Timeline of the evolutionary history of life
This timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. In biology, evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, individual organisms and molecules, such as DNA and proteins; the similarities between all present day organisms indicate the presence of a common ancestor from which all known species and extinct, have diverged through the process of evolution. More than 99 percent of all species, amounting to over five billion species, that lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. However, a May 2016 scientific report estimates that 1 trillion species are on Earth, with only one-thousandth of one percent described.
While the dates given in this article are estimates based on scientific evidence, there has been controversy between more traditional views of increased biodiversity through a cone of diversity with the passing of time and the view that the basic pattern on Earth has been one of annihilation and diversification and that in certain past times, such as the Cambrian explosion, there was great diversity. Species go extinct as environments change, as organisms compete for environmental niches, as genetic mutation leads to the rise of new species from older ones. Biodiversity on Earth takes a hit in the form of a mass extinction in which the extinction rate is much higher than usual. A large extinction-event represents an accumulation of smaller extinction- events that take place in a brief period of time; the first known mass extinction in earth's history was the Great Oxygenation Event 2.4 billion years ago. That event led to the loss of most of the planet's obligate anaerobes. Researchers have identified five major extinction events in earth's history since: End of the Ordovician: 440 million years ago, 86% of all species lost, including graptolites Late Devonian: 375 million years ago, 75% of species lost, including most trilobites End of the Permian, "The Great Dying": 251 million years ago, 96% of species lost, including tabulate corals, most extant trees and synapsids End of the Triassic: 200 million years ago, 80% of species lost, including all of the conodonts End of the Cretaceous: 66 million years ago, 76% of species lost, including all of the ammonites, ichthyosaurs, plesiosaurs and nonavian dinosaurs Smaller extinction-events have occurred in the periods between these larger catastrophes, with some standing at the delineation points of the periods and epochs recognized by scientists in geologic time.
The Holocene extinction event is under way. Factors in mass extinctions include continental drift, changes in atmospheric and marine chemistry and other aspects of mountain formation, changes in glaciation, changes in sea level, impact events. In this timeline, Ma means "million years ago," ka means "thousand years ago," and ya means "years ago." 4000 Ma and earlier. 4000 Ma – 2500 Ma 2500 Ma – 542 Ma. Contains the Palaeoproterozoic and Neoproterozoic eras. 542 Ma – present The Phanerozoic Eon the "period of well-displayed life," marks the appearance in the fossil record of abundant, shell-forming and/or trace-making organisms. It is subdivided into three eras, the Paleozoic and Cenozoic, which are divided by major mass extinctions. 542 Ma – 251.0 Ma and contains the Cambrian, Silurian, Devonian and Permian periods. From 251.4 Ma to 66 Ma and containing the Triassic and Cretaceous periods. 66 Ma – present Dawkins, Richard. The Ancestor's Tale: A Pilgrimage to the Dawn of Life. Boston: Houghton Mifflin Company.
ISBN 978-0-618-00583-3. LCCN 2004059864. OCLC 56617123. "Understanding Evolution: your one-stop resource for information on evolution". University of California, Berkeley. Retrieved 2015-03-18. "Life on Earth". Tree of Life Web Project. University of Arizona. January 1, 1997. Retrieved 2015-03-18. Explore complete phylogenetic tree interactively Brandt, Niel. "Evolutionary and Geological Timelines". TalkOrigins Archive. Houston, TX: The TalkOrigins Foundation, Inc. Retrieved 2015-03-18. "Palaeos: Life Through Deep Time". Palaeos. Retrieved 2015-03-18. Kyrk, John. "Evolution". Cell Biology Animation. Retrieved 2015-03-18. Interactive timeline from Big Bang to present "Plant Evolution". Plant and Animal Evolution. University of Waikato. Retrieved 2015-03-18. Sequence of Plant Evolution "The History of Animal Evolution". Plant and Animal Evolution. University of Waikato. Retrieved 2015-03-18. Sequence of Animal Evolution Yeo, Dannel. "History of Life on Earth". Archived from the original on 2015-03-15. Retrieved 2015-03-19.
