Geochronology
Geochronology is the science of applying dates in the past to rocks. Sometimes these rocks receive dates because they contain fossils or artifacts that can be dated.

# Geologic time
On the right is a geologic clock representation. It 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 two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.
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 compresses the most recent eon. Therefore the second scale shows the most recent eon with an expanded scale. The second scale compresses the most recent era, so the most recent era is expanded in the third scale. Since the Quaternary is a very short period with short epochs, it is further expanded in the fourth scale. The second, third, and fourth timelines are therefore each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on the third timeline on the right, another reason for expanding the fourth scale. The Pleistocene (P) epoch. Q stands for the Quaternary period.

# Notations
Let
- ALMA represent the Asian Land Mammal Age,
- b2k represent before AD 2000,
- BP represent before present, as the chart is for 2008, this may require an added -8 for b2k,
- ELMMZ represent the European Land Mammal Mega Zone,
- FAD represent first appearance datum,
- FO represent first occurrence,
- Ga represent Gegaannum, billion years ago, or -109 b2k,
- GICC05 represent Greenland Ice Core Chronology 2005,
- GRIP represent Greenland Ice Core Project,
- GSSP represent Global Stratotype Section and Point,
- HO represent highest occurrence,
- ICS represent the International Commission on Stratigraphy,
- IUGS represent the International Union of Geological Sciences,
- LAD represent last appearance datum,
- LO represent lowest occurrence,
- Ma represent Megaannum, million years ago, or -106 b2k,
- NALMA represent the North American Land Mammal Age,
- NGRIP represent North Greenland Ice Core Project, and
- SALMA represent South American Land Mammal Age.
"The term b2 k  refers to the ice-core zero age of AD 2000; note that this is 50 years different from the zero yr for radiocarbon, which is AD 1950 ."

# Stratigraphy
Dates have been assigned to specific geologic stratigraphy frames, columns, or columnar units.

# Geochronologic time frames

# Orbitally forced cyclicity
"Chemical and physical proxies from sedimentary rock sequences are frequently used for palaeoclimatic studies and for detecting orbitally forced cyclicity in marine Cenozoic sequences and calibrating recognized sedimentary cycles to time-periodicity."
"Spectral analysis of the  record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from  dm-scale couplets."
"Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time."

# Phanerozoic
The Phanerozoic eon includes the Paleozoic, Mesozoic, and Cenozoic.

# Cenozoic
"The GSSP section near El Kef contains one main feature that allows for a direct correlation of this marine section with continental sections: the Ir anomaly at the base of the Boundary Clay."
The Global Boundary Stratotype Section and Point for the base of the Danian Stage is also the base GSSP for the Paleocene, Paleogene, "Tertiary", and Cenozoic at El Kef, Tunisia.

# Calabrian
"The  GSSP occurs at the base of the marine claystone conformably overlying sapropelic bed e within Segment B in the Vrica section. This lithological level represents the primary marker for the recognition of the boundary, and is assigned an astronomical age of 1.80 Ma on the basis of sapropel calibration."
"The boundary falls between the highest occurrence of Discoaster brouweri (below) and the lowest common occurrence of left-coiling Neogloboquadrina pachyderma (above), and below the lowest occurrences of medium-sized Gephyrocapsa (including G. oceanica) and Globigerinoides tenellus."
In the image on the right, the Vrica section includes specifically the GSSP of the Calabrian Stage fixed at the top of layer e.

# Mesozoic
In the diagram on the right, the Permian-Triassic boundary is at the base of the Induan limestone that occurs within the Yinkeng Formation.
"The Global Stratotype Section and Point (GSSP) of the Permian-Triassic boundary  is defined at the base of Hindeodus parvus horizon, i.e. the base of Bed 27c of Meishan section D, Changxing County, Zhejiang Province, South China."
"Hindeodus parvus is now recognized as the index fossil" occurring in the Zone above the P-T boundary.

# Cretaceous
The Cretaceous period is the third and final period in the Mesozoic Era. It began 145.5 million years ago after the Jurassic Period and ended 65.5 million years ago, before the  Paleogene Period of the Cenozoic Era.
"Paleogeographically, the sub-alpine terrain of southeastern France  was located on the proximal part of the South-European Tethys margin. It includes the Vocontian Basin, which experienced relatively high rates of subsidence during Jurassic and Early Cretaceous times, bordered by carbonate platforms limited by a net of extensional or strikeslip faults (Graciansky et al., 1999)."
This phraseology connects "Early Cretaceous" with "times".
The aerial image on the right shows the quarry pit in Mantua Township in central New Jersey has been owned by the Inversand Company for nearly a century.
"When an asteroid hit the Earth around 66 million years ago, it wiped out almost 75 percent of the plants and animals on the planet. All dinosaurs, except those that would eventually give rise to modern birds, were killed following the impact. Yet despite such a vast die-off, no bone bed containing a concentration of fossils as a result of this event has been found."
We dont know yet , but we are testing this hypothesis by examining the fossils, the sediments and the chemistry.
"At the end of the Cretaceous, when the dinosaurs met their maker, the region was a shallow tropical sea full of fish, sea turtles, crocodiles, and even mosasaurs. But at some point around 66 million years ago, whether it was due to the asteroid impact or some other cause, many of the inhabitants of the sea died and were preserved in a large bone bed."
On the left is a specimen of Catapleura repanda from the Rowan quarry found in the Cretaceous marl.

# Paleozoic
The paleozoic spans the time from 542.0  1.0 x 106 b2k to 251.0  0.7 x 106 b2k and is a geologic era.

# Guzhangian
"The Global boundary Stratotype Section and Point (GSSP) for the base of the Guzhangian Stage (Cambrian Series 3) is defined at the base of a limestone (calcisiltite) layer 121.3 m above the base of the Huaqiao Formation in the Louyixi section along the Youshui River (Fengtan Reservoir), about 4 km northwest of Luoyixi (4 km southeast of Wangcun), in northwestern Hunan, China."
"The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata  (base of the L. laevigata Zone)."

