Geological / Evolutionary Time

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Geological / Evolutionary Time

content by Niel Brandt and International Commission on Stratigraphy

Evolutionary Timeline
Geological Timeline
A mnemonic device to help them learn the order of geological time divisions -  oldest to youngest:

Evolutionary Timeline

Time  (Myr ago)
4600 Formation of the approximately homogeneous solid Earth by planetesimal accretion 
4300 Melting of the Earth due to radioactive and gravitational heating which leads to its differentiated interior structure as well as outgassing of molecules such as water, methane, ammonia, hydrogen, nitrogen, and carbon dioxide 
4300 Atmospheric water is photodissociated by ultraviolet light to give oxygen atoms which are incorporated into an ozone layer and hydrogen molecules which escape into space 
4000 Bombardment of the Earth by planetesimals stops 
3800 The Earth's crust solidifies--formation of the oldest rocks found on Earth 
3800 Condensation of atmospheric water into oceans 
3500-2800 Prokaryotic cell organisms develop 
3500-2800 Beginning of photosynthesis by blue-green algae which releases oxygen molecules into the atmosphere and steadily works to strengthen the ozone layer and change the Earth's chemically reducing atmosphere into a chemically oxidizing one 
2400 Rise in the concentration of oxygen molecules stops the deposition of uraninites (since they are soluble when combined with oxygen) and starts the deposition of banded iron formations 
2000 The Oklo natural fission reactor in Gabon goes into operation 
1600 The last reserves of reduced iron are used up by the increasing atmospheric oxygen--last banded iron formations 
1500 Eukaryotic cell organisms develop 
1500-600 Rise of multicellular organisms 
580-545 Fossils of Ediacaran organisms are made 
545 Cambrian explosion of hard-bodied organisms 
528-526 Fossilization of the Chengjiang site 
517-515 Fossilization of the Burgess Shale 
500-450 Rise of the fish--first vertebrates 
430 Waxy coated algae begin to live on land 
420 Millipedes have evolved--first land animals 
375 The Appalachian mountains are formed via a plate tectonic collision between North America, Africa, and Europe 
375 Appearance of primitive sharks 
350-300 Rise of the amphibians 
350 Primitive insects have evolved 
350 Primitive ferns evolve--first plants with roots 
300-200 Rise of the reptiles 
300 Winged insects have evolved 
280 Beetles and weevils have evolved 
250 Permian period mass extinction 
230 Roaches and termites have evolved 
225 Modern ferns have evolved 
225 Bees have evolved 
200 Pangaea starts to break apart 
200 Primitive crocodiles have evolved 
200 Appearance of mammals 
145 Archaeopteryx walks the Earth 
136 Primitive kangaroos have evolved 
100 Primitive cranes have evolved 
90 Modern sharks have evolved 
65 K-T Boundary--extinction of the dinosaurs and beginning of the reign of mammals 
60 Rats, mice, and squirrels have evolved 
60 Herons and storks have evolved 
55 Rabbits and hares have evolved 
50 Primitive monkeys have evolved 
28 Koalas have evolved 
20 Parrots and pigeons have evolved 
20-12 The chimpanzee and hominid lines evolve 
10-4 Ramapithecus exist 
4 Development of hominid bipedalism 
4-1 Australopithecus exist 
3.5 The Australopithecus Lucy walks the Earth 
2 Widespread use of stone tools 
2-0.01 Most recent ice age 
1.6-0.2 Homo erectus exist 
1-0.5 Homo erectus tames fire 
0.3 Geminga supernova explosion at a distance of roughly 60 pc--roughly as bright as the Moon
0.2-0.03 Homo sapiens neanderthalensis exist 
0.05-0 Homo sapiens sapiens exist 
0.04-0.012 Homo sapiens sapiens enter Australia from southeastern Asia and North America from northeastern Asia
0.025-0.01 Most recent glaciation--an ice sheet covers much of the northern United States 
0.02 Homo sapiens sapiens paint the Altamira Cave
0.012 Homo sapiens sapiens have domesticated dogs in Kirkuk, Iraq 
0.01 First permanent Homo sapiens sapiens settlements 
0.01 Homo sapiens sapiens learn to use fire to cast copper and harden pottery 
0.006 Writing is developed in Sumeria 

Geological Timeline

Table of geologic time 2004

webmaster note: this topic area is subject to frequent minor revisions 

The following table summarizes the major events and characteristics of the periods of time making up the geologic time scale. As above, this time scale is based on the International Commission on Stratigraphy.

