Role in the history of life Microbial mat

1 role in history of life

1.1 earliest mats
1.2 photosynthesis
1.3 origin of eukaryotes
1.4 life on land
1.5 earliest multicellular animals
1.6 cambrian substrate revolution
1.7 current status

role in history of life














































































































































  proterozoic eon

  archean eon

  hadean eon






the earliest mats

microbial mats among oldest clear signs of life, microbially induced sedimentary structures (miss) formed 3,480 million years ago have been found in western australia. @ stage mats structure may have been similar of modern mats not include photosynthesizing bacteria. possible non-photosynthesizing mats present 4,000 million years ago. if so, energy source have been hydrothermal vents (high-pressure hot springs around submerged volcanoes), , evolutionary split between bacteria , archea may have occurred around time.

the earliest mats small, single-species biofilms of chemotrophs relied on hydrothermal vents supply both energy , chemical food . within short time (by geological standards) build-up of dead microorganisms have created ecological niche scavenging heterotrophs, possibly methane-emitting , sulfate-reducing organisms have formed new layers in mats , enriched supply of biologically useful chemicals.

photosynthesis

it thought photosynthesis, biological generation of energy light, evolved shortly after 3,000 million years ago. isotope analysis suggests oxygenic photosynthesis may have been widespread 3,500 million years ago. eminent researcher earth s earliest life, william schopf, argues that, if 1 did not know age, 1 classify of fossil organisms in australian stromatolites 3,500 million years ago cyanobacteria, oxygen-producing photosynthesizers. there several different types of photosynthetic reaction, , analysis of bacterial dna indicates photosynthesis first arose in anoxygenic purple bacteria, while oxygenic photosynthesis seen in cyanobacteria , later in plants last evolve.

the earliest photosynthesis may have been powered infra-red light, using modified versions of pigments original function detect infra-red heat emissions hydrothermal vents. development of photosynthetic energy generation enabled microorganisms first colonize wider areas around vents , use sunlight energy source. role of hydrothermal vents limited supplying reduced metals oceans whole rather being main supporters of life in specific locations. heterotrophic scavengers have accompanied photosynthesizers in migration out of hydrothermal ghetto .

the evolution of purple bacteria, not produce or use oxygen can tolerate it, enabled mats colonize areas locally had relatively high concentrations of oxygen, toxic organisms not adapted it. microbial mats have been separated oxidized , reduced layers, , specialization have increased productivity. may possible confirm model analyzing isotope ratios of both carbon , sulfur in sediments laid down in shallow water.

the last major stage in evolution of microbial mats appearance of cyanobacteria, photsynthesizers both produce , use oxygen. gave undersea mats typical modern structure: oxygen-rich top layer of cyanobacteria; layer of photsynthesizing purple bacteria tolerate oxygen; , oxygen-free, h2s-dominated lower layers of heterotrophic scavengers, methane-emitting , sulfate-reducing organisms.

it estimated appearance of oxygenic photosynthesis increased biological productivity factor of between 100 , 1,000. photosynthetic reactions require reducing agent, significance of oxygenic photosynthesis uses water reducing agent, , water more plentiful geologically produced reducing agents on photosynthesis depended. resulting increases in populations of photosynthesizing bacteria in top layers of microbial mats have caused corresponding population increases among chemotrophic , heterotrophic microorganisms inhabited lower layers , fed respectively on by-products of photosynthesizers , on corpses , / or living bodies of other mat organisms. these increases have made microbial mats planet s dominant ecosystems. point onwards life produced more of resources needed did geochemical processes.

oxygenic photosynthesis in microbial mats have increased free oxygen content of earth s atmosphere, both directly emitting oxygen , because mats emitted molecular hydrogen (h2), of have escaped earth s atmosphere before re-combine free oxygen form more water. microbial mats played major role in evolution of organisms first tolerate free oxygen , use energy source. oxygen toxic organisms not adapted it, increases metabolic efficiency of oxygen-adapted organisms — example anaerobic fermentation produces net yield of 2 molecules of adenosine triphosphate, cells internal fuel , per molecule of glucose, while aerobic respiration produces net yield of 36. oxygenation of atmosphere prerequisite evolution of more complex eukaryote type of cell, multicellular organisms built.

cyanobacteria have complete biochemical toolkits of mat-forming organisms: photosynthesis mechanisms of both green bacteria , purple bacteria; oxygen production; , calvin cycle, converts carbon dioxide , water carbohydrates , sugars. acquired many of these sub-systems existing mat organisms, combination of horizontal gene transfer , endosymbiosis followed fusion. whatever causes, cyanobacteria self-sufficient of mat organisms , well-adapted strike out on own both floating mats , first of phytoplankton, forms basis of marine food chains.

origin of eukaryotes

the time @ eukaryotes first appeared still uncertain: there reasonable evidence fossils dated between 1,600 million years ago , 2,100 million years ago represent eukaryotes, presence of steranes in australian shales may indicate eukaryotes present 2,700 million years ago. there still debate origins of eukaryotes, , many of theories focus on idea bacterium first became endosymbiont of anaerobic archean , fused become 1 organism. if such endosymbiosis important factor, microbial mats have encouraged it. there 2 possible variations of scenario:

the boundary between oxygenated , oxygen-free zones of mat have moved when photosynthesis shut down @ night , down when photosynthesis resumed after next sunrise. symbiosis between independent aerobic , anaerobic organisms have enabled both live comfortably in zone subject oxygen tides , , subsequent endosymbiosis have made such partnerships more mobile.
the initial partnership may have been between anaerobic archea required molecular hydrogen (h2) , heterotrophic bacteria produced , live both , without oxygen.

life on land

microbial mats ~1,200 million years ago provide first evidence of life in terrestrial realm.

the earliest multicellular animals















before , after cambrian substrate revolution

the ediacara biota earliest accepted evidence of multicellular animals . ediacaran strata elephant skin texture characteristic of microbial mats contain fossils, , ediacaran fossils hardly ever found in beds not contain these microbial mats. adolf seilacher categorized animals as: mat encrusters , permanently attached mat; mat scratchers , grazed surface of mat without destroying it; mat stickers , suspension feeders partially embedded in mat; , undermat miners , burrowed underneath mat , fed on decomposing mat material.

the cambrian substrate revolution

in cambrian, however, organisms began burrow vertically protection or food, breaking down microbial mats, , allowing water , oxygen penetrate considerable distance below surface , kill oxygen-intolerant microorganisms in lower layers. result of cambrian substrate revolution, marine microbial mats confined environments in burrowing non-existent or negligible: harsh environments, such hyper-saline lagoons or brackish estuaries, uninhabitable burrowing organisms broke mats; rocky floors burrowers cannot penetrate; depths of oceans, burrowing activity today @ similar level in shallow coastal seas before revolution.

current status

although cambrian substrate revolution opened new niches animals, not catastrophic microbial mats, did reduce extent.