Geologic time scale - wikipedia Geologic time scale This clock representation shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth ; its upper boundary is now regarded as 4.0 Ga ( billion years ago ). Other subdivisions reflect the evolution of life ; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale. The geologic time scale ( GTS ) is a system of chronological dating that relates geological strata ( stratigraphy ) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth 's history. The tables of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy ( ICS ). Contents 1 Terminology 2 Rationale 3 History and nomenclature of the time scale 3.1 Early history 3.2 Establishment of primary principles 3.3 Formulation of geologic time scale 3.4 Naming of geologic periods, eras and epochs 3.5 Dating of time scales 3.6 The Anthropocene 4 Table of geologic time 4.1 Proposed Precambrian timeline 5 See also 6 Notes 7 References 8 Further reading 9 External links Terminology The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic. The first three of these can be referred to collectively as the Precambrian supereon. Eons are divided into eras, which are in turn divided into periods, epochs and ages. The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. Therefore, the second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, and the most recent period is expanded in the fourth timeline. Millions of Years Corresponding to eons, eras, periods, epochs and ages, the terms `` eonothem '', `` erathem '', `` system '', `` series '', `` stage '' are used to refer to the layers of rock that belong to these stretches of geologic time in Earth 's history. Geologists qualify these units as `` early '', `` mid '', and `` late '' when referring to time, and `` lower '', `` middle '', and `` upper '' when referring to the corresponding rocks. For example, the lower Jurassic Series in chronostratigraphy corresponds to the early Jurassic Epoch in geochronology. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not ; thus `` early Miocene '' but `` Early Jurassic. '' Rationale Evidence from radiometric dating indicates that Earth is about 4.54 billion years old. The geology or deep time of Earth 's past has been organized into various units according to events which took place. Different spans of time on the GTS are usually marked by corresponding changes in the composition of strata which indicate major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous -- Paleogene extinction event, which marked the demise of the non-avian dinosaurs and many other groups of life. Older time spans, which predate the reliable fossil record ( before the Proterozoic eon ), are defined by their absolute age. Geologic units from the same time but different parts of the world often look different and contain different fossils, so the same time - span was historically given different names in different locales. For example, in North America, the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on succession of trilobites. In East Asia and Siberia, the same unit is split into Alexian, Atdabanian, and Botomian stages. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology and define universal horizons that can be used around the world. Some other planets and moons in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth 's Moon. Dominantly fluid planets, such as the gas giants, do not preserve their history in a comparable manner. 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 the Earth 's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment is still debated. History and nomenclature of the time scale Life timeline view discuss edit - 4500 -- -- - 4000 -- -- - 3500 -- -- - 3000 -- -- - 2500 -- -- - 2000 -- -- - 1500 -- -- - 1000 -- -- - 500 -- -- 0 -- water Single - celled life photosynthesis Eukaryotes Multicellular life Land life Dinosaurs Mammals Flowers ← Earliest Earth ( − 4540 ) ← Earliest water ← Earliest life ← LHB meteorites ← Earliest oxygen ← Atmospheric oxygen ← Oxygen crisis ← Earliest sexual reproduction ← Ediacara biota ← Cambrian explosion ← Earliest humans h n r o z o i r o r o z o i r h n d n Pongola Huronian Cryogenian Andean Karoo Quaternary Axis scale : millions of years ago. Orange labels : ice ages. Also see : Human timeline and Nature timeline Main articles : History of geology and History of paleontology Graphical representation of Earth 's history as a spiral Early history In Ancient Greece, Aristotle ( 384 - 322 BCE ) observed that fossils of seashells in rocks resembled those found on beaches -- he inferred that the fossils in rocks were formed by living animals, and he reasoned that the positions of land and sea had changed over long periods of time. Leonardo da Vinci ( 1452 -- 1519 ) concurred with Aristotle 's interpretation that fossils represented the remains of ancient life. The 11th - century Persian geologist Avicenna ( Ibn Sina, died 1037 ) and the 13th - century Dominican bishop Albertus Magnus ( died 1280 ) extended Aristotle 's explanation into a theory of a petrifying fluid. Avicenna also first proposed one of the principles underlying geologic time scales, the law of superposition of strata, while discussing the origins of mountains in The Book of Healing ( 1027 ). The Chinese naturalist Shen Kuo ( 1031 -- 1095 ) also recognized the concept of `` deep time ''. Establishment of primary principles In the late 17th century Nicholas Steno ( 1638 -- 1686 ) pronounced the principles underlying geologic ( geological ) time scales. Steno argued that rock layers ( or strata ) were laid down in succession, and that each represents a `` slice '' of time. He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it. While Steno 's principles were simple, applying them proved challenging. Over the course of the 18th century geologists realized that : Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition Strata laid down at the same time in different areas could