Difference between revisions of "Geologic time scale" - New World Encyclopedia

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The '''geologic time scale''' is used by [[geologist]]s and other scientists to describe the timing and relationships between events that have occurred during the [[history]] of the [[Earth]].  The tables of geologic periods presented here are in accordance with the dates and [[nomenclature]] proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geologic Survey.
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[[Image:Geologic clock.jpg|thumb|right|300px|This clock representation shows some of the major units of geological time and definitive events of Earth history.]]
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The '''geologic time scale''' is used by [[geology|geologist]]s and other scientists to map the timing and relationships between events that have occurred during the [[history]] of the [[Earth]].  
  
Based on current geological evidence, the Earth is estimated to be about 4570 million years old (4570 "Ma"). The geologic or ''deep time'' of Earth's past has been organized into various units according to events that took place in each period. Different spans of time on the time scale are usually delimited by major [[geology|geologic]] or [[paleontology|paleontologic]] events, such as [[mass extinction]]s. For example, the boundary between the [[Cretaceous]] period and the [[Palaeogene]] period is defined by the [[Cretaceous-Tertiary extinction event|extinction event]] that marked the demise of the [[dinosaur]]s and of many marine [[species]].  
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Based on [[radiometric dating]] techniques, the Earth is estimated to be about 4,570 million years (4570 "[[Ma]]") old. The geological time scale is a means of mapping the history of the earth. It combines estimates of the age of geological formations as provided by radiometric dating techniques with the direct evidence of sequences and events in the rock record as assembled by geologists. In this way the geologic or ''deep time'' of Earth's past can be organized into various units according to events that took place in each period. Different spans of time on the time scale are usually delimited by major [[geology|geologic]] or [[paleontology|paleontologic]] events, such as [[mass extinction]]s. For example, the boundary between the [[Cretaceous]] period and the [[Palaeogene]] period is defined by the [[Mass extinction#Cretaceous-Tertiary extinction event|extinction event]] that marked the demise of the [[dinosaur]]s and of many marine [[species]].
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{{toc}}
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The earth history mapped on the geologic time scale contrasts with that mapped by young-earth [[creationism|creationists]], which see the earth as only thousands of years old.  
  
 
==Terminology==
 
==Terminology==
  
The largest defined unit of time is the Eon. Eons are divided into Eras, which are in turn divided into Periods, Epochs, and Stages. At the same time, [[paleontology|paleontologists]] define a system of ''faunal stages'', of varying lengths, based on changes in the observed [[fossil]] assemblages. In many cases, such faunal stages have been adopted in building the geologic nomenclature, though in general there are far more recognized faunal stages than defined geologic time units.
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In the geological time scale, the largest defined unit of time is the eon, which is further divided successively into eras, periods, epochs, and stages. Overlaid on this general pattern developed by geologists is a complementary mapping by [[paleontology|paleontologists]] who have defined a system of ''faunal stages'' of varying lengths, based on changes in the observed [[fossil]] assemblages. In many cases, such faunal stages have been adopted in building the geologic nomenclature, though in general there are far more recognized faunal stages than defined geologic time units.
  
[[Geologist]]s tend to talk in terms of Upper/Late, Lower/Early, and Middle parts of periods and other units—for example, "Upper [[Jurassic]]", "Middle [[Cambrian]]". Because geologic units occurring at the same timebut from different parts of the world, can often look different and contain different fossils, there are many examples where the same period was historically given different names in different locales. For example, in [[North America]] the Early [[Cambrian]] is refered to as the ''Waucoban series'' that is then subdivided into zones based on [[trilobita|trilobites]]. The same timespan is split into ''Tommotian'', ''Atdabanian'', and Botomian stages in East [[Asia]] and [[Siberia]]. It is a key aspect of the work of the International Commission on Stratigraphy to reconcile this conflicting terminology and define universal horizons that can be used around the world.
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[[Geologist]]s tend to talk in terms of Upper/Late, Lower/Early, and Middle parts of periods and other units—for example, "Upper [[Jurassic]]", "Middle [[Cambrian]]". Because geologic units occurring at the same time but from different parts of the world can often look different and contain different fossils, there are many examples where the same period was historically given different names in different locales. For example, in [[North America]] the Early [[Cambrian]] is referred to as the ''Waucoban series,'' which is then subdivided into zones based on [[trilobita|trilobites]]. The same time span is split into ''Tommotian'', ''Atdabanian'', and ''Botomian'' stages in East [[Asia]] and [[Siberia]]. It is a key aspect of the work of the International Commission on stratigraphy to reconcile this conflicting terminology and define universal horizons that can be used around the world.
  
==Graphical timelines==
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==History of the time scale==
Presented is an overview of the geologic time periods. The second and third timelines are each subsections of their preceding timeline as indicated by asterisks.
 
{{Timeline Geological Timescale}}
 
  
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Nicholas Steno laid down the principles underlying geologic time scales in the late seventeenth century. Steno argued that rock layers (strata) are laid down in succession, and that each represents a “slice” of time. He also formulated the principle of superposition, which states that any given stratum is probably older than those above it and younger than those below it.
  
