PHOSPHORUS AND LIFE — HOPKINS 



239 



occur at certain places on the exposed sedimentary rock surface. 

 Several explanations have been put forward and it is possible that 

 no single explanation accounts for all the deposits. Sudden temper- 

 ature changes in the sea once covering these sites may have caused 

 enormous mass destruction of life among sea animals and organisms; 

 heavy destruction of sea life through causes of this nature are not 

 unknown today. Abnormally high precipitation of phosphate together 

 with the deposition of bone phosphate would follow. Bottom-water 

 currents in the sea may have set up chemical disturbances resulting 

 in an intensified precipitation of deep-sea phosphate ions. Another 

 explanation is that sea-floor currents and the local contour of the sea 

 floor itself have segregated the precipitated calcium phosphate and 

 prevented it from entering siliceous dilution in sedimentary rock 

 itself. Whatever their true explanations may be, the fact remains 

 that marine-cycle losses of phosphate have in various places accumu- 

 lated in concentrated "rock phosphate" forms instead of penetrating 

 siliceous rock as a minor diluent. 



PHOSPHATE 

 ROCK DEPOSITS 

 (ex former 

 Marine Cycle) 



Apatite in Igneous 

 or Sedimentary Rock 



Dilute Solution o£ 



Sea-bird 

 Guano. Fish 

 and fish waste 

 used as Manure 



Figure 2. — Simple diagram for land cycle of phosphorus circulation. 



The first mineral phosphates used by Lawes were from nodulated 

 deposits (coprolites) in Suffolk and Cambridgeshire. Until 1900 

 various nodule deposits in England were worked, but in the period 

 1850-1900 many much richer phosphate rock deposits were found 

 abroad, notably the huge beds of North Africa, America, and Russia. 

 A large and widespread industry has arisen to produce superphos- 

 phate and other phosphatic fertilizers from these minerals deposited 

 as a result of the marine cycle. By this means the agricultural accel- 

 eration of the land cycle is at least partially compensated, though as 

 human numbers increase and demands for cereal crops intensify, more 

 and more phosphatic fertilizer is required. 



It is pertinent to consider how long this intervention of man can 

 preserve a balance. The known world reserves of suitable rock phos- 