have entirely different appearances The strata of any given area represented only part of Earth 's long history The Neptunist theories popular at this time ( expounded by Abraham Werner ( 1749 -- 1817 ) in the late 18th century ) proposed that all rocks had precipitated out of a single enormous flood. A major shift in thinking came when James Hutton presented his Theory of the Earth ; or, an Investigation of the Laws Observable in the Composition, Dissolution, and Restoration of Land Upon the Globe before the Royal Society of Edinburgh in March and April 1785. It has been said that `` as things appear from the perspective of the 20th century, James Hutton in those readings became the founder of modern geology ''. Hutton proposed that the interior of Earth was hot, and that this heat was the engine which drove the creation of new rock : land was eroded by air and water and deposited as layers in the sea ; heat then consolidated the sediment into stone, and uplifted it into new lands. This theory, known as `` Plutonism '', stood in contrast to the `` Neptunist '' flood - oriented theory. Formulation of geologic time scale The first serious attempts to formulate a geologic time scale that could be applied anywhere on Earth were made in the late 18th century. The most influential of those early attempts ( championed by Werner, among others ) divided the rocks of Earth 's crust into four types : Primary, Secondary, Tertiary, and Quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a `` Tertiary Period '' as well as of `` Tertiary Rocks. '' Indeed, `` Tertiary '' ( now Paleogene and Neogene ) remained in use as the name of a geological period well into the 20th century and `` Quaternary '' remains in formal use as the name of the current period. The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brongniart in the early 19th century, enabled geologists to divide Earth history more precisely. It also enabled them to correlate strata across national ( or even continental ) boundaries. If two strata ( however distant in space or different in composition ) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies between 1820 and 1850 of the strata and fossils of Europe produced the sequence of geologic periods still used today. Naming of geologic periods, eras and epochs Early work on developing the geologic time scale was dominated by British geologists, and the names of the geologic periods reflect that dominance. The `` Cambrian '', ( the classical name for Wales ) and the `` Ordovician '', and `` Silurian '', named after ancient Welsh tribes, were periods defined using stratigraphic sequences from Wales. The `` Devonian '' was named for the English county of Devon, and the name `` Carboniferous '' was an adaptation of `` the Coal Measures '', the old British geologists ' term for the same set of strata. The `` Permian '' was named after Perm, Russia, because it was defined using strata in that region by Scottish geologist Roderick Murchison. However, some periods were defined by geologists from other countries. The `` Triassic '' was named in 1834 by a German geologist Friedrich Von Alberti from the three distinct layers ( Latin trias meaning triad ) -- red beds, capped by chalk, followed by black shales -- that are found throughout Germany and Northwest Europe, called the ' Trias '. The `` Jurassic '' was named by a French geologist Alexandre Brongniart for the extensive marine limestone exposures of the Jura Mountains. The `` Cretaceous '' ( from Latin creta meaning ' chalk ' ) as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris basin and named for the extensive beds of chalk ( calcium carbonate deposited by the shells of marine invertebrates ) found in Western Europe. British geologists were also responsible for the grouping of periods into eras and the subdivision of the Tertiary and Quaternary periods into epochs. In 1841 John Phillips published the first global geologic time scale based on the types of fossils found in each era. Phillips ' scale helped standardize the use of terms like Paleozoic ( `` old life '' ) which he extended to cover a larger period than it had in previous usage, and Mesozoic ( `` middle life '' ) which he invented. Dating of time scales Main article : Chronological dating When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, time scales could be estimated only very imprecisely since estimates of rates of change were uncertain. While creationists had been proposing dates of around six or seven thousand years for the age of Earth based on the Bible, early geologists were suggesting millions of years for geologic periods, and some were even suggesting a virtually infinite age for Earth. Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification. Until the discovery of radioactivity in 1896 and the development of its geological applications through radiometric dating during the first half of the 20th century, the ages of various rock strata and the age of Earth were the subject of considerable debate. The first geologic time scale that included absolute dates was published in 1913 by the British geologist Arthur Holmes. He greatly furthered the newly created discipline of geochronology and published the world - renowned book The Age of the Earth in which he estimated Earth 's age to be at least 1.6 billion years. In 1977, the Global Commission on Stratigraphy ( now the International Commission on Stratigraphy ) began to define global references known as GSSP ( Global Boundary Stratotype Sections and Points ) for geologic periods and faunal stages. The commission 's most recent work is described in the 2004 geologic time scale of Gradstein et al. A UML model for how the timescale is structured, relating it to the GSSP, is also available. The Anthropocene The term `` Anthropocene '' is used informally by popular culture and a growing number of scientists to describe the current epoch in which we are living. The term was coined by Paul Crutzen