99-655: The Pliocene ( / ˈ p l aɪ . ə s iː n , ˈ p l aɪ . oʊ -/ PLY -ə-seen, PLY -oh- ; also Pleiocene ) is the epoch in the geologic time scale that extends from 5.33 to 2.58 million years ago (Ma). It is the second and most recent epoch of the Neogene Period in the Cenozoic Era . The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to
198-473: A monotreme , appeared. The predatory South American phorusrhacids were rare in this time; among the last was Titanis , a large phorusrhacid that migrated to North America and rivaled mammals as top predator. Other birds probably evolved at this time, some modern (such as the genera Cygnus , Bubo , Struthio and Corvus ), some now extinct. Alligators and crocodiles died out in Europe as
297-597: A formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch. Nevertheless, the definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult. An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have outlined a template to improve the pre-Cryogenian geologic time scale based on
396-466: A geochronologic unit can be changed (and is more often subject to change) when refined by geochronometry while the equivalent chronostratigraphic unit (the revision of which is less frequent) remains unchanged. For example, in early 2022, the boundary between the Ediacaran and Cambrian periods (geochronologic units) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at
495-560: A known geological context. The geological history of Mars has been divided into two alternate time scales. The first time scale for Mars was developed by studying the impact crater densities on the Martian surface. Through this method four periods have been defined, the Pre-Noachian (~4,500–4,100 Ma), Noachian (~4,100–3,700 Ma), Hesperian (~3,700–3,000 Ma), and Amazonian (~3,000 Ma to present). Ice-rafted Ice rafting
594-635: A machine-readable Resource Description Framework / Web Ontology Language representation of the time scale, which is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end-point. Some other planets and satellites in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus , Mars and
693-471: A relative interval of geologic time. A chronostratigraphic unit is a body of rock, layered or unlayered, that is defined between specified stratigraphic horizons which represent specified intervals of geologic time. They include all rocks representative of a specific interval of geologic time, and only this time span. Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic units. A geochronologic unit
792-429: A specific and reliable order. This allows for a correlation of strata even when the horizon between them is not continuous. The geologic time scale is divided into chronostratigraphic units and their corresponding geochronologic units. The subdivisions Early and Late are used as the geochronologic equivalents of the chronostratigraphic Lower and Upper , e.g., Early Triassic Period (geochronologic unit)
891-547: A system/series (early/middle/late); however, the International Commission on Stratigraphy advocates for all new series and subseries to be named for a geographic feature in the vicinity of its stratotype or type locality . The name of stages should also be derived from a geographic feature in the locality of its stratotype or type locality. Informally, the time before the Cambrian is often referred to as
990-458: A wider sense, correlating strata across national and continental boundaries based on their similarity to each other. Many of the names below erathem/era rank in use on the modern ICC/GTS were determined during the early to mid-19th century. During the 19th century, the debate regarding Earth's age was renewed, with geologists estimating ages based on denudation rates and sedimentary thicknesses or ocean chemistry, and physicists determining ages for
1089-500: Is a numeric-only, chronologic reference point used to define the base of geochronologic units prior to the Cryogenian. These points are arbitrarily defined. They are used where GSSPs have not yet been established. Research is ongoing to define GSSPs for the base of all units that are currently defined by GSSAs. The standard international units of the geologic time scale are published by the International Commission on Stratigraphy on
SECTION 10
#17327649460691188-479: Is a subdivision of geologic time. It is a numeric representation of an intangible property (time). These units are arranged in a hierarchy: eon, era, period, epoch, subepoch, age, and subage. Geochronology is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g., radiometric dating ) or relative means (e.g., stratigraphic position , paleomagnetism , stable isotope ratios ). Geochronometry
1287-475: Is a way of representing deep time based on events that have occurred throughout Earth's history , a time span of about 4.54 ± 0.05 Ga (4.54 billion years). It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the Cretaceous–Paleogene extinction event , marks
