The Ocean 



- lOXOO 



- 9X>00 



- 8.000 



- 7.000 



- 6.000 



- 5.000 



- AOOO 



- 3.000 



- ZOQO 



ATMOSPHERIC 



-SS'C 0.00 038 g cm"' 



ATMOSPHERK 



STRATOSPHERE 



TROPOSPHERE 



Fig. 1. Diagrammatic representation of the main boundary surfaces in tlie structure of the 



Earth and the density changes at each. The figures at the right are the heights or depths in 



metres above or below sea level. 



land and sea. The coastal limits of the continents projecting above the surface of the 

 ocean are known almost everywhere with satisfactory accuracy. It is only in the polar 

 regions where vast areas of land are buried under ice that it is difficult to determine 

 accurately the limits between continent and sea. These uncertainties have recently 

 been considerably reduced, however. Apart from this reservation, of the 510-01 

 million km^ of the Earth's surface not less than 361 -1 million km^ is ocean and only 

 148-9 milHon km^ is land (Kossinna, 1921). The ratio of land to sea is 1 : 2-43 or 29-20 

 relative to 70-80%. The uncertainty in these values is not more than a few hundredths. 

 The Earth's surface is thus mostly oceanic. Similar relationships hold for the Northern 

 and Southern Hemispheres taken separately: in the Northern Hemisphere 60-7% water, 

 39-3% land; in the Southern Hemisphere 80-9% water, 19-1% land. Water still pre- 

 dominates in the Northern Hemisphere, while in the Southern Hemisphere land is 

 very markedly in the minority. A great circle can be drawn dividing the surface of the 