and Eugene Stoermer in 2000 to describe the current time, in which humans have had an enormous impact on the environment. It has evolved to describe an `` epoch '' starting some time in the past and on the whole defined by anthropogenic carbon emissions and production and consumption of plastic goods that are left in the ground. Critics of this term say that the term should not be used because it is difficult, if not nearly impossible, to define a specific time when humans started influencing the rock strata -- defining the start of an epoch. Others say that humans have not even started to leave their biggest impact on Earth, and therefore the Anthropocene has not even started yet. Whatever the case, the ICS has not officially approved the term, as of September 2015. Table of geologic time The following table summarizes the major events and characteristics of the periods of time making up the geologic time scale. This table is arranged with the most recent geologic periods at the top, and the most ancient at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. The content of the table is based on the current official geologic time scale of the International Commission on Stratigraphy, with the epoch names altered to the early / late format from lower / upper as recommended by the ICS when dealing with chronostratigraphy. A service providing a Resource Description Framework / Web Ontology Language representation of the timescale is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end - point. Supereon Eon Era Period Epoch Age Major events Start, million years ago n / a Phanerozoic Cenozoic Quaternary Holocene chrons : Subatlantic Subboreal Atlantic Boreal Preboreal Quaternary Ice Age recedes, and the current interglacial begins. Sahara forms from savannah. Rise of human civilization, beginning of agriculture. Stone Age cultures give way to Bronze Age ( 3300 BC ) and Iron Age ( 1200 BC ), giving rise to many pre-historic cultures throughout the world. Little Ice Age ( stadial ) causes brief cooling in Northern Hemisphere from 1400 to 1850. Following the Industrial Revolution, atmospheric CO levels rise from around 280 parts per million volume ( ppmv ) to the current level of 400 ppmv. 0.0117 Pleistocene Late ( locally Tarantian Tyrrhenian Eemian Sangamonian ) Flourishing and then extinction of Pleistocene megafauna. Evolution of anatomically modern humans. Quaternary Ice Age continues with glaciations and interstadials ( and the accompanying fluctuations from 100 to 300 ppmv in atmospheric CO levels ), further intensification of Icehouse Earth conditions, roughly 1.6 Ma. Last glacial maximum ( 30000 years ago ), last glacial period ( 18000 -- 15000 years ago ). Dawn of human stone - age cultures, with increasing technical complexity relative to previous ice age cultures, such as engravings and clay statues ( e.g. Venus of Lespugue ), particularly in the Mediterranean and Europe. Lake Toba supervolcano erupts 75000 years before present, causing a volcanic winter that possibly pushes humanity to the brink of extinction. Pleistocene ends with Oldest Dryas, Older Dryas / Allerød and Younger Dryas climate events, with Younger Dryas forming the boundary with the Holocene. 0.126 Middle ( formerly Ionian ) 0.781 Calabrian 1.8 Gelasian 2.58 Neogene Pliocene Piacenzian Intensification of present Icehouse conditions, present ( Quaternary ) ice age begins roughly 2.58 Ma ; cool and dry climate. Australopithecines, many of the existing genera of mammals, and recent mollusks appear. Homo habilis appears. 3.6 Zanclean 5.333 Miocene Messinian Moderate Icehouse climate, punctuated by ice ages ; Orogeny in Northern Hemisphere. Modern mammal and bird families become recognizable. Horses and mastodons diverse. Grasses become ubiquitous. First apes appear ( for reference see the article : `` Sahelanthropus tchadensis '' ). Kaikoura Orogeny forms Southern Alps in New Zealand, continues today. Orogeny of the Alps in Europe slows, but continues to this day. Carpathian orogeny forms Carpathian Mountains in Central and Eastern Europe. Hellenic orogeny in Greece and Aegean Sea slows, but continues to this day. Middle Miocene Disruption occurs. Widespread forests slowly draw in massive amounts of CO, gradually lowering the level of atmospheric CO from 650 ppmv down to around 100 ppmv. 7.246 Tortonian 11.63 Serravallian 13.82 Langhian 15.97 Burdigalian 20.44 Aquitanian 23.03 Paleogene Oligocene Chattian Warm but cooling climate, moving towards Icehouse ; Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of flowering plants 28.1 Rupelian 33.9 Eocene Priabonian Moderate, cooling climate. Archaic mammals ( e.g. Creodonts, Condylarths, Uintatheres, etc. ) flourish and continue to develop during the epoch. Appearance of several `` modern '' mammal families. Primitive whales diversify. First grasses. Reglaciation of Antarctica and formation of its ice cap ; Azolla event triggers ice age, and the Icehouse Earth climate that would follow it to this day, from the settlement and decay of seafloor algae drawing in massive amounts of atmospheric carbon dioxide, lowering it from 3800 ppmv down to 650 ppmv. End of Laramide and Sevier Orogenies of the Rocky Mountains in North America. Orogeny of the Alps in Europe begins. Hellenic Orogeny begins in Greece and Aegean Sea. 37.8 Bartonian 41.2 Lutetian 47.8 Ypresian 56 Paleocene Thanetian Climate tropical. Modern plants appear ; Mammals diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals ( up to bear or small hippo size ). Alpine orogeny in Europe and Asia begins. Indian Subcontinent collides with Asia 55 Ma, Himalayan Orogeny starts between 52 and 48 Ma. 59.2 Selandian 61.6 Danian 66 Mesozoic Cretaceous Late Maastrichtian Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonoidea, belemnites, rudist bivalves, echinoids and sponges all common. Many new types of dinosaurs ( e.g. Tyrannosaurs, Titanosaurs, duck bills, and horned dinosaurs ) evolve on land, as do Eusuchia ( modern crocodilians ) ; and mosasaurs and modern sharks appear in the sea. Primitive birds gradually replace pterosaurs. Monotremes, marsupials and placental mammals appear. Break up of Gondwana. Beginning of Laramide and Sevier Orogenies of the Rocky Mountains. atmospheric CO close to present - day levels. 