Supereon Eon Era Period[6] Series / Epoch Faunal stage[7] / Geologic age Major events Start, million years ago[7]

Phanerozoic Cenozoic[8] Neogene[8] Holocene Quaternary The last glacial period ends and rise of human civilization. Quaternary Ice Age recedes, and the current interglacial begins. Younger Dryas cold spell occurs, Sahara Desert forms from savannah, and agriculture begins, allowing humans to build cities. Paleolithic/Neolithic (Stone Age) cultures begin around 10,000 BC, giving way to Copper Age (3500 BC) and Bronze Age (2500 BC). Cultures continue to grow in complexity and technical advancement through the Iron Age (1200 BC), giving rise to many pre-historic cultures throughout the world, eventually leading into Classical Antiquity, such as Ancient Rome and even to the Middle Ages and present day. Also refer to the List of archaeological periods for clarification on early cultures and ages. Mount Tambora erupts in 1815, causing the Year Without a Summer (1816) in Europe and North America from a volcanic winter. atmospheric CO2 levels start creeping from 100 ppmv at the end of the last glaciation to the current level of 385 parts per million volume (ppmv), causing global warming and climate change, possibly from anthropogenic sources, such as the Industrial Revolution[9] 0.011430 ± 0.00013[8][10]
Pleistocene Late/Tyrrhenian Stage Flourishing and then extinction of many large mammals (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 Carbon Dioxide levels[9]), further intensification of Icehouse Earth conditions, roughly 1.6 MYA[11]. Last glacial maximum (30,000 years ago), last glacial period (18,000-15,000 years ago). Dawn of human stone-age cultures, with increasing technical complexity than previous ice age cultures, such as engravings and clay statues (Venus of Lespugue), particularly in the Mediterranean and Europe. Lake Toba supervolcano erupts 75,000 years before present, causing a volcanic winter and pushes humanity to the brink of extinction. 0.126 ± 0.005*
Middle 0.500?
Early 1.806 ± 0.005*
Gelasian 2.588 ± 0.005*
Pliocene Piacenzian/Blancan Intensification of present Icehouse conditions, Present (Quaternary) ice age begins roughly 2.58 MYA; cool and dry climate. Australopithecines, many of the existing genera of mammals, and recent mollusks appear. Homo habilis appears. 3.600 ± 0.005*
Zanclean 5.332 ± 0.005*
Miocene Messinian Moderate Icehouse climate, puncuated by ice ages; Orogeny in northern hemisphere. Modern mammal and bird families became 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. Carpathean 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 atmospheric Carbon Dioxide, gradually lowering the level atmospheric CO2 from 650 ppmv down to around 100 ppmv[9]. 7.246 ± 0.05*
Tortonian 11.608 ± 0.05*
Burdigalian 13.65 ± 0.05*
Serravallian 15.97 ± 0.05*
Langhian 20.43 ± 0.05*
Aquitanian 23.03 ± 0.05*
Paleogene[8] 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 28.4 ± 0.1*
Rupelian 33.9 ± 0.1*
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[9], 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. 37.2 ± 0.1*
Bartonian 40.4 ± 0.2*
Lutetian 48.6 ± 0.2*
Ypresian 55.8 ± 0.2*
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 MYA[11], Himalayan Orogeny starts between 52 and 48 MYA. 58.7 ± 0.2*
Selandian 61.7 ± 0.3*
Danian 65.5 ± 0.3*
Mesozoic Cretaceous Upper/Late Maastrichtian Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonites, 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 Carbon Dioxide close to present-day levels. 70.6 ± 0.6*
Campanian 83.5 ± 0.7*
Santonian 85.8 ± 0.7*
Coniacian 89.3 ± 1.0*
Turonian 93.5 ± 0.8*
Cenomanian 99.6 ± 0.9*
Lower/Early Albian 112.0 ± 1.0*
Aptian 125.0 ± 1.0*
Barremian 130.0 ± 1.5*
Hauterivian 136.4 ± 2.0*
Valanginian 140.2 ± 3.0*
Berriasian 145.5 ± 4.0*
Jurassic Upper/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. Rantigata and Cimmerian Orogenies taper off. Atmospheric Carbon Dioxide levels 4-5 times the present day levels (1200-1500 ppmv, compared to today's 385 ppmv[9]). 150.8 ± 4.0*
Kimmeridgian 155.7 ± 4.0*
Oxfordian 161.2 ± 4.0*
Middle Callovian 164.7 ± 4.0
Bathonian 167.7 ± 3.5*
Bajocian 171.6 ± 3.0*
Aalenian 175.6 ± 2.0*
Lower/Early Toarcian 183.0 ± 1.5*
Pliensbachian 189.6 ± 1.5*
Sinemurian 196.5 ± 1.0*
Hettangian 199.6 ± 0.6*
