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54-507: Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, Columbia , assembled by global-scale 2.0–1.8 Ga collisional events. Rodinia broke up in the Neoproterozoic, with its continental fragments reassembled to form Pannotia 633–573 Ma. In contrast with Pannotia, little is known about Rodinia's configuration and geodynamic history. Paleomagnetic evidence provides some clues to

108-446: A fixed frame of reference (such as the fixed stars, Latin sidera , singular sidus ). Its average duration is 365.256 363 004 days (365 d 6 h 9 min 9.76 s) (at the epoch J2000.0 = January 1, 2000, 12:00:00 TT ). Today the mean tropical year is defined as the period of time for the mean ecliptic longitude of the Sun to increase by 360 degrees. Since the Sun's ecliptic longitude

162-618: A leap year there are 366 days. A leap year occurs every fourth year during which a leap day is intercalated into the month of February. The name "Leap Day" is applied to the added day. In astronomy, the Julian year is a unit of time defined as 365.25 days, each of exactly 86,400 seconds ( SI base unit ), totaling exactly 31,557,600 seconds in the Julian astronomical year. The Revised Julian calendar , proposed in 1923 and used in some Eastern Orthodox Churches , has 218 leap years every 900 years, for

216-435: A person carrying a bundle of wheat denoting "harvest". Slavic besides godŭ "time period; year" uses lěto "summer; year". Astronomical years do not have an integer number of days or lunar months. Any calendar that follows an astronomical year must have a system of intercalation such as leap years. In the Julian calendar , the average (mean) length of a year is 365.25 days. In a non-leap year, there are 365 days, in

270-696: A reference event in the past (called the epoch ) as the beginning of the era. The Gregorian calendar era is the world's most widely used civil calendar . Its epoch is a 6th century estimate of the date of birth of Jesus of Nazareth . Two notations are used to indicate year numbering in the Gregorian calendar: the Christian " Anno Domini " (meaning "in the year of the Lord"), abbreviated AD; and " Common Era ", abbreviated CE, preferred by many of other faiths and none. Year numbers are based on inclusive counting , so that there

324-719: A rift developed between the continental masses of present-day Australia, East Antarctica, India and the Congo and Kalahari cratons on one side and later Laurentia, Baltica, Amazonia and the West African and Rio de la Plata cratons on the other. This rift developed into the Adamastor Ocean during the Ediacaran . Around 550 Ma, near the boundary between the Ediacaran and Cambrian, the first group of cratons fused again with Amazonia, West Africa and

378-431: A single, persistent "Paleopangaea" supercontinent. As evidence, he suggests an observation that the palaeomagnetic poles from the continental crust assigned to this time conform to a single path between 825 and 633 Ma and latterly to a near-static position between 750 and 633 Ma. This latter solution predicts that break-up was confined to the Ediacaran period and produced the dramatic environmental changes that characterised

432-550: A time interval in Julian years is a way to precisely specify an amount of time (not how many "real" years), for long time intervals where stating the number of ephemeris days would be unwieldy and unintuitive. By convention, the Julian year is used in the computation of the distance covered by a light-year . In the Unified Code for Units of Measure (but not according to the International Union of Pure and Applied Physics or

486-749: Is a 12-month period used for calculating annual financial statements in businesses and other organizations. In many jurisdictions, regulations regarding accounting require such reports once per twelve months, but do not require that the twelve months constitute a calendar year. For example, in Canada and India the fiscal year runs from April 1; in the United Kingdom it runs from April 1 for purposes of corporation tax and government financial statements, but from April 6 for purposes of personal taxation and payment of state benefits; in Australia it runs from July 1; while in

540-490: Is about 20 minutes shorter than the sidereal year. The mean tropical year is approximately 365 days, 5 hours, 48 minutes, 45 seconds, using the modern definition ( = 365.24219 d × 86 400 s). The length of the tropical year varies a bit over thousands of years because the rate of axial precession is not constant. The anomalistic year is the time taken for the Earth to complete one revolution with respect to its apsides . The orbit of

594-524: Is an integral approximation to the year equaling 365 days, which wanders in relation to more exact years. Typically the vague year is divided into 12 schematic months of 30 days each plus 5 epagomenal days. The vague year was used in the calendars of Ethiopia , Ancient Egypt , Iran , Armenia and in Mesoamerica among the Aztecs and Maya . It is still used by many Zoroastrian communities. A heliacal year