72.1 ± 0.2 Campanian 83.6 ± 0.2 Santonian 86.3 ± 0.5 Coniacian 89.8 ± 0.3 Turonian 93.9 Cenomanian 100.5 Early Albian ~ 113 Aptian ~ 125 Barremian ~ 129.4 Hauterivian ~ 132.9 Valanginian ~ 139.8 Berriasian ~ 145 Jurassic Late Tithonian Gymnosperms ( especially conifers, Bennettitales and cycads ) and ferns common. Many types of dinosaurs, such as sauropods, carnosaurs, and stegosaurs. Mammals common but small. First birds and lizards. Ichthyosaurs and plesiosaurs diverse. Bivalves, Ammonites and belemnites abundant. Sea urchins very common, along with crinoids, starfish, sponges, and terebratulid and rhynchonellid brachiopods. Breakup of Pangaea into Gondwana and Laurasia. Nevadan orogeny in North America. Rangitata and Cimmerian orogenies taper off. Atmospheric CO levels 3 -- 4 times the present day levels ( 1200 -- 1500 ppmv, compared to today 's 400 ppmv ). 152.1 ± 0.9 Kimmeridgian 157.3 ± 1.0 Oxfordian 163.5 ± 1.0 Middle Callovian 166.1 ± 1.2 Bathonian 168.3 ± 1.3 Bajocian 170.3 ± 1.4 Aalenian 174.1 ± 1.0 Early Toarcian 182.7 ± 0.7 Pliensbachian 190.8 ± 1.0 Sinemurian 199.3 ± 0.3 Hettangian 201.3 ± 0.2 Triassic Late Rhaetian Archosaurs dominant on land as dinosaurs, in the oceans as Ichthyosaurs and nothosaurs, and in the air as pterosaurs. Cynodonts become smaller and more mammal - like, while first mammals and crocodilia appear. Dicroidium flora common on land. Many large aquatic temnospondyl amphibians. Ceratitic ammonoids extremely common. Modern corals and teleost fish appear, as do many modern insect clades. Andean Orogeny in South America. Cimmerian Orogeny in Asia. Rangitata Orogeny begins in New Zealand. Hunter - Bowen Orogeny in Northern Australia, Queensland and New South Wales ends, ( c. 260 -- 225 Ma ) ~ 208.5 Norian ~ 227 Carnian ~ 237 Middle Ladinian ~ 242 Anisian 247.2 Early Olenekian 251.2 Induan 251.902 ± 0.06 Paleozoic Permian Lopingian Changhsingian Landmasses unite into supercontinent Pangaea, creating the Appalachians. End of Permo - Carboniferous glaciation. Synapsid reptiles ( pelycosaurs and therapsids ) become plentiful, while parareptiles and temnospondyl amphibians remain common. In the mid-Permian, coal - age flora are replaced by cone - bearing gymnosperms ( the first true seed plants ) and by the first true mosses. Beetles and flies evolve. Marine life flourishes in warm shallow reefs ; productid and spiriferid brachiopods, bivalves, forams, and ammonoids all abundant. Permian - Triassic extinction event occurs 251 Ma : 95 % of life on Earth becomes extinct, including all trilobites, graptolites, and blastoids. Ouachita and Innuitian orogenies in North America. Uralian orogeny in Europe / Asia tapers off. Altaid orogeny in Asia. Hunter - Bowen Orogeny on Australian continent begins ( c. 260 -- 225 Ma ), forming the MacDonnell Ranges. 254.14 ± 0.07 Wuchiapingian 259.1 ± 0.4 Guadalupian Capitanian 265.1 ± 0.4 Wordian 268.8 ± 0.5 Roadian 272.95 ± 0.5 Cisuralian Kungurian 283.5 ± 0.6 Artinskian 290.1 ± 0.26 Sakmarian 295 ± 0.18 Asselian 298.9 ± 0.15 Carbon - iferous Pennsylvanian Gzhelian Winged insects radiate suddenly ; some ( esp. Protodonata and Palaeodictyoptera ) are quite large. Amphibians common and diverse. First reptiles and coal forests ( scale trees, ferns, club trees, giant horsetails, Cordaites, etc. ). Highest - ever atmospheric oxygen levels. Goniatites, brachiopods, bryozoa, bivalves, and corals plentiful in the seas and oceans. Testate forams proliferate. Uralian orogeny in Europe and Asia. Variscan orogeny occurs towards middle and late Mississippian Periods. 303.7 ± 0.1 Kasimovian 307 ± 0.1 Moscovian 315.2 ± 0.2 Bashkirian 323.2 ± 0.4 Mississippian Serpukhovian Large primitive trees, first land vertebrates, and amphibious sea - scorpions live amid coal - forming coastal swamps. Lobe - finned rhizodonts are dominant big fresh - water predators. In the oceans, early sharks are common and quite diverse ; echinoderms ( especially crinoids and blastoids ) abundant. Corals, bryozoa, goniatites and brachiopods ( Productida, Spiriferida, etc. ) very common, but trilobites and nautiloids decline. Glaciation in East Gondwana. Tuhua Orogeny in New Zealand tapers off. 330.9 ± 0.2 Viséan 346.7 ± 0.4 Tournaisian 358.9 ± 0.4 Devonian Late Famennian First clubmosses, horsetails and ferns appear, as do the first seed - bearing plants ( progymnosperms ), first trees ( the progymnosperm Archaeopteris ), and first ( wingless ) insects. Strophomenid and atrypid brachiopods, rugose and tabulate corals, and crinoids are all abundant in the oceans. Goniatite ammonoids are plentiful, while squid - like coleoids arise. Trilobites and armoured agnaths decline, while jawed fishes ( placoderms, lobe - finned and ray - finned fish, and early sharks ) rule the seas. First amphibians still aquatic. `` Old Red Continent '' of Euramerica. Beginning of Acadian Orogeny for Anti-Atlas Mountains of North Africa, and Appalachian Mountains of North America, also the Antler, Variscan, and Tuhua Orogeny in New Zealand. 