<P> Due to mass segregation, the core of the Earth is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements . </P> <P> The most abundant elements in the ocean by proportion of mass in percent are oxygen (85.84), hydrogen (10.82), chlorine (1.94), sodium (1.08), magnesium (0.1292), sulfur (0.091), calcium (0.04), potassium (0.04), bromine (0.0067), carbon (0.0028), and boron (0.00043). </P> <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>

The two most abundant elements in earth’s atmosphere today are