The Origin of the Biosphere 



25 



In a few words, if we assume that the crust of the Earth was formed as a slag 

 from the mantle of the Earth and that, overall, it removed into itself from the 

 mantle from J to | of all the radioactive elements of the Earth, then the analogy 

 between the chondrites, so far as concerns their U, Th and K contents, and the 

 mean composition of the silicate phase of the Earth at least, is unshakeable at 

 present. Nor do the data which Birch has just obtained, showing an identical 

 heat flow per unit area of surface of the continents and ocean beds, contradict 

 this view [i, 3]. 



The role of gravitational heat, particularly in the earliest phases of the develop- 

 ment of the Earth, is not clear. 



However, by far the most important event in the history of the development 

 of the thermal balance of our planet was the formation of the crust of the Earth 

 with its alteration of the distribution of radioactive and other elements and of 

 heat within the terrestrial globe, and its disturbance of thermal equihbrium. 



THE FORMATION OF THE CRUST OF THE EARTH 



The interdependence of the formation of the crust of the Earth, the hydro- 

 sphere and the atmosphere is widely accepted and would appear to be an 

 incontestable truth. 



Table i 

 Possible modes of formation of the crust of the Earth 



From the hot material of the protoplanet 



From the cold material of the Earth 



Differentiation of substances into phases 

 at temperatures above 2000° A. Loss of 

 light gases (Ha, He). Formation of the 

 permanent nucleus of the Earth. 



Formation of the thick crust of the Earth 

 (during 10^-10^ years) and possibilities 

 of differentiation of basaltic and granitic 

 layers. 



Absence of volcanism. 



Primary density of the atmosphere con- 

 taining H2O, CO2, H2 etc. and also inert 

 gases in cosmic abundance. 



Cooling of the surface of the Earth. 

 Great weathering processes. Condensa- 

 tion of all the water to form the primary 

 'acid' ocean. Formation of continents. 

 Formation of the secondary oxygen- 

 containing atmosphere as we know it 

 today (by precipitation of CaCOa and 

 by photosynthesis). 



Cold, solid heterogeneous material (Fe 

 and silicates) losing chemically inert 

 and volatile compounds. 



Absence of gas pressure. 



Heating with the formation of a thin, 

 growing crust of the Earth by melting 

 out. (Temp. 1000° A).* 



Growth of the Fe-nucleus of the earth. 



Earthly and later underwater volcanism. 

 Degassing. Formation of the primitive 

 atmosphere (without inert gases), 

 vapours, H2O, CO2, HF etc. 



Cooling of the significant surface of the 

 Earth. Weathering. Water condensation. 

 Formation of the ocean. Formation of 

 continents with ancient nuclei of forma- 

 tions which developed as a result of 

 plutonic activity (granitic envelope). 



Contemporary, secondary, oxygen-con- 

 taining atmosphere resulting from pre- 

 cipitation of CaCOa and photosynthesis. 



* The presence of H2O, CO2, HF etc. may have lowered the temperature. 



