Misplaced Pages

#849150

53-881: The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of the Early Archean Eon (which is now an obsolete name) alongside the Paleoarchean Era. The International Commission on Stratigraphy now officially recognizes the Eoarchean Era as the first part of the Archaean Eon , preceded by the Hadean Eon, during which the Earth is believed to have been essentially molten. The Eoarchaean's lower boundary or starting point of 4.031 Gya (4031 million years ago )

106-454: A reef -like build-up rather than by "falling" out of the water, and this build-up has been at least influenced and perhaps sometimes caused by the actions of microbes. Stromatolites , bioherms (domes or columns similar internally to stromatolites) and biostromes (distinct sheets of sediment) are among such microbe-influenced build-ups. Other types of microbial mat have created wrinkled "elephant skin" textures in marine sediments, although it

159-487: A bacterium first became an endosymbiont of an anaerobic archean and then fused with it to become one organism. If such endosymbiosis was an important factor, microbial mats would have encouraged it. There are two known variations of this scenario: Microbial mats from ~ 1,200  million years ago provide the first evidence of life in the terrestrial realm. The Ediacara biota are the earliest widely accepted evidence of multicellular animals. Most Ediacaran strata with

212-418: A combination of competition and co-operation. Since the metabolic capabilities of bacteria (what they can "eat" and what conditions they can tolerate) generally depend on their phylogeny (i.e. the most closely related groups have the most similar metabolisms), the different layers of a mat are divided both by their different metabolic contributions to the community and by their phylogenetic relationships. In

265-555: A dormant state. Microbial mats that live in tidal zones, such as those found in the Sippewissett salt marsh , often contain a large proportion of similar microorganisms that can survive for several hours without water. Microbial mats and less complex types of biofilm are found at temperature ranges from –40 °C to +120 °C, because variations in pressure affect the temperatures at which water remains liquid. They even appear as endosymbionts in some animals, for example in

318-488: A few centimeters in thickness, of which only the top few millimeters are oxygenated. Underwater microbial mats have been described as layers that live by exploiting and to some extent modifying local chemical gradients , i.e. variations in the chemical composition. Thinner, less complex biofilms live in many sub-aerial environments, for example on rocks, on mineral particles such as sand, and within soil . They have to survive for long periods without liquid water, often in

371-822: A large asteroid, about 37 to 58 kilometres (23–36 mi) wide, collided with the Earth. The Buck Reef chert and the Josefsdal chert, two rock formations in the Barberton Greenstone Belt, both contain microbial mats with fossilized bacteria from the Paleoarchean era. The Kromberg Formation, near the top of the Onverwacht Group which itself is a part of the Barberton Greenstone Belt, dates back to approximately 3.416–3.334 Ga and contains evidence of microbial life reproducing via multiple fission and binary fission. Similarities between

424-408: A layer of photosynthesizing purple bacteria that could tolerate oxygen; and oxygen-free, H 2 S -dominated lower layers of heterotrophic scavengers, mainly methane-emitting and sulfate-reducing organisms. It is estimated that the appearance of oxygenic photosynthesis increased biological productivity by a factor of between 100 and 1,000. All photosynthetic reactions require a reducing agent , but

477-657: A middle purple layer inhabited by photosynthesizing purple bacteria. Some other mats have a white layer inhabited by chemotrophic sulfur oxidizing bacteria and beneath them an olive layer inhabited by photosynthesizing green sulfur bacteria and heterotrophic bacteria. However, this layer structure is not changeless during a day: some species of cyanobacteria migrate to deeper layers at morning, and go back at evening, to avoid intensive solar light and UV radiation at mid-day. Microbial mats are generally held together and bound to their substrates by slimy extracellular polymeric substances which they secrete. In many cases some of

530-804: A short time (by geological standards) the build-up of dead microorganisms would have created an ecological niche for scavenging heterotrophs , possibly methane-emitting and sulfate-reducing organisms that would have formed new layers in the mats and enriched their supply of biologically useful chemicals. It is generally thought that photosynthesis , the biological generation of chemical energy from light, evolved shortly after 3,000  million years ago (3 billion). However an isotope analysis suggests that oxygenic photosynthesis may have been widespread as early as 3,500  million years ago . There are several different types of photosynthetic reaction, and analysis of bacterial DNA indicates that photosynthesis first arose in anoxygenic purple bacteria , while