1386-748: Is referred to as the Early Pliocene. In the system of In the Paratethys area (central Europe and parts of western Asia) the Pliocene contains the Dacian (roughly equal to the Zanclean) and Romanian (roughly equal to the Piacenzian and Gelasian together) stages. As usual in stratigraphy, there are many other regional and local subdivisions in use. In Britain , the Pliocene is divided into
1485-401: Is the field of geochronology that numerically quantifies geologic time. A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed-upon reference point on a stratigraphic section that defines the lower boundaries of stages on the geologic time scale. (Recently this has been used to define the base of a system) A Global Standard Stratigraphic Age (GSSA)
1584-697: Is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units. The geologic time scale
1683-456: Is the transport of various materials by ice . Various objects deposited on ice may eventually become embedded in the ice. When the ice melts after a certain amount of drifting, these objects are deposited onto the bottom of the water body , e.g., onto a river bed or an ocean floor . These deposits are called ice rafted debris ( IRD ) or ice rafted deposits . Ice rafting was a primary mechanism of sediment transport during glacial episodes of
1782-594: Is used in place of Lower Triassic System (chronostratigraphic unit). Rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, e.g., the rocks that represent the Silurian System are the Silurian System and they were deposited during the Silurian Period. This definition means the numeric age of
1881-670: The Anthropocene is a proposed epoch/series for the most recent time in Earth's history. While still informal, it is a widely used term to denote the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact. As of April 2022 the Anthropocene has not been ratified by the ICS; however, in May 2019 the Anthropocene Working Group voted in favour of submitting
1980-539: The Brothers of Purity , who wrote on the processes of stratification over the passage of time in their treatises . Their work likely inspired that of the 11th-century Persian polymath Avicenna (Ibn Sînâ, 980–1037) who wrote in The Book of Healing (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognised fossils as "petrifications of
2079-575: The Great American Interchange . Herbivores got bigger, as did specialized predators. In North America, rodents , large mastodons and gomphotheres , and opossums continued successfully, while hoofed animals ( ungulates ) declined, with camel , deer , and horse all seeing populations recede. Three-toed horses ( Nannippus ), oreodonts , protoceratids , and chalicotheres became extinct. Borophagine dogs and Agriotherium became extinct, but other carnivores including
SECTION 20
#17327649460692178-634: The Hardangervidda plateau to 1200 m in the Early Pliocene. In Southern Sweden similar movements elevated the South Swedish highlands leading to a deflection of the ancient Eridanos river from its original path across south-central Sweden into a course south of Sweden. The Pliocene is bookended by two significant events in the evolution of human ancestors. The first is the appearance of the hominin Australopithecus anamensis in
2277-403: The International Commission on Stratigraphy (ICS) stages is not established. During the Pliocene epoch (5.3 to 2.6 million years ago (Ma)), the Earth's climate became cooler and drier, as well as more seasonal, marking a transition between the relatively warm Miocene to the cooler Pleistocene . However, the beginning of the Pliocene was marked by an increase in global temperatures relative to
2376-685: The Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America's distinctive native ungulate fauna, though other South American lineages like its predatory mammals were already extinct by this point and others like xenarthrans continued to do well afterwards. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters decreasing temperatures in
2475-525: The Pleistocene when sea levels were very low and much of the land was covered by large masses (sheets) of ice. The rafting of various size sediments into deeper ocean waters by icebergs became a rather important process. Ice rafting is still a process occurring today, although its impact is significantly less and much harder to gauge. The melting of large icebergs deposits sediment of various sizes, usually referred to as glacial marine sediment , onto
2574-536: The Precambrian or pre-Cambrian (Supereon). While a modern geological time scale was not formulated until 1911 by Arthur Holmes , the broader concept that rocks and time are related can be traced back to (at least) the philosophers of Ancient Greece . Xenophanes of Colophon (c. 570–487 BCE ) observed rock beds with fossils of shells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which
2673-543: The weasel family diversified, and dogs and short-faced bears did well. Ground sloths , huge glyptodonts , and armadillos came north with the formation of the Isthmus of Panama. The latitudinal diversity gradient among terrestrial North American mammals became established during this epoch some time after 4 Ma. In Eurasia rodents did well, while primate distribution declined. Elephants , gomphotheres and stegodonts were successful in Asia (the largest land mammals of