Exploring Time. The Science Channel. 2007. Retrieved 2015-03-19. Roberts, Ben. "Plant evolution timeline". University of Cambridge. Archived from the original on 2015-03-13. Retrieved 2015-03-19. Art of the Nature Timelines on Wikipedia
Evolutionary history of life
The evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to the present. Earth formed about 4.5 billion years ago and evidence suggests life emerged prior to 3.7 Ga. The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor. 1 trillion species live on Earth of which only 1.75–1.8 million have been named and 1.6 million documented in a central database. These living species represent less than one percent of all species that have lived on earth; the earliest evidence of life comes from biogenic carbon signatures and stromatolite fossils discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland. In 2015, possible "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. In March 2017, putative evidence of the oldest forms of life on Earth was reported in the form of fossilized microorganisms discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, not long after the formation of the Earth 4.54 billion years ago.
Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean Epoch and many of the major steps in early evolution are thought to have taken place in this environment. The evolution of photosynthesis, around 3.5 Ga led to a buildup of its waste product, oxygen, in the atmosphere, leading to the great oxygenation event, beginning around 2.4 Ga. The earliest evidence of eukaryotes dates from 1.85 Ga, while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions. Sexual reproduction, which involves the fusion of male and female reproductive cells to create a zygote in a process called fertilization is, in contrast to asexual reproduction, the primary method of reproduction for the vast majority of macroscopic organisms, including all eukaryotes; however the origin and evolution of sexual reproduction remain a puzzle for biologists though it did evolve from a common ancestor, a single celled eukaryotic species.
Bilateria, animals with a front and a back, appeared by 555 Ma. The earliest complex land plants date back to around 850 Ma, from carbon isotopes in Precambrian rocks, while algae-like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2.7 Ga. Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event. Ediacara biota appear during the Ediacaran period, while vertebrates, along with most other modern phyla originated about 525 Ma during the Cambrian explosion. During the Permian period, including the ancestors of mammals, dominated the land, but most of this group became extinct in the Permian–Triassic extinction event 252 Ma. During the recovery from this catastrophe, archosaurs became the most abundant land vertebrates. After the Cretaceous–Paleogene extinction event 66 Ma killed off the non-avian dinosaurs, mammals increased in size and diversity.
Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. The oldest meteorite fragments found on Earth are about 4.54 billion years old. The Moon has the same composition as Earth's crust but does not contain an iron-rich core like the Earth's. Many scientists think that about 40 million years after the formation of Earth, it collided with a body the size of Mars, throwing into orbit crust material that formed the Moon. Another hypothesis is that the Earth and Moon started to coalesce at the same time but the Earth, having much stronger gravity than the early Moon, attracted all the iron particles in the area; until 2001, the oldest rocks found on Earth were about 3.8 billion years old, leading scientists to estimate that the Earth's surface had been molten until then. Accordingly, they named this part of Earth's history the Hadean. However, analysis of zircons formed 4.4 Ga indicates that Earth's crust solidified about 100 million years after the planet's formation and that the planet acquired oceans and an atmosphere, which may have been capable of supporting life.
Evidence from the Moon indicates that from 4 to 3.8 Ga it suffered a Late Heavy Bombardment by debris, left over from the formation of the Solar System, the Earth should have experienced an heavier bombardment due
Age of the Earth
The age of the Earth is 4.54 ± 0.05 billion years. This age may represent the age of the Earth's accretion, of core formation, or of the material from which the Earth formed; this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples. Following the development of radiometric age-dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old; the oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Calcium–aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the Solar System—are 4.567 billion years old, giving a lower limit for the age of the solar system. It is hypothesised that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions and the meteorites.
Because the time this accretion process took is not yet known, predictions from different accretion models range from a few million up to about 100 million years, the difference between the age of Earth and of the oldest rocks is difficult to determine. It is difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of different ages. Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence; these layers contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer. Nicolas Steno in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata, his observations led him to formulate important stratigraphic concepts. In the 1790s, William Smith hypothesized that if two layers of rock at differing locations contained similar fossils it was plausible that the layers were the same age.