583-667: A type of biofilm that is large enough to see with the naked eye and robust enough to survive moderate physical stresses. These colonies of bacteria form on surfaces at many types of interface , for example between water and the sediment or rock at the bottom, between air and rock or sediment, between soil and bed-rock, etc. Such interfaces form vertical chemical gradients , i.e. vertical variations in chemical composition, which make different levels suitable for different types of bacteria and thus divide microbial mats into layers, which may be sharply defined or may merge more gradually into each other. A variety of microbes are able to transcend

SECTION 10

#1732764994850

636-568: A wet environment where sunlight is the main source of energy, the uppermost layers are generally dominated by aerobic photosynthesizing cyanobacteria (blue-green bacteria whose color is caused by their having chlorophyll ), while the lowest layers are generally dominated by anaerobic sulfate-reducing bacteria . Sometimes there are intermediate (oxygenated only in the daytime) layers inhabited by facultative anaerobic bacteria. For example, in hypersaline ponds near Guerrero Negro (Mexico) various kind of mats were explored. There are some mats with

689-519: Is a multi-layered sheet or biofilm of microbial colonies , composed of mainly bacteria and/or archaea . Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces , but a few survive in deserts. A few are found as endosymbionts of animals . 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 microorganisms that can feed on or at least tolerate

742-471: Is likely that they acquired many of these sub-systems from existing mat organisms, by some combination of horizontal gene transfer and endosymbiosis followed by fusion. Whatever the causes, cyanobacteria are the most self-sufficient of the mat organisms and were well-adapted to strike out on their own both as floating mats and as the first of the phytoplankton , which forms the basis of most marine food chains . The time at which eukaryotes first appeared

795-436: Is limited or impossible, including rocky seabeds and shores, and hyper-saline and brackish lagoons. They are found also on the floors of the deep oceans. Because of microbial mats' ability to use almost anything as "food", there is considerable interest in industrial uses of mats, especially for water treatment and for cleaning up pollution . Microbial mats may also be referred to as algal mats and bacterial mats. They are

848-574: Is located in the Pilbara Craton , and contains sedimentary rock from the Paleoarchean Era. It is estimated to be 3.48 billion years old. The Dresser Formation includes a great variety of structures caused by ancient life including stromatolites and MISS once formed by microbial mats. Such microbial mats belong to the oldest ascertained life form and may include fossilized bacteria. The Strelley Pool Chert , also located in

901-516: Is non-existent or negligible: very harsh environments, such as hyper-saline lagoons or brackish estuaries, which are uninhabitable for the burrowing organisms that broke up the mats; rocky "floors" which the burrowers cannot penetrate; the depths of the oceans, where burrowing activity today is at a similar level to that in the shallow coastal seas before the revolution. Although the Cambrian substrate revolution opened up new niches for animals, it

954-610: Is officially recognized by the International Commission on Stratigraphy. The name comes from two Greek words: eos (dawn) and Archaios (ancient). The first supercontinent candidate Vaalbara appeared around the end of this period at about 3,600  million years ago . The beginning of the Eoarchean is characterized by heavy asteroid bombardment within the Inner Solar System :

1007-678: Is possible that Vaalbara did not form until the Mesoarchean or Neoarchean eras. It is also unclear whether there was any exposed land during the Paleoarchean era. Although several Paleoarchean formations such as the Dresser Formation , the Josefsdal Chert, and the Mendon Formation show some evidence of being above the surface, over 90 percent of Archean continental crust has been destroyed, making

1060-462: Is still uncertain: there is reasonable evidence that fossils dated between 1,600  million years ago and 2,100  million years ago represent eukaryotes, but the presence of steranes in Australian shales may indicate that eukaryotes were present 2,700  million years ago . There is still debate about the origins of eukaryotes, and many of the theories focus on the idea that

1113-400: Is toxic to organisms that are not adapted to it, but greatly increases the metabolic efficiency of oxygen-adapted organisms — for example anaerobic fermentation produces a net yield of two molecules of adenosine triphosphate , cells' internal "fuel", per molecule of glucose , while aerobic respiration produces a net yield of 36. The oxygenation of the atmosphere was a prerequisite for