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648-427: Is measured with respect to the equinox, the tropical year comprises a complete cycle of the seasons and is the basis of solar calendars such as the internationally used Gregorian calendar . The modern definition of mean tropical year differs from the actual time between passages of, e.g., the northward equinox, by a minute or two, for several reasons explained below. Because of the Earth's axial precession , this year

702-629: Is named after the 19th-century German astronomer and mathematician Friedrich Bessel . The following equation can be used to compute the current Besselian epoch (in years): The TT subscript indicates that for this formula, the Julian date should use the Terrestrial Time scale, or its predecessor, ephemeris time . The exact length of an astronomical year changes over time. Numerical value of year variation Mean year lengths in this section are calculated for 2000, and differences in year lengths, compared to 2000, are given for past and future years. In

756-465: Is no "year zero". Years before the epoch are abbreviated BC for Before Christ or BCE for Before the Common Era . In Astronomical year numbering , positive numbers indicate years AD/CE, the number 0 designates 1 BC/BCE, −1 designates 2 BC/BCE, and so on. Other eras include that of Ancient Rome , Ab Urbe Condita ("from the foundation of the city ), abbreviated AUC; Anno Mundi ("year of

810-445: Is one of two models for the configuration and history of the continental crust in the latter part of Precambrian times. The other is Paleopangea , Piper's own concept. Piper proposes an alternative hypothesis for this era and the previous ones. This idea rejects that Rodinia ever existed as a transient supercontinent subject to progressive break-up in the late Proterozoic and instead that this time and earlier times were dominated by

864-815: Is the accusative singular ; annī is genitive singular and nominative plural; annō the dative and ablative singular) is from a PIE noun *h₂et-no- , which also yielded Gothic aþn "year" (only the dative plural aþnam is attested). Although most languages treat the word as thematic *yeh₁r-o- , there is evidence for an original derivation with an *-r/n suffix, *yeh₁-ro- . Both Indo-European words for year, *yeh₁-ro- and *h₂et-no- , would then be derived from verbal roots meaning "to go, move", *h₁ey- and *h₂et- , respectively (compare Vedic Sanskrit éti "goes", atasi "thou goest, wanderest"). A number of English words are derived from Latin annus , such as annual , annuity , anniversary , etc.; per annum means "each year", annō Dominī means "in

918-505: Is the time taken for astronomical objects to complete one orbit . For example, a year on Earth is the time taken for Earth to revolve around the Sun . Generally, a year is taken to mean a calendar year , but the word is also used for periods loosely associated with the calendar or astronomical year, such as the seasonal year , the fiscal year , the academic year , etc. The term can also be used in reference to any long period or cycle, such as

972-413: Is the interval between the heliacal risings of a star. It differs from the sidereal year for stars away from the ecliptic due mainly to the precession of the equinoxes . The Sothic year is the heliacal year, the interval between heliacal risings, of the star Sirius . It is currently less than the sidereal year and its duration is very close to the Julian year of 365.25 days. The Gaussian year

1026-526: Is the sidereal year for a planet of negligible mass (relative to the Sun) and unperturbed by other planets that is governed by the Gaussian gravitational constant . Such a planet would be slightly closer to the Sun than Earth's mean distance. Its length is: The Besselian year is a tropical year that starts when the (fictitious) mean Sun reaches an ecliptic longitude of 280°. This is currently on or close to January 1. It

1080-531: Is the time taken for the Sun (as seen from the Earth) to complete one revolution with respect to the same lunar node (a point where the Moon's orbit intersects the ecliptic). The year is associated with eclipses : these occur only when both the Sun and the Moon are near these nodes; so eclipses occur within about a month of every half eclipse year. Hence there are two eclipse seasons every eclipse year. The average duration of

1134-521: The Great Year . Due to the Earth's axial tilt , the course of a year sees the passing of the seasons , marked by changes in weather , the hours of daylight , and, consequently, vegetation and soil fertility . In temperate and subpolar regions around the planet, four seasons are generally recognized: spring , summer , autumn , and winter . In tropical and subtropical regions, several geographical sectors do not present defined seasons; but in

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1188-584: The International Union of Geological Sciences (IUGS). It was launched in 1972 and originally termed the International Geological Correlation Programme , the source of the acronym IGCP which it retains. For decades the programme was known as the International Geoscience Programme . In November 2015 the name was changed to International Geoscience and Geoparks Programme as the global geoparks were made part of

