96 EVOLUTION OF THE EARTH 



Such an idea was advanced by Richter, and later inde- 

 pendently suggested and discussed by Helmholtz and Kelvin. 13 

 On the assumption that some of the heavenly bodies have 

 always been the abode of life, and from the fact that small 

 solid particles, which presumably have formerly been an 

 integral part of such bodies, are moving everywhere in space, 

 Richter pictures these particles as the vehicles which dis- 

 seminate 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 

 is as old as the universe itself living matter has never 

 originated but has been transported from world to world. 

 Hence the acceptance of this permanent dualism of living and 

 lifeless matter does not answer the broad question as to the 

 origin of life, but transfers its origin to a "conveniently inac- 

 cessible corner of the universe where its solution is impossible. " 

 However, the question before us is the origin of life upon the 

 earth, and the plausibility of this cosmozoa theory depends on 

 two assumptions that life exists elsewhere in the universe 

 and that life can be maintained during the interstellar voyage. 

 Neither assumption has, of course, any empirical foundation 

 whatsoever, though the second offers at least something 

 tangible for discussion. 



Many of the lower forms of life, such as the bacteria and 

 protozoa, have the power of developing, particularly under 

 the influence of unfavorable environmental conditions, pro- 

 tective coverings of various sorts about themselves and of 

 assuming a resting condition in which all the metabolic activi- 

 ties characteristic of active life are reduced to the lowest ebb. 

 In this spore or encysted state they are immune to extremes of 

 temperature and desiccation to which they readily succumb 

 during vegetative life. It has recently been found, for example, 



13 Verworn, M., Allgemeine Physiologic, 5th ed., 1909. English translation 

 of 2d edition by F. S. Lee, 1899. 