==History of the time scale==
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Steno's principles were simple, but applying them to real rocks proved complex. During the eighteenth century, [[geology|geologists]] came to realize that: 1) Sequences of strata were often eroded, distorted, tilted, or even inverted after deposition; 2) strata laid down at the same time in different areas could have entirely different appearances; and 3) the strata of any given area represented only part of the Earth's long history.
  
The principles underlying geologic time scales were laid down by [[Nicholas Steno]] in the late 17th century. Steno argued that rock layers (strata) are laid down in succession, and that each represents a "slice" of time.  He also formulated the [[Law of superposition|principle of superposition]], which states that any given stratum is probably older than those above it and younger than those below it. Steno's principles were simple; applying them to real rocks proved complex.  Over the course of the 18th century geologists came to realize that: 1) Sequences of strata were often eroded, distorted, tilted, or even inverted after deposition; 2) Strata laid down at the same time in different areas could have entirely different appearances; 3) The strata of any given area represented only part of the Earth's long history.
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The first serious attempts to formulate a geological time scale that could be applied anywhere on [[Earth]] took place in the late eighteenth century. The most influential of those early attempts (championed by Abraham Werner, among others) divided the rocks of the Earth's crust into four types: primary, secondary, tertiary, and quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks." Indeed, "Tertiary" and "Quaternary" remained in use as names of geological periods well into the twentieth century.
  
The first serious attempts to formulate a geological time scale that could be applied anywhere on Earth took place in the late 18th century.  The most influential of those early attempts (championed by [[Abraham Werner]], among others) divided the rocks of the Earth's crust into four types: Primary, Secondary, Tertiary, and Quaternary.  Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks."  Indeed, "Tertiary" and "Quaternary" remained in use as names of geological periods well into the 20th century.
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The identification of strata by the [[fossil]]s they contained, pioneered by William Smith, [[Georges Cuvier]], and Alexandre Brogniart in the early nineteenth century, enabled geologists to divide Earth history more finely and precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies of the strata and fossils of [[Europe]] produced between 1820 and 1850 formed the sequence of geological periods still used today.  
  
The identification of strata by the fossils they contained, pioneered by [[William Smith]], [[Georges Cuvier]], and [[Alexandre Brogniart]] in the early 19th century, enabled geologists to divide Earth history more finely and precisely.  It also enabled them to correlate strata across national (or even continental) boundaries.  If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies of the strata and fossils of Europe produced, between 1820 and 1850, the sequence of geological periods still used today.  
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[[Britain|British]] geologists dominated the process, and the names of the periods reflect that dominance. The "[[Cambrian]]," "[[Ordovician]]," and "[[Silurian]]" periods were named for ancient British tribes (and defined using stratigraphic sequences from Wales). The "[[Devonian]]" was named for the British county of Devon, and the name "[[Carboniferous]]" was simply an adaptation of "the Coal Measures," the old British geologists' term for the same set of strata. The "[[Permian]]," though defined using strata in [[Russia]], was delineated and named by British geologist Roderick Murchison.  
  
British geologists dominated the process, and the names of the periods reflect that dominance.  The "Cambrian," "Ordovician," and "Silurian" periods were named for ancient British tribes (and defined using stratigraphic sequences from Wales).  The "Devonian" was named for the British county of [[Devon]], and the name "Carboniferous" was simply an adaptation of "the Coal Measures," the old British geologists' term for the same set of strata.  The "Permian," though defined using strata in Russia, was delineated and named by a British geologist: [[Roderick Murchison]].  <!-- The next three periods in the sequence . . . —>
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British geologists were also responsible for the grouping of periods into eras and the subdivision of the Tertiary and Quaternary periods into epochs.
  
British geologists were also responsible for the grouping of periods into Eras and the subdivision of the Tertiary and Quaternary periods into epochs.
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When William Smith and [[Sir Charles Lyell]] first recognized that rock strata represented successive time periods, there was no way to determine what time scale they represented. Young earth [[Creationism|creationist]]s proposed dates of only a few thousand years, while others suggested large (and even infinite) ages. For over one hundred years, the age of the [[Earth]] and of the rock strata was the subject of considerable debate until advances in the latter part of the twentieth century allowed [[radioactive dating]] to provide relatively firm dates to geologic horizons. In the intervening century and a half, geologists and paleontologists constructed time scales based solely on the relative positions of different strata and fossils.
  
When [[William Smith (geologist)|William Smith]] and [[Sir Charles Lyell]] first recognized that [[rock strata]] represented successive time periods, there was no way to determine what time scale they represented.  [[Creationist]]s proposed dates of only a few thousand years, while others suggested large (and even infinite) ages.  For over 100 years, the age of the [[Earth]] and of the rock strata was the subject of considerable debate until advances in the latter part of the 20th century allowed [[radioactive dating]] to provide relatively firm dates to geologic horizons.  In the intervening century and a half, geologists and paleontologists constructed time scales based solely on the relative positions of different strata and fossils.
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In 1977, the Global Commission on Stratigraphy (now the International Commission) started an effort to define global references (Global Boundary Stratotype Section and Points) for geologic periods and faunal stages. Their most recent work is described in the 2004 geologic time scale of Gradstein, Ogg, and Smith (2005), and used as the foundation of the table on this page. The tables of geologic periods presented here are in accordance with the dates and [[nomenclature]] proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geological Survey.
  