2772-535: The 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian Stage, which lasted from 2.59 to 1.81 Ma, and is now included in the Pleistocene. As with other older geologic periods, the geological strata that define the start and end are well-identified but the exact dates of the start and end of
2871-691: The Commission on Stratigraphy (applied in 1965) to become a member commission of IUGS led to the founding of the ICS. One of the primary objectives of the ICS is "the establishment, publication and revision of the ICS International Chronostratigraphic Chart which is the standard, reference global Geological Time Scale to include the ratified Commission decisions". Following on from Holmes, several A Geological Time Scale books were published in 1982, 1989, 2004, 2008, 2012, 2016, and 2020. However, since 2013,
2970-612: The Cretaceous and the early Cenozoic . This may have contributed to further cooling of the oceans worldwide. The Pliocene seas were alive with sea cows , seals , sea lions , sharks and whales . Epoch (geology) The geologic time scale or geological time scale ( GTS ) is a representation of time based on the rock record of Earth . It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology that aims to determine
3069-474: The Earth's Moon . Dominantly fluid planets, such as the giant planets , do not comparably preserve their history. Apart from the Late Heavy Bombardment , events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets. Construction of a time scale that links the planets is, therefore, of only limited relevance to
Pliocene - Misplaced Pages Continue
3168-529: The Earth's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment are still a matter of debate. The geologic history of Earth's Moon has been divided into a time scale based on geomorphological markers, namely impact cratering , volcanism , and erosion . This process of dividing the Moon's history in this manner means that
3267-628: The Greek words πλεῖον ( pleion , "more") and καινός ( kainos , "new" or "recent") and means roughly "continuation of the recent", referring to the essentially modern marine mollusc fauna. In the official timescale of the ICS , the Pliocene is subdivided into two stages . From youngest to oldest they are: The Piacenzian is sometimes referred to as the Late Pliocene, whereas the Zanclean
3366-450: The ICS has taken responsibility for producing and distributing the ICC citing the commercial nature, independent creation, and lack of oversight by the ICS on the prior published GTS versions (GTS books prior to 2013) although these versions were published in close association with the ICS. Subsequent Geologic Time Scale books (2016 and 2020 ) are commercial publications with no oversight from
3465-404: The ICS, and do not entirely conform to the chart produced by the ICS. The ICS produced GTS charts are versioned (year/month) beginning at v2013/01. At least one new version is published each year incorporating any changes ratified by the ICS since the prior version. The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to
3564-415: The ICS. While some regional terms are still in use, the table of geologic time conforms to the nomenclature , ages, and colour codes set forth by the International Commission on Stratigraphy in the official International Chronostratigraphic Chart. The International Commission on Stratigraphy also provide an online interactive version of this chart. The interactive version is based on a service delivering
3663-687: The International Chronostratigraphic Chart; however, regional terms are still in use in some areas. The numeric values on the International Chronostratigrahpic Chart are represented by the unit Ma (megaannum, for 'million years '). For example, 201.4 ± 0.2 Ma, the lower boundary of the Jurassic Period, is defined as 201,400,000 years old with an uncertainty of 200,000 years. Other SI prefix units commonly used by geologists are Ga (gigaannum, billion years), and ka (kiloannum, thousand years), with
3762-513: The Late Miocene and Pliocene, indicating increased aridification. Further aridification of Central Asia was caused by the development of Northern Hemisphere glaciation during the Late Pliocene. A sediment core from the northern South China Sea shows an increase in dust storm activity during the middle Pliocene. The South Asian Summer Monsoon (SASM) increased in intensity after 2.95 Ma, likely because of enhanced cross-equatorial pressure caused by
3861-579: The Pleistocene glacial-interglacial cycles. During the late Pliocene and early Pleistocene, 3.6 to 2.6 Ma, the Arctic was much warmer than it is at the present day (with summer temperatures some 8 °C warmer than today). That is a key finding of research into a lake-sediment core obtained in Eastern Siberia, which is of exceptional importance because it has provided the longest continuous late Cenozoic land-based sedimentary record thus far. During