# Precambrian
Def. "the time and geology dated before the Phanerozoic" or the "eon (or supereon) and rock formations dated before 541.01.0 million years ago, coinciding with the first appearance of the fossils of hard-shelled animals"
is called the precambrian.
Usage notes
- "The International Commission on Stratigraphy, which attempts to standardize the vocabulary of the field, is revising the boundaries between time periods based on physical-science methods rather than the kinds of fossils present."
- "The boundary between the Precambrian and the Phanerozoic has been changed from time to time and will be subject to change".

# Proterozoic
Def. "the eon from 2,500 Ma to 541.01.0 Ma, the beginning of the Phanerozoic, marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life" is called the Proterozoic.

# Upper Adelaidean
The Adelaidean appears to encompass the Delamerian Granites and the Adelaide Rift Complex.
"The deposits include the type sections for the often globally correlated Sturtian and Marinoan glacial sequences (e.g., Preiss, 2000) and the Global Stratotype Section and Point (GSSP) for the newly defined Ediacaran Period (Knoll et al., 2004)."
The later Adelaidean includes the Burra and Caliana Groups.

# Neoproterozoic
Def. "a geologic era within the Proterozoic eon; comprises the Tonian, Cryogenian and Ediacaran periods from about 1000 to 544 million years ago, when algae and sponges flourished" is called the Neoproterozoic.

# Ediacaran
"In the central Flinders Ranges the 4.5 km thick Umberatana Group encompasses the two main phases of glacial deposition (see Thomas et al., 2012). The carbonaceous, calcareous and pyritic Tindelpina Shale Member, of the interglacial Tapley Hill Formation, caps the Fe-rich diamictite and tillite formations of the Sturt glaciation. The upper Cryogenian glacials of the Elatina Formation are truncated by the Nuccaleena Formation at the base of the Wilpena Group and the Ediacaran System."
"In 2004, the Global Stratotype Section and Point (GSSP) for the terminal Proterozoic was placed near the base of the Nuccaleena Formation in Enorama Creek in the central Flinders Ranges , thus establishing the Ediacaran System and Period (Knoll et al., 2006). As the Nuccaleena Formation has not been accurately dated, a date of c. 635 Ma from near-correlative levels in Namibia and China is presumed for the base of the Ediacaran (Hoffmann et al., 2004; Condon et al., 2005; Zhang et al., 2005)."
Def. "a geologic period within the Neoproterozoic era from about 620 to 542 million years ago" is called the Ediacaran.

# Baykonurian
The Baykonurian occurs about 547 Ma.

# Gaskiers glaciation
The Gaskiers glaciation is a period of widespread glacial deposits (e.g. diamictites) that lasted under 340 thousand years, between 579.63  0.15 and 579.88  0.44 million years ago  i.e. late in the Ediacaran Period  making it the last major glacial event of the Precambrian.
Deposits attributed to the Gaskiers - assuming that they were all deposited at the same time - have been found on eight separate palaeocontinents, in some cases occurring close to the equator (at a latitude of 10-30), where the 300 m-thick name-bearing section at Gaskiers-Point La Haye (Newfoundland) is packed full of striated dropstones. Its 13C values are really low (pushing 8 ), consistent with a period of environmental abnormality. The bed lies just below some of the oldest fossils of the Ediacaran biota, where there is in fact a 9 million year gap between the diamictites and the 570 Ma macrofossils.