1242-444: The International Union of Geological Sciences , see below), the symbol a (without subscript) always refers to the Julian year, a j , of exactly 31 557 600 seconds . The SI multiplier prefixes may be applied to it to form "ka", "Ma", etc. Each of these three years can be loosely called an astronomical year . The sidereal year is the time taken for the Earth to complete one revolution of its orbit , as measured against

1296-463: The Proto-Indo-European noun *yeh₁r-om "year, season". Cognates also descended from the same Proto-Indo-European noun (with variation in suffix ablaut ) are Avestan yārǝ "year", Greek ὥρα ( hṓra ) "year, season, period of time" (whence " hour "), Old Church Slavonic jarŭ , and Latin hornus "of this year". Latin annus (a 2nd declension masculine noun; annum

1350-593: The United States the fiscal year of the federal government runs from October 1. An academic year is the annual period during which a student attends an educational institution . The academic year may be divided into academic terms , such as semesters or quarters. The school year in many countries starts in August or September and ends in May, June or July. In Israel the academic year begins around October or November, aligned with

1404-409: The perigee of the Moon's orbit. This period is associated with the apparent size of the full moon , and also with the varying duration of the synodic month . The duration of one full moon cycle is: The lunar year comprises twelve full cycles of the phases of the Moon, as seen from Earth. It has a duration of approximately 354.37 days. Muslims use this for celebrating their Eids and for marking

1458-415: The seasonal tropics , the annual wet and dry seasons are recognized and tracked. A calendar year is an approximation of the number of days of the Earth's orbital period, as counted in a given calendar . The Gregorian calendar , or modern calendar, presents its calendar year to be either a common year of 365 days or a leap year of 366 days, as do the Julian calendars . For the Gregorian calendar,

1512-424: The Earth is elliptical; the extreme points, called apsides, are the perihelion , where the Earth is closest to the Sun, and the aphelion , where the Earth is farthest from the Sun. The anomalistic year is usually defined as the time between perihelion passages. Its average duration is 365.259636 days (365 d 6 h 13 min 52.6 s) (at the epoch J2011.0). The draconic year, draconitic year, eclipse year, or ecliptic year

1566-828: The North American Craton (the later paleocontinent of Laurentia ), surrounded in the southeast with the East European Craton (the later paleocontinent of Baltica ), the Amazonian Craton and the West African Craton ; in the south with the Río de la Plata and São Francisco cratons ; in the southwest with the Congo and Kalahari cratons ; and in the northeast with Australia , India and eastern Antarctica . The positions of Siberia and North and South China north of

1620-511: The North American craton differ strongly depending on the reconstruction: Little is known about the paleogeography before the formation of Rodinia. Paleomagnetic and geologic data are only definite enough to form reconstructions from the breakup of Rodinia onwards. Rodinia is considered to have formed between 1.3 and 1.23 Ga and broke up again before 750 Ma. Rodinia was surrounded by the superocean Mirovia . According to J.D.A. Piper, Rodinia

1674-606: The Rio de la Plata cratons during the Pan-African orogeny, which caused the development of Gondwana. In a separate rifting event about 610 Ma, the Iapetus Ocean formed. The eastern part of this ocean formed between Baltica and Laurentia, the western part between Amazonia and Laurentia. Because the timeframe of this separation and the partially contemporaneous Pan-African orogeny are difficult to correlate, it might be that all continental mass

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1728-699: The United Kingdom, and 200 for pupils in Australia. In India the academic year normally starts from June 1 and ends on May 31. Though schools start closing from mid-March, the actual academic closure is on May 31 and in Nepal it starts from July 15. Schools and universities in Australia typically have academic years that roughly align with the calendar year (i.e., starting in February or March and ending in October to December), as

1782-619: The United States, notably Boston Latin School , may divide the year into five or more marking periods. Some state in defense of this that there is perhaps a positive correlation between report frequency and academic achievement. There are typically 180 days of teaching each year in schools in the US, excluding weekends and breaks, while there are 190 days for pupils in state schools in Canada, New Zealand and