372.2 ± 1.6 Frasnian 382.7 ± 1.6 Middle Givetian 387.7 ± 0.8 Eifelian 393.3 ± 1.2 Early Emsian 407.6 ± 2.6 Pragian 410.8 ± 2.8 Lochkovian 419.2 ± 3.2 Silurian Pridoli First vascular plants ( the rhyniophytes and their relatives ), first millipedes and arthropleurids on land. First jawed fishes, as well as many armoured jawless fish, populate the seas. Sea - scorpions reach large size. Tabulate and rugose corals, brachiopods ( Pentamerida, Rhynchonellida, etc. ), and crinoids all abundant. Trilobites and mollusks diverse ; graptolites not as varied. Beginning of Caledonian Orogeny for hills in England, Ireland, Wales, Scotland, and the Scandinavian Mountains. Also continued into Devonian period as the Acadian Orogeny, above. Taconic Orogeny tapers off. Lachlan Orogeny on Australian continent tapers off. 423 ± 2.3 Ludlow Ludfordian 425.6 ± 0.9 Gorstian 427.4 ± 0.5 Wenlock Homerian 430.5 ± 0.7 Sheinwoodian 433.4 ± 0.8 Llandovery Telychian 438.5 ± 1.1 Aeronian 440.8 ± 1.2 Rhuddanian 443.8 ± 1.5 Ordovician Late Hirnantian Invertebrates diversify into many new types ( e.g., long straight - shelled cephalopods ). Early corals, articulate brachiopods ( Orthida, Strophomenida, etc. ), bivalves, nautiloids, trilobites, ostracods, bryozoa, many types of echinoderms ( crinoids, cystoids, starfish, etc. ), branched graptolites, and other taxa all common. Conodonts ( early planktonic vertebrates ) appear. First green plants and fungi on land. Ice age at end of period. 445.2 ± 1.4 Katian 453 ± 0.7 Sandbian 458.4 ± 0.9 Middle Darriwilian 467.3 ± 1.1 Dapingian 470 ± 1.4 Early Floian ( formerly Arenig ) 477.7 ± 1.4 Tremadocian 485.4 ± 1.9 Cambrian Furongian Stage 10 Major diversification of life in the Cambrian Explosion. Numerous fossils ; most modern animal phyla appear. First chordates appear, along with a number of extinct, problematic phyla. Reef - building Archaeocyatha abundant ; then vanish. Trilobites, priapulid worms, sponges, inarticulate brachiopods ( unhinged lampshells ), and numerous other animals. Anomalocarids are giant predators, while many Ediacaran fauna die out. Prokaryotes, protists ( e.g., forams ), fungi and algae continue to present day. Gondwana emerges. Petermann Orogeny on the Australian continent tapers off ( 550 -- 535 Ma ). Ross Orogeny in Antarctica. Adelaide Geosyncline ( Delamerian Orogeny ), majority of orogenic activity from 514 -- 500 Ma. Lachlan Orogeny on Australian continent, c. 540 -- 440 Ma. Atmospheric CO content roughly 15 times present - day ( Holocene ) levels ( 6000 ppmv compared to today 's 400 ppmv ) ~ 489.5 Jiangshanian ~ 494 Paibian ~ 497 Series 3 Guzhangian ~ 500.5 Drumian ~ 504.5 Stage 5 ~ 509 Series 2 Stage 4 ~ 514 Stage 3 ~ 521 Terreneuvian Stage 2 ~ 529 Fortunian ~ 541 ± 1.0 Precambrian Proterozoic Neoproterozoic Ediacaran Good fossils of the first multi-celled animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm - like Trichophycus, etc. First sponges and trilobitomorphs. Enigmatic forms include many soft - jellied creatures shaped like bags, disks, or quilts ( like Dickinsonia ). Taconic Orogeny in North America. Aravalli Range orogeny in Indian Subcontinent. Beginning of Petermann Orogeny on Australian continent. Beardmore Orogeny in Antarctica, 633 -- 620 Ma. ~ 635 Cryogenian Possible `` Snowball Earth '' period. Fossils still rare. Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. ~ 720 Tonian Rodinia supercontinent persists. Sveconorwegian orogeny ends. Trace fossils of simple multi-celled eukaryotes. First radiation of dinoflagellate - like acritarchs. Grenville Orogeny tapers off in North America. Pan-African orogeny in Africa. Lake Ruker / Nimrod Orogeny in Antarctica, 1,000 ± 150 Ma. Edmundian Orogeny ( c. 920 -- 850 Ma ), Gascoyne Complex, Western Australia. Adelaide Geosyncline laid down on Australian continent, beginning of Adelaide Geosyncline ( Delamerian Orogeny ) in Australia. 1000 Mesoproterozoic Stenian Narrow highly metamorphic belts due to orogeny as Rodinia forms. Sveconorwegian orogeny starts. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny ( c. 1,080 Ma ), Musgrave Block, Central Australia. 1200 Ectasian Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. 1400 Calymmian Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1,600 Ma, Mount Isa Block, Queensland 1600 Paleoproterozoic Statherian First complex single - celled life : protists with nuclei. Columbia is the primordial supercontinent. Kimban Orogeny in Australian continent ends. Yapungku Orogeny on Yilgarn craton, in Western Australia. Mangaroon Orogeny, 1,680 -- 1,620 Ma, on the Gascoyne Complex in Western Australia. Kararan Orogeny ( 1,650 Ma ), Gawler Craton, South Australia. 1800 Orosirian The atmosphere becomes oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny. Penokean and Trans - Hudsonian Orogenies in North America. Early Ruker Orogeny in Antarctica, 2,000 -- 1,700 Ma. Glenburgh Orogeny, Glenburgh Terrane, Australian continent c. 2,005 -- 1,920 Ma. Kimban Orogeny, Gawler craton in Australian continent begins. 2050 Rhyacian Bushveld Igneous Complex forms. Huronian glaciation. 2300 Siderian Oxygen catastrophe : banded iron formations forms. Sleaford Orogeny on Australian continent, Gawler Craton 2,440 -- 2,420 Ma. 2500 Archean Neoarchean Stabilization of most modern cratons ; possible mantle overturn event. Insell Orogeny, 2,650 ± 150 Ma. Abitibi greenstone belt in present - day Ontario and Quebec begins to form, stabilizes by 2,600 Ma. 2800 Mesoarchean First stromatolites ( probably colonial cyanobacteria ). Oldest macrofossils. Humboldt Orogeny in Antarctica. Blake River Megacaldera Complex begins to form in present - day Ontario and Quebec, ends by roughly 2,696 Ma. 3200 Paleoarchean First known oxygen - producing bacteria. Oldest definitive microfossils. Oldest cratons on Earth ( such as the Canadian Shield and the Pilbara Craton ) may have formed during this period. Rayner Orogeny in Antarctica. 3600 Eoarchean Simple single - celled life ( probably bacteria and archaea ). Oldest probable microfossils. The first life forms and self - replicating RNA molecules evolve around 4,000 Ma, after the Late Heavy Bombardment ends on Earth. Napier Orogeny in Antarctica, 4,000 ± 200 Ma. ~ 4000 Hadean Early Imbrian ( Neohadean ) ( unofficial ) Indirect photosynthetic evidence ( e.g., kerogen ) of primordial life. This era overlaps the beginning of the Late Heavy Bombardment of the Inner Solar System, produced possibly by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter and Saturn. Oldest known rock ( 4,031 to 3,580 Ma ). 