William Smith's nephew and student, John Phillips calculated by such means that Earth was about 96 million years old. In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, several hundred thousand years before, the rest of the universe. Lomonosov's ideas were speculative. In 1779 the Comte du Buffon tried to obtain a value for the age of Earth using an experiment: He created a small globe that resembled Earth in composition and measured its rate of cooling; this led him to estimate. Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. In 1830, geologist Charles Lyell, developing ideas found in James Hutton's works, popularized the concept that the features of Earth were in perpetual change and reforming continuously, the rate of this change was constant; this was a challenge to the traditional view, which saw the history of Earth as static, with changes brought about by intermittent catastrophes.
Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform. In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years, he assumed that Earth had formed as a molten object, determined the amount of time it would take for the near-surface to cool to its present temperature. His calculations did not account for heat produced via radioactive decay or, more convection inside the Earth, which allows more heat to escape from the interior to warm rocks near the surface. More constraining were Kelvin's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse. Geologists such as Charles Lyell had trouble accepting such a short age for Earth. For biologists 100 million years seemed much too short to be plausible. In Darwin's theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time.
According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3.5 to 3.8 billion years ago, the amount of time which passed since the last universal ancestor of all living organisms as shown by geological dating. In a lecture in 1869, Darwin's great advocate, Thomas H. Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions; the physicist Hermann von Helmholtz and astronomer Simon Newcomb contributed their own calculations of 22 and 18 million years to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born. Their values were consistent with Thomson's calculations. However, they assumed; the process of solar nuclear fusion was not yet known to science. In 1895 John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity."Other scientists backed up Thomson's figures.
History of Earth
The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution; the geological time scale, as defined by international convention, depicts the large spans of time from the beginning of the Earth to the present, its divisions chronicle some definitive events of Earth history. Earth formed around 4.54 billion years ago one-third the age of the universe, by accretion from the solar nebula. Volcanic outgassing created the primordial atmosphere and the ocean, but the early atmosphere contained no oxygen. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. While the Earth was in its earliest stage, a giant impact collision with a planet-sized body named Theia is thought to have formed the Moon. Over time, the Earth cooled, causing the formation of a solid crust, allowing liquid water on the surface.
The Hadean eon represents the time before a reliable record of life. The following Archean and Proterozoic eons produced the beginnings of life on Earth and its earliest evolution; the succeeding eon is the Phanerozoic, divided into three eras: the Palaeozoic, an era of arthropods and the first life on land. Recognizable humans emerged at most 2 million years ago, a vanishingly small period on the geological scale; the earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era, after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, "If life arose quickly on Earth … it could be common in the universe."Photosynthetic organisms appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen.
Life remained small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, culminated in the Cambrian Explosion about 541 million years ago. This sudden diversification of life forms produced most of the major phyla known today, divided the Proterozoic Eon from the Cambrian Period of the Paleozoic Era, it is estimated that 99 percent of all species that lived on Earth, over five billion, have gone extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million are documented, but over 86 percent have not been described. However, it was claimed that 1 trillion species live on Earth, with only one-thousandth of one percent described; the Earth's crust has changed since its formation, as has life has since its first appearance. Species continue to evolve, taking on new forms, splitting into daughter species, or going extinct in the face of ever-changing physical environments; the process of plate tectonics continues to shape the Earth's continents and oceans and the life they harbor.
Human activity is now a dominant force affecting global change, harming the biosphere, the Earth's surface and atmosphere with the loss of wild lands, over-exploitation of the oceans, production of greenhouse gases, degradation of the ozone layer, general degradation of soil and water quality. In geochronology, time is measured in mya, each unit representing the period of 1,000,000 years in the past; the history of Earth is divided into four great eons, starting 4,540 mya with the formation of the planet. Each eon saw the most significant changes in Earth's composition and life; each eon is subsequently divided into eras, which in turn are divided into periods, which are further divided into epochs. The history of the Earth can be organized chronologically according to the geologic time scale, split into intervals based on stratigraphic analysis; the following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon.