1836-477: The average (mean) year length of 365.242 2222 days, close to the length of the mean tropical year, 365.242 19 days (relative error of 9·10). In the year 2800 CE, the Gregorian and Revised Julian calendars will begin to differ by one calendar day. The Gregorian calendar aims to ensure that the northward equinox falls on or shortly before March 21 and hence it follows the northward equinox year , or tropical year . Because 97 out of 400 years are leap years,

1890-595: The average length of the calendar year (the mean year) across the complete leap cycle of 400 years is 365.2425 days (97 out of 400 years are leap years). In English, the unit of time for year is commonly abbreviated as "y" or "yr". The symbol "a" (for Latin : annus , year) is sometimes used in scientific literature, though its exact duration may be inconsistent. English year (via West Saxon ġēar ( /jɛar/ ), Anglian ġēr ) continues Proto-Germanic *jǣran ( *j ē₁ ran ). Cognates are German Jahr , Old High German jār , Old Norse ár and Gothic jer , from

1944-621: The breaking up of Rodinia or to a slowing down of tectonic processes . The idea that a supercontinent existed in the early Neoproterozoic arose in the 1970s, when geologists determined that orogens of this age exist on virtually all cratons . Examples are the Grenville orogeny in North America and the Dalslandian orogeny in Europe. Since then, many alternative reconstructions have been proposed for

1998-490: The configuration of the cratons in this supercontinent. Most of these reconstructions are based on the correlation of the orogens on different cratons. Though the configuration of the core cratons in Rodinia is now reasonably well known, recent reconstructions still differ in many details. Geologists try to decrease the uncertainties by collecting geological and paleomagnetical data. Most reconstructions show Rodinia's core formed by

2052-531: The crustal rocks rise up relative to their surroundings. This rising creates areas of higher altitude where the air is cooler and ice is less likely to melt with changes in season, and it may explain the evidence of abundant glaciation in the Ediacaran. The rifting of the continents created new oceans and seafloor spreading , which produces warmer, less dense oceanic crust . Lower-density, hot oceanic crust will not lie as deep as older, cool oceanic lithosphere. In periods with relatively large areas of new lithosphere,

2106-407: The eclipse year is This term is sometimes erroneously used for the draconic or nodal period of lunar precession , that is the period of a complete revolution of the Moon's ascending node around the ecliptic: 18.612 815 932 Julian years ( 6 798 .331 019 days; at the epoch J2000.0). The full moon cycle is the time for the Sun (as seen from the Earth) to complete one revolution with respect to

2160-485: The historical Jalali calendar , known as the Solar Hijri calendar (1925), is a purely solar calendar with an irregular pattern of leap days based on observation (or astronomical computation), aiming to place new year ( Nowruz ) on the day of vernal equinox (for the time zone of Tehran ), as opposed to using an algorithmic system of leap years. A calendar era assigns a cardinal number to each sequential year, using

2214-743: The increased rainfall may have reduced greenhouse gas levels to below the threshold required to trigger the period of extreme glaciation known as Snowball Earth . Increased volcanic activity also introduced into the marine environment biologically active nutrients, which may have played an important role in the earliest animals' development. [REDACTED] Africa [REDACTED] Antarctica [REDACTED] Asia [REDACTED] Australia [REDACTED] Europe [REDACTED] North America [REDACTED] South America [REDACTED] Afro-Eurasia [REDACTED] Americas [REDACTED] Eurasia [REDACTED] Oceania Gigaannus A year

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2268-473: The marine life of its time. In the Cryogenian , Earth experienced large glaciations , and temperatures were at least as cool as today. Substantial parts of Rodinia may have been covered by glaciers or the southern polar ice cap . Low temperatures may have been exaggerated during the early stages of continental rifting. Geothermal heating peaks in crust about to be rifted, and since warmer rocks are less dense,

2322-543: The mean length of the Gregorian calendar year is 365.242 5 days; with a relative error below one ppm (8·10) relative to the current length of the mean tropical year ( 365.242 189 days) and even closer to the current March equinox year of 365.242 374 days that it aims to match. Historically, lunisolar calendars intercalated entire leap months on an observational basis. Lunisolar calendars have mostly fallen out of use except for liturgical reasons ( Hebrew calendar , various Hindu calendars ). A modern adaptation of

2376-415: The ocean floors come up, causing the sea level to rise. The result was a greater number of shallower seas. The increased evaporation from the oceans' larger water area may have increased rainfall, which in turn increased the weathering of exposed rock. By inputting data on the ratio of stable isotopes O:O into computer models, it has been shown that in conjunction with quick weathering of volcanic rock ,

