Geochronology
Editor-In-Chief: Henry A. Hoff
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).[1] 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 [b2k] 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 [...]."[2]
Stratigraphy
Dates have been assigned to specific geologic stratigraphy frames, columns, or columnar units.
Geochronologic time frames
| Name (English)[3] | base/start (Ma)[4] | top/end (Ma)[4] | status | subdivision of | usage | named after | author, year |
|---|---|---|---|---|---|---|---|
| Adelaidean | 1,300 | 542 | age | Proterozoic | Australia | Adelaide | |
| Aimchanian | 1100 | age | Proterozoic | Siberia | |||
| Algonkian | 543 | age | Proterozoic | international | Algonquian native peoples of Canada | ||
| Amazonian | ~1,800 | present | Martian epoch | Martian epoch | Mars | Amazonis Planitia | |
| Animikean | 2,225 | 1,400 | age | Proterozoic | North America (obsolete) | ||
| Aphebian | 2500 | 1600 | age | Proterozoic | North America | ||
| Archean | none | 2,500 | eon | Precambrian | ICS | ||
| Azoic | eon | Precambrian | |||||
| Baikalian | 850 | 650 | age | Proterozoic | Siberia | Lake Baikal | |
| Basin Groups 1-9 | 4,150 | 3,850 | subperiod | Prenectarium | Moon (unofficial) | groups of impact basins | |
| Brioverian | ~680 | ~600 | age | Neoproterozoic | Armorican Massif, France | ||
| Burzyan | 1,400 | 1,375 | age | Proterozoic | Russia | ||
| Calymmian | 1,600 | 1,400 | period | Proterozoic | ICS | ||
| Carpentarian | 1,800 | 1,300 | age | Proterozoic | Australia | Gulf of Carpentaria | |
| Cryogenian | 850 | 635.5 ± 1.2[5] | period | Proterozoic | ICS | frozen beginning | |
| Cryptic | 4,567 | 4,150 | epoch | Prenectarian | Moon (unofficial) | hidden | |
| Early Imbrian | 3850 | 3800 | period | Moon | Mare Imbrium | ||
| Ectasian | 1,400 | 1,200 | period | Proterozoic | ICS | ||
| Ediacaran | 635.5 ± 1.2[5] | 542.0 ± 1.0 | period | Proterozoic | ICS | Ediacara Hills (Australia) | |
| Eoarchean | none | 3.600 | era | Archean | ICS | ||
| Eratosthenian | 3,200 | 1,100 | period | Moon | Eratosthenes | ||
| Fupingan | 3,100 | 2,600 | age | Archaean | China | ||
| Hadean | none | 4000 | eon | Precambrian | ICS | Hades, hell | Cloud, 1972 |
| Hadrynian | 850 | 542 | age | Neoproterozoic | North America | ||
| Helikian | 1,600 | 850 | age | Proterozoic | North America | ||
| Hesperian | ~3,500 | ~1,800 | Martian epoch | Mars | Hesperia Planum | ||
| Huronian | 2,500 | 1,400 | age | Proterozoic | worldwide (obsolete) | ||
| Imbrian | 3,850 | 3,200 | period | Moon | Mare Imbrium | ||
| Isuan | 3,800 | 3,500 | age | Archaean | Europe | ||
| Jinningian | 1,750 | 800 | age | Proterozoic | China | ||
| Karatau | 1,100 | 800 | age | Proterozoic | Russia | ||
| Luliangian | 2,350 | 1,750 | age | Proterozoic | China | ||
| Mayanan | 1100 | 850 | age | Proterozoic | Siberia | ||
| Mesoarchean | 3,200 | 2,800 | era | Archean | ICS | ||
| Mesoproterozoic | 1,600 | 1,000 | era | Proterozoic | ICS | ||
| Mokolian | 2,050 | 900 | age | Proterozoic | South Africa | ||
| Namibian | 900 | 542 | age | Neoproterozoic | South Africa | Namibia | |
| Nectarian | 3920 | 3850 | period | Moon | Mare Nectaris | ||
| Neoarchean | 2,800 | 2,500 | era | Archean | ICS | ||
| Neoproterozoic | 1,000 | 542.0 ± 1.0 | era | ICS | |||
| Noachian | none | ~3,500 | Martian epoch | Mars | Noachis Terra | ||
| Nullaginian | 2,500 | 1,800 | age | Proterozoic | Australia | ||
| Orosirian | 2,050 | 1,800 | period | Proterozoic | ICS | ||
| Paleoarchean | 3,600 | 3,200 | era | Archean | ICS | ||
| Paleoproterozoic | 2,500 | 1,600 | era | Proterozoic | ICS | ||
| Precambrian | none | 542.0 ± 1.0 | none (before: eon) | worldwide | before the Cambrian | ||
| Prenectarian | 4567 | 3850 | period | Moon | before the Nectarian | ||
| Proterozoic | 2,500 | 542.0 ± 1.0 | eon | ICS | |||
| Randian | 3,000 | 2,500 | age | Archaean | South Africa | ||
| Rhyacian | 2,300 | 2,050 | period | Proterozoic | ICS | ||
| Riphean | 1,650 | 650 | age | Proterozoic | worldwide (obsolete) | ||
| Siderian | 2,500 | 2,300 | period | Proterozoic | ICS | ||
| Sinian | 800 | 542 | age | Neoproterozoic | China | ||
| Statherian | 1,800 | 1,600 | period | Proterozoic | ICS | ||
| Stenian | 1,200 | 1,000 | period | Proterozoic | ICS | ||
| Sturtian | ~730 | age | Neoproterozoic | worldwide, unofficial | |||
| Swazian | 4,000 | 3,000 | age | Archaean | South Africa | ||
| Tonian | 1,000 | 850 | period | Proterozoic | ICS | ||
| Vaalian | 2,500 | 2,050 | age | Proterozoic | South Africa | ||
| Vendian | ~610 | 542.0 ± 1.0 | subera | Proterozoic | worldwide (obsolete) | ||
| Wutaian | 2,600 | 2,350 | age | Archaean-Proterozoic | China | ||
| Yurmatian | 1,375 | 1,100 | age | Proterozoic | Russia |
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."[6]
"Spectral analysis of the [magnetic susceptibility (MS)] record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95–128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from [decimeter (dm)] dm-scale couplets."[6]
"Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time."[6]
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."[7]
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 [Calabrian] 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."[8]
"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."[8]
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."[9]
"Hindeodus parvus is now recognized as the index fossil" occurring in the Zone above the P-T boundary.[9]
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 strike–slip faults (Graciansky et al., 1999)."[6]
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.[10]
"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."[10]
“We don’t know yet [if it dates from the mass extinction], but we are testing this hypothesis by examining the fossils, the sediments and the chemistry.”[11]
"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."[10]
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."[12]
"The GSSP level contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata [in the image on the left] (base of the L. laevigata Zone)."[12]
Precambrian
Def. "the time and geology dated before the Phanerozoic"[13] or the "eon (or supereon) and rock formations dated before 541.0±1.0 million years ago, coinciding with the first appearance of the fossils of hard-shelled animals"[13]
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."[13]
- "The boundary between the Precambrian and the Phanerozoic has been changed from time to time and will be subject to change".[13]
Proterozoic
Def. "the eon from 2,500 Ma to 541.0±1.0 Ma, the beginning of the Phanerozoic, marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life"[14] 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)."[15]
The later Adelaidean includes the Burra and Caliana Groups.[15]
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"[16] 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."[17]
"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 [in the image on the right], 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)."[17]
Def. "a geologic period within the Neoproterozoic era from about 620 to 542 million years ago"[18] 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.[19]
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.[20] Its δ13
C values are really low (pushing 8 ‰), consistent with a period of environmental abnormality.[20] 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.[20]
Varanger glaciation
The Varangian apparently spans 610 to 575 Ma.
Elatina glaciation
{{free media}}"The Elatina glaciation has not been dated directly, and only maximum and minimum age limits of c. 640 and 580 Ma, respectively, are indicated."[21]
"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 [...]."[21]
"Feeder dykes for volcanic rocks near the base of the [Adelaide Geosyncline] 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)."[21]
"No volcanism is known in the region during the Elatina glaciation."[21]
"The Neoproterozoic–early Palaeozoic succession in the Adelaide Geosyncline was deformed by the Delamerian Orogeny at 514 – 490 Ma (Drexel & Preiss 1995; Foden et al. 2006)."[21]
"The Yerelina Subgroup at the top of the Cryogenian Umberatana Group embraces all the glaciogenic formations of the Elatina glaciation (Preiss et al. 1998)."[21]
"The Yerelina Subgroup is unconformably to disconformably overlain by the Ediacaran Wilpena Group."[21]
"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."[21]
"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)."[21]
"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."[21]
"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."[21]
"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)."[21]
"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."[21]
"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)."[21]
"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)."[21]
"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)."[21]
"A U–Pb 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 Th–U–total Pb age of 680 ± 23 Ma for euhedral laths of monazite, interpreted as authigenic, from the Enorama Shale of the Upalinna Subgroup."[21]
Nantuo glaciation
- ↑ stratigraphy.org. International Commission on Stratigraphy 2008. Retrieved 9 March 2009.
- ↑ Mike Walker, Sigfus Johnsen, Sune Olander Rasmussen, Trevor Popp, Jørgen-Peder Steffensen, Phil Gibbard, Wim Hoek, John Lowe, John Andrews, Svante Björck, Les C. Cwynar, Konrad Hughen, Peter Kershaw, Bernd Kromer, Thomas Litt, David J. Lowe, Takeshi Nakagawa, Rewi Newnham and Jakob Schwander (2009). "Formal definition and dating of the GSSP (Global Stratotype Section and Point) for the base of the Holocene using the Greenland NGRIP ice core, and selected auxiliary records" (PDF). Journal of Quaternary Science. 24 (1): 3–17. doi:10.1002/jqs.1227. Retrieved 2015-01-18.