In 1977, the Global Commission on Stratigraphy (now the International Commission) started an effort to define global references ([[Global Boundary Stratotype Section and Point|Global Boundary Stratotype Sections and Points]]) for geologic periods and faunal stages.  Their most recent work is described in the 2004 geologic time scale of Gradstein et al. (ISBN 0521786738), and used as the foundation of this page.
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==Graphical timelines==
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An overview of the geologic time periods. The second and third timelines are each subsections of their preceding timeline as indicated by asterisks.
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{{Timeline Geological Timescale}}
  
 
==Table of geologic time==
 
==Table of geologic time==
 
{| class="wikitable" border="3" style="font-size:95%;"
 
{| class="wikitable" border="3" style="font-size:95%;"
 
|-
 
|-
! [[Eon (geology)|Eon]]
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! Eon
! [[Era (geology)|Era]]
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! Era
 
! colspan="2" | Period<sup>1</sup>
 
! colspan="2" | Period<sup>1</sup>
 
! Series/<br>Epoch
 
! Series/<br>Epoch
Line 45: Line 49:
 
| colspan="2" style="background:#FDCC8A" rowspan="4" | [[Neogene]]<sup>3</sup>
 
| colspan="2" style="background:#FDCC8A" rowspan="4" | [[Neogene]]<sup>3</sup>
 
| style="background:#FFFFB3" | [[Holocene]]
 
| style="background:#FFFFB3" | [[Holocene]]
| End of [[ice age|recent glaciation]] and rise of modern [[civilization]]
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| End of [[ice age|recent glaciation]] and rise of modern [[civilization]].
| style="background:#FFFFB3" | 0.011430 ± 0.00013 <sup>9</sup>
+
| style="background:#FFFFB3" | 0.011430 ± 0.00013 <sup>4</sup>
 
|-
 
|-
 
| style="background:#FFFF62" | [[Pleistocene]]
 
| style="background:#FFFF62" | [[Pleistocene]]
| Flourishing and then extinction of many large [[mammal]]s ([[Pleistocene megafauna]]); Evolution of fully modern [[human]]s
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| Flourishing and then extinction of many large [[mammal]]s (Pleistocene megafauna); Creation of fully modern [[human]]s.
 
| style="background:#FFFF62" | 1.806 ± 0.005 <sup>*</sup>
 
| style="background:#FFFF62" | 1.806 ± 0.005 <sup>*</sup>
 
|-
 
|-
 
| style="background:#FEEBAC" |[[Pliocene]]
 
| style="background:#FEEBAC" |[[Pliocene]]
| Intensification of present [[ice age]]. Cool and dry [[climate]]; [[Australopithecine]]s appear, many of the existing genera of mammals, and recent [[mollusc]]s appear
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| Intensification of present [[ice age]]. Cool and dry [[climate]]; [[Australopithecine]]s appear, many of the existing genera of mammals, and recent [[mollusc]]s appear.
 
| style="background:#FEEBAC" | 5.332 ± 0.005 <sup>*</sup>
 
| style="background:#FEEBAC" | 5.332 ± 0.005 <sup>*</sup>
 
|-
 
|-
 
| style="background:#FFDE00" | [[Miocene]]
 
| style="background:#FFDE00" | [[Miocene]]
| Moderate climate; [[Orogeny|Mountain building]] in [[northern hemisphere]]; Modern [[mammal]] and [[bird]] families became recognizable. [[Equidae|Horses]] and [[mastodont]]s diverse.  [[Grass]]es become ubiquitous. First [[hominoid]]s appear. <!-- for reference see the article: "Sahelanthropus tchadensis" —>
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| Moderate climate; Mountain building in northern hemisphere; Modern [[mammal]] and [[bird]] families became recognizable. [[Grass]]es become ubiquitous. First [[hominoid]]s appear. <!-- for reference see the article: "Sahelanthropus tchadensis" —>
 
| style="background:#FFDE00" | 23.03 ± 0.05 <sup>*</sup>
 
| style="background:#FFDE00" | 23.03 ± 0.05 <sup>*</sup>
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#FFB300" | [[Paleogene]]<br><sup>3</sup>
 
| rowspan="3" colspan="2" style="background:#FFB300" | [[Paleogene]]<br><sup>3</sup>
 
| style="background:#EAC672" | [[Oligocene]]
 
| style="background:#EAC672" | [[Oligocene]]
| Warm climate; Rapid [[evolution]] and diversification of fauna, especially [[mammal]]s. Major evolution and dispersal of modern types of [[angiosperm]]s
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| Warm climate; Rapid [[evolution]] and diversification of fauna, especially [[mammal]]s. Major evolution and dispersal of modern types of [[angiosperm]]s.
 
| style="background:#EAC672" | 33.9±0.1 <sup>*</sup>
 
| style="background:#EAC672" | 33.9±0.1 <sup>*</sup>
 
|-
 
|-
 
| style