2430-502: The paleolatitude of individual pieces of the Earth's crust , but not to their longitude, which geologists have pieced together by comparing similar geologic features, often now widely dispersed. The extreme cooling of the global climate around 717–635 Ma (the so-called Snowball Earth of the Cryogenian period) and the rapid evolution of primitive life during the subsequent Ediacaran and Cambrian periods are thought to have been triggered by

2484-591: The second month of the Hebrew calendar. Some schools in the UK, Canada and the United States divide the academic year into three roughly equal-length terms (called trimesters or quarters in the United States), roughly coinciding with autumn, winter, and spring. At some, a shortened summer session, sometimes considered part of the regular academic year, is attended by students on a voluntary or elective basis. Other schools break

2538-475: The southern hemisphere experiences summer from December to February. The Julian year, as used in astronomy and other sciences, is a time unit defined as exactly 365.25 days of 86,400 SI seconds each (" ephemeris days "). This is the normal meaning of the unit "year" used in various scientific contexts. The Julian century of 36 525 ephemeris days and the Julian millennium of 365 250 ephemeris days are used in astronomical calculations. Fundamentally, expressing

2592-508: The start of the fasting month of Ramadan . A Muslim calendar year is based on the lunar cycle. The Jewish calendar is also essentially lunar, except that an intercalary lunar month is added once every two or three years, in order to keep the calendar synchronized with the solar cycle as well. Thus, a lunar year on the Jewish (Hebrew) calendar consists of either twelve or thirteen lunar months. The vague year, from annus vagus or wandering year,

2646-542: The tables a day is 86,400 SI seconds long. Some of the year lengths in this table are in average solar days , which are slowly getting longer (at a rate that cannot be exactly predicted in advance) and are now around 86,400.002 SI seconds . International Geoscience Programme The International Geoscience and Geoparks Programme ( IGCP ) is a cooperative enterprise of UNESCO (the United Nations Educational, Scientific and Cultural Organization) and

2700-668: The transition between the Precambrian and Phanerozoic . However, this theory has been widely criticized, as incorrect applications of paleomagnetic data have been pointed out. In 2009 UNESCO's International Geoscience Programme project 440, named "Rodinia Assembly and Breakup," concluded that Rodinia broke up in four stages between 825 and 550 Ma: The Rodinia hypothesis assumes that rifting did not start everywhere simultaneously. Extensive lava flows and volcanic eruptions of Neoproterozoic age are found on most continents, evidence for large scale rifting about 750 Ma. As early as 850 to 800 Ma,

2754-547: The world"), used for the Hebrew calendar and abbreviated AM; and the Japanese imperial eras . The Islamic Hijri year , (year of the Hijrah , Anno Hegirae abbreviated AH), is a lunar calendar of twelve lunar months and thus is shorter than a solar year. Financial and scientific calculations often use a 365-day calendar to simplify daily rates. A fiscal year or financial year

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2808-454: The year into two main semesters, a first (typically August through December) and a second semester (January through May). Each of these main semesters may be split in half by mid-term exams, and each of the halves is referred to as a quarter (or term in some countries). There may also be a voluntary summer session or a short January session. Some other schools, including some in the United States, have four marking periods. Some schools in

2862-720: The year of the Lord". The Greek word for "year", ἔτος , is cognate with Latin vetus "old", from the PIE word *wetos- "year", also preserved in this meaning in Sanskrit vat-sa-ras "year" and vat-sa- "yearling (calf)", the latter also reflected in Latin vitulus "bull calf", English wether "ram" (Old English weðer , Gothic wiþrus "lamb"). In some languages, it is common to count years by referencing to one season, as in "summers", or "winters", or "harvests". Examples include Chinese 年 "year", originally 秂 , an ideographic compound of

2916-490: Was again joined in one supercontinent between roughly 600 and 550 Ma. This hypothetical supercontinent is called Pannotia . Unlike later supercontinents, Rodinia was entirely barren. It existed before complex life colonized on dry land. Based on sedimentary rock analysis, Rodinia's formation happened when the ozone layer was not as extensive as it is now. Ultraviolet light discouraged organisms from inhabiting its interior. Nevertheless, its existence significantly influenced

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