Abundance of the chemical elements in the Sun and outer planets is similar to that in the universe. Due to solar heating, the elements of Earth and the inner rocky planets of the Solar System have undergone an additional depletion of volatile hydrogen, helium, neon, nitrogen, and carbon (which volatilizes as methane). The crust, mantle, and core of the Earth show evidence of chemical segregation plus some sequestration by density. Lighter silicates of aluminum are found in the crust, with more magnesium silicate in the mantle, while metallic iron and nickel compose the core. The abundance of elements in specialized environments, such as atmospheres, or
Abundance of the chemical elements in having a great deal more magnesium and significantly more iron, while having much less aluminum and sodium. 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. 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). The order of elements by volume-fraction (which is approximately molecular mole-fraction) in the