# Varanger glaciation
The Varangian apparently spans 610 to 575 Ma.

# Elatina glaciation
"The Elatina glaciation has not been dated directly, and only maximum and minimum age limits of c. 640 and 580 Ma, respectively, are indicated."
"The Elatina glaciation is of global importance for several reasons:
- its diverse and excellently preserved glacial and periglacial facies represent a de facto type region for late Cryogenian glaciation in general;
- the Elatina Fm. has yielded the most robust palaeomagnetic data for any Cryogenian glaciogenic succession; and
- the recently established Ediacaran System and Period (Knoll et al. 2004, 2006; Preiss 2005) has its Global Stratotype Section and Point (GSSP) placed near the base of the Nuccaleena Fm. overlying the Elatina Fm. in the central Flinders Ranges ."
"Feeder dykes for volcanic rocks near the base of the  sedimentary succession have been dated at 867  47 and 802  35 Ma (Zhao & McCulloch 1993; Zhao et al. 1994) and 827  6 Ma (Wingate et al. 1998)."
"No volcanism is known in the region during the Elatina glaciation."
"The Neoproterozoicearly Palaeozoic succession in the Adelaide Geosyncline was deformed by the Delamerian Orogeny at 514  490 Ma (Drexel & Preiss 1995; Foden	et al. 2006)."
"The Yerelina Subgroup at the top of the Cryogenian Umberatana Group embraces all the glaciogenic formations of the Elatina glaciation (Preiss et al. 1998)."
"The Yerelina Subgroup is unconformably to disconformably overlain by the Ediacaran Wilpena Group."
"Deposition in the North Flinders Zone commenced, possibly following an erosional break, with the 1070-m-thick Fortress Hill Fm., which comprises laminated siltstone with gritty lenses and scattered dropstones, some faceted, marking the onset of glacial deposition (Coats & Preiss 1987; Preiss et al. 1998). Clast lithologies include granite, quartzite, limestone, oolitic limestone and dolostone. The Fortress Hill Fm. is typical of the dominantly fine-grained units of the Yerelina Subgroup that are interpreted by Preiss (1992) as outer marine-shelf deposits."
"The Fortress Hill Fm. is sharply overlain by sandstone and conglomerate at the base of the Mount Curtis Tillite (90 m) that may record a lowering of relative sea level and mark a sequence boundary (Preiss et al. 1998)."
"The Mount Curtis Tillite is a sparse diamictite with erratics of pebble to boulder size, some faceted and striated, in massive and laminated, grey-green dolomitic siltstone. Clast lithologies are mostly quartzite, limestone and dolostone, but also include granite and porphyry (Coats & Preiss 1987). Granite boulders attain 3 x 8 m."
"The Mount Curtis Tillite is overlain by the medium-grained, feldspathic Balparana Sandstone (130 m), which contains interbeds and lenses of calcareous siltstone and pebble conglomerate."
"The Balparana Sandstone is disconformably overlain by the Wilpena Group. The main source for the glaciogenic deposits may have been the Curnamona Province to the present east  and possibly the now-buried Muloorina Ridge immediately north of the North Flinders Zone (Preiss 1987)."
"The lower-most, laminated siltstone facies of the Fortress Hill Fm. shows progressively greater amounts of scattered, ice-rafted granules and pebbles. The shallow-water Gumbowie Arkose (45  90 m) disconformably overlies these early deposits at a possible sequence boundary and is conformably succeeded by the Pepuarta Tillite (120  197 m), which is a sparse diamictite with scattered clasts up to boulder size in massive and laminated, grey calcareous siltstone. Faceted and striated boulders reach 2.5 m in diameter. Clast lithologies include pink granite, granite gneiss, grey porphyry, quartz-granule conglomerate, various quartzites, and vein quartz. The siltstone facies with scattered large clasts of extrabasinal provenance implies deposition from floating ice."
"The widespread Grampus Quartzite (60 m) disconformably overlies the Pepuarta Tillite, possibly at a sequence boundary defining a third genetic sequence of the Yerelina Subgroup (Preiss et al. 1998)."
"It is conformably overlain by the laminated to cross-laminated, calcareous, pale grey Ketchowla Siltstone (271 m) (Preiss 1992). The Ketchowla Siltstone contains scattered ice-rafted granules, pebbles and boulders up to 1 m across, and is ascribed by Preiss (1992) to outer marine-shelf deposition under generally waning glacial conditions. It is overlain disconformably by the Nuccaleena Fm., with any Ketchowla Siltstone deposited in the North Flinders Zone having been completely removed by erosion at this sequence boundary (Preiss 2000)."
"The outer marine-shelf successions of the Fortress Hill Fm. and Ketchowla Siltstone record the waxing and waning of glacial conditions, respectively. The Pepuarta Tillite and the correlative Mount Curtis Tillite mark the glacial maximum of the Elatina glaciation (Preiss et al. 1998)."
"A UPb age of 657  17 Ma was obtained for a zircon grain of uncertain provenance from the Marino Arkose Member of the underlying Upalinna Subgroup (Preiss 2000). Re  Os dating gave an age of 643.0  2.4 Ma for black shale from the Tindelpina Shale Member at the base of the Tapley Hill Fm., which overlies glacial deposits of Sturtian age in the Adelaide Geosyncline (Kendall et al. 2006). Zoned igneous zircon from a tuffaceous layer near the top of the Sturtian-age glaciogenic succession gave a SHRIMP U  Pb	age of c. 658 Ma (Fanning & Link 2006). Mahan et al. (2007) reported a ThUtotal Pb age of 680  23 Ma for euhedral laths of monazite, interpreted as authigenic, from the Enorama Shale of the Upalinna Subgroup."

# Nantuo glaciation
The Nantuo glaciation apparently occurred 654  3.8 Ma.

# Ice Brook glaciation
The Ice Brook glaciation apparently spans 651 to 659 Ma.

# Ghaub glaciation
"Dropstone-bearing glaciomarine sedimentary rocks of the Ghaub Formation within metamorphosed Neoproterozoic basinal strata (Swakop Group) in central Namibia contain interbedded mafic lava flows and thin felsic ash beds. U-Pb zircon geochronology of an ash layer constrains the deposition of the glaciomarine sediments to 635.5  1.2 Ma, providing an age for what has been described as a Marinoan-type glaciation. In addition, this age provides a maximum limit for the proposed lower boundary of the terminal Proterozoic (Ediacaran) system and period. Combined with reliable age constraints from other Neoproterozoic glacial unitsthe ca. 713 Ma Gubrah Member (Oman) and the 580 Ma Gaskiers Formation (Newfoundland)these data provide unequivocal evidence for at least three, temporally discrete, glacial episodes during Neoproterozoic time with interglacial periods, characterized by prolonged positive 13C excursions, lasting at most 5080 m.y."
"Dropstones are ubiquitous within the finer-grained (Ghaub) lithofacies, and their presence, along with the facies context for subglacial and near grounding-line deposition, indicates a glacigenic origin for the Ghaub Formation, despite its subtropical paleolatitude and distal foreslope setting."

# Marinoan
Apparently the major glacial period the Marinoan occurred during the Cryogenian.
A similar period of rifting, to the break up along the margins of Laurentia, at about 650 Ma occurred with the deposition of the Ice Brook Formation in North America, contemporaneously with the Marinoan in Australia.
The Marinoan glaciation ended approximately 635 Ma, at the end of the Cryogenian.
The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 635 Ma, where the end of the glaciation may have been sped by the release of methane from equatorial permafrost.
The name is derived from the stratigraphic terminology of the Adelaide Geosyncline (Adelaide Rift Complex) in South Australia and taken from the Adelaide suburb of Marino to subdivide the Neoproterozoic rocks of the Adelaide area and encompass all strata from the top of the Brighton Limestone to the base of the Cambrian. The corresponding time period, referred to as the Marinoan Epoch, spanned from the middle Cryogenian to the top of the Ediacaran and included a glacial episode within the Marinoan Epoch, the Elatina glaciation, after the 'Elatina Tillite' (now Elatina Formation). The term Marinoan glaciation came into common usage because it was the glaciation that occurred during the Marinoan Epoch.
The term Marinoan glaciation was applied globally to any glaciogenic formations assumed to correlate with the Elatina glaciation in South Australia. The Elatina glaciation in South Australia and the Gaskiers also occurs within the wide ranging Marinoan Epoch.
The Earth may have underwent a number of glaciations during the Neoproterozoic era.
There were three (or possibly four) significant ice ages during the late Neoproterozoic, periods of nearly complete glaciation of Earth are often referred to as "Snowball Earth", where it is hypothesized that at times the planet was covered by ice 1  (Expression error: Unexpected round operator. ) thick.
During the Marinoan glaciation, characteristic glacial deposits indicate that Earth suffered one of the most severe ice ages in its history, where glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.
The melting of the Snowball Earth is associated with greenhouse warming due to the accumulation of high levels of carbon dioxide in the atmosphere.
Glacial deposits in South Australia are approximately the same age (about 630 Ma), confirmed by similar stable carbon isotopes, mineral deposits (including sedimentary barite), and other unusual sedimentary structures.
Two diamictite-rich layers in the top 1 km (0.621371192 mi) of the 7 km (4.349598344 mi) Neoproterozoic strata of the northeastern Svalbard archipelago represent the first and final phases of the Marinoan glaciation.
The Marinoan "is separated from the Sturtian by a thick succession of sedimentary rocks containing no evidence of glaciation.  This glacial phase could correspond to the recently described Ice Brooke formation in the northern Canadian Cordillera."

