ORIGIN OF LIFE UPON THE EARTH 171
and algae, sustain temperatures as high as 63° C. and, as a rule, are killed by a temperature of 73® C, which is probably the coagulation point of their proteins. Setchell found bacteria living in water of hot springs at 89° C^* In the next higher order of the ChlorophyceflB (green algae) the temperature fatal to life is lower, being 43° C.°' Very much higher temperatures are endured by the spores of certain bacilli which survive until temperatures of from 105° C. to 120° C. are reached. There appears to be no known limit to the amount of dry cold which they can withstand."^
It is this power of the relatively water-free spores to resist heat and cold which has suggested to Eichter (1865), to Kelvin, and to Arrhenius (1908) that living germs may have pervaded space and may have reached our planet either in company with meteorites (Kelvin)^' or driven by the pressure of light (Arrhenius).*^® The fact that so far as we know life has only originated once and not repeatedly appears to dispose of these hypotheses ; nor is it courageous to put off the prob- lem of life origin into cosmic space instead of resolutely seeking it within the forces and elements of our own humble planet.
The thermal conditions of living matter point to the probability that life originated when portions at least of the earth's surface and waters had temperatures of between 89° C. and 6° C; and also to the possi- bility of the origin of life before the atmospheric vapors admitted a regular supply of sunlight.
After the sun's heat living matter appears to have captured the sun's light which is essential, directly or indirectly, to all living energy higher than that of the most primitive bacteria. The discovery by La- voisier (1743-1794) and the development (1804) by de Saussure** of the theory of photosynthesis, namely, that sunshine, combining solar heat and light, is a perpetual source of living energy, laid the foundations of biochemistry and opened the way for the establishment of the law of the conservation of energy within the living organism. This was the first conception of the cycle of the elements continually passing through plants and animals which was so grandly formulated by Cuvier in 1817 :«^
»« Op, dt,, p. 68. M Loeb, Jacques, 1906, p. 106.
87 Galtnres of bacteria have even been exposed to the temperature of liquid
hydrogen, (about — 250" C.) without destroying their vitaUty or sensibly im-
j^gfxiiLg their biologic qualities. This temperature is far below that at which
Y ebemieal reaction is known to take place, and is only about 23 degrees above
^^ ttibsolute zero point at which, it is beUeved, molecular movement ceases. On
^e other hand, when bacteria are frozen in water during the formation of nat-
ice the death rate is high. See Jordan, Edwin O., 1908, p. 69.
•sPonlton, Edward B., 1896, p. 818.
<• Pirsson, Louis V., and Schuchert, Charles, 1915, pp. 535, 536. <o De Saussure, N. T., 1804. •1 Cuvier, Baron Georges L. C. T. D., 1817, p. 13.
�� �
