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61-597: The park lies on either side of the Tapajós River. The habitat is dense lowland rain forest and there are areas of white-sand grasslands beside the upper reaches of the Tapajós. This river rises in the Precambrian crystalline shields area of ancient igneous rock and carries little sediment. The river acts as a barrier so that some of the animals and plants on one bank are not found on the other. The first base in

122-517: 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 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 ,

183-708: A supereon , but this is also an informal term, not defined by the ICS in its chronostratigraphic guide. Eozoic (from eo- "earliest") was a synonym for pre-Cambrian , or more specifically Archean . A specific date for the origin of life has not been determined. Carbon found in 3.8 billion-year-old rocks (Archean Eon) from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia . Probable fossils 100 million years older have been found in

244-449: 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

305-421: A height of about 50 m (160 ft), and the light filtering through the canopy is sufficient to produce a biodiverse understorey of vines, lichens, mosses and orchids. Many of the mammals in the park are nocturnal, and some such as the giant otter , Amazonian manatee and giant anteater are endangered. There are also large numbers of reptiles, fish and other aquatic creatures. The park can be reached from

366-626: 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

427-435: 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

488-735: A possible 2450 Ma red alga from the Kola Peninsula , 1650 Ma carbonaceous biosignatures in north China, the 1600 Ma Rafatazmia , and a possible 1047 Ma Bangiomorpha red alga from the Canadian Arctic. The earliest fossils widely accepted as complex multicellular organisms date from the Ediacaran Period. A very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota . Hard-shelled creatures appeared toward

549-710: 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

610-565: 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

671-495: 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

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732-765: 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

793-442: 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

854-408: 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, the average length of the calendar year (the mean year) across the complete leap cycle of 400 years

915-534: 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

976-612: Is known to occur during the RNA replication of extant coronaviruses . Evidence of the details of plate motions and other tectonic activity in the Precambrian is difficult to interpret. It is generally believed that small proto-continents existed before 4280 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1130 Ma. The supercontinent, known as Rodinia , broke up around 750 Ma. A number of glacial periods have been identified going as far back as

1037-427: 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

1098-637: 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

1159-471: 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

1220-815: 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

1281-413: 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

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1342-534: 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

1403-539: 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

1464-472: Is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis ). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma. The term "Precambrian"

1525-454: Is thought to have formed about 1300-900 Ma, to have included most or all of Earth's continents and to have broken up into eight continents around 750–600 million years ago. Ma (unit) A year 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

1586-731: Is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey and the International Commission on Stratigraphy regard the term as informal. Because the span of time falling under the Precambrian consists of three eons (the Hadean , the Archean , and the Proterozoic ), it is sometimes described as

1647-534: The Huronian epoch, roughly 2400–2100 Ma. One of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a " Snowball Earth ". The atmosphere of the early Earth is not well understood. Most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and

1708-444: 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

1769-472: 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

1830-607: 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

1891-522: The geologic time scale . It spans from the formation of Earth about 4.6 billion years ago ( Ga ) to the beginning of the Cambrian Period, about 538.8 million years ago ( Ma ), when hard-shelled creatures first appeared in abundance. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history , and what is known has largely been discovered from

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1952-482: The oxygen catastrophe . At first, oxygen would have quickly combined with other elements in Earth's crust, primarily iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, and the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. A terminology has evolved covering

2013-409: 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

2074-401: The 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic , and fossils from the Precambrian (e.g. stromatolites ) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed , obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata. It

2135-424: 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

2196-495: The Tapajós with the Amazon River . Santarém has an airport. Any roads usually require four-wheel-drive vehicles and river transport is normally used in this region. Precambrian The Precambrian ( / p r i ˈ k æ m b r i . ə n , - ˈ k eɪ m -/ pree- KAM -bree-ən, -⁠KAYM- ; or Pre-Cambrian , sometimes abbreviated pC , or Cryptozoic ) is the earliest part of Earth's history , set before

2257-725: 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

2318-637: 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

2379-477: 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,

2440-404: The city of Itaituba. The Transpantaneira runs from east to west through the park but does not really live up to its name. The road is paved as far as Itaituba but other parts are unpaved earth roads topped with gravel that deteriorate during the rainy season, November to April, and need much repair work each May and June. The park can be accessed from Santarém, Pará , which is at the confluence of

