Planets are formed by the condensation of nebulous matter. As the mass condenses it contracts. The volatilized elements vary greatly in their degrees of volatility and some of them, in the process of cooling through radiation, and from the increasing distance from the central mass (sun), reach their points of liquefaction earlier than others. From the liquid state. they finally reach the viscid or molten state, and ultimately the solid state. Thus the different substances become distributed according to their constitutions in the mass of the planet. The heavier substances with high condensing points occupy the center and general mass, while the lighter ones with low condensing points remain at the surface. Some of these, like nitrogen, do not combine with others, and remain elementary. Others, like hydrogen and carbon, combine with part of the oxygen. The first of these combinations resulted primarily in the formation of vast masses of steam, which later partly condensed into vapor and still later into water or even ice. Jupiter seems to consist largely of vapor. The earth doubtless once had an aqueous (steam or vapor) envelope as thick as would be made by converting all the waters of the oceans and seas into vapor. The oxygen also seizes all the carbon and converts it into the dioxide, which is a gas at all ordinary temperatures. After the formation of a crust all round a planet there still remains a large amount of water occupying the cavities of the surface, and an atmosphere of oxygen, nitrogen, carbon dioxide, and aqueous vapor. (Ward 1919:115)
WARD, Lester. 1919. Pure sociology: a treatise on the origin and spontaneous development of society. New York: The Macmillan Company.