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 r^inrlnsj^p [[|af fhp earf h was molte n 

 at the completion of its growth. A molten state f^iiprp;^*^^'^ ^ 

 rapid earth-growt h due to an original clustering of the matter 

 whose convergence built up the planet. Larger nuclei hun- 

 d reds of miles in diameter and smaller ones comparable to the 

 planetoids moved in elliptic and nearly intersecting orbits. 

 , Mutual perturbations kept mnHifyin g- these orbits and provid-^ 

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

 _sions led to a development of energy of im pnr^ gnfflnpni- f-n" 

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

 _ outer portions. The earth kept growing at the same time 

 Jpy sweepin g up large qua ntities of finer material, but a molten 

 state sug gests that the greater growth was due to the infall 

 ot 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 mnjf nbunrlnnf mnt^^^-^^ i" ^hp deep 



^ody of the earth is metallic iron. Now the blast furnace 



