Major contributors to sedimentary organic matter

Autotrophes, and particularly phototrophes, provide the energy needed by all other organisms, the 

There is one further major contributor to sedimentary organic matter, bacteria. A large proportion of the energy flow in ecosystems can pass through the detrital food chain, in which heterotrophic bacteria are prominent participants. Heterotrophic bacteria are important in all sedimentary environments, and although they consume organic detritus they supplement the organic matter with their own remains. In some environments autotrophic bacteria may also be important (e.g. the Black Sea see Section 3.4.3c). 

Throughout the Archaean, prokaryotes, in the form of photosynthetic bacteria and cyanobacteria, were the main producers of organic carbon. The resting stages (cysts) of early unicellular eukaryotic organisms, probably representing planktonic algae and referred to as acritarchs, first appeared in the fossil record at c. 1.85 Ga and became abundant from c.l.OGa. 

The abundance of the fossilized remains of herbivorous zooplankton (see Boxes 1.9 and 1.12) is relatively low for the early Palaeozoic but increases subsequently for orders such as the radiolarians and foraminiferans (both protozoa of the class Rhizopoda). Grazing of phytoplankton by zooplankton greatly reduces the 

Fungi appear to have evolved alongside the algae, and there are unicellular (yeasts) as well as colonial forms. Their evolutionary record is, however, difficult to piece together due to the lack of preservable parts. Fossil remains have been found in Archaean marine sediments and today fungi are highly successful in terrestrial environments. Fungi probably invaded the land at the same time as plants. 

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