AND ITS INHABITANTS 33 



uplifted tracts of later times is apparently about sufficient to 

 account for all the salt in the sea. In fact, the estimates of 

 erosion through known geologic time based on the nature of 

 rock exposures and the thickness of sediments have fully 

 equaled or exceeded the amount given by the quantity of salt 

 in solution. Weathering, erosion, and the accumulation of 

 salt had therefore played no considerable part previous to the 

 time recorded by the oldest rocks. The earlier physical con- 

 ditions must have been very different from those which later 

 prevailed. 



FAVORED HYPOTHESIS OF AN EARTH INITIALLY MOLTEN 



Indications of a primordial molten state. The indications 

 of primordial tidal retardation and the limited amount of salts 

 in the sea both point to the conclusion that the earth was molten 

 at the completion of its growth. A molten state suggests a 

 rapid earth-growth due to an original clustering of the matter 

 whose convergence built up the planet. Larger nuclei hun- 

 dreds of miles in diameter and smaller ones comparable to the 

 planetoids moved in elliptic and nearly intersecting orbits. 

 Mutual perturbations kept modifying these orbits and provid- 

 ing new chances for collisions, union, and growth. Such colli- 

 sions led to a development of energy of impact sufficient to 

 produce in the growing earth a molten state, at least in the 

 outer portions. The earth kept growing at the same time 

 by sweeping up large quantities of finer material, but a molten 

 state suggests that the greater growth was due to the infall 

 of larger nuclei. Finally, but one outstanding nucleus, the 

 moon, was left beside the earth, and the earth-moon system 

 attained a condition of stability and completed growth. 



If the composition of the earth as a whole is similar to 

 that of the meteorites, those samples of matter which come to 

 us from the heavens, the most abundant material in the deep 

 body of the earth is metallic iron. Now the blast furnace 