3960-428: The Pliocene may have accelerated on the disappearance of forests and the spread of grasslands and savannas. During the Pliocene the earth climate system response shifted from a period of high frequency-low amplitude oscillation dominated by the 41,000-year period of Earth's obliquity to one of low-frequency, high-amplitude oscillation dominated by the 100,000-year period of the orbital eccentricity characteristic of
4059-501: The Pliocene were such proboscideans as Deinotherium , Anancus , and Mammut borsoni ,) though proboscidean diversity declined significantly during the Late Pliocene. Hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Bovines and antelopes were successful; some camel species crossed into Asia from North America. Hyenas and early saber-toothed cats appeared, joining other predators including dogs, bears, and weasels. Africa
Pliocene - Misplaced Pages Continue
4158-545: The Western Atlantic, assemblages of bivalves exhibited remarkable stasis with regards to their basal metabolic rates throughout the various climatic changes of the Pliocene. The Pliocene was a high water mark for species diversity among Caribbean corals. From 5 to 2 Ma, coral species origination rates were relatively high in the Caribbean, although a noticeable extinction event and drop in diversity occurred at
4257-581: The Zanclean until around 3.5 Ma. During the Piacenzian, from about 3.5 to 2.6 Ma, the region was forested at irregular intervals and contained a significant Saharan palaeoriver until 3.35 Ma, when trade winds began to dominate over fluvial transport of pollen. Around 3.26 Ma, a strong aridification event that was followed by a return to more humid conditions, which was itself followed by another aridification around 2.7 Ma. From 2.6 to 2.4 Ma, vegetation zones began repeatedly shifting latitudinally in response to glacial-interglacial cycles. The climate of eastern Africa
4356-445: The action of gravity. However, it is now known that not all sedimentary layers are deposited purely horizontally, but this principle is still a useful concept. The principle of lateral continuity that states layers of sediments extend laterally in all directions until either thinning out or being cut off by a different rock layer, i.e. they are laterally continuous. Layers do not extend indefinitely; their limits are controlled by
4455-505: The age of rocks). It is used primarily by Earth scientists (including geologists , paleontologists , geophysicists , geochemists , and paleoclimatologists ) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies , paleomagnetic properties, and fossils . The definition of standardised international units of geologic time
4554-409: The amount and type of sediment in a sedimentary basin , and the geometry of that basin. The principle of cross-cutting relationships that states a rock that cuts across another rock must be younger than the rock it cuts across. The law of included fragments that states small fragments of one type of rock that are embedded in a second type of rock must have formed first, and were included when
4653-513: The base of the Cambrian, and thus the boundary between the Ediacaran and Cambrian systems (chronostratigraphic units) has not been changed; rather, the absolute age has merely been refined. Chronostratigraphy is the element of stratigraphy that deals with the relation between rock bodies and the relative measurement of geological time. It is the process where distinct strata between defined stratigraphic horizons are assigned to represent
4752-529: The bodies of plants and animals", with the 13th-century Dominican bishop Albertus Magnus (c. 1200–1280) extending this into a theory of a petrifying fluid. These works appeared to have little influence on scholars in Medieval Europe who looked to the Bible to explain the origins of fossils and sea-level changes, often attributing these to the ' Deluge ', including Ristoro d'Arezzo in 1282. It
4851-735: The climate cooled. Venomous snake genera continued to increase as more rodents and birds evolved. Rattlesnakes first appeared in the Pliocene. The modern species Alligator mississippiensis , having evolved in the Miocene, continued into the Pliocene, except with a more northern range; specimens have been found in very late Miocene deposits of Tennessee . Giant tortoises still thrived in North America, with genera like Hesperotestudo . Madtsoid snakes were still present in Australia. The amphibian order Allocaudata became extinct. In
4950-495: The cooler Messinian . This increase was related to the 1.2 million year obliquity amplitude modulation cycle . By 3.3-3.0 Ma, during the Mid-Piacenzian Warm Period (mPWP), global average temperature was 2–3 °C higher than today, while carbon dioxide levels were the same as today (400 ppm). Global sea level was about 25 m higher, though its exact value is uncertain. The northern hemisphere ice sheet
