26 Marine Microbiology 



and carbonates (problems of genesis of deposits of sulfur, of 

 sulfidic ores of iron and some other metals, the precipitation of 

 dense limestone, and the weathering of rocks and minerals). A 

 veiy important problem is to determine the role of microbes in 

 genesis, preservation and accumulation of liquid hydrocarbons. 



During the deposition of salt beds microbes may be active 

 until the mother-brine is evaporated. These salt deposits in some 

 cases are significant to the accumulation of bituminous sub- 

 stances, to the precipitation of sulfur, iron oxide, or iron sulfide, 

 so that various microbial activities may occur under various 

 specific conditions, e.g., of pH or Eh. Finally, living halophilic 

 microbes interfere with the crystallization process. They are in- 

 corporated into crystals of Halite or other salt minerals or in 

 brine drops witliin the crystals. For some time the bacteria may 

 be alive, then they die and are presei"ved in the salt where we 

 find not only common bacterial cells but also the threads of 

 Chlamydohacteria (type Leptothrix) and hyphae of fungi. 



Geomicrobiological research along these lines can be con- 

 ducted in two ways. The first is concerned with observations of 

 recent conditions in the field or in model experiments. We can 

 investigate, for example, the behaviour of microbes in sediments. 

 We can determine the species living in sediments, their micro- 

 habitats, how long they can live during the diagenesis, how they 

 are transported witliin the sediment, how their metabolism x^ro- 

 ceeds under natural conditions, and their age and origin of 

 population in deeper and older layers of a sediment. 



The second is more difficult. It is concerned with the re- 

 construction of special events in earlier geological periods, events 

 in which microbial activities are assumed or open to question. 

 Microbes of the type Bacteria and Cyanophyceae are in a phylo- 

 genetical sense the oldest organisms we know. We are allowed to 

 assume that they have been "ready" in general at least during 

 the Archaicum so that we can count on their activity during the 

 later geological ages. We suppose that the factors governing life 

 conditions have been essentially the same as they are, in general, 

 today. 



The geological processes in question take place with other 

 time scales than current biota life span, thus we have to accelerate 



