Original: Although only a few centimetres thick at most , microbial mats create a wide range of internal chemical environments , and hence generally consist of layers of micro-organisms that can feed on or at least tolerate the dominant chemicals at their level and which are usually of closely-related species .
Simplified: Although usually only a few centimetres thick , microbial mats create a wide range of internal chemical environments . They consist of layers of microorganisms that can feed on or tolerate the chemicals at their level .