Page:Popular Science Monthly Volume 57.djvu/310

300 Returning to the earth, let us consider the products of these violent reactions. The hydrogen and hydrides of boron, silicon, sulphur and carbon, combined with the oxygen of the atmosphere, forming water and boric, silicic, sulphurous and carbonic acids, which in turn acted on the metallic oxides and hydroxides, forming sulphites, carbonates, borates and simple and complex silicates; some quickly, some slowly, some at low temperatures and atmospheric pressure, others at high temperatures in liquid or semi-liquid condition and under the pressure of rock masses above. To determine the relative age of existing rock layers, or the mode of their formation, whether by eruptive action, by surface heat, by deposition of finely divided material under water, or by metamorphic changes of the cooled silicate under subsequent action of water, pressure and heat, is the province of the geologist. The present writer refrains from an opinion whether any of the first formed solid crust could or could not survive to the present day in its primary form, considering the exposure to water, acids, heat and pressure which it suffered.

Yet an idea may be formed of the condition of the earth's surface when it had cooled so far that the more violent chemical action had ceased. It consisted chiefly of silicates, simple and complex; of some of the original binary compounds, which are scarce affected by water or acids, such as the silicide of carbon (carborundum), of stable oxides, chlorides and sulphides, with other compounds in smaller proportion, and free elements in greater proportion than at the present day. Everywhere, from crevices in the surface, hydrocarbons, phosphoretted hydrogen (phosphine) and ammonia were issuing as gases; the atmosphere was heavy with these gases and with carbon dioxide.

No scientific observations thus far show how or from what definite compounds plant life or animal life was first evolved from lifeless matter; but it is certain that the materials were much more abundant and the conditions more favorable at the period when it was evolved than at the present day. An ocean much warmer and less saline than now, a damp atmosphere like that of a hothouse, an abundance of plant food and a choice of raw material, were at hand. The chief foods required for plant life are nitrogen in the form of ammonia or nitrates, carbon dioxide, phosphorus as phosphates, sulphates of lime, of magnesia and of the alkalies, and water. As to the raw material for the first formation of the living cell, it is impossible to say what compounds of carbon were employed; suffice it to note that the known simple and complex binary compounds of carbon were there ready for use; the hydrocarbons, carbon monoxide and carbon dioxide were oozing from the earth's surface, from the ocean floor as well as from the land, or hanging heavy in the air above it. If warmth or increased pressure were desiderata, an ocean warm to its greatest depths could afford any pressure