5049-569: The cooling of the Earth or the Sun using basic thermodynamics or orbital physics. These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations of Lord Kelvin and Clarence King were held in high regard at the time due to their pre-eminence in physics and geology. All of these early geochronometric determinations would later prove to be incorrect. The discovery of radioactive decay by Henri Becquerel , Marie Curie , and Pierre Curie laid
SECTION 50
#17327649460695148-457: The developments in mass spectrometry pioneered by Francis William Aston , Arthur Jeffrey Dempster , and Alfred O. C. Nier during the early to mid- 20th century would finally allow for the accurate determination of radiometric ages, with Holmes publishing several revisions to his geological time-scale with his final version in 1960. The establishment of the IUGS in 1961 and acceptance of
5247-404: The different layers of stone unless they had been upon the shore and had been covered over by earth newly thrown up by the sea which then became petrified? And if the above-mentioned Deluge had carried them to these places from the sea, you would find the shells at the edge of one layer of rock only, not at the edge of many where may be counted the winters of the years during which the sea multiplied
5346-493: The early Pliocene, around 4.2 million years ago. The second is the appearance of Homo , the genus that includes modern humans and their closest extinct relatives, near the end of the Pliocene at 2.6 million years ago. Key traits that evolved among hominins during the Pliocene include terrestrial bipedality and, by the end of the Pliocene, encephalized brains (brains with a large neocortex relative to body mass and stone tool manufacture. Improvements in dating methods and in
5445-474: The early-mid Pliocene (5 Ma – 3 Ma), after three-million-year intervals with modern or glacial ice volume became longer and collapse occurs only at times when warmer global temperature coincide with strong austral summer insolation anomalies. Continents continued to drift , moving from positions possibly as far as 250 km from their present locations to positions only 70 km from their current locations. South America became linked to North America through
5544-568: The end of this interval. Oceans continued to be relatively warm during the Pliocene, though they continued cooling. The Arctic ice cap formed , drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic. The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that had existed since
5643-495: The epoch are slightly uncertain. The boundaries defining the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pleistocene. The upper boundary was set at the start of the Pleistocene glaciations. Charles Lyell (later Sir Charles) gave the Pliocene its name in Principles of Geology (volume 3, 1833). The word pliocene comes from
5742-549: The first time since the Cretaceous , with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates , South American natives, were mostly wiped out, except for the macrauchenids and toxodonts , which managed to survive. Small weasel-like carnivorous mustelids , coatis and short-faced bears migrated from the north. Grazing glyptodonts , browsing giant ground sloths and smaller caviomorph rodents , pampatheres , and armadillos did
5841-536: The following stages (old to young): Gedgravian, Waltonian , Pre-Ludhamian, Ludhamian, Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian, Pastonian and Beestonian . In the Netherlands the Pliocene is divided into these stages (old to young): Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Praetiglian , Tiglian A, Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian . The exact correlations between these local stages and
5940-414: The foundational principles of determining the correlation of strata relative to geologic time. Over the course of the 18th-century geologists realised that: The apparent, earliest formal division of the geologic record with respect to time was introduced during the era of Biblical models by Thomas Burnet who applied a two-fold terminology to mountains by identifying " montes primarii " for rock formed at
6039-465: The geologic time scale of Earth. This table is arranged with the most recent geologic periods at the top, and the oldest at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. As such, this table is not to scale and does not accurately represent the relative time-spans of each geochronologic unit. While the Phanerozoic Eon looks longer than
SECTION 60
#17327649460696138-492: The ground work for radiometric dating, but the knowledge and tools required for accurate determination of radiometric ages would not be in place until the mid-1950s. Early attempts at determining ages of uranium minerals and rocks by Ernest Rutherford , Bertram Boltwood , Robert Strutt , and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913. The discovery of isotopes in 1913 by Frederick Soddy , and
6237-465: The late Zanclean, Italy remained relatively warm and humid. Central Asia became more seasonal during the Pliocene, with colder, drier winters and wetter summers, which contributed to an increase in the abundance of C 4 plants across the region. In the Loess Plateau , δ13C values of occluded organic matter increased by 2.5% while those of pedogenic carbonate increased by 5% over the course of
