300 POPULAR SCIENCE MONTHLY. 



Keturning 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 atmos- 

 phere 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 mat- 

 ter; 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 hy- 

 drocarbons, 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 de- 

 siderata, an ocean warm to its greatest depths could afford any pressure 