- ↑ Names from local versions of the geologic timescale can often be found in the local language. The English name is usually found by replacing the suffix in the local language for -an or -ian. Examples for "local" suffices are -en (French), -ano (Spanish), -ium (German), -aidd (Welsh) or -aan (Flemish Dutch). The English name "Norian", for example, becomes Noriano in Spanish, Norium in German, Noraidd in Welsh or Norien in French.
- ↑ 4.0 4.1 Time is given in Megaannum (million years BP, unless other units are given in the table. BP stands for "years before present". For ICS-units the absolute ages are taken from Gradstein et al. (2004).
- ↑ 5.0 5.1
- ↑ 6.0 6.1 6.2 6.3 Slah Boulila, Bruno Galbrun, Linda A. Hinnov, Pierre-Yves Collin (January). "High-resolution cyclostratigraphic analysis from magnetic susceptibility in a Lower Kimmeridgian (Upper Jurassic) marl–limestone succession (La Méouge, Vocontian Basin, France)". Sedimentary Geology. 203 (1–2): 54–63. Retrieved 2015-01-27. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ Eustoquio Molina, Laia Alegret, Ignacio Arenillas, José A. Arz, Njoud Gallala, Jan Hardenbol, Katharina von Salis, Etienne Steurbaut, Noël Vandenberghe, and Dalila Zaghbib-Turki (December). "The Global Boundary Stratotype Section and Point for the base of the Danian Stage (Paleocene, Paleogene, "Tertiary", Cenozoic) at El Kef, Tunisia - Original definition and revision" (PDF). Episodes. 29 (4): 263–73. Retrieved 2015-01-19. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ 8.0 8.1 Maria Bianca Cita, Philip L. Gibbard, Martin J. Head, and the ICS Subcommission on Quaternary Stratigraphy (September). "Formal ratification of the GSSP for the base of the Calabrian Stage (second stage of the Pleistocene Series, Quaternary System)" (PDF). Episodes. 35 (3): 388–97. Retrieved 2015-01-18. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ 9.0 9.1 Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao (June). "The Global Stratotype Section and Point (GSSP) of the Permian-Triassic Boundary" (PDF). Episodes. 24 (2): 102–14. Retrieved 2015-01-20. line feed character in
|title=at position 47 (help); Check date values in:|date=, |year= / |date= mismatch(help) - ↑ 10.0 10.1 10.2 Josh L Davis (12 January 2016). Paleontologists Believe They Have Discovered The First Fossil Bed From The Dinosaur Extinction Event Itself. iflscience. Retrieved 16 January 2016.
- ↑ Kenneth Lacovara (12 January 2016). Paleontologists Believe They Have Discovered The First Fossil Bed From The Dinosaur Extinction Event Itself. iflscience. Retrieved 16 January 2016.
- ↑ 12.0 12.1 Shanchi Peng, Loren E. Babcock, Jingxun Zuo, Huanling Lin, Xuejian Zhu, Xianfeng Yang, Richard A. Robison, Yuping Qi, Gabriella Bagnoli, and Yong’an Chen (March). "The Global Boundary Stratotype Section and Point (GSSP) of the Guzhangian Stage (Cambrian) in the Wuling Mountains, Northwestern Hunan, China" (PDF). Episodes. 32 (1): 41–55. Retrieved 2015-01-21. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ 13.0 13.1 13.2 13.3 DCDuring (4 November 2014). "Precambrian". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 2015-02-12.
- ↑ SemperBlotto (31 May 2005). "Proterozoic". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 10 March 2019.
- ↑ 15.0 15.1 K.H. Mahan, B.P. Wernicke, and M.J. Jercinovic (15 January). "Th–U–total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan glacial deposits" (PDF). Earth and Planetary Science Letters. 289 (1–2): 76–86. Retrieved 2015-01-17. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ Neoproterozoic, In: Wiktionary. San Francisco, California: Wikimedia Foundation, Inc. 7 October 2013. Retrieved 13 February 2015.
- ↑ 17.0 17.1 James G. Gehling and Mary L. Droser (March). "Ediacaran stratigraphy and the biota of the Adelaide Geosyncline, South Australia" (PDF). Episodes. 35 (1): 236–46. Retrieved 2015-01-19. Check date values in:
|date=, |year= / |date= mismatch(help) - ↑ SemperBlotto (1 June 2005). "Ediacaran". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 10 March 2019.
- ↑ F. M. Gradstein, Gabi Ogg, Mark Schmitz, The Geologic Time Scale, Elsevier, 2012, p. 428.
- ↑ 20.0 20.1 20.2
- ↑ 21.00 21.01 21.02 21.03 21.04 21.05 21.06 21.07 21.08 21.09 21.10 21.11 21.12 21.13 21.14 21.15 21.16 George E. Williams, Victor A. Gostin, David M. McKirdy, Wolfgang V. Preiss & Phillip W. Schmidt (2011). "The Elatina glaciation (late Cryogenian), South Australia" (PDF). Geological Society, London, Memoirs. 36: 713–721. doi:10.1144/M36.70. Retrieved 13 March 2019.