Therefore, the second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline; the standard model for the formation of the Solar System is the solar nebula hypothesis. In this model, the Solar System formed from a large, rotating cloud of interstellar dust and gas called the solar nebula, it was composed of hydrogen and helium created shortly after the Big Bang 13.8 Ga and heavier elements ejected by supernovae. About 4.5 Ga, the nebula began a contraction that may have been triggered by the shock wave from a nearby supernova. A shock wave would have made the nebula rotate; as the cloud began to accelerate, its angular momentum and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation. Small perturbations due to collisions and the angular momentum of other large debris
Google Play is a digital distribution service operated and developed by Google LLC. It serves as the official app store for the Android operating system, allowing users to browse and download applications developed with the Android software development kit and published through Google. Google Play serves as a digital media store, offering music, books and television programs, it offered Google hardware devices for purchase until the introduction of a separate online hardware retailer, Google Store, on March 11, 2015, it offered news publications and magazines before the revamp of Google News in May 15, 2018. Applications are available through Google Play either free of charge or at a cost, they can be downloaded directly on an Android device through the Play Store mobile app or by deploying the application to a device from the Google Play website. Applications exploiting hardware capabilities of a device can be targeted to users of devices with specific hardware components, such as a motion sensor or a front-facing camera.
The Google Play store had over 82 billion app downloads in 2016 and has reached over 3.5 million apps published in 2017. It has been the subject of multiple issues concerning security, in which malicious software has been approved and uploaded to the store and downloaded by users, with varying degrees of severity. Google Play was launched on March 6, 2012, bringing together the Android Market, Google Music, the Google eBookstore under one brand, marking a shift in Google's digital distribution strategy; the services included in the Google Play are Google Play Books, Google Play Games, Google Play Movies & TV, Google Play Music. Following their re-branding, Google has expanded the geographical support for each of the services; as of 2017, Google Play features over 3.5 million Android applications. Users in over 145 countries can purchase apps, although Google notes on its support pages that "Paid content may not be available in some provinces or territories if the governing country is listed above."
Developers in over 150 locations can distribute apps on Google Play, though not every location supports merchant registration. To distribute apps, developers have to pay a one-time $25 registration fee for a Google Play Developer Console account. App developers can control which countries an app is distributed to, as well as the pricing for the app and in-app purchases in each country. Developers receive 70% of the application price, while the remaining 30% goes to the distribution partner and operating fees. Developers can set up sales, with the original price struck out and a banner underneath informing users when the sale ends. Google Play allows developers to release early versions of apps to a select group of users, as alpha or beta tests. Developers can release apps through staged rollouts, in which "your update reaches only a percentage of your users, which you can increase over time." Users can pre-order select apps to have the items delivered as soon. Some network carriers offer billing for Google Play purchases, allowing users to opt for charges in the monthly phone bill rather than on credit cards.
Users can request refunds within 48 hours after a purchase if "something you bought isn't working, isn't what you expected, was bought by accident, or you changed your mind about the purchase". Apps meeting specific usability requirements can qualify as a Wear OS app. Google Play Games is an online gaming service for Android that features real-time multiplayer gaming capabilities, cloud saves and public leaderboards, achievements; the service was introduced at the Google I/O 2013 Developer Conference, the standalone mobile app was launched on July 24, 2013. Google Play Music is online music locker, it features over 40 million songs, gives users free cloud storage of up to 50,000 songs. As of May 2017, Google Play Music is available in 64 countries. Google Play Books is an ebook digital distribution service. Google Play offers over five million ebooks available for purchase, users can upload up to 1,000 of their own ebooks in the form of PDF or EPUB file formats; as of January 2017, Google Play Books is available in 75 countries.
Google Play Books can be found on the archive.org website available for readers and for download. Google Play Movies & TV is a video on demand service offering movies and television shows available for purchase or rental, depending on availability; as of January 2017, movies are available in over 110 countries, while TV shows are available only in Australia, Canada, Germany, Switzerland, the United States and the United Kingdom. Google Play Newsstand is a news aggregator and digital newsstand service offering subscriptions to digital magazines and topical news feeds; as of January 2017, the basic Newsstand service, with topical news feeds, is available worldwide. Paid Newsstand content is available in over 35 countries. In May 15, 2018, the mobile app merged with Google Weather to form Google News; the Newsstand section continued to appear on the Google Play website until November 5, 2018. Google Play, before March 2015, had a Devices section for users to purchase Google Nexus devices, Chromecasts, other Google-branded hardware, accessories.