4130 Nectarian ( Mesohadean ) ( unofficial ) Possible first appearance of plate tectonics. This unit gets its name from the lunar geologic timescale when the Nectaris Basin and other greater lunar basins form by big impact events. Earliest evidence for life based on unusually high amounts of light isotopes of carbon, a common sign of life. 4280 Basin Groups ( Paleohadean ) ( unofficial ) End of the Early Bombardment Phase. Oldest known mineral ( Zircon, 4,404 ± 8 Ma ). Asteroids and comets bring water to Earth. 4533 Cryptic ( Eohadean ) ( unofficial ) Formation of Moon ( 4,533 to 4,527 Ma ), probably from giant impact, since the end of this era. Formation of Earth ( 4,570 to 4,567.17 Ma ), Early Bombardment Phase begins. Formation of Sun ( 4,680 to 4,630 Ma ). 4600 Proposed Precambrian timeline The ICS 's Geologic Time Scale 2012 book which includes the new approved time scale also displays a proposal to substantially revise the Precambrian time scale to reflect important events such as the formation of the Earth or the Great Oxidation Event, among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for the pertinent time span. ( See also Period ( geology ) # Structure. ) Hadean Eon -- 4600 -- 4031 MYA Chaotian Era -- 4600 -- 4404 MYA -- the name alluding both to the mythological Chaos and the chaotic phase of planet formation Jack Hillsian or Zirconian Era -- 4404 -- 4031 MYA -- both names allude to the Jack Hills Greenstone Belt which provided the oldest mineral grains on Earth, zircons Archean Eon -- 4031 -- 2420 MYA Paleoarchean Era -- 4031 -- 3490 MYA Acastan Period -- 4031 -- 3810 MYA -- named after the Acasta Gneiss Isuan Period -- 3810 -- 3490 MYA -- named after the Isua Greenstone Belt Mesoarchean Era -- 3490 -- 2780 MYA Vaalbaran Period -- 3490 -- 3020 MYA -- a portmanteau based on the names of the Kapvaal ( Southern Africa ) and Pilbara ( Western Australia ) cratons Pongolan Period -- 3020 -- 2780 MYA -- named after the Pongola Supergroup Neoarchean Era -- 2780 -- 2420 MYA Methanian Period -- 2780 -- 2630 MYA -- named for the inferred predominance of methanotrophic prokaryotes Siderian Period -- 2630 -- 2420 MYA -- named for the voluminous banded iron formations formed within its duration Proterozoic Eon -- 2420 -- 541 MYA Paleoproterozoic Era -- 2420 -- 1780 MYA Oxygenian Period -- 2420 -- 2250 MYA -- named for displaying the first evidence for a global oxidizing atmosphere Jatulian or Eukaryian Period -- 2250 -- 2060 MYA -- names are respectively for the Lomagundi -- Jatuli δ C isotopic excursion event spanning its duration, and for the ( proposed ) first fossil appearance of eukaryotes Columbian Period -- 2060 -- 1780 MYA -- named after the supercontinent Columbia Mesoproterozoic Era -- 1780 -- 850 MYA Rodinian Period -- 1780 -- 850 MYA -- named after the supercontinent Rodinia, stable environment Neoproterozoic Era -- 850 -- 541 MYA Cryogenian Period -- 850 -- 630 MYA -- named for the occurrence of several glaciations Ediacaran Period -- 630 -- 541 MYA Shown to scale : Compare with the current official timeline, not shown to scale : See also Age of the Earth Bubnoff unit Cosmic calendar Deep time Evolutionary history of life Geological history of Earth Geology of Mars / areology Geon Graphical timeline of the universe History of the Earth History of geology History of paleontology List of fossil sites Logarithmic timeline Lunar geologic timescale Natural history New Zealand geologic time scale Prehistoric life Timeline of the Big Bang Timeline of evolution Timeline of the geologic history of the United States Timeline of human evolution Timeline of natural history Timeline of paleontology Notes Jump up ^ Not enough is known about extra-solar planets for worthwhile speculation. Jump up ^ Paleontologists often refer to faunal stages rather than geologic ( geological ) periods. The stage nomenclature is quite complex. For a time - ordered list of faunal stages, see. ^ Jump up to : Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the International Commission on Stratigraphy 2015 time scale except the Hadean eon. Where errors are not quoted, errors are less than the precision of the age given. * indicates boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon. Jump up ^ References to the `` Post-Cambrian Supereon '' are not universally accepted, and therefore must be considered unofficial. Jump up ^ Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. The 2009 version of the ICS time chart recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status. ^ Jump up to : For more information on this, see Atmosphere of Earth # Evolution of Earth 's atmosphere, Carbon dioxide in the Earth 's atmosphere, and Climate change. Specific graphs of reconstructed CO levels over the past ~ 550, 65, and 5 million years can be seen at File : Phanerozoic Carbon Dioxide. png, File : 65 Myr Climate Change. png, File : Five Myr Climate Change. png, respectively. Jump up ^ The start time for the Holocene epoch is here given as 11,700 years ago. For further discussion of the dating of this epoch, see Holocene. Jump up ^ In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods. Jump up ^ The Precambrian is also known as Cryptozoic. ^ Jump up to : The Proterozoic, Archean and Hadean are often collectively referred to as the Precambrian Time or sometimes, also the Cryptozoic. ^ Jump up to : Defined by absolute age ( Global Standard Stratigraphic Age ). Jump up ^ The age of the oldest measurable craton, or continental crust, is dated to 3,600 -- 3,800 Ma. Jump up ^ Though commonly used, the Hadean is not a formal eon and no lower bound for the Archean and Eoarchean have been agreed upon. The Hadean has also sometimes been called the Priscoan or the Azoic. Sometimes, the Hadean can be found to be subdivided according to the lunar geologic timescale. These eras include the Cryptic and Basin Groups ( which are subdivisions of the Pre-Nectarian era ), Nectarian, and Early Imbrian units. ^ Jump up to : These unit names were taken from the lunar geologic timescale and refer to geologic events that did not occur on Earth. Their use for Earth geology is unofficial. Note that their start times do not dovetail perfectly with the later, terrestrially defined boundaries. References ^ Jump up to : `` International Stratigraphic Chart ''. International Commission on Stratigraphy. Archived from the original on 30 May 2014. ^ Jump up to : International Commission on Stratigraphy. `` Chronostratigraphic Units ''. International Stratigraphic Guide. Archived from the original on 9 December 2009. Retrieved 14 December 2009. Jump up ^ `` Age of the Earth ''. U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 2006 - 01 - 10. Jump up ^ Dalrymple, G. Brent ( 2001 ). `` The age of the Earth in the twentieth century : a problem ( mostly ) solved ''. Special Publications, Geological Society of London. 