Triassic Upper/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. Dicrodium 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 MYA) 203.6 ± 1.5*
Norian 216.5 ± 2.0*
Carnian 228.0 ± 2.0*
Middle Ladinian 237.0 ± 2.0*
Anisian 245.0 ± 1.5*
Lower/Early ("Scythian") Olenekian 249.7 ± 1.5*
Induan 251.0 ± 0.7*
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 mya: 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 MYA). Forms the MacDonnell Ranges. 253.8 ± 0.7*
Wuchiapingian 260.4 ± 0.7*
Guadalupian Capitanian 265.8 ± 0.7*
Wordian/Kazanian 268.4 ± 0.7*
Roadian/Ufimian 270.6 ± 0.7*
Cisuralian Kungurian 275.6 ± 0.7*
Artinskian 284.4 ± 0.7*
Sakmarian 294.6 ± 0.8*
Asselian 299.0 ± 0.8*
Upper/Late 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. 303.9 ± 0.9*
Kasimovian 306.5 ± 1.0*
Middle Moscovian 311.7 ± 1.1*
Lower/Early Bashkirian 318.1 ± 1.3*
Upper/Late 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. 326.4 ± 1.6*
Middle Viséan 345.3 ± 2.1*
Lower/Early Tournaisian 359.2 ± 2.5*
Devonian Upper/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. 374.5 ± 2.6*
Frasnian 385.3 ± 2.6*
Middle Givetian 391.8 ± 2.7*
Eifelian 397.5 ± 2.7*
Lower/Early Emsian 407.0 ± 2.8*
Pragian 407.0 ± 2.8*
Lochkovian 416.0 ± 2.8*
Silurian Pridoli no faunal stages defined 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. 418.7 ± 2.7*
Ludlow/Cayugan Ludfordian 421.3 ± 2.6*
Gorstian 422.9 ± 2.5*
Wenlock Homerian/Lockportian 426.2 ± 2.4*
Sheinwoodian/Tonawandan 428.2 ± 2.3*
Llandovery/Alexandrian Telychian/Ontarian 436.0 ± 1.9*
Aeronian 439.0 ± 1.8*
Rhuddanian 443.7 ± 1.5*
Ordovician Upper/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. 445.6 ± 1.5*
other faunal stages 460.9 ± 1.6*
Middle Darriwilian 468.1 ± 1.6*
other faunal stages 471.8 ± 1.6*
Lower/Early Arenig 471.8 ± 1.7*
Tremadocian 488.3 ± 1.7*
Cambrian Furongian other faunal stages Major diversification of life in the Cambrian Explosion. Many 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 many other animals numerous. 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 MYA). Ross Orogeny in Antarctica. Adelaide Geosyncline (Delamerian Orogeny), majority of orogenic activity from 514-500 MYA. Lachlan Orogeny on Australian Continent, c. 540-440 MYA. Atmospheric Carbon Dioxide content roughly 20-35 times present-day (Holocene) levels (6000 ppmv compared to today's 385 ppmv)[9]</ref> 496.0 ± 2.0*
501.0 ± 2.0*
Middle other faunal stages 513.0 ± 2.0
Lower/Early other faunal stages 542.0 ± 1.0*
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 MYA. 630 +5/-30*
Cryogenian Possible "Snowball Earth" period. Fossils still rare. Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. 850[15]
Tonian Rodinia supercontinent persists. 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, 1000 ± 150 MYA. Edmundian Orogeny (c. 920 - 850 MYA), Gascoyne Complex, Western Australia. Adelaide Geosyncline laid down on Australian Continent, beginning of Adelaide Geosyncline (Delamerian Orogeny) in that continent. 1000[15]
Stenian Narrow highly metamorphic belts due to orogeny as Rodinia formed. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny (c. 1080 MYA), Musgrave Block, Central Australia. 1200[15]
Ectasian Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. 1400[15]
Calymmian Platform covers expand. Barramundi Orogeny, MacArthur Basin, Northern Australia, and Isan Orogeny, c. 1600 MYA, Mount Isa Block, Queensland 1600[15]
Statherian First complex single-celled life: protists with nuclei. Columbia is the primordial supercontinent. Kimban Orogeny in Australian Continent ends. Yapungku Orogeny on North Yilgarn craton, in Western Australia. Mangaroon Orogeny, 1680-1620 MYA, on the Gascoyne Complex in Western Australia. Kararan Orogeny (1650- MYA), Gawler Craton, South Australia. 1800[15]
Orosirian The atmosphere became oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny. Penokean and Trans-Hudsonian Orogenies in North America. Early Ruker Orogeny in Antarctica, 2000 - 1700 MYA. Glenburgh Orogeny, Glenburgh Terrane, Australian Continent c. 2005 - 1920 MYA. Kimban Orogeny, Gawler craton in Australian Continent begins. 2050[15]
Rhyacian Bushveld Formation formed. Huronian glaciation. 2300[15]
Siderian Oxygen Catastrophe: banded iron formations formed. Sleaford Orogeny on Australian Continent, Gawler Craton 2440-2420 MYA. 2500[15]
