6 THE AGE OF THE EARTH 



equatorial than the polar regions, so that in the latter the 

 loss of heat by radiation would be in excess. This might 

 of itself lead to convectional currents in the molten 

 ocean. The effect on the atmosphere is very difficult to 

 trace, but it is obvious that if a high-pressure area 

 originated over some cooler region of the ocean, the winds 

 blowing out of it would drive before them the cooler 

 superficial layers of molten material, and as these were 

 replaced by hotter lava streaming from below, the ten- 

 dency would be to convert the high into a low-pressure 

 area, and to reverse the direction of the winds. Conversely 

 under a low-pressure area the in-blowing w r inds would 

 drive in the cooler superficial layers of molten matter that 

 had been swept away from the anticyclones. If the 

 difference in pressure under the cyclonic and anti-cyclonic 

 areas were considerable, some of the gas absorbed under 

 the anti-cyclones might escape beneath the cyclones, and 

 in a later stage of cooling might give rise to vast floating 

 islands of scoria. Such islands might be the first fore- 

 shado wings of the future continents. Whatever the 

 ultimate effect of the reaction of the winds on the currents 

 of the molten ocean, it is probable that some kind of 

 circulation was set up in the latter. The universal 

 molten ocean was by no means homogeneous : it was 

 constantly undergoing changes in composition as it 

 reacted chemically with the internal metallic nucleus : 

 its currents would streak the different portions out in 

 directions which in the northern hemisphere would run 

 from N.E. to S.W., and thus the differences which dis- 

 tinguish particular petrological regions of our planet may 

 have commenced their existence at a very early stage. Is 

 it possible that as our knowledge extends we shall be able 

 by a study of the distribution of igneous rocks and 

 minerals to draw some conclusions as to the direction of 

 these hypothetical lava currents ? Our planet was pro- 