190 ( 1 ) : 205 -- 221. Bibcode : 2001GSLSP. 190... 205D. doi : 10.1144 / GSL. SP. 2001.190. 01.14. Jump up ^ `` Statutes of the International Commission on Stratigraphy ''. Retrieved 26 November 2009. Jump up ^ Janke, Paul R. `` Correlating Earth 's History ''. Jump up ^ Rudwick, M.J.S. ( 1985 ). The Meaning of Fossils : Episodes in the History of Palaeontology. University of Chicago Press. p. 24. ISBN 0 - 226 - 73103 - 0. Jump up ^ Fischer, Alfred G. ; Garrison, Robert E. ( 2009 ). `` The role of the Mediterranean region in the development of sedimentary geology : A historical overview ''. Sedimentology. 56 : 3. Bibcode : 2009Sedim... 56... 3F. doi : 10.1111 / j. 1365 - 3091.2008. 01009. x. Jump up ^ `` The contribution of Ibn Sina ( Avicenna ) to the development of the Earth Sciences '' ( PDF ). Jump up ^ Sivin, Nathan ( 1995 ). Science in Ancient China : Researches and Reflections. Brookfield, Vermont : Ashgate Publishing Variorum series. III, 23 -- 24. Jump up ^ Hutton, James ( 1788 ). `` Theory of the Earth ; or an investigation of the laws observable in the composition, dissolution, and restoration of land upon the Globe ''. Transactions of the Royal Society of Edinburgh. 1 ( 2 ) : 209 -- 308. doi : 10.1017 / s0080456800029227. Retrieved 2016 - 09 - 06. ^ Jump up to : McPhee, John ( 1981 ). Basin and Range. New York : Farrar, Straus and Giroux. Jump up ^ Great Soviet Encyclopedia ( in Russian ) ( 3rd ed. ). Moscow : Sovetskaya Enciklopediya. 1974. vol. 16, p. 50. Jump up ^ Rudwick, Martin ( 2008 ). Worlds Before Adam : The Reconstruction of Geohistory in the Age of Reform. pp. 539 -- 545. Jump up ^ `` Geologic Time Scale ''. Jump up ^ `` How the discovery of geologic time changed our view of the world ''. Bristol University. Jump up ^ Gradstein, Felix M. ; Ogg, James G. ; Smith, Alan G., eds. ( 2005 ). A Geologic Time Scale 2004. Cambridge University Press. ISBN 0 - 521 - 78673 - 8. Jump up ^ Cox, Simon J.D. ; Richard, Stephen M. ( 2005 ). `` A formal model for the geologic time scale and global stratotype section and point, compatible with geospatial information transfer standards ''. Geosphere. The Geological Society of America. 1 ( 3 ) : 119 -- 137. Bibcode : 2005Geosp... 1... 119C. doi : 10.1130 / GES00022. 1. Retrieved 31 December 2012. Jump up ^ `` Official website ''. Archived from the original on 20 September 2005. Jump up ^ `` Anthropocene : Age of Man -- Pictures, More From National Geographic Magazine ''. ngm.nationalgeographic.com. Retrieved 2015 - 09 - 22. Jump up ^ Stromberg, Joseph. `` What is the Anthropocene and Are We in It ? ''. Retrieved 2015 - 09 - 22. Jump up ^ `` Subcomission on Quaternary Stratigraphy, ICS '' Working Groups ``. quaternary.stratigraphy.org. Retrieved 2015 - 09 - 22. Jump up ^ `` Geologic Timescale Elements in the International Chronostratigraphic Chart ''. Retrieved 2014 - 08 - 03. Jump up ^ Cox, Simon J.D. `` SPARQL endpoint for CGI timescale service ''. Archived from the original on 2014 - 08 - 06. Retrieved 2014 - 08 - 03. Jump up ^ Cox, Simon J.D. ; Richard, Stephen M. `` A geologic timescale ontology and service ''. Earth Science Informatics. 8 : 5 -- 19. doi : 10.1007 / s12145 - 014 - 0170 - 6. Jump up ^ `` The Paleobiology Database ''. Archived from the original on 11 February 2006. Retrieved 2006 - 03 - 19. Jump up ^ `` Archived copy '' ( PDF ). Archived from the original ( PDF ) on 29 December 2009. Retrieved 23 December 2009. Jump up ^ `` NASA Scientists React to 400 ppm Carbon Milestone ''. NASA. Retrieved 15 January 2014. ^ Jump up to : Royer, Dana L. ( 2006 ). `` CO-forced climate thresholds during the Phanerozoic '' ( PDF ). Geochimica et Cosmochimica Acta. 70 ( 23 ) : 5665 -- 75. Bibcode : 2006GeCoA... 70.5665 R. doi : 10.1016 / j. gca. 2005.11. 031. Jump up ^ Bowring, Samuel A. ; Williams, Ian S. ( 1999 ). `` Priscoan ( 4.00 -- 4.03 Ga ) orthogneisses from northwestern Canada ''. Contributions to Mineralogy and Petrology. 134 ( 1 ) : 3. Bibcode : 1999CoMP... 134... 3B. doi : 10.1007 / s004100050465. The oldest rock on Earth is the Acasta Gneiss, and it dates to 4.03 Ga, located in the Northwest Territories of Canada. ^ Jump up to : `` The Eons of Chaos and Hades '' ( PDF ). Solid Earth. January 26, 2010. Jump up ^ `` Geology.wisc.edu '' ( PDF ). ^ Jump up to : Van Kranendonk, Martin J. ( 2012 ). `` 16 : A Chronostratigraphic Division of the Precambrian : Possibilities and Challenges ''. In Felix M. Gradstein ; James G. Ogg ; Mark D. Schmitz ; abi M. Ogg. The geologic time scale 2012 ( 1st ed. ). Amsterdam : Elsevier. pp. 359 -- 365. ISBN 978 - 0 - 44 - 459425 - 9. ^ Jump up to : Goldblatt, C. ; Zahnle, K.J. ; Sleep, N.H. ; Nisbet, E.G. ( 2010 ). `` The Eons of Chaos and Hades '' ( PDF ). Solid Earth. Copernicus Publications on behalf of the European Geosciences Union. 1 : 1 -- 3. Bibcode : 2010SolE... 1... 1G. Jump up ^ Chambers, John E. ( July 2004 ). `` Planetary accretion in the inner Solar System '' ( PDF ). Earth and Planetary Science Letters. 223 ( 3 -- 4 ) : 241 -- 252. Bibcode : 2004E&PSL. 223... 241C. doi : 10.1016 / j. epsl. 2004.04. 