SUMMARY 

 Bentley Glass 



Department of Biology, The Johns Hopkins University 



It is next to impossible to think of life originating or existing 

 inider terrestrial circumstances except through the agency, remote 

 or immediate, of light. All organisms, as we know them, require 

 energy in chemical form and control the storage, release, and utiliza- 

 tion of that energy by means of complex protein molecules which 

 function as enzymes. To acquire energy and to trap it in suitable 

 chemical compounds is the primary business of life, most effectively 

 done by absorbing radiant energy. An enormous range in frequency 

 and wavelength of solar radiation bathes our earth, yet most of this 

 is of no avail to life. The shortest wavelengths, highest in energy, 

 cannot be trapped by living mechanisms. Such radiation destroys 

 the enzymes and mutates the genes. The greatest part of the ultra- 

 violet, also lethal, is absorbed by the upper atmosphere. The invisible 

 wavelengths longer than light waves are constituted of quanta of too 

 little energy to drive the machinery of metabolism. In the single 

 octave of radiation with wavelengths between 3500 A and 7000 A, 

 comprising the near ultraviolet and visible portions of the spectrum, 

 living organisms find it possible to subsist between disintegration and 

 inertia. Life is thus ultimately a photochemical phenomenon. 



True, there are chemosynthetic bacteria, which get along quite 

 readily without light. These organisms in fact obtain energy for the 

 reduction of carbon dioxide and the synthesis of their organic com- 

 pounds by oxidizing simple inorganic compounds, either with molecu- 

 lar oxygen or by means of some inorganic oxidant such as nitrate, 

 sulfate, or carbonate. But it is now widely believed that the atmos- 

 phere of the earth was originally reducing, that the oxygen of the 

 atmosphere is entirely the product of photosynthesis over the ages, 

 and that all oxygen was originally combined in the form of oxides. 

 If that was so, the chemosynthetic bacteria cannot have been truly 

 primitive, but perhaps followed or paralleled the advent of photo- 

 synthesis. (See A. I. Oparin, The Origin of Life on the Earth, 3rd 

 ed., pp. 450-455) . The first organisms, primitive heterotrophs, proba- 



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