the earth 's atmosphere is made of 21 percent oxygen by volume
composition_of_earth is 35_percent_iron. composition_of_earth is not 28_percent_oxygen. earth's_atmosphere has oxygen oxygen is gas_at_1_atmosphere. earth is 35_percent_iron. composition_of_earth is not 35_percent_iron. world has oxygen_and_nitrogen_atmosphere earth has atmosphere earth's_atmosphere has not oxygen composition_of_earth is 28_percent_oxygen.