6336-926: The latter often represented in calibrated units ( before present ). The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the suffix (e.g. Phanerozoic Eonothem becomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes in the history of life on Earth: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named for lithology (e.g., Cretaceous), geography (e.g., Permian ), or are tribal (e.g., Ordovician ) in origin. Most currently recognised series and subseries are named for their position within
6435-561: The layers of sand and mud brought down by the neighboring rivers and spread them over its shores. And if you wish to say that there must have been many deluges in order to produce these layers and the shells among them it would then become necessary for you to affirm that such a deluge took place every year. These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against Genesis were not readily accepted and dissent from religious doctrine
6534-537: The litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardising globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The International Chronostratigraphic Chart represents this ongoing effort. Several key principles are used to determine
6633-571: The lower boundary of the Paleogene System/Period and thus the boundary between the Cretaceous and Paleogene systems/periods. For divisions prior to the Cryogenian , arbitrary numeric boundary definitions ( Global Standard Stratigraphic Ages , GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record. Historically, regional geologic time scales were used due to
6732-520: The north, and grasslands spread on all continents (except Antarctica). Eastern Africa in particular saw a huge expansion of C 4 grasslands. Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs , deserts appeared in Asia and Africa. Both marine and continental faunas were essentially modern, although continental faunas were a bit more primitive than today. The land mass collisions meant great migration and mixing of previously isolated species, such as in
6831-750: The now-separated Atlantic Ocean. Africa 's collision with Europe formed the Mediterranean Sea , cutting off the remnants of the Tethys Ocean . The border between the Miocene and the Pliocene is also the time of the Messinian salinity crisis . During the Late Pliocene, the Himalayas became less active in their uplift, as evidenced by sedimentation changes in the Bengal Fan . The land bridge between Alaska and Siberia ( Beringia )
6930-511: The onset of continental glaciation in the Arctic, suggesting that vegetation changes in Australia during the Pliocene behaved similarly to during the Late Pleistocene and were likely characterised by comparable cycles of aridity and humidity. The equatorial Pacific Ocean sea surface temperature gradient was considerably lower than it is today. Mean sea surface temperatures in the east were substantially warmer than today but similar in
7029-400: The opposite, migrating to the north and thriving there. The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos , and the huge Diprotodon . Carnivorous marsupials continued hunting in the Pliocene, including dasyurids , the dog-like thylacine and cat-like Thylacoleo . The first rodents arrived in Australia. The modern platypus ,
7128-408: The pertinent time span. As of April 2022 these proposed changes have not been accepted by the ICS. The proposed changes (changes from the current scale [v2023/09]) are italicised: Proposed pre-Cambrian timeline (GTS2012), shown to scale: Current ICC pre-Cambrian timeline (v2023/09), shown to scale: The following table summarises the major events and characteristics of the divisions making up
7227-452: The present, but this gives little space for the most recent eon. 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, and the most recent epoch is expanded in the fifth timeline. Horizontal scale is Millions of years (above timelines) / Thousands of years (below timeline) First suggested in 2000,
7326-489: The principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships. From this Steno reasoned that strata were laid down in succession and inferred relative time (in Steno's belief, time from Creation ). While Steno's principles were simple and attracted much attention, applying them proved challenging. These basic principles, albeit with improved and more nuanced interpretations, still form
7425-521: The relative relationships of rocks and thus their chronostratigraphic position. The law of superposition that states that in undeformed stratigraphic sequences the oldest strata will lie at the bottom of the sequence, while newer material stacks upon the surface. In practice, this means a younger rock will lie on top of an older rock unless there is evidence to suggest otherwise. The principle of original horizontality that states layers of sediments will originally be deposited horizontally under
