16 



The Ocean 



This shows a stepwise form and is divided by four inflection points into five parts which 

 may be regarded as natural regions of the land and of the sea: 



(1) Summits. All land above 1000 m (approx, 40 million km-, mean height 2040 m, 

 maximum height: Mount Everest 8882 m) 



(2) Continental plateaus. Land below 1000 m and the continental shelf to —200 m 

 (approx. 136 million km^, mean height 230 m) 



(3) Continental slope. From the edge of the shelf at —200 m to mean crust level 

 —2440 m (approx. 39 million km^ mean depth 1270 m) 



(4) Deep-sea bottom. Sea bottom from —2440 to —5750 m (approx, 284 million 

 km', mean depth 4420 m) 



(5) Deep-sea depressions and trenches. Below —5750m (approx. II milhon km^ 

 mean depth 6100 m, greatest depth: "Emden" deep in the Philippines trench 

 10,800 m). 



This marked distribution into high and low areas divides the surface of the Earth 

 into: (1) a high continental block which includes all land areas, the adjacent and parts 

 of the marginal seas and the continental shelf and projects about 3100 m above the 

 mean crust level, and (2) the deep sea which lies in basins in the Earth's crust whose 

 bottom is about 2000 m below the mean crust level. The division of the Earth's 

 crust between the continental block and the deep sea is shown in the summary in 

 Table 3 and is illustrated schematically in Fig. 10. These show clearly the sharp division 

 between the two parts: the continental block and the deep sea; the continental slope 



Table 3 



Oceans 



per 

 cent 



per cent of total 

 Earth surface 



3611xl0»km2 



70-8% of the 

 Earth surface 



JO-8 



Continents 



148-9 X 10" km2 

 29-2% of the 

 Earth surface 



29-2 



Total 



1000 



Total deep sea: 601%; Continental plateau (continents plus shelf): 34-4%; 

 Continental slope: 5-5 % 



1000 



