sentences: the earth 's atmosphere is made of 0 to 4 percent hydrogen / water vapor by volume
docs: composition_of_earth is 28_percent_oxygen. earth has atmosphere composition_of_earth is 2.7_percent_nickel. planet_earth has atmosphere nitrogen is gas_at_1_atmosphere. earths_atmosphere has nitrogen composition_of_earth is 0.4_percent_aluminum. composition_of_earth is 35_percent_iron. composition_of_earth is 12.7_percent_nickel. earth's_atmosphere has oxygen