2501-614: The current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian , the first period of the Phanerozoic Eon , which is named after Cambria , the Latinized name for Wales , where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons ( Hadean , Archean , Proterozoic ) of

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2562-401: The current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs . The Precambrian could be divided into five "natural" eons, characterized as follows: The movement of Earth's plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent containing most or all of

2623-453: The early years of the Earth's existence, as radiometric dating has allowed absolute dates to be assigned to specific formations and features. The Precambrian is divided into three eons: the Hadean (4567.3–4031 Ma), Archean (4031-2500 Ma) and Proterozoic (2500-538.8 Ma). See Timetable of the Precambrian . It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than

2684-407: 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

2745-705: The end of that time span, marking the beginning of the Phanerozoic Eon. By the middle of the following Cambrian Period, a very diverse fauna is recorded in the Burgess Shale , including some which may represent stem groups of modern taxa. The increase in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life. While land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Tracks from an animal with leg-like appendages have been found in what

2806-491: 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

2867-433: 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 the seasonal tropics , the annual wet and dry seasons are recognized and tracked. A calendar year

2928-541: The landmass. The earliest known supercontinent was Vaalbara . It formed from proto-continents and was a supercontinent 3.636 billion years ago. Vaalbara broke up c. 2.845–2.803 Ga ago. The supercontinent Kenorland was formed c. 2.72 Ga ago and then broke sometime after 2.45–2.1 Ga into the proto-continent cratons called Laurentia , Baltica , Yilgarn craton and Kalahari . The supercontinent Columbia , or Nuna, formed 2.1–1.8 billion years ago and broke up about 1.3–1.2 billion years ago. The supercontinent Rodinia

2989-742: The limits of the Amazônia, Campos Amazônicos and Mapinguari national parks, the Itaituba I , Itaituba II and Crepori national forests and the Tapajós Environmental Protection Area . All of these were reduced in size except the Campos Amazônicos. This last alteration reduced the area of the park to 1,070,737 hectares (2,645,850 acres). Except for about 2% of more open forest, the whole park consists of dense humid tropical forest. The larger trees reach

3050-543: 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

3111-406: The park is about 53 km (33 mi) from Itaituba, and there is some illegal cutting of timber and gold mining in the eastern parts closest to Itaituba and Trairão. To the west the park adjoins the 827,877 hectares (2,045,730 acres) Pau-Rosa National Forest , created in 2001. The proposed South Amazon Ecological Corridor would link the park to other protected areas and indigenous territories in

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3172-424: The region. The Amazônia National Park was created by federal decree 73.683 of 19 February 1974. Its limits were altered by decree on 18 January 1985. The management plan was published on 31 December 1988, but was not made official at that time. The consultative council was created on 26 November 2004. The limits of the park were altered on 13 February 2006 and again on 12 August 2011. Law 12678 of 25 June 2012 amended

3233-526: The same area. However, there is evidence that life could have evolved over 4.280 billion years ago. There is a fairly solid record of bacterial life throughout the remainder (Proterozoic Eon) of the Precambrian. Complex multicellular organisms may have appeared as early as 2100 Ma. However, the interpretation of ancient fossils is problematic, and "... some definitions of multicellularity encompass everything from simple bacterial colonies to badgers." Other possible early complex multicellular organisms include

3294-605: 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

3355-475: 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

3416-512: 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,

3477-560: 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

3538-454: 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

3599-732: 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

3660-482: Was lacking in free oxygen . There is, however, evidence that an oxygen-rich atmosphere existed since the early Archean. At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism . This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis , sometimes called

3721-852: Was mud 551 million years ago. The RNA world hypothesis asserts that RNA evolved before coded proteins and DNA genomes. During the Hadean Eon (4,567–4,031 Ma) abundant geothermal microenvironments were present that may have had the potential to support the synthesis and replication of RNA and thus possibly the evolution of a primitive life form. It was shown that porous rock systems comprising heated air-water interfaces could allow ribozyme - catalyzed RNA replication of sense and antisense strands that could be followed by strand-dissociation, thus enabling combined synthesis, release and folding of active ribozymes. This primitive RNA replicative system also may have been able to undergo template strand switching during replication ( genetic recombination ) as

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