# Gucheng
The Gucheng is apparently comparable to the Marinoan.

# Jiangkou
The Jiangkou spans the Chang'an through the Gucheng.

# Chang'an
The Chang'an occurred about 715.9  2.8 Ma.

# Port Askaig glaciation
The Port Askaig glaciation is above the Elbobreen-Wilsonbreen glaciation.

# Elbobreen-Wilsonbreen glaciation
The Elbobreen-Wilsonbreen glaciation in Svalbard occurred c. 720 Ma.

# Cryogenian ice age
"Late Proterozoic glaciogenic deposits are known from all the continents. They provide evidence of the most widespread and long-ranging glaciation on Earth."
Def. "a geologic period within the Neoproterozoic era from about  to 600 million years ago" is called the Cryogenian.
The end of the period also saw the origin of heterotrophic plankton, which would feed on unicellular algae and prokaryotes, ending the bacterial dominance of the oceans.
Apparently two major glacial periods occurred during the Cryogenian: the Marinoan and the Sturtian, formerly considered together as the Varanger glaciations, from their first detection in Norway's Varanger Peninsula.
The Cryogenian is a geologic period that lasted from 720-635 Mya.
The Cryogenian period was ratified in 1990 by the International Commission on Stratigraphy.
Several glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers reaching sea level in low paleolatitudes.
Glaciers extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.
The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply frozen planetary oceans called "Snowball Earth".
"Most Neoproterozoic glacial deposits accumulated as glacially influenced marine strata along rifted continental margins or interiors."
Fossils of testate amoeba (or Arcellinida) first appear during the Cryogenian period.
During the Cryogenian period, the oldest known fossils of sponges, Otavia the first sponge-like animal (and therefore animals) make an appearance.
New groups of life evolved during this period, including the red algae and green algae, stramenopiles, ciliates, dinoflagellates, and testate amoeba.
The base of the period is defined by a fixed rock age, that was originally set at 850 million years, but changed in 2015 to 720 million years.

# Sturtian
The Sturtian glaciation was a glaciation, or perhaps multiple glaciations, during the Cryogenian Period.
The break up along the margins of Laurentia at about 750 Ma occurs at about the same time as the deposition of the Rapitan Group in North America, contemporaneously with the Sturtian in Australia.
The Sturtian glaciation persisted from 720 to 660 million years ago.
A Sturtian age was assigned to the Numees diamictites.
The duration of the Sturtian glaciation has been variously defined, with dates ranging from 717 to 643 Ma. Or, the period spans 715 to 680 Ma.
"Glaciogenic rocks figure prominently in the Neoproterozoic stratigraphy of southeastern Australia and the northern Canadian Cordillera]. The Sturtian glaciogenic succession (c. 740 Ma) unconformably overlies rocks of the Burra Group."
The Sturtian succession includes two major diamictite-mudstone sequences, which represent glacial advance and retreat cycles, stratigraphically correlated with the Rapitan Group of North America.
The Sturtian is named after the Sturt River Gorge, near Bellevue Heights, South Australia.
Reusch's Moraine in northern Norway may have been deposited during this period.

# Numees
The Numees has a Sturtian age.

# Tereeken
The Tereeken occurred < 727  8 Ma.

# Rapitan glaciation
"The Rapitan Group (Cryogenian) of western Canada is similar to the Chuos Formation in both lithofacies and basin context, representing deposition in a paraglacial rift basin (Young, 1976; Eisbacher, 1985). An iron-rich, dropstone-bearing unit (the Sayunei Formation) is capped by a diamictite unit (the Shezal Formation) (Hoffman and Halverson, 2011). Measured sections (Fig. 3 of Eisbacher, 1985) illustrate that the most complete successions have a basal ferruginous shale sequence bearing occasional dropstones. These deposits pass gradationally upward, via 540 m jaspillite-hematite ironstone at the top of the Sayunei Formation, into diamictites. The ironstone is laterally persistent in depocentres (Eisbacher, 1985). Sea-ice removal may have triggered local grounding line advance, resulting in deposition of the Shezal Formation (Eisbacher, 1985): Hoffman and Halverson (2011) recognised this as a possible catalyst for ironstone precipitation. In addition to an abiotic rusting of the seas model, a biologically-mediated mechanism was also considered. Once the ice cover thinned and finally disappeared, anoxic and oxygenic photosynthesis could have precipitated Fe2O3-precursor from anoxic Fe(II)-rich basin waters (Hoffman et al., 2011).  Such a biogenic mechanism for ironstone precipitation, via for example photosynthetic stromatolites, would be in agreement with our observations in Namibia."

# Port Nolloth
The Port Nolloth extends from the Kaigas formation upwards to the Murmees.

# Kaigas formation
The Kaigas glaciation was a hypothesized snowball earth event in the Neoproterozoic Era, preceding the Sturtian glaciation inferred based on the interpretation of Kaigas Formation conglomerates in the stratigraphy overlying the Kalahari Craton as correlative with pre-Sturtian Numees formation glacial diamictites; however, the Kaigas formation was later determined to be non-glacial, and a Sturtian age was assigned to the Numees diamictites.