7524-804: The reorganisation of the Indonesian Throughflow. In the south-central Andes , an arid period occurred from 6.1 to 5.2 Ma, with another occurring from 3.6 to 3.3 Ma. These arid periods are coincident with global cold periods, during which the position of the Southern Hemisphere westerlies shifted northward and disrupted the South American Low Level Jet, which brings moisture to southeastern South America. From around 3.8 Ma to about 3.3 Ma, North Africa experienced an extended humid period. In northwestern Africa, tropical forests extended up to Cape Blanc during
7623-473: The rest, it merely spans ~539 million years (~12% of Earth's history), whilst the previous three eons collectively span ~3,461 million years (~76% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic). The use of subseries/subepochs has been ratified by
7722-630: The rock record to bring it in line with the post-Tonian geologic time scale. This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian, and the proposals in the "Geological Time Scale" books 2004, 2012, and 2020. Their recommend revisions of the pre-Cryogenian geologic time scale were (changes from the current scale [v2023/09] are italicised): Proposed pre-Cambrian timeline (Shield et al. 2021, ICS working group on pre-Cryogenian chronostratigraphy), shown to scale: Current ICC pre-Cambrian timeline (v2023/09), shown to scale: The book, Geologic Time Scale 2012,
7821-527: The scene. Bears, dogs and weasels (originally from North America) joined cats, hyenas and civets as the African predators, forcing hyenas to adapt as specialized scavengers. Most mustelids in Africa declined as a result of increased competition from the new predators, although Enhydriodon omoensis remained an unusually successful terrestrial predator. South America was invaded by North American species for
7920-474: The sea had at times transgressed over the land and at other times had regressed . This view was shared by a few of Xenophanes's contemporaries and those that followed, including Aristotle (384–322 BCE) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of deep time was also recognised by Chinese naturalist Shen Kuo (1031–1095) and Islamic scientist -philosophers, notably
8019-544: The second rock was forming. The relationships of unconformities which are geologic features representing a gap in the geologic record. Unconformities are formed during periods of erosion or non-deposition, indicating non-continuous sediment deposition. Observing the type and relationships of unconformities in strata allows geologist to understand the relative timing the strata. The principle of faunal succession (where applicable) that states rock strata contain distinctive sets of fossils that succeed each other vertically in
8118-471: The surrounding environment. Anthropologists tended to focus on intrinsic models while geologists and vertebrate paleontologists tended to put greater emphasis on habitats. Alternatives to the savanna hypothesis include the woodland/forest hypothesis, which emphasizes the evolution of hominins in closed habitats, or hypotheses emphasizing the influence of colder habitats at higher latitudes or the influence of seasonal variation. More recent research has emphasized
8217-548: The time during which the rocks were laid down, and the collection of rocks themselves (i.e., it was correct to say Tertiary rocks, and Tertiary Period). Only the Quaternary division is retained in the modern geologic time scale, while the Tertiary division was in use until the early 21st century. The Neptunism and Plutonism theories would compete into the early 19th century with a key driver for resolution of this debate being
8316-735: The time of the 'Deluge', and younger " monticulos secundarios" formed later from the debris of the " primarii" . Anton Moro (1687–1784) also used primary and secondary divisions for rock units but his mechanism was volcanic. In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on by Giovanni Targioni Tozzetti (1712–1783) and Giovanni Arduino (1713–1795) to include tertiary and quaternary divisions. These divisions were used to describe both
8415-573: The time scale boundaries do not imply fundamental changes in geological processes, unlike Earth's geologic time scale. Five geologic systems/periods ( Pre-Nectarian , Nectarian , Imbrian , Eratosthenian , Copernican ), with the Imbrian divided into two series/epochs (Early and Late) were defined in the latest Lunar geologic time scale. The Moon is unique in the Solar System in that it is the only other body from which humans have rock samples with
8514-501: The use of climate proxies have provided scientists with the means to test hypotheses of the evolution of human ancestors. Early hypotheses of the evolution of human traits emphasized the selective pressures produced by particular habitats. For example, many scientists have long favored the savannah hypothesis . This proposes that the evolution of terrestrial bipedality and other traits was an adaptive response to Pliocene climate change that transformed forests into more open savannah . This
