Page:The Scientific Monthly vol. 3.djvu/21

 THE EVOLUTION OF LIFE 15

spread with the granitic batholiths and the more superficial volcanic out- ponrings. There were volcanic ashes; there were gravels^ sands, and micas derived from the granites; there were clays from the dissolution of granitic feldspars; there were loam mixtures of clay and sand; there was gypsum from mineral springs. Bare rocks and soils were inhospit- able ingredients for any but the most rudimentary forms of life, such as were adapted to feed directly upon the chemical elements and their simplest compounds or to transform their energy without the friendly aid of sunshine. The only forms of life to-day which can exist in such an inhospitable environment as that of the lifeless earth are certain of the simplest bacteria.

It is interesting to note that in the period when the sun'a heat was partly shut off by vapors the early volcanic condition of the earth's surface may have supplied life with fundamentally important chemical elements as well as with the heat-energy of the waters or of the soil. Volcanic emanations contain'* free hydrogen, both oxides of carbon, and frequently. hydrocarbons such as methane (GH4) and ammonium chlo- ride : the last compound is often very abundant. Volcanic waters some- times contain ammonium (NH4) salts, from which life may have de- rived its first nitrogen supply. In the DeviFs Inkpot, Yellowstone Park, ammonium sulphate forms 83 per cent, of the dissolved saline matter : it is also the principal constituent of the mother liquor of the boric fumaroles of Tuscany, after the boric acid has crystallized out. A hot spring on the margin of Clear Lake, California, contains 107.76 grains per gallon of ammonium bicarbonate.

There were absent in the primordial earth the greater part of the fine sediments and detrital material which now cover three-fourths of the earth's surface, and from which a large part of the sodium content has been leached. The original surface of the earth was thus composed of igneous rocks to the exclusion of all others,'* the essential constituents of these rocks being the lime-soda feldspars from which the sodium of the ocean has since been leached. Waters issuing from such rocks are, as a rule, relatively richer in silica than waters issuing from modern sedimentary areas. They thus furnished a favorable environment for the development of such low organisms (or their ancestors) as the existing diatoms, radiolarians, and sponges. These have skeletons composed of hydrated silica, mineralogically of opal.

The decomposition and therefore the erosion of the massive rocks was slower then than at present for none of the life agencies of bacteria, of algse, of lichens, and of the higher plants, which are now at work on granites and volcanic rocks in all the humid portions of the earth, had yet appeared. On the other hand, much larger areas of these rocks were exposed than at present. In brief, to imagine the primal

« Clarke, F. W., 1916, Chap. VIIL, also pp. 197, 199, 243, 244. » Becker, George F., 1910, p. 12.

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