbon from CO₂ by the use of energy from sunlight.

The main dissolved constituents of the oceans are ions which do not create very insoluble compounds. Large amounts of several common elements like Ca and Si are carried into the sea in soluble form through rivers, but several are precipitated either through inorganic or by biological processes of high abundance The remaining ions (Na⁺, Cl^-, Mg²⁺) create soluble compounds and are removed only through evaporation.