8613-586: The variability selection hypothesis, which proposes that variability in climate fostered development of hominin traits. Improved climate proxies show that the Pliocene climate of east Africa was highly variable, suggesting that adaptability to varying conditions was more important in driving hominin evolution than the steady pressure of a particular habitat. The change to a cooler, drier, more seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of
8712-503: The west. This condition has been described as a permanent El Niño state, or “El Padre.” Several mechanisms have been proposed for this pattern, including increased tropical cyclone activity . The extent of the West Antarctic Ice Sheet oscillated at the 40 kyr period of Earth's obliquity. Ice sheet collapse occurred when the global average temperature was 3 °C warmer than today and carbon dioxide concentration
8811-533: The work of James Hutton (1726–1797), in particular his Theory of the Earth , first presented before the Royal Society of Edinburgh in 1785. Hutton's theory would later become known as uniformitarianism , popularised by John Playfair (1748–1819) and later Charles Lyell (1797–1875) in his Principles of Geology . Their theories strongly contested the 6,000 year age of the Earth as suggested determined by James Ussher via Biblical chronology that
8910-429: Was accepted at the time by western religion. Instead, using geological evidence, they contested Earth to be much older, cementing the concept of deep time. During the early 19th century William Smith , Georges Cuvier , Jean d'Omalius d'Halloy , and Alexandre Brongniart pioneered the systematic division of rocks by stratigraphy and fossil assemblages. These geologists began to use the local names given to rock units in
9009-510: Was at 400 ppmv. This resulted in open waters in the Ross Sea . Global sea-level fluctuation associated with ice-sheet collapse was probably up to 7 meters for the west Antarctic and 3 meters for the east Antarctic. Model simulations are consistent with reconstructed ice-sheet oscillations and suggest a progression from a smaller to a larger West Antarctic ice sheet in the last 5 million years. Intervals of ice sheet collapse were much more common in
9108-421: Was championed by Grafton Elliot Smith in his 1924 book, The Evolution of Man , as "the unknown world beyond the trees", and was further elaborated by Raymond Dart as the killer ape theory . Other scientists, such as Sherwood L. Washburn , emphasized an intrinsic model of hominin evolution. According to this model, early evolutionary developments triggered later developments. The model placed little emphasis on
9207-486: Was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominins ) and baboon-like monkeys such as the Dinopithecus appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtook pigs in numbers of species. Early giraffes appeared. Horses and modern rhinos came onto
9306-482: Was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma. The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific Ocean beds. Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during
9405-447: Was first flooded near the start of the Pliocene, allowing marine organisms to spread between the Arctic and Pacific Oceans. The bridge would continue to be periodically flooded and restored thereafter. Pliocene marine formations are exposed in northeast Spain , southern California , New Zealand , and Italy . During the Pliocene parts of southern Norway and southern Sweden that had been near sea level rose. In Norway this rise elevated
9504-415: Was in some places unwise, scholars such as Girolamo Fracastoro shared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd. Niels Stensen, more commonly known as Nicolas Steno (1638–1686), is credited with establishing four of the guiding principles of stratigraphy. In De solido intra solidum naturaliter contento dissertationis prodromus Steno states: Respectively, these are
9603-548: Was not until the Italian Renaissance when Leonardo da Vinci (1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge': Of the stupidity and ignorance of those who imagine that these creatures were carried to such places distant from the sea by the Deluge...Why do we find so many fragments and whole shells between
9702-485: Was the last commercial publication of an international chronostratigraphic chart that was closely associated with the ICS. It included a proposal to substantially revise the pre-Cryogenian time scale to reflect important events such as the formation of the Solar System and the Great Oxidation Event , among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for
9801-544: Was very similar to what it is today. Unexpectedly, the expansion of grasslands in eastern Africa during this epoch appears to have been decoupled from aridification and not caused by it, as evidenced by their asynchrony. Southwestern Australia hosted heathlands , shrublands , and woodlands with a greater species diversity compared to today during the Middle and Late Pliocene. Three different aridification events occurred around 2.90, 2.59, and 2.56 Ma, and may have been linked to
#68931