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 required. From the decomposition of the nitrides and phosphides below the surface, ammonia and phosphine were escaping into the ocean and into the air. The conditions then during long periods of time were especially favorable for marine life, and as sand and mud accumulated on the rocky surface of the earth, for land plants; the absence of a thick soil being more than compensated for by the abundance of plant food, notably of carbon dioxide and ammonia. The statement may be found in excellent modern text-books of chemistry that ammonia is always formed by the decomposition of plants and animals, accompanied by the further statement that ammonia is a requisite for plant food. No plants--no ammonia; no ammonia--no plants. If this were true, the beginning of plant life would indeed have been a struggle for existence; that it is not true is shown above. This decomposition of nitrides has ceased practically on the actual surface of the earth at the present day because the nitrides have all been decomposed; yet it may be mentioned that specimens of rock freshly quarried in Sweden were recently found to give off ammonia when wet with water, showing the presence of nitrides. Below the actual earth’s surface it is probable that nitrides still exist in large quantity, for ammonia is one of the constituents of volcanic gases; to believe that volcanic ammonia is a product of plant or animal decomposition is difficult; to suppose it formed by the action of steam on nitrides in the earth’s interior is simple.