A separate online hardware retailer called the Google Store was introduced on March 11, 2015, replacing the Devices section of Google Play. Google Play originated from three distinct products: Android Market, Google Music and Google eBookstore; the Android Market was announced by Google on August 28, 2008, was mad
The Wikimedia Foundation, Inc. is an American non-profit and charitable organization headquartered in San Francisco, California. It is known for participating in the Wikimedia movement, it hosts sites like Wikipedia. The foundation was founded in 2003 by Jimmy Wales as a way to fund Wikipedia and its sibling projects through non-profit means; as of 2017, the foundation employs over 300 people, with annual revenues in excess of US$109.9 million. María Sefidari is chair of the board. Katherine Maher has been the executive director since March 2016; the Wikimedia Foundation has the stated goal of developing and maintaining open content, wiki-based projects and providing the full contents of those projects to the public free of charge. Another main objective of the Wikimedia Foundation is political advocacy; the Wikimedia Foundation was granted section 501 status by the U. S. Internal Revenue Code as a public charity in 2005, its National Taxonomy of Exempt Entities code is B60. The foundation's by-laws declare a statement of purpose of collecting and developing educational content and to disseminate it and globally.
In 2001, Jimmy Wales, an Internet entrepreneur, Larry Sanger, an online community organizer and philosophy professor, founded Wikipedia as an Internet encyclopedia to supplement Nupedia. The project was funded by Bomis, Jimmy Wales's for-profit business; as Wikipedia's popularity increased, revenues to fund the project stalled. Since Wikipedia was depleting Bomis's resources and Sanger thought of a charity model to fund the project; the Wikimedia Foundation was incorporated in Florida on June 20, 2003. It applied to the United States Patent and Trademark Office to trademark Wikipedia on September 14, 2004; the mark was granted registration status on January 10, 2006. Trademark protection was accorded by Japan on December 16, 2004, and, in the European Union, on January 20, 2005. There were plans to license the use of the Wikipedia trademark for some products, such as books or DVDs; the name "Wikimedia", a compound of wiki and media, was coined by American author Sheldon Rampton in a post to the English mailing list in March 2003, three months after Wiktionary became the second wiki-based project hosted on Wales' platform.
In April 2005, the U. S. Internal Revenue Service approved the foundation as an educational foundation in the category "Adult, Continuing education", meaning all contributions to the foundation are tax-deductible for U. S. federal income tax purposes. On December 11, 2006, the foundation's board noted that the corporation could not become the membership organization planned but never implemented due to an inability to meet the registration requirements of Florida statutory law. Accordingly, the by-laws were amended to remove all reference to membership activities; the decision to change the bylaws was passed by the board unanimously. On September 25, 2007, the foundation's board gave notice that the operations would be moving to the San Francisco Bay Area. Major considerations cited for choosing San Francisco were proximity to like-minded organizations and potential partners, a better talent pool, as well as cheaper and more convenient international travel than is available from St. Petersburg, Florida.
The move from Florida was completed by 31 January 2008 with the headquarters on Stillman Street in San Francisco. In 2009, the Wikimedia Foundation's headquarters moved to New Montgomery Street. Lila Tretikov was appointed executive director of the Wikimedia Foundation in May 2014, she resigned in March 2016. Former chief communications officer Katherine Maher was appointed the interim executive director, a position made permanent in June 2016. In October 2017, the headquarters moved to One Montgomery Tower. Content on most Wikimedia Foundation websites is licensed for redistribution under v3.0 of the Attribution and Share-alike Creative Commons licenses. This content is sourced from contributing volunteers and from resources with few or no copyright restrictions, such as copyleft material and works in the public domain. In addition to Wikipedia, the foundation operates eleven other wikis that follow the free content model with their main goal being the dissemination of knowledge; these include, by launch date: Several additional projects exist to provide infrastructure or coordination of the free knowledge projects.