Archean[14] Neoarchean[14] Stabilization of most modern cratons; possible mantle overturn event. Insell Orogeny, 2650 ± 150 MYA. Abitibi greenstone belt in present-day Ontario and Quebec begins to form, stablizes by 2600 MYA. 2800[15]
Mesoarchean[14] 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 2696 MYA. 3200[15]
Paleoarchean[14] 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[16]. Rayner Orogeny in Antarctica. 3600[15]
Eoarchean[14] Simple single-celled life (probably bacteria and perhaps archaea). Oldest probable microfossils. 3800
Lower Imbrian[14][18] This era overlaps the end of the Late Heavy Bombardment of the inner solar system. c.3850
Nectarian[14][18] This era gets its name from the lunar geologic timescale when the Nectaris Basin and other major lunar basins were formed by large impact events. c.3920
Basin Groups[14][18] Oldest known rock (4030 Ma)[19]. The first Lifeforms and self-replicating RNA molecules may have evolved on earth around 4000 Ma during this era. Naiper Orogeny in Antarctica, 4000 ± 200 MYA. c.4150
Cryptic[14][18] Oldest known mineral (Zircon, 4406±8 Ma[20]). Formation of Earth (4567.17 to 4570 Ma) c.4570
  1. ^ John McPhee, Basin and Range, New York:Farrar, Straus and Giroux, 1981, pp.95-100.
  2. ^ John McPhee, Basin and Range, pp.113-114.
  3. ^ (1974) Great Soviet Encyclopedia, 3rd ed. (in Russian), Moscow: Sovetskaya Enciklopediya, vol. 16, p. 50. 
  4. ^ Felix M. Gradstein, James G. Ogg, Alan G. Smith (Editors); A Geologic Time Scale 2004, Cambridge University Press, 2005, (ISBN 0-521-78673-8)
  5. ^ Cox & Richard, A formal model for the geologic time scale and global stratotype section and point, compatible with geospatial information transfer standards, Geosphere, volume 1, pp 119-137, Geological Society of America, 2005
  6. ^ Paleontologists often refer to faunal stages rather than geologic (geological) periods. The stage nomenclature is quite complex. See The Paleobiology Database. Retrieved on 2006-03-19. for an excellent time ordered list of faunal stages.
  7. ^ a b 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 2004 time scale. Dates labeled with a * indicate boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon: see List of Global Boundary Stratotype Sections and Points for a complete list.
  8. ^ a b c d Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. However, the International Commission on Stratigraphy has recently decided to stop endorsing the terms Quaternary and Tertiary as part of the formal nomenclature.
  9. ^ a b c d e f For more information on this, see the following articles: Earth's atmosphere, Carbon Dioxide, Carbon dioxide in the Earth's atmosphere, Image:Phanerozoic_Carbon_Dioxide.png, Image:65 Myr Climate Change.png, Image:Five Myr Climate Change.png, and Template:DF temperature
  10. ^ The start time for the Holocene epoch is here given as 11,430 years ago ± 130 years (that is, between 9610 BC-9560 BC and 9350 BC-9300 BC). For further discussion of the dating of this epoch, see Holocene.
  11. ^ a b MYA = Million Years Ago
  12. ^ a b In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
  13. ^ The Precambrian is also known as Cryptozoic.
  14. ^ a b c d e f g h i j k l m n The Proterozoic, Archean and Hadean are often collectively referred to as the Precambrian Time or sometimes, also the Cryptozoic.
  15. ^ a b c d e f g h i j k l Defined by absolute age (Global Standard Stratigraphic Age).
  16. ^ The age of the oldest measurable craton, or continental crust, is dated to 3600-3800 Ma
  17. ^ 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 time scale. These eras include the Cryptic and Basin Groups (which are subdivisions of the pre-Nectarian era), Nectarian, and Lower Imbrian eras.
  18. ^ a b c d These era names were taken from the Lunar geologic timescale. Their use for Earth geology is unofficial.
  19. ^ Oldest rock on earth is the Acasta Gneiss, and it dates to 4.03 Ga, located in the Northwest Territories of Canada.
  20. ^

A mnemonic device to help them learn the order of geological time divisions -  oldest to youngest:

    Can Cambrian Old Ordovician Students Silurian Drink(more) Devonian Carbonated Carboniferous Punch Permian Than Triassic Junior Jurassic Colleagues? Cretaceous Tough Tertiary Question! Quaternary
You are welcome to email  your improvements on this effort!