What are Microbial Mats?
Photosynthetic microbial mats are a type of microbial mat that obtains its energy from sunlight. On the early Earth, before higher multicellular organisms evolved, photosynthetic microbial mats literally covered the planet, and microbes were the only life forms. Later, as higher plants evolved, photosynthetic mat communities had to compete for sunlight and nutrients. The evolution of animals brought further pressures because mats are a nutritious food. So, although microbial mats are trying to grow almost everywhere almost all of the time, it is only in special places the microbes have the opportunity to grow the large amounts of biomass comparable to what was found on early Earth. Examples of places where microbial mats are found in modern times include extremely productive salt marshes and high energy carbonate beaches such as in the Bahamas. In many cases, microbial mats flourish in so-called “extreme environments” where the extreme temperatures, dryness or saltiness act to exclude
Microbial mats are multi-layered sheets of microorganisms — mostly bacteria and archaea (another domain of bacteria-sized microbes) that dominated much of the planet for billions of years, before the evolution of multicellular organisms, which promptly ate those microbes up as soon as they arrived on the scene. Microbial mats are often found at the interface between two substances, especially in moist or submerged environments, such as the sea floor. These microbial mats are held together by extracellular polymeric substances — also known as scum — which reinforce their structure and adhere them to the substrate. Fossil evidence of microbial mats appears as far back as 3,500 million years ago, serving as the earliest direct evidence of life on Earth. Initially, the microbes in the mats were chemoautotrophic — meaning they got their energy and carbon by combining together chemicals found mostly at hydrothermal vents on the ocean floor. Then, about 2,600 million years ago, the microb
Microbial mats may be described as laminated self-sustaining ecosystems. They may be described as laminated because the pigmentation and by-products of major functional groups provides mats with a distinct layered appearance. As light enters a mat it is selectively attenuated according to how photrophic organisms have evolved to exploit certain wavelengths. They are self-sustaining because they possess the essential biocomplexity for carrying out the essential biogeochemical processes that sustain life. Present-day mats are believed to be descendants of the first extant biological communities on Earth, stromatolites. Fossils of major mat constituents, cyanobacteria, have been found in stromatolitic structures dating to 3.5 billion years ago!