SECTION 20

#1732764994850

1166-583: Is toxic to organisms that are not adapted to it. Microbial mats would have been separated into oxidized and reduced layers, and this specialization would have increased their productivity. It may be possible to confirm this model by analyzing the isotope ratios of both carbon and sulfur in sediments laid down in shallow water. The last major stage in the evolution of microbial mats was the appearance of cyanobacteria , photosynthesizers which both produce and use oxygen . This gave undersea mats their typical modern structure: an oxygen-rich top layer of cyanobacteria;

1219-436: Is usually available about those for which only the hard parts are usually preserved. Microbial mats help to preserve soft-bodied fossils by: The ability of microbial mat communities to use a vast range of "foods" has recently led to interest in industrial uses. There have been trials of microbial mats for purifying water, both for human use and in fish farming , and studies of their potential for cleaning up oil spills . As

1272-542: The Barberton Greenstone Belt in the Kaapvaal Craton and the eastern part of the Pilbara Craton indicate that the two formations were once joined as part of the supercontinent Vaalbara , one of Earth's earliest supercontinents . Both cratons formed at the beginning of the Paleoarchean era. While some paleomagnetic data suggests that they were connected during the Paleoarchean era, it

1325-867: The Late Heavy Bombardment . The largest Eoarchean rock formation is the Isua Greenstone Belt on the south-west coast of Greenland , which dates from 3.8 billion years. The Acasta Gneiss within the Canadian Shield have been dated to be 4,031 Ma and are therefore the oldest preserved rock formations. In 2008, another rock formation was discovered in the Nuvvuagittuq Greenstone Belt in northern Québec, Canada , which has been dated to be 4,280  million years ago . These formations are presently under intense investigation. Oxygen isotope ratios show that

1378-542: The S2 meteorite impact that occurred in this era was from 50 to 200 times the size of the meteorite impact that largely caused the Cretaceous–Paleogene extinction event . It occurred approximately 3.26 billion years ago. The impact immediately redistributed iron(II) (Fe ) from the lower oceanic chemocline through tsunamis that probably continued for days. In the next years and decades, several things occurred. Dust from

1431-712: The bolide containing phosporous and iron fell on land and into the sea. Weathering and erosion brought new material ("fallback") into the sea, including new crystallite (also called grains ) pseudomorphs . The heat generated through the collision continuously boiled the upper layers of water, which concentrated the Fe , organic carbon , and various nutrients. Over thousands of years, these processes created iron(III) hydroxide ( Fe(OH) 3 ) in both sea and sediment that would benefit iron-favoring bacteria and archaea . This meant that these Paleoarchean life forms would have recovered rapidly. Microbial mat A microbial mat

1484-547: The early Archean ), is a geologic era within the Archean Eon . The name derives from Greek "Palaios" ancient . It spans the period of time 3,600 to 3,200 million years ago . The era is defined chronometrically and is not referenced to a specific level of a rock section on Earth . The earliest confirmed evidence of life comes from this era, and Vaalbara , one of Earth's earliest supercontinents , may have formed during this era. The geological record from

1537-729: The hydrological cycle had begun by the early Eoarchaean and possibly earlier. Carbonate precipitation (caused by heating of sea water by hydrothermal vents) acted as an important sink regulating the concentration of carbon dioxide in the atmosphere during this era. 3,850 million years old apatite from Greenland shows evidence of Carbon-12 enrichment. This has sparked a debate whether there might have been photosynthetic life before 3.8 billion years ago. Paleoarchean Gradstein et al., 2012 Isuan Period, 3810–3490 Ma The Paleoarchean ( / ˌ p eɪ l i oʊ . ɑːr ˈ k iː ə n , ˌ p æ l -/ PAY -lee-oh-ar- KEE -ən, PAL- ), also spelled Palaeoarchaean (formerly known as

1590-485: The oxygenic photosynthesis seen in cyanobacteria and much later in plants was the last to evolve. The earliest photosynthesis may have been powered by infra-red light, using modified versions of pigments whose original function was to detect infra-red heat emissions from hydrothermal vents. The development of photosynthetic energy generation enabled the microorganisms first to colonize wider areas around vents and then to use sunlight as an energy source. The role of

1643-424: The "elephant skin" texture characteristic of microbial mats contain fossils, and Ediacaran fossils are hardly ever found in beds that do not contain these microbial mats. Adolf Seilacher categorized the animals as: "mat encrusters", which were permanently attached to the mat; "mat scratchers", which grazed the surface of the mat without destroying it; "mat stickers", suspension feeders that were partially embedded in

