ORIGIN OF LIFE 223 



1. Cosmozoa Theory 



The establishment of biogenesis and the dawning realization 

 of the unique complexity of the structure of matter in the living 

 state have led several scientists to suggest that life has never 

 arisen de novo on the Earth but has been carried hither from else- 

 where in the universe — the so-called cosmozoa theory. 



On the assumption that some of the heavenly bodies have al- 

 ways been the abode of life, and from the fact that small solid 

 particles, which presumably have been a part of such bodies, are 

 moving everywhere in space, these particles have been pictured 

 as the vehicles which disseminate the simplest forms of life through 

 interstellar space to find lodgment and development upon such 

 planets as afford a suitable environment. Clearly, from this point 

 of view, life may be as old as the universe itself. 



The plausibility of the cosmozoa theory depends on two assump- 

 tions: that life exists elsewhere in the universe, and that life can 

 be maintained during the interstellar voyage. Neither assumption 

 has, of course, any foundation of established fact whatsoever, 

 though the second offers at least something tangible for discussion. 



As we know, many of the Bacteria and Protozoa, especially 

 when under the influence of unfavorable surroundings, have the 

 power of developing protective coverings about themselves and 

 of assuming a dormant condition in which all the metabolic ac- 

 tivities are reduced to the lowest ebb. In this spore or encysted 

 state they can endure extremes of temperature and dryness which 

 would quickly prove fatal during active life. For instance, it 

 seems clear that the spores of certain kinds of Bacteria can survive 

 a temperature approaching that below which no chemical reactions 

 are known to occur, and others can endure as high as 140° C. for a 

 short time. The cysts of some relatively highly specialized Pro- 

 tozoa can retain their vitality for at least half a century, while the 

 seeds of some plants have been found to retain the power of germi- 

 nation for nearly a century; though statements that grain from 

 ancient Egyptian tombs still maintains its power of growth has 

 been positively disproved. (Fig. 200.) 



But the hardships to which living matter would be exposed 

 when started on its interstellar journey are not to be minimized. 

 Meteors in their fall through the Earth's atmosphere become 

 heated to incandescence and, if they are the vehicle of transfer, 