031. Jump up ^ El Albani, Abderrazak ; Bengtson, Stefan ; Canfield, Donald E. ; Riboulleau, Armelle ; Rollion Bard, Claire ; Macchiarelli, Roberto ; et al. ( 2014 ). `` The 2.1 Ga Old Francevillian Biota : Biogenicity, Taphonomy and Biodiversity ''. PLoS ONE. 9 ( 6 ) : e99438. Bibcode : 2014PLoSO... 999438E. doi : 10.1371 / journal. pone. 0099438. PMC 4070892. PMID 24963687. Jump up ^ El Albani, Abderrazak ; Bengtson, Stefan ; Canfield, Donald E. ; Bekker, Andrey ; Macchiarelli, Roberto ; Mazurier, Arnaud ; Hammarlund, Emma U. ; et al. ( 2010 ). `` Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago '' ( PDF ). Nature. 466 ( 7302 ) : 100 -- 104. Bibcode : 2010Natur. 466... 100A. doi : 10.1038 / nature09166. PMID 20596019. Further reading Aubry, Marie - Pierre ; Van Couvering, John A. ; Christie - Blick, Nicholas ; Landing, Ed ; Pratt, Brian R. ; Owen, Donald E. ; Ferrusquia - Villafranca, Ismael ( 2009 ). `` Terminology of geological time : Establishment of a community standard '' ( PDF ). Stratigraphy. 6 ( 2 ) : 100 -- 105. Retrieved 18 November 2011. Gradstein, F.M. ; Ogg, J.G. ( 2004 ). A Geologic Time scale 2004 -- Why, How and Where Next ! ( PDF ). Retrieved 18 November 2011. Gradstein, Felix M. ; Ogg, James G. ; Smith, Alan G. ( 2004 ). A Geologic Time Scale 2004. New York ; Cambridge, UK : Cambridge University Press. ISBN 0 - 521 - 78142 - 6. Retrieved 18 November 2011 Paperback ISBN 0 - 521 - 78673 - 8 Gradstein, Felix M. ; Ogg, James G. ; Smith, Alan G. ; Bleeker, Wouter ; Laurens, Lucas, J. ( June 2004 ). `` A new Geologic Time Scale, with special reference to Precambrian and Neogene '' ( PDF ). Episodes. 27 ( 2 ) : 83 -- 100. Retrieved 18 November 2011. Ialenti, Vincent. `` Embracing ' Deep Time ' Thinking. '' ``. NPR Cosmos & Culture. Ialenti, Vincent. `` Pondering ' Deep Time ' Could Inspire New Ways To View Climate Change ''. NPR Cosmos & Culture. Knoll, Andrew H. ; Walter, Malcolm R. ; Narbonne, Guy M. ; Christie - Blick, Nicholas ( 30 July 2004 ). `` A New Period for the Geologic Time Scale '' ( PDF ). Science. 305 ( 5684 ) : 621 -- 622. doi : 10.1126 / science. 1098803. PMID 15286353. Retrieved 18 November 2011. Levin, Harold L. ( 2010 ). `` Time and Geology ''. The Earth Through Time. Hoboken, New Jersey : John Wiley & Sons. ISBN 978 - 0 - 470 - 38774 - 0. Retrieved 18 November 2011. Montenari, Michael ( 2016 ). Stratigraphy and Timescales ( 1st ed. ). Amsterdam : Academic Press ( Elsevier ). ISBN 978 - 0 - 12 - 811549 - 7. External links Wikimedia Commons has media related to Geologic time scale. The Wikibook Historical Geology has a page on the topic of : Geological column NASA : Geologic Time GSA : Geologic Time Scale British Geological Survey : Geological Timechart GeoWhen Database International Commission on Stratigraphy Time Scale Chronos.org National Museum of Natural History -- Geologic Time SeeGrid : Geological Time Systems Information model for the geologic time scale Exploring Time from Planck Time to the lifespan of the universe Episodes, Gradstein, Felix M. et al. ( 2004 ) A new Geologic Time Scale, with special reference to Precambrian and Neogene, Episodes, Vol. 27, no. 2 June 2004 ( pdf ) Lane, Alfred C, and Marble, John Putman 1937. Report of the Committee on the measurement of geologic time Lessons for Children on Geologic Time Deep Time -- A History of the Earth : Interactive Infographic Geologic history of Earth Cenozoic era1 ( present -- 66.0 Mya ) Quaternary ( present -- 2.588 Mya ) Holocene ( present -- 11.784 kya ) Pleistocene ( 11.784 kya -- 2.588 Mya ) Neogene ( 2.588 -- 23.03 Mya ) Pliocene ( 2.588 -- 5.333 Mya ) Miocene ( 5.333 -- 23.03 Mya ) Paleogene ( 23.03 -- 66.0 Mya ) Oligocene ( 23.03 -- 33.9 Mya ) Eocene ( 33.9 -- 56.0 Mya ) Paleocene ( 56.0 -- 66.0 Mya ) Mesozoic era1 ( 66.0 -- 252.17 Mya ) Cretaceous ( 66.0 -- 145.0 Mya ) Late ( 66.0 -- 100.5 Mya ) Early ( 100.5 -- 145.0 Mya ) Jurassic ( 145.0 -- 201.3 Mya ) Late ( 145.0 -- 163.5 Mya ) Middle ( 163.5 -- 174.1 Mya ) Early ( 174.1 -- 201.3 Mya ) Triassic ( 201.3 -- 252.17 Mya ) Late ( 201.3 -- 237 Mya ) Middle ( 237 -- 247.2 Mya ) Early ( 247.2 -- 252.17 Mya ) Paleozoic era1 ( 252.17 -- 541.0 Mya ) Permian ( 252.17 -- 298.9 Mya ) Lopingian ( 252.17 -- 259.8 Mya ) Guadalupian ( 259.8 -- 272.3 Mya ) Cisuralian ( 272.3 -- 298.9 Mya ) Carboniferous ( 298.9 -- 358.9 Mya ) Pennsylvanian ( 298.9 -- 323.2 Mya ) Mississippian ( 323.2 -- 358.9 Mya ) Devonian ( 358.9 -- 419.2 Mya ) Late ( 358.9 -- 382.7 Mya ) Middle ( 382.7 -- 393.3 Mya ) Early ( 393.3 -- 419.2 Mya ) Silurian ( 419.2 -- 443.8 Mya ) Pridoli ( 419.2 -- 423.0 Mya ) Ludlow ( 423.0 -- 427.4 Mya ) Wenlock ( 427.4 -- 433.4 Mya ) Llandovery ( 433.4 -- 443.8 Mya ) Ordovician ( 443.8 -- 485.4 Mya ) Late ( 443.8 -- 458.4 Mya ) Middle ( 458.4 -- 470.0 Mya ) Early ( 470.0 -- 485.4 Mya ) Cambrian ( 485.4 -- 541.0 Mya ) Furongian ( 485.4 -- 497 Mya ) Series 3 ( 497 -- 509 Mya ) Series 2 ( 509 -- 521 Mya ) Terreneuvian ( 521 -- 541.0 Mya ) Proterozoic eon2 ( 541.0 Mya -- 2.5 Gya ) Neoproterozoic era ( 541.0 Mya -- 1 Gya ) Ediacaran ( 541.0 - ~ 635 Mya ) Cryogenian ( ~ 635 - ~ 720 Mya ) Tonian ( ~ 720 Mya - 1 Gya ) Mesoproterozoic era ( 1 -- 1.6 Gya ) Stenian ( 1 - 1.2 Gya ) Ectasian ( 1.2 - 1.4 Gya ) Calymmian ( 1.4 - 1.6 Gya ) Paleoproterozoic era ( 1.6 -- 2.5 Gya ) Statherian ( 1.6 - 1.8 Gya ) Orosirian ( 1.8 - 2.05 Gya ) Rhyacian ( 2.05 - 2.3 Gya ) Siderian ( 2.3 - 2.5 Gya ) Archean eon2 ( 2.5 -- 4 Gya ) Eras Neoarchean ( 2.5 -- 2.8 Gya ) Mesoarchean ( 2.8 -- 3.2 Gya ) Paleoarchean ( 3.2 -- 3.6 Gya ) Eoarchean ( 3.6 -- 4 Gya ) Hadean eon2 ( 4 -- 4.6 Gya ) kya = thousands years ago. Mya = millions years ago. Gya = billions years ago. 1 = Phanerozoic eon. 2 = Precambrian supereon. Source : ( 2015 / 01 ). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time -- Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013. 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Question: what unit of geologic time is the greatest span of time
Answer: eons