LIFE IN GREAT DEPTHS 165 



ZoBell concludes his report by saying that it is the 

 long-range objective of the marine microbiologist to 

 learn everything possible about the occurrence, char- 

 acteristics, and activities of bacteria and allied micro- 

 organisms in the sea, with a view to gaining a fuller 

 understanding of the oceans of the world. 



It is of much interest to note how through the ex- 

 pansion of our knowledge during a century the known 

 zone of life has continuously expanded. From a depth 

 of only 1,800 feet, as indicated by Forbes, the zero 

 line of organic life has been displaced downward, 

 reaching finally to 35,000 feet in the deepest part of 

 the Philippine Trench. Except where local conditions 

 leading to stagnant bottom water cause an accumula- 

 tion of poisonous hydrogen sulphide, no azoic zone 

 seems to exist even in the greatest ocean depths. On the 

 contrary the realm of marine life extends even into the 

 abyssal trenches where nutrient substances are largely 

 supplied by bacteria to animals living under enormous 

 pressure, in intense cold, and in complete darkness. 