Eoarchean - Misplaced Pages Continue

1696-529: The Paleoarchean era is very limited. Due to deformation and metamorphism , most rocks from the Paleoarchean era cannot provide any useful information. There are only two locations in the world containing rock formations that are intact enough to preserve evidence of early life: the Kaapvaal Craton in Southern Africa and the Pilbara Craton in Western Australia . The Dresser Formation

1749-532: The Pilbara Craton, contains stromatolites that may have been created by bacteria 3.4 billion years ago. However, it is possible that these stromatolies are abiogenic and were actually formed through evaporitic precipitation then deposited on the sea floor. The Barberton Greenstone Belt , located in the Kaapvaal Craton, also contains evidence of life. It was created around 3.26 Ga when

1802-502: The bacteria form filaments (threads), which tangle and thus increase the colonies' structural strength, especially if the filaments have sheaths (tough outer coverings). This combination of slime and tangled threads attracts other microorganisms which become part of the mat community, for example protozoa , some of which feed on the mat-forming bacteria, and diatoms , which often seal the surfaces of submerged microbial mats with thin, parchment -like coverings. Marine mats may grow to

1855-432: The dominant chemicals at their level and which are usually of closely related species. In moist conditions mats are usually held together by slimy substances secreted by the microorganisms. In many cases some of the bacteria form tangled webs of filaments which make the mat tougher. The best known physical forms are flat mats and stubby pillars called stromatolites , but there are also spherical forms. Microbial mats are

1908-500: The earliest form of life on Earth for which there is good fossil evidence, from 3,500  million years ago , and have been the most important members and maintainers of the planet's ecosystems . Originally they depended on hydrothermal vents for energy and chemical "food", but the development of photosynthesis allowed mats to proliferate outside of these environments by utilizing a more widely available energy source, sunlight. The final and most significant stage of this liberation

1961-591: The environment, as a general rule the by-products of each group of microorganisms serve as "food" for other groups. In effect each mat forms its own food chain , with one or a few groups at the top of the food chain as their by-products are not consumed by other groups. Different types of microorganism dominate different layers based on their comparative advantage for living in that layer. In other words, they live in positions where they can out-perform other groups rather than where they would absolutely be most comfortable — ecological relationships between different groups are

2014-459: The evolution of the more complex eukaryote type of cell, from which all multicellular organisms are built. Cyanobacteria have the most complete biochemical "toolkits" of all the mat-forming organisms: the photosynthesis mechanisms of both green bacteria and purple bacteria; oxygen production; and the Calvin cycle , which converts carbon dioxide and water into carbohydrates and sugars . It

2067-456: The existence of exposed land practically impossible to confirm or deny. It is likely that during the Paleoarchean era, there was a large amount of continental crust, but it was still underwater and would not emerge until later in the Archean era. Hotspot islands may have been the only exposed land at the time. Due to a much hotter mantle and an elevated oceanic geothermal gradient compared to

2120-420: The free oxygen content of the Earth's atmosphere, both directly by emitting oxygen and because the mats emitted molecular hydrogen (H 2 ), some of which would have escaped from the Earth's atmosphere before it could re-combine with free oxygen to form more water. Microbial mats thus played a major role in the evolution of organisms which could first tolerate free oxygen and then use it as an energy source. Oxygen

2173-641: The hindguts of some echinoids . Microbial mats use all of the types of metabolism and feeding strategy that have evolved on Earth—anoxygenic and oxygenic photosynthesis ; anaerobic and aerobic chemotrophy (using chemicals rather than sunshine as a source of energy); organic and inorganic respiration and fermentation (i..e converting food into energy with and without using oxygen in the process); autotrophy (producing food from inorganic compounds) and heterotrophy (producing food only from organic compounds, by some combination of predation and detritivory ). Most sedimentary rocks and ore deposits have grown by

Eoarchean - Misplaced Pages Continue

2226-475: The hydrothermal vents was now limited to supplying reduced metals into the oceans as a whole rather than being the main supporters of life in specific locations. Heterotrophic scavengers would have accompanied the photosynthesizers in their migration out of the "hydrothermal ghetto". The evolution of purple bacteria, which do not produce or use oxygen but can tolerate it, enabled mats to colonize areas that locally had relatively high concentrations of oxygen, which

