42 HUMAN BIOLOGY 



often have boiled away until the temperature fell to about 

 I20°c., when permanent deposits of water were formed, 

 but the atmospheric pressure, because of the still large, 

 though now reduced, quantity of water as vapor in the 

 atmosphere, must have been about or more than twenty 

 times as great as it is today. As these condensations occurred 

 almost continuously or consecutively, there must have 

 been, also continuously, electrical discharges of enormous 

 voltage which ionized the constituents of the .atmosphere 

 and caused the formation of new compounds which must 

 have played a part in later syntheses, especially in local 

 condensations of water which, on reduction of volume 

 through evaporation, retained them as solutes more or less 

 concentrated. 



What were these constituents? For an answer we must go 

 to what spectroscopy has revealed regarding the con- 

 stituents in the gaseous envelopes of the cooler stars. It 

 has been found that in stars of the type k* (with temperature 

 of not more than 4000°c.) hydrocarbons are present, and 

 in the n stars (with a temperature of about 3000°c.) and the 

 R stars (with a temperature of about 2300°c.) carbon 

 monoxide, cyanogen, methane, oxygen and nitrogen are 

 found. In the atmosphere of each of not a few of the deriva- 

 tions of such stars, as planets are, each with a diameter of 

 more than 4000 miles, these gases, with water vapor, must 

 have obtained, and thus the atmosphere of the earth in the 

 earliest period of its history was very probably so constituted. 

 What the proportion of each gas was cannot be known, 

 but undoubtedly carbon dioxide was more and oxygen less 

 abundant than in the atmosphere of today, for the carbon 

 of the coal deposits was then combined with oxygen as 

 carbon dioxide from which it was set free by vegetable 

 life, and thus the oxygen content of the atmosphere was 

 increased. Thus the earth inherited its primeval atmosphere. 



In that atmosphere when condensations of the water 

 vapor began there must have been other inorganic con- 

 stituents, especially the chlorides of sodium and potassium, 

 since rain water today carries from the sea these salts to the 

 land surface, for M. J. Pierre found in the rain water collected 



* Of the Harvard classification. 