For instance, Outreach gives guidelines for best practices on encouraging the use of Wikimedia sites. These include: Wikimedia movement affiliates are independent, but formally recognized, groups of people intended to work together to support and contribute to the Wikimedia movement; the Wikimedia Foundation's Board of Trustees has approved three active models for movement affiliates: chapters, thematic organizations, user groups. Movement affiliates are intended to organize and engage in activities to support and contribute to the Wikimedia movement, such as regional conferences, edit-a-thons, public relations, public policy advocacy, GLAM engagement, Wikimania. Recognition of a chapter and thematic organization is approved by the foundation's board. Recommendations on recognition of chapters and thematic organizations are made to the foundation's board by an Affiliations Committee, composed of Wikimedia community volunteers; the Affiliations Committee approves the recognition of individual user groups.
While movement affiliates are formally recognized by the Wikimedia Foundation, they are independent of the Wikimedia Foundation, with no legal control of nor responsibility for the Wikimedia projects. The foundation began recognizing chapters in 2004. In 2010, development on additional models began. In 2012, the foundation approved, fina
A wiki is a website on which users collaboratively modify content and structure directly from the web browser. In a typical wiki, text is written using a simplified markup language and edited with the help of a rich-text editor. A wiki is run using wiki software, otherwise known as a wiki engine. A wiki engine is a type of content management system, but it differs from most other such systems, including blog software, in that the content is created without any defined owner or leader, wikis have little inherent structure, allowing structure to emerge according to the needs of the users. There are dozens of different wiki engines in use, both standalone and part of other software, such as bug tracking systems; some wiki engines are open source. Some permit control over different functions. Others may permit access without enforcing access control. Other rules may be imposed to organize content; the online encyclopedia project Wikipedia is the most popular wiki-based website, is one of the most viewed sites in the world, having been ranked in the top ten since 2007.
Wikipedia is not a single wiki but rather a collection of hundreds of wikis, with each one pertaining to a specific language. In addition to Wikipedia, there are tens of thousands of other wikis in use, both public and private, including wikis functioning as knowledge management resources, notetaking tools, community websites, intranets; the English-language Wikipedia has the largest collection of articles. Ward Cunningham, the developer of the first wiki software, WikiWikiWeb described wiki as "the simplest online database that could work". "Wiki" is a Hawaiian word meaning "quick". Ward Cunningham and co-author Bo Leuf, in their book The Wiki Way: Quick Collaboration on the Web, described the essence of the Wiki concept as follows: A wiki invites all users—not just experts—to edit any page or to create new pages within the wiki Web site, using only a standard "plain-vanilla" Web browser without any extra add-ons. Wiki promotes meaningful topic associations between different pages by making page link creation intuitively easy and showing whether an intended target page exists or not.
A wiki is not a crafted site created by experts and professional writers, designed for casual visitors. Instead, it seeks to involve the typical visitor/user in an ongoing process of creation and collaboration that changes the website landscape. A wiki enables communities of contributors to write documents collaboratively. All that people require to contribute is a computer, Internet access, a web browser, a basic understanding of a simple markup language. A single page in a wiki website is referred to as a "wiki page", while the entire collection of pages, which are well-interconnected by hyperlinks, is "the wiki". A wiki is a database for creating and searching through information. A wiki allows non-linear, evolving and networked text, while allowing for editor argument and interaction regarding the content and formatting. A defining characteristic of wiki technology is the ease with which pages can be created and updated. There is no review by a moderator or gatekeeper before modifications are accepted and thus lead to changes on the website.
Many wikis are open to alteration by the general public without requiring registration of user accounts. Many edits can be made in real-time and appear instantly online, but this feature facilitates abuse of the system. Private wiki servers require user authentication to edit pages, sometimes to read them. Maged N. Kamel Boulos, Cito Maramba, Steve Wheeler write that the open wikis produce a process of Social Darwinism. "'Unfit' sentences and sections are ruthlessly culled and replaced if they are not considered'fit', which results in the evolution of a higher quality and more relevant page. While such openness may invite'vandalism' and the posting of untrue information, this same openness makes it possible to correct or restore a'quality' wiki page." Some wikis have an Edit button or link directly on the page being viewed, if the user has permission to edit the page. This can lead to a text-based editing page where participants can structure and format wiki pages with a simplified markup language, sometimes known as Wikitext, Wiki markup or Wikicode.
An example of this is the VisualEditor on Wikipedia. WYSIWYG controls do not, always provide