Geochemical implications of compositional variation

We have also seen examples of how compound distributions within a given chemical class vary between 

The evolution of organisms throughout geological time means that we do not necessarily see the same types of organic matter in what are otherwise similar sedimentary environments. For example, stromatolites are more frequently found in sediments deposited before the cyanobacterial communities had to cope with predation by herbivores and compete for habitats with other photosynthetic organisms. Higher plant inputs are not seen prior to land colonization in the Silurian. The 

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