<Tr> <Th_colspan="4"> Not included in above dry atmosphere: </Th> </Tr> <Tr> <Td> Water vapor </Td> <Td> H O </Td> <Td> 10--50,000 </Td> <Td> 0.001%--5% </Td> </Tr> <Tr> <Th_colspan="4"> notes: <P> volume fraction is equal to mole fraction for ideal gas only, also see volume (thermodynamics) ppmv: parts per million by volume Water vapor is about 0.25% by mass over full atmosphere Water vapor strongly varies locally </P> </Th> </Tr> <P> volume fraction is equal to mole fraction for ideal gas only, also see volume (thermodynamics) ppmv: parts per million by volume Water vapor is about 0.25% by mass over full atmosphere Water vapor strongly varies locally </P>

What sphere makes up most of the earth's surface