74 



ANALYSIS OF THE ENVIRONMENT 



follows that a viscous state is necessary 

 which is not too near an ideal soUd or an 

 ideal liquid; in the intermediate colloidal 

 gel and sol we find suflficient solidity to per- 

 mit organization and enough Hquidity to 

 allow change. Life, as we know it, is a 

 matter of the colloidal state.' 



ABSOLUTE 

 4000° 



3000^ 



2000' 



000 



0^ 



mz^. 



CENTIGRADE 



3500° CARBON 



1755° PLATINUM 



658.7 ALUM IN Ul 



100° 

 0° 



-273* 



Fig. 2. Lower end of the temperature scale, 

 showing melting points of carbon, platinum, 

 and aluminum. The cross hatched space indi- 

 cates the biokinetic temperature zone; dotted 

 spaces show temperatures tolerated by some 

 dry protoplasms. ( Modified from Belehradek. ) 



4. There must be a source or sources of 

 energy and of new materials; there is also 

 a need for controlled reaction rates. Thus in 

 the liberation of metabolic energy, food 

 stuffs are burned by oxygen at controlled 

 rates to supply the body needs. If these re- 

 actions occurred spontaneously, without 

 special enzymes regulating the rates, this 



* We reserve judgment concerning the rela- 

 tion of crystalline virus to life in general. 



control would be impossible, the burning 

 would get out of hand, and no sugar or 

 other food reserves could exist.** Limited 

 but renewable amounts of all needed mate- 

 rials and energy must be locally available 

 to permit hving processes to continue. Thus 

 the sun's radiation is a source of energy 

 that reaches the earth in limited amounts, 

 but which so far has been endlessly re- 

 newed and shows no sign of becoming 

 exhausted in the near future. 



We have gained a much better under- 

 standing of energy generation in the sun in 

 the last few decades. The present age of the 

 sun is now estimated to approximate two 

 thousand million years. "During the next 

 ten-thousand-million years the sun is ex- 

 pected to increase about a hundred-fold in 

 luminosity, after which all of its hydrogen 

 will have been converted to hehum. It will 

 then rapidly dechne and disappear as a 

 star of the so-called 'main-sequence.' "t 



5. The absorption of lethal ultraviolet 

 rays of the atmosphere is of great impor- 

 tance. Life, again as we know it, could not 

 occur on the earth today if these shorter 

 abiotic rays were not screened out. Such 

 rays are produced by the sun, which acts 

 in this respect as a black-body radiator with 

 a surface temperature of 6000° C. and an 

 internal temperature of several milhon de- 

 grees. Oxygen absorbs wavelengths shorter 

 than about 200 angstrom units (A), but 

 is somewhat less effective in screening out 

 those up to 2530 A. The absorption causes 

 oxygen to become ozone, which absorbs 

 waves shorter than 3000 A, though it does 

 not completely ehminate those longer than 

 2860 A. Today radiations shorter than 2830 

 A fail to reach the earth's surface. 



This fifth consideration raises some in- 

 teresting matters that deserve brief atten- 

 tion immediately. The question whether the 

 present day type of atmospheric screening 

 has always existed cannot be answered with 

 certainty. One set of students think that 

 oxygen was present in the atmosphere while 

 the earth was cooling; others postulate a 

 primeval atmosphere without oxygen. Ac- 

 cording to the latter point of view, the 

 condensation of water vapor from the prim- 

 itive atmosphere made a shallow sea and 



** Gerard, R. W., personal communication, 

 1942. 



f Personal communication from Otto Struve, 

 who cites Gamow (1940). 



