<P> The order of elements by volume - fraction (which is approximately molecular mole - fraction) in the atmosphere is nitrogen (78.1%), oxygen (20.9%), argon (0.96%), followed by (in uncertain order) carbon and hydrogen because water vapor and carbon dioxide, which represent most of these two elements in the air, are variable components . Sulfur, phosphorus, and all other elements are present in significantly lower proportions . </P> <P> According to the abundance curve graph (above right), argon, a significant if not major component of the atmosphere, does not appear in the crust at all . This is because the atmosphere has a far smaller mass than the crust, so argon remaining in the crust contributes little to mass - fraction there, while at the same time buildup of argon in the atmosphere has become large enough to be significant . </P> <P> For a complete list of the abundance of elements in urban soils, see Abundances of the elements (data page) #Urban soils . </P> <Table> Elemental abundance in the human body show <Tr> <Th> Element </Th> <Th> Proportion (by mass) </Th> </Tr> <Tr> <Td> Oxygen </Td> <Td> 65 </Td> </Tr> <Tr> <Td> Carbon </Td> <Td> 18 </Td> </Tr> <Tr> <Td> Hydrogen </Td> <Td> 10 </Td> </Tr> <Tr> <Td> Nitrogen </Td> <Td> </Td> </Tr> <Tr> <Td> Calcium </Td> <Td> 1.5 </Td> </Tr> <Tr> <Td> Phosphorus </Td> <Td> 1.2 </Td> </Tr> <Tr> <Td> Potassium </Td> <Td> 0.2 </Td> </Tr> <Tr> <Td> Sulfur </Td> <Td> 0.2 </Td> </Tr> <Tr> <Td> Chlorine </Td> <Td> 0.2 </Td> </Tr> <Tr> <Td> Sodium </Td> <Td> 0.1 </Td> </Tr> <Tr> <Td> Magnesium </Td> <Td> 0.05 </Td> </Tr> <Tr> <Td> Iron </Td> <Td> <0.05 </Td> </Tr> <Tr> <Td> Cobalt </Td> <Td> <0.05 </Td> </Tr> <Tr> <Td> Copper </Td> <Td> <0.05 </Td> </Tr> <Tr> <Td> Zinc </Td> <Td> <0.05 </Td> </Tr> <Tr> <Td> Iodine </Td> <Td> <0.05 </Td> </Tr> <Tr> <Td> Selenium </Td> <Td> <0.01 </Td> </Tr> </Table>

Hydrogen is the most abundant element in both earth's crust and the universe