2279-475: The limits of diffusion by using "nanowires" to shuttle electrons from their metabolic reactions up to two centimetres deep in the sediment – for example, electrons can be transferred from reactions involving hydrogen sulfide deeper within the sediment to oxygen in the water, which acts as an electron acceptor. The best-known types of microbial mat may be flat laminated mats, which form on approximately horizontal surfaces, and stromatolites , stubby pillars built as

2332-432: The lower layers and which fed respectively on the by-products of the photosynthesizers and on the corpses and / or living bodies of the other mat organisms. These increases would have made microbial mats the planet's dominant ecosystems. From this point onwards life itself produced significantly more of the resources it needed than did geochemical processes. Oxygenic photosynthesis in microbial mats would also have increased

2385-576: The mat; and "undermat miners", which burrowed underneath the mat and fed on decomposing mat material. In the Early Cambrian, however, organisms began to burrow vertically for protection or food, breaking down the microbial mats, and thus allowing water and oxygen to penetrate a considerable distance below the surface and kill the oxygen-intolerant microorganisms in the lower layers. As a result of this Cambrian substrate revolution , marine microbial mats are confined to environments in which burrowing

2438-626: The mats' structure may already have been similar to that of modern mats that do not include photosynthesizing bacteria. It is even possible that non-photosynthesizing mats were present as early as 4,000  million years ago . If so, their energy source would have been hydrothermal vents (high-pressure hot springs around submerged volcanoes ), and the evolutionary split between bacteria and archea may also have occurred around this time. The earliest mats may have been small, single-species biofilms of chemotrophs that relied on hydrothermal vents to supply both energy and chemical "food". Within

2491-435: The microbes slowly move upwards to avoid being smothered by sediment deposited on them by water. However, there are also spherical mats, some on the outside of pellets of rock or other firm material and others inside spheres of sediment. A microbial mat consists of several layers, each of which is dominated by specific types of microorganism , mainly bacteria . Although the composition of individual mats varies depending on

2544-503: The present day, plate tectonics in its modern form did not exist during the Paleoarchean. Instead, a model of "flake tectonics" has been proposed for this era of geologic time. According to this model, instead of normal subduction of oceanic plates, extensively silicified upper oceanic crust delaminated from lower oceanic crust and was deposited in a manner similar to ophiolites from the later Proterozoic and Phanerozoic eons. Researchers from Harvard, Stanford, and ETH Zürich reckon that

2597-470: The shallow seabed until the Cambrian substrate revolution , when animals living in shallow seas increased their burrowing capabilities and thus broke up the surfaces of mats and let oxygenated water into the deeper layers, poisoning the oxygen-intolerant microorganisms that lived there. Although this revolution drove mats off soft floors of shallow seas, they still flourish in many environments where burrowing

2650-450: The significance of oxygenic photosynthesis is that it uses water as a reducing agent, and water is much more plentiful than the geologically produced reducing agents on which photosynthesis previously depended. The resulting increases in the populations of photosynthesizing bacteria in the top layers of microbial mats would have caused corresponding population increases among the chemotrophic and heterotrophic microorganisms that inhabited

2703-529: Was many years before these textures were recognized as trace fossils of mats. Microbial mats have increased the concentration of metal in many ore deposits, and without this it would not be feasible to mine them—examples include iron (both sulfide and oxide ores), uranium, copper, silver and gold deposits. Microbial mats are among the oldest clear signs of life, as microbially induced sedimentary structures (MISS) formed 3,480  million years ago have been found in western Australia . At that early stage

SECTION 50

#1732764994850

2756-479: Was not catastrophic for microbial mats, but it did greatly reduce their extent. Most fossils preserve only the hard parts of organisms, e.g. shells. The rare cases where soft-bodied fossils are preserved (the remains of soft-bodied organisms and also of the soft parts of organisms for which only hard parts such as shells are usually found) are extremely valuable because they provide information about organisms that are hardly ever fossilized and much more information than

2809-446: Was the development of oxygen-producing photosynthesis, since the main chemical inputs for this are carbon dioxide and water. As a result, microbial mats began to produce the atmosphere we know today, in which free oxygen is a vital component. At around the same time they may also have been the birthplace of the more complex eukaryote type of cell , of which all multicellular organisms are composed. Microbial mats were abundant on

#849150