On the concentration of certain elements at the earth's surface

Abstract

A survey of the abundances of elements in the ocean and sedimentary rocks as compared to their abundances in the weathered igneous rocks shows that carbon, nitrogen, oxygen as water, chlorine, bromine and boron are highly concentrated in the surface materials and that thicknesses of from 17 to 89 km of the outer part of the earth would be required to produce these elements if all of them now present in the igneous rocks were removed. A study of the available information indicates that many other elements would be concentrated at the earth’s surface if chlorine, bromine and boron were concentrated there by a high-temperature volatilization process either from volcanoes or in an original high-temperature atmosphere of the earth . It is concluded that the removal of these elements from the outer parts of the earth occurred through solution in water at low or moderate temperatures ( ~ 100°C or less), since they are soluble and other elements are not. Iodine should belong to this group, but its position is uncertain because of doubtful analytical data. Sulphur may belong in some degree with the volatiles, i.e. carbon as methane or carbon dioxide, nitrogen as ammonia or molecular nitrogen, and water. It is shown that the low abundances of mercury and arsenic in the sediments are inconsistent with a temperature of formation of the earth’s surface regions higher than a few hundred degrees centigrade. The presence of appreciable quantities of nitrogen in the igneous rocks indicates that this element was present in condensed phases during the earth ’s formation, and a survey of the conditions of stability of such compounds indicates temperatures of about 200°C or less. It has not been possible to decide whether liquid water was present on the primitive earth .