# Vendian
The Vendian occurred about 740 Ma.

# Chuos glaciation
"The "grainstone prism" was a major submarine drainage system localized in a paleovalley carved during the Chuos glaciation, which was occupied by a transverse ice-stream that cut the Duurwater trough during the Ghaub glaciation."
"Despite early indications of two distinct glaciations (Kroner and Rankama, 1972; Guj, 1974), the prevailing view of a single glaciogenic horizon that could serve as a basis for correlation throughout the Otavi Group (Hedberg, 1979; SACS, 1980; Miller, 1997) led to the former "Otavi Tillite" (le Roex, 1941) being assigned to the Chuos Formation of Gevers (1931), a glaciogenic diamictite with an intimately associated banded iron formation that is widely distributed within the orogens bounding the Otavi platform (Martin, 1965a, 1965b). More recently, two glaciations have been firmly established in the Otavi Group (Hoffmann and Prave, 1996; Hoffman et al., 1998a; Hoffman and Halverson, 2008), the older Chuos Formation and a younger glaciation represented by the "Otavi Tillite" (le Roex, 1941), and its correlative carbonate-clast breccia unit of the Fransfontein homocline (Frets, 1969; Guj, 1974). Hoffmann and Prave (1996) renamed this younger glaciogenic unit the Ghaub Formation, after a farm near the section originally described by le Roex (1941)."
The "Chuos glaciation occurred during a period of active faulting, which is reflected by the diversity of its debris and a low-angle (1.5) structural unconformity  that cuts out ~2 km of strata (Hoffman et al., 1998a)."
The Rasthof Formation  the postglacial cap carbonate overlying the Chuos diamictite".
Below the Chuos glaciation is the Naauwpoort dated at 746  2 Ma giving an upper age limit to the base of the Chuos.
"UPb ages from the Askevold Formation (Hoffman et al., 1996)  are from further west: this formation is not preserved beneath the Chuos Formation in ."
"Earlier analyses of the Chuos Formation concentrated on meta-sediments in the vicinity of its type section south of Windhoek and in the Damara Belt (Gevers, 1931; de Kock and Gevers, 1933; Martin et al., 1985; Henry et al., 1986; Badenhorst, 1988). More modern stratigraphic analyses several hundred kilometres to the west of the Otavi Mountain Land demonstrate that the Chuos Formation is cradled in a rift-related, fault bounded palaeotopography (Hoffman and Halverson, 2008), and hence its substrate also changes along strike, across the southern flank of the Owambo Basin. In the area of Ghaub and Varianto farms, the study interval comprises the Nabis Sandstone Formation of the Nosib Group, overlain by the Chuos Formation and succeeded by the Berg Aukas Formation . This particular area has been mapped at the 1:250,000 scale (Geological Survey of Namibia, 2008). Age constraints include 747  2 Ma from the	Naauwport volcanics, locally beneath the Chuos Formation (Hoffman et al., 1996) and 635  1 Ma from ash beds in the younger Ghaub Formation (Hoffmann et al., 2004)."

# Beiyixi glaciaton
The Beiyixi is later than 755 Ma.

# Kundelungu
The Kundelungu is dated to 765  5 Ma.

# Sinian
The Sinian spans approximately 800 to 542 Ma.

# Hadrynian
The Hadrynian (North America) spans 850 to 542 Ma.

# Namibian
The Namibian (South Africa) spans 900 to 542 Ma.

# Mesoproterozoic
Def. "a geologic era within the Proterozoic eon; comprises the Calymmian, Ectasian and Stennian periods from about 1600 to 900 million years ago, when the Rodinia supercontinent was formed" is called the Mesoproterozoic.

# Tonian
The Tonian spans 1000 to 850 Ma.
The first putative metazoans (animal) fossils dated to the late Tonian (c. 800 Mya), e.g., the Otavia antiqua, which has been described as a sponge, where dating is consistent with molecular data recovered through genetic studies on modern metazoan species; more recent studies have concluded that the base of the animal phylogenetic tree is in the Tonian.
Def. "a geologic period within the Neoproterozoic era from about 1000 to 850 million years ago" is called the Tonian.

# Karatau
The Karatau spans 1100 to 800 Ma.

# Stenian
The Stenian spans 1200 to 1000 Ma.
Def. the "final geologic period in the Mesoproterozoic Era, from 1200 million to 1000 million years ago" is called the Stenian.
The "Mount John Shale Member of the overlying Wade Creek Sandstone has been dated (Rb/Sr method) at 1.1280.1  109 yr BP1."

# Adelaidean
The Adelaidean (Australia) spans 1300 to 542 Ma.

# Ectasian
Def. "a geologic period within the Mesoproterozoic era from about 1400 to 1200 million years ago" is called the Ectasian.

# Calymmian
Def. "a geologic period within the Mesoproterozoic era from about 1600 to 1400 million years ago" is called the Calymmian.

# Helikian
The Helikian (North America) spans 1600 to 850 Ma.

# Paleoproterozoic
Def. "a geologic era within the Proterozoic eon; comprises the Siderian, Rhyacian, Orosirian and Statherian periods from about 2500 to 1600 million years ago, when cyanobacteria increased the amount of oxygen in the atmosphere and changed life on Earth for ever" is called the Paleoproterozoic.

