This article will be permanently flagged as inappropriate and made unaccessible to everyone. Are you certain this article is inappropriate? Excessive Violence Sexual Content Political / Social
Email Address:
Article Id: WHEBN0000062694 Reproduction Date:
Stromatolites or stromatoliths (; from Greek στρώμα, strōma, mattress, bed, stratum, and λίθος, lithos, rock) are layered bio-chemical cyanobacteria.[1] Stromatolites provide ancient records of life on Earth by fossil remains which might date from more than 3.5 billion years ago. Lichen stromatolites are a proposed mechanism of formation of some kinds of layered rock structure that is formed above water, where rock meets air, by repeated colonization of the rock by endolithic lichens.[2][3]
A variety of stromatolite morphologies exists, including conical, stratiform, branching, domal,[4] and columnar types. Stromatolites occur widely in the fossil record of the Precambrian, but are rare today. Very few ancient stromatolites contain fossilized microbes. While features of some stromatolites are suggestive of biological activity, others possess features that are more consistent with abiotic (non-biological) precipitation. Finding reliable ways to distinguish between biologically formed and abiotic stromatolites is an active area of research in geology.[5]
Time lapse photography of modern stromatolite formation in a laboratory setting gives some revealing clues regarding varied cumulative structures observed in nature. Due to intense UV (ultra violet) radiation during the day, the stromatolitic bacteria restrict their vigorous activity to night time. Fine grain sediments are bound together by excretions, adhered atop one another by the bacteria's flagella, forming layers that correspond to periods of high activity. Thus, these sometimes elaborate structures are the means of providing shelter and protection from the harsh environment constructed by certain microscopic organisms, working somewhat in unison.
Some aragonite nanocrystals (both features of current stromatolites),[5] and because of the persistence of an inferred biological signal through changing environmental circumstances.[6][7]
Stromatolites are a major constituent of the fossil record as to first forms of life on earth and date to 3.5 billion years ago. They peaked about 1.25 billion years ago[6] and subsequently declined in abundance and diversity,[8] so that by the start of the Cambrian they had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victim to grazing creatures (the [9][10][11]
Proterozoic stromatolite fossils may be primordial forms of the eukaryote chlorophytes (that is, green algae). One genus of stromatolite very common in the geologic record is Collenia.
The connection between grazer and stromatolite abundance is well documented in the younger Ordovician evolutionary radiation; stromatolite abundance also increased after the end-Ordovician and end-Permian extinctions decimated marine animals, falling back to earlier levels as marine animals recovered.[12] Fluctuations in metazoan population and diversity may not have been the only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes.[13]
While oncolites are similar to stromatolites and are also known from the fossil record. Thrombolites are poorly laminated or non-laminated clotted structures formed by cyanobacteria, common in the fossil record and in modern sediments.[5]
The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of south western Namibia provides an extremely well exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx.[14]
Modern stromatolites are mostly found in hypersaline lakes and marine lagoons where extreme conditions due to high saline levels exclude animal grazing. One such location is Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia where excellent specimens are observed today, and another is Lagoa Salgada ("Salty Lake"), state of Rio Grande do Norte, Brazil, where modern stromatolites can be observed as bioherm (domal type) and beds. Inland stromatolites can also be found in saline waters in Cuatro Ciénegas, a unique ecosystem in the Mexican desert, and in Lake Alchichica, a maar lake in Mexico's Oriental Basin. The only open marine environment where modern stromatolites are known to prosper is the Exuma Cays in the Bahamas.[15][16]
In 2010, a fifth type of Chlorophyll, namely Chlorophyll f was discovered by Dr. Min Chen from stromatolites in Shark Bay.[17]
Laguna Bacalar in Mexico's southern [18]
A little further to the south, a 1.5 km stretch of reef-forming stromatolites (primarily of the Scytonema genus) occurs in Chetumal Bay in Belize, just south of the mouth of the Rio Hondo and the Mexican border.[19]
Freshwater stromatolites are found in Lake Salda in southern Turkey. The waters are rich in magnesium and the stromatolite structures are made of hydromagnesite.[20]
Another pair of instances of freshwater stromatolites are at Pavilion and Kelly Lakes in British Columbia, Canada. Pavilion Lake has the largest known freshwater stromatolites and has been researched by NASA as part of xenobiology research.[21] NASA, the Canadian Space Agency and numerous universities from around the world are collaborating on a project centered around studying microbialite life in the lakes. Called the "Pavilion Lake Research Project" (PLRP) its aim is to study what conditions on the lakes' bottoms are most likely to harbor life and develop a better hypothesis on how environmental factors affect microbialite life. The end goal of the project is to better understand what condition would be more likely to harbor life on other planets.[22] There is a citizen science project online called "MAPPER" where anyone can help sort through thousands of photos of the lake bottoms and tag microbialites, algae and other lake bed features.[23]
Microbialites have been discovered in an open pit pond at an abandoned asbestos mine near Clinton Creek, Yukon, Canada.[24] These microbialites are extremely young and presumably began forming soon after the mine closed in 1978. The combination of a low sedimentation rate, high calcification rate, and low microbial growth rate appears to result in the formation of these microbialites. Microbialites at an historic mine site demonstrates that an anthropogenically constructed environment can foster microbial carbonate formation. This has implications for creating artificial environments for building modern microbialites including stromatolites.
A very rare type of non-lake dwelling stromatolite lives in the Nettle Cave at Jenolan Caves, NSW, Australia.[25] The cyanobacteria live on the surface of the limestone, and are sustained by the calcium rich dripping water, which allows them to grow toward the two open ends of the cave which provide light.[26]
Stromatolites composed of calcite have been found in both the Blue Lake in the dormant volcano, Mount Gambier and at least eight cenote lakes including the Little Blue Lake in the Lower South-East of South Australia. [27]
Australia, States and territories of Australia, Perth, Government of Western Australia, Local Government Areas of Western Australia
Canada, Manitoba, New Brunswick, Newfoundland and Labrador, Ontario
Ontario, Quebec City, Quebec, Ottawa, Aboriginal peoples in Canada
Tallinn, Sweden, Soviet Union, Tartu, Estonian language
Period (geology), Paleogene, Neogene, Precambrian, Paleoproterozoic
Martinsville, Virginia, Natural history, Archaeology, Stromatolite, Bedford County, Virginia
Cretaceous, Bacteria, Triassic, Jurassic, Elm
Cretaceous, Jurassic, Triassic, Devonian, Ediacaran
Fish, Amphipoda, Animal, Fresh water, Phytoplankton
Earth, Science, Solar System, Evolution, Global warming