THE EVOLUTIONARY CAREER 303 



the period when sedimentary rocks were being formed, but these 

 earUest rocks have been so greatly metamorphosed that the fossils 

 that they may have contained are no longer recognizable. 

 Graphitic materials and calcium carbonate in certain forms occur 

 in Proterozoic and Archeozoic rocks and there does not appear to 

 be any other mode of origin of these materials except by organic 

 processes. Again the very early forms of organisms were doubt- 

 less such that they were not easily preserved in fossil form. 

 Therefore there are indications that living things existed in 

 Proterozoic and Archeozoic times, but there is no evidence that 

 enables us to ascertain what were their forms. 



loirt. The Original Terrestrial Physical Conditions. 

 That being so, we can only speculate as to what the first organisms 

 were in function and structure and even this speculation is strictly 

 limited by lack of knowledge of the original terrestrial conditions. 

 When the vaporous materials of which our planet was formed 

 condensed a hea\y metallic kernel, or centrosphere, first liquefied 

 and over this w^as laid down the stony lithosphere, or earth-crust. 

 As we know it now, this lithoscope is a complex mixture of silicates 

 of aluminium, potassium, sodium, magnesium, with other metals 

 in the forms of oxides, etc. Everywhere the uppermost layer 

 of the earth's crust consists mainly of a *' magma," heavy and 

 basic in the lower levels and light and acidic near the surface. 

 This magma we may regard as the original earth-rind. It is 

 difi^erentiated locally and it is overlaid locally by sedimentary rocks 

 derived from its own disintegration and weathering. 



The original sea. It has generally been held that the water 

 vapour of the original earth-material condensed to form the ocean, 

 which had then much of its present mass. But it is now known 

 that molten magma at a high temperature can combine with water 

 in a high proportion of the latter. Therefore it is probable that 

 the original ocean was very small in mass and that the original 

 dry land consisted of bare rock of the granitic type. Throughout 

 geological time there have been earth-crust disturbances in the 

 course of which molten magma came to the surface as larva 

 outflows and in volcanic eruptions. When this happened the 

 water that had been in combination with the magma became 

 liberated, as steam, into the atmosphere, as the magma cooled. 

 Therefore the volume of the oceans has gradually increased 

 throughout geological time. It is also probable that the original 



