The other elements Se, Te, and Po are very scarce.
Occurrence of oxygen
Oxygen is the most abundant of all elements. It exists in the free form as dioxygen molecules O2 and makes up 20.9% by volume and 23% by weight of the atmosphere. Most of this has been produced by photosynthesis, the process where the chlorophyll in the green parts of plants uses the sun's energy to make foodstuffs such as glucose sugar.
6CO2 + 6H2O + energy from the sun C6H12O6 + 6O2
Oxygen makes up 46.6% by weight of the earth's crust, where it is the major constituent of silicate minerals. Oxygen also occurs as many metal oxide ores, and as deposits of oxosalts such as carbonates, sulfates, nitrates and borates. Oceans cover three quarters of the earth's surface, and oxygen makes up 89% by weight of the water in the oceans. Ozone O3 exists in the upper atmosphere and is of great importance.
Sulfur is the sixteenth most abundant element and constitutes 0.034% by weight of the earth's crust. It occurs mainly in the combined form as numerous sulfide ores, and as sulfates (particularly gypsum CaSO4.2H2O). It is not economic to mine these to obtain S, although gypsum is mined for other uses. The native element can be obtained from volcanic sources in many places, but these sources are little used now except in Japan and Mexico. From Biblical times up till the present century volcanic sources provided the major source of S. In early times S in the form of brimstone (burning rock) was used for fumigation. From the thirteenth century until the middle of the nineteenth century it was used to make gunpowder. In the present century the major use has been to make H2SO4.