The existence of radiant energy (heat and light), is the fundamental precondition of all the subsequent creative formations. It is more universal than gravitation, and absolutely co-extensive with the universe,[215] the connecting bond between all worlds. It determines the temperature of space, of the atmosphere, and of the earth, and, in fact, most of the phenomena of meteorology. It is essential to the life and growth of the plant, and ultimately of the animal; without it, indeed, no life could exist upon the earth. Next in importance is the atmosphere, which has peculiar relations to light and heat. It softens the intensity of light, and diffuses it in every direction; it absorbs and retains heat, and, infolding the earth as with a mantle, keeps it warm. It conditions the formation of clouds, and determines the fall of genial showers. It is the medium in which combustion and change, and all the phenomena of life, take place. Its oxygen has been the chief world-builder, and its nitrogen has been aptly styled the _zoögen_ or generator of life. The gathering of the waters into lakes and seas, the phenomena of aqueous circulation, the formation of soils through its agency--these were all preconditions of vegetable life. "Reasoning deductively, it is equally presumable that vegetable life preceded animal life in order of appearance.... Vegetation is capable of drawing its sustenance from the mineral world, while animals rely exclusively upon organic food. The vegetable stands between the animal and the mineral, performing a sort of commissary function in behalf of the animal. The animal--even the carnivorous animal--implies the vegetable. All things considered, we are led to believe that plant life had a history upon our earth a full epoch before the existence of animals."[216] Finally, all geological preparations and ideas converge in man. "The beneficent provisions of the earth's crust not only prophesy man, but they reach their finality in man. It was only for human uses that the coal was treasured in the recesses of the earth; for human uses alone the mountains have lifted up their burdens of iron; for human uses only the grandest movements of geological history elaborated and distributed the soils. It is only for man that the forests yield their abundant supplies of timber and fuel. For man the edible and medicinal vegetables were provided. For man the natures of the domestic animals were moulded, and their domestic attachments are directed to no other being."[217] Thus through the long ages of geological time the earth was preparing for the dwelling-place of man, and in the earliest forms of animal life his coming was prefigured and foretold.