# Jinningian
The Jinningian (China) spans 1750 to 800 Ma.

# Carpentarian
The Carpentarian spans 1800 to 1300 Ma.
"The 1400 to 1500 My old Kombolgie Formation  of the MacArthur Basin of the Northern Territory overlies or has overlain unconformity-type uranium deposits".
"A study of clay minerals isolated from carbonate rocks of the McMinn Formation provides an isochron age of 1429  31 Ma and thus the age for cessation of the Proterozoic McArthur basin sedimentation."
"A second sequence of measurements on a homogeneous dolomite siltstone ca. 23 km southeast of the McArthur River (H.Y.C.) Pb-Zn deposits yields an Rb-Sr age of 1537  52 Ma for the Upper Barney Creek Formation in broad agreement with recent age determinations on feldspar beds of this horizon."
The "sediments in the McArthur basin (the type locality of the Carpentarian) were deposited between 1800-1400 Ma."
The "microflora of blue-green and green or red algal affinities is from chertified stromatolitic dolomites of the Bungle Bungle Dolomite which outcrops in the Osmond Range of Western Australia."
The Bungle Bungle Dolomite  is considerably  and that an age of about 1.5109 yr for the microbiota  is consistent with the data available."
Radiometric dating has shown that the Kattsund-Koster dyke swarm is about 1421 million years old and the dyke swarm may be related to extensional tectonics.
In the image on the right, the oldest rock is a gray sediment gneiss that was deformed, heated, and partly melted about 1,560 million years ago in the Gothic mountain range (no melted fragments visible in the rock). In its final phase, a gabbromagma penetrated, a mixed rock formed; rounded balls of dark gabbro in light gray gneiss, or bright networks of molten sediment gneiss in the gabbro. A younger gray-white pegmatite passes through the mixed rock at the lighthouses. Walks of the even younger black Koster diabase cut through all rocks.

# Statherian
Def. "a geologic period within the Paleoproterozoic era from about 1800 to 1600 million years ago" is called the Statherian.

# Orosirian
Def. "a geologic period within the Paleoproterozoic era from about 2050 to 1800 million years ago" is called the Orosirian.
The "isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada,  record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as  0.8. Such negative values occurring shortly after the  GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible.  A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition."
On the right is an image of the Vredefort crater, located at 270'0"S 2730'0"E, the largest verified impact crater on Earth, more than 300 kilometres (Expression error: Missing operand for *. ) across when it was formed.

# Mokolian
The Mokolian (South Africa) spans 2050 to 900 Ma.

# Animikean
Animikean General Stage is from 2225 to 1400 Ma.

# Rhyacian
Def. "a geologic period within the Paleoproterozoic era from about 2300 to 2050 million years ago" is called the Rhyacian.

# Makganyene glaciation
"In its eastern domain, the Transvaal Supergroup of South Africa contains two glacial diamictites, in the Duitschland and Boshoek Fms. The base of the Timeball Hill Fm., which underlies the Boshoek Fm., has a Re-Os date of 2,316  7 My ago (13). The Boshoek Fm. correlates with the Makganyene diamictite in the western domain of the Transvaal Basin, the Griqualand West region. The Makganyene diamictite interfingers with the overlying Ongeluk flood basalts, which are correlative to the Hekpoort volcanics in the eastern domain and have a paleolatitude of 11  5 (14). In its upper few meters, the Makganyene diamictite also contains basaltic andesite clasts, interpreted as being clasts of the Ongeluk volcanics. The low paleolatitude of the Ongeluk volcanics implies that the glaciation recorded in the Makganyene and Boshoek Fms. was planetary in extent: a snowball Earth event (15). Consistent with earlier whole-rock PbPb measurements of the Ongeluk Fm. (16), the Hekpoort Fm. contains detrital zircons as young as 2,225  3 My ago (17), an age nearly identical to that of the Nipissing diabase in the Huronian Supergroup."
The "Makganyene glaciation begins some time after 2.32 Ga and ends at 2.22 Ga, the three Huronian glaciations predate the Makganyene snowball."

# Huronian ice age
The Huronian Ice Age is known "mainly from Canada and the United States in North America, where dated rocks range from 2500 to 2100 million years old."
"The period from 2.45 Ga until some point before 2.22 Ga saw a series of three glaciations recorded in the Huronian Supergroup of Canada (11) . The final glaciation in the Huronian, the Gowganda, is overlain by several kilometers of sediments in the Lorrain, Gordon Lake, and Bar River formations (Fms.). The entire sequence is penetrated by the 2.22 Ga Nipissing diabase (12); the Gowganda Fm. is therefore significantly older than 2.22 Ga."
"The three Huronian glacial units, penetrated and capped by the Nipissing diabase, predate the Makganyene diamictite in the Transvaal. The uppermost Huronian glacial unit, the Gowganda Fm., is overlain by hematitic units, perhaps reflecting a rise in O2. The basal Timeball Hill Fm. contains pyrite with minimal  MIF (26), whereas the upper Timeball Hill Fm., which we suggest is correlative to the Lorrain or Bar River Fms., contains red beds. The Makganyene diamictite records a low-latitude, snowball glaciation (29), perhaps triggered by the destruction of a CH4 greenhouse. It is overlain by the Kalahari Mn Field in the Hotazel Fm., the deposition of which requires free O2."
"In its eastern domain, the Transvaal Supergroup of South Africa contains two glacial diamictites, in the Duitschland and Boshoek Fms. The base of the Timeball Hill Fm., which underlies the Boshoek Fm., has a Re-Os date of 2,316  7 My ago (13). The Boshoek Fm. correlates with the Makganyene diamictite in the western domain of the Transvaal Basin, the Griqualand West region. The Makganyene diamictite interfingers with the overlying Ongeluk flood basalts, which are correlative to the Hekpoort volcanics in the eastern domain and have a paleolatitude of 11  5 (14). In its upper few meters, the Makganyene diamictite also contains basaltic andesite clasts, interpreted as being clasts of the Ongeluk volcanics. The low paleolatitude of the Ongeluk volcanics implies that the glaciation recorded in the Makganyene and Boshoek Fms. was planetary in extent: a snowball Earth event (15). Consistent with earlier whole-rock PbPb measurements of the Ongeluk Fm. (16), the Hekpoort Fm. contains detrital zircons as young as 2,225  3 My ago (17), an age nearly identical to that of the Nipissing diabase in the Huronian Supergroup. As the Makganyene glaciation begins some time after 2.32 Ga and ends at 2.22 Ga, the three Huronian glaciations predate the Makganyene snowball."
"In contrast to the Makganyene Fm., the three Huronian diamictites are unconstrained in latitude. Poles from the Matachewan dyke swarm, at the base of the Huronian sequence, do indicate a latitude of 5.5 (18), but 2 km of sedimentary deposits separate the base of the Huronian from the first glacial unit (19), which makes it difficult to draw conclusions about the latitude of the glacial units based on these poles. Low latitude poles in the Lorrain Fm. (20, 21), which conformably overlies the Gowganda diamictite, are postdepositional overprints (22)."
"Some of the earliest continental red beds were deposited in the Firstbrook member of the Gowganda Fm. and in the Lorrain and Bar River Fms. in Canada, as well as in the upper Timeball Hill Fm. in South Africa. The basal Timeball Hill Fm. has recently been dated at 2,316  7 My ago (13). In our proposed correlation, all of the red bed-bearing units were deposited after the last Huronian glaciation and before the Makganyene glaciation. The formation of the red beds could involve local O2, although it does not demand it (34). Syngenetic pyrite from the basal Timeball Hall Fm. shows only slight MIF of S (26), consistent with the initiation of planetary oxygenation or enhanced glacial activity."

# Siderian
Def. "a geologic period within the Paleoproterozoic era from about 2500 to 2300 million years ago" is called the Siderian

# Aphebian
The Aphebian spans 2500 to 1600 Ma. The Penrhyn Group is a part of the Aphebian.
The Byam Martin Mountains are made up of Archean-Aphebian igneous crystalline rock and Proterozoic metasedimentary and metamorphic rock, such as gneiss with sharp peaks and ridges, divided by deep glacier-filled valleys are typical features in the range.
Nain Archean gneiss is overlain to the north of the community of Nain, Newfoundland and Labrador by the undeformed Ramah Group shale, sandstone and quartzite from the Aphebian.

# Transvaal
The Transvaal is approximately 2700 Ma.

# Neoarchean
Def. "a geologic era within the Archaean eon from about 2800 to 2500 million years ago" or the "era from 2,800 Ma to 2,500 Ma" is called the Neoarchean.

# Pongola glaciation
The Pongola glaciation is dated "at 2.9 Ga". It extends to 2780 Ma.
"The oldest known midlatitude glaciation, recorded in the Pongola Supergroup diamictite, occurred at 2.9 Ga (10)."

# Randian
The Randian spans about 3000 to 2500 Ma.
"The Witwatersrand Basin formed over a period of 360 Ma between 3074 and 2714 Ma. Pulses of sedimentation within the sequence and its precursors were episodic, occurring between 3086-3074 Ma (Dominion Group), 2970-2914 Ma (West Rand Group) and 2894-2714 Ma (Central Rand Group). Detritus was derived from a mixed granite-greenstone source of two distinct ages; the first comprises Barberton-type greenstone belts and granitoids > 3100 Ma old, and the second consists of the greenstone belt-like Kraaipan Formation and associated granitoids  3100 Ma old."
"Metamorphism of the Witwatersrand Basin occurred at ca. 2500, 2300 and 2000 Ma. The first two events coincided with the progressive loading of the basin by Ventersdorp and Transvaal cover sequences, whereas the last reflects intrusion of the Bushveld Complex and/or the Vredefort catastrophism."
"The Kaapvaal Craton is the name given to the ancient segment of continental crust which formed in southern Africa between about 3.7 to 2.7 Ga. Much of this continental nucleus actually formed prior to 3.1 Ga by the formation of an extensive granitoid basement and amalgamation with arc-like oceanic terranes represented by mafic/ultramafic volcanics and associated sediments (De Wit et al., 1992)."
"The minimum age of Witwatersrand deposition is provided by the age of the Ventersdorp lavas which immediately overlie the sequence over wide areas. The lower basaltic portion of these lavas has been dated at 2714  8 Ma, whereas higher up in the succession quartz porphyries have been dated at 2709  4 Ma ."
"The Crown lava, which occurs just beneath the West Rand- Central Rand Group transition about half way up the sequence, has been provisionally dated at 2914  8 Ma , a figure which provides approximate maximum and minimum constraints on Central Rand and West Rand Group deposition, respectively. Detrital zircon grains from the Orange Grove quartzite and the Promise reef, both in the West Rand Group, range in age between 3330  5 and 2970  3 Ma; the latter date represents a maximum constraint on the depositional age of the West Rand Group, with the minimum age determined by the Crown lava at 2914 Ma ."
"Detrital zircon grains from conglomerate reefs in the auriferous Central Rand Group become progressively younger upwards in the stratigraphy and the youngest grains occur in the Elsburg and Ventersdorp Contact (VCR) reefs (2894  10 and 2780  5 Ma, respectively). The VCR must, therefore, have been laid down sometime after 2780 Ma ago, but before or at 2714 Ma which is the age of the Ventersdorp lavas (Armstrong et al., 1991)."
"Dominion sedimentation occurred over a relatively brief interval some time after 3086 Ma but before 3074 Ma ago."
"West Rand Group deposition commenced subsequent to 2970 Ma and, consequently, a significant hiatus of some 100 million years appears to exist between the Dominion and West Rand Groups. The latter pulse of sedimentation was largely complete by 2914 Ma, when the Crown lava was extruded, The onset of Central Rand Group deposition commenced after 2914 Ma but may have started as late as 2894 Ma, the age of the youngest detrital zircon grain in the Elsburg reef ."
"The Gaborone granite and Kanye rhyolites were emplaced at 2785  Ma in an interlude which may have stimulated Turffontein Subgroup deposition (i.e the upper portion of the auriferous Central Rand Group; ), although no detrital zircons of this age have yet been found in the latter sequence."

# Mesoarchean
Def. "a geologic era within the Archaean eon from about 3200 to 2800 million years ago; stromatolites have existed from this time" or the "era from 3,200 Ma to 2,800 Ma" is called the Mesoarchean.

# Paleoarchean
Def. "a geologic era within the Archaean eon from about 3600 to 3200 million years ago; the first aerobic bacteria appeared at this time" or the "era from 3,600 Ma to 3,200 Ma" is called the paleoarchean.

# Archean
Archaean is an alternate spelling of Archean.
Def. "the geologic eon from about 3,800 to 2,500 million years ago; comprises the Eoarchean, Paleoarchean, Mesoarchean and Neoarchean eras; marked by an atmosphere with little oxygen, the formation of the first continents and oceans and the emergence of simple life" or the "eon from 2,500 Ma to 4,000 Ma" is called the Archaean, or Archean.
"About 3 billion years ago, in the Archean eon, the emergence of plate tectonics moved thin and small rafts of rocks at a rate much faster than they do today. Over time, the volcanic islands butted together into large blocks of continental crust, with most of the action (in what is todays Canada) starting around the Red Lake area, a prolific gold-mining camp in northwest Ontario."
"During the Archean and Proterozoic, the cratons  that would soon form the core of Canada were stitched together along vast mountain chains. The rocks, which were made up mostly of greenstone belts and intrusives, were variably metamorphosed and eroded, and the margins of the continents were blanketed with sediments. Orogenic gold mineralization, banded-iron formations, magmatic nickel-copper, volcanogenic massive sulphide and sedex deposits predominated. Uranium mineralization fluxed into major structures during near the end of the Proterozoic."
Def. the "period of time determined to exist prior to 2.5 billion  years ago" is called the Archaeozoic or Archeozoic.

# Isuan
The Isuan spans approximately 3800 to 3500 Ma.
Isuan Period  38103490 MYA  named after the Isua Greenstone Belt.
"The TTG basement of the Ancient Gneiss Complex of Swaziland contains minor relics which are as old as 3650-3500 Ma (Compston and Kroner, 1988) and, therefore, predate the Barberton greenstone belt."

# Swazian
The Swazian spans approximately 4000 to 3000 Ma.
The Swazian is a poorly defined geological stage in South Africa extending from about four billion years ago to 3 billion years ago, encompassing some of the Hadean and much of the Archean on the Geologic time scale. Other scales assign the Swazian to parts of the Paleoarchean and Mesoarchean, 3.5 to 2.8 billion years ago.
"The best exposed portion of the Archaean basement on the Kaapvaal Craton is the Barberton region and Swaziland to the east of the Witwatersrand Basin , where detailed study over several decades has provided an extensive data base for the study of early crustal evolution. The region is now known to comprise a collage of amalgamated terranes each of which consists of tonalite-trondhjemite-granodiorite (TTG) gneisses and an associated assemblage of metavolcano-sedimentary supracrustal rocks (Lowe, 1994). These terranes were mainly formed at ca. 3480-3440 and 3250-3220 Ma (Armstrong et al., 1990; De Ronde and De Wit, 1994; Kamo and Davis, 1994), although isolated remnants of TTG material and associated metavolcanics in the southwestern portion of the belt are as old as 3550-3530 Ma (Kroner et al., 1991 )."
The "Westerdam granite (3086  3 Ma) was emplaced just prior to Dominion sedimentation, the Coligny granite (3031  11 Ma) was emplaced prior to West Rand Group deposition and the Schweizer-Reneke granite (2880  2 Ma) may have preceded Central Rand Group sedimentation ."

# Azoic
Def. destitute "of any vestige of organic life, or at least of animal life; anterior to the existence of animal life; formed when there was no animal life on the globe" is called the azoic.
The Azoic "stands as the first  in geologic history, whether science can point out unquestionably the rocks of that age or not." When fossils had been found in strata which had previously been classified as Azoic, the boundary was simply moved lower. "Such changes are part of the progress of the science."

# Hypozoic
Def. "older than the lowest rocks which contain organic remains" is called hypozoic.
"In Scandinavia, as well as along the Alps, and Grampians, hypozoic strata are predominant, while mica schist and gneiss are rare in the Harz, Cornwall, and Wales."

# Eoarchean
Def. "a geologic era within the Archaean eon from about 4600 to 3600 million years ago; the first single-celled life began at this time" or the "era from 4,000 Ma to 3,600 Ma" is called the Eoarchean.
"Greenland greenlandite is part of a 3.8 billion year old, highly metamorphosed succession of rocks. These represent the oldest known supracrustal rocks on Earth (the oldest crustal Earth rocks include 4.03 billion year old Acasta Gneiss, 4.28 b.y. rocks from the eastern Hudson Bay area, and 4.45-4.55 b.y. rocks in the subsurface of Baffin Island, Canada)."
The rock, in the images at left and right, a tonalite gneiss, of the Acasta Gneiss exposed on an island about 300 kilometres north of Yellowknife in the Slave craton in Northwest Territories, Canada, was metamorphosed 3.58 to 4.031 billion years ago and is the oldest known intact crustal fragment on Earth.
The metamorphic rock exposed in the outcrop of the Acasta Gneiss Complex, northwestern Canada, was previously a granitoid that formed 4.2 billion years ago, an age based on radiometric dating of zircon crystals at 4.2 Ga.

# Hadean
Def. "the geologic eon from about 4,600 to 3,800 million years ago; marked by the formation of the solar system, a stable Earth-Moon orbit and the first rocks" or the "eon before 4,000 Ma" is called the Hadean.

# Locations on Earth
At the Inversand quarry, "Located in South Jersey, the cradle of dinosaur paleontology, the quarry in Mantua Township, N.J., contains thousands of fossils dating back 65 million years."

# Hypotheses
- Each time frame or span of time in geochronology has at least one dating technique.
- Late Jurassic and Upper Jurassic are different time frames.
- The overall size ofor efficiency of carbon export fromthe biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma).

# Acknowledgements
The content on this page was first contributed by: Henry A. Hoff.
Initial content for this page in some instances came from Wikiversity.