THE EVOLUTION OF LIFE 19
When we consider that these ^^ chemical life elements/' so essential to living matter^ were for a great period of time either absent or present in a highly dilnte condition in the ocean^ it appears that we must aban- don the ancient Greek conception of the origin of life in the sea, and again reach the conclusion that the lowliest organisms originated either in moist earths or in those terrestrial waters which contained nitrogen. Nitrates occasionally arise from the union of nitrogen and oxygen in electrical discharges during thunderstorms and were presumably thus produced before life began. Such nitrogen compounds, so essential for the development of protoplasm, may have been specially concentrated in pools of water to degrees particularly favorable for the origin of proto- plasm.^
From terrestrial waters or soils life may have gradually extended into the sea. It appears, too, that every great subsequent higher life phase — ^the bacterial phase, the chloroptfyllic algal phase, the protozoan phase — ^was also primarily of fresh-water and secondarily of marine habitat. It is probable that the succession of marine forms was itself determined to some extent by adaptation to the increasing concentration of saline constituents in sea-water. That the invasion of the sea upon the continental areas occurred at a very early period is demonstrated by the extreme richness and profusion of marine life at the base of the Cambrian.
As compared with primordial sea-water which was relatively fresh and free from salts and from nitrogen existing sea-water is an ideal chemical mediimi for life. As a proof of the special adaptability of existing sea-water to present biochemical conditions, a very interesting comparison is that between the chemical composition of the chief body fluid of the highest animals, namely, the blood serum, and the chemical composition of sea-water, as given by Henderson.**
Chemical Composition or Ska.-wateb and ot Blood Serxtm
"Life Etomenta" In Se»-water In Blood Serum
Sodimn 30.59 39.0
Magnesiimi 3.79 0.4
CalciTim 1.20 1.0
Potaaaium 1.11 2.7
Chlorine 55.27 45.0
SO4 7.66
CO, 0.21 12.0
BTomine 0.19
P,0, 0.4
That life originated in water (H2O) there can be little doubt. The
^ Snggested by Professor W. J. Gies.
M Henderson, Laurence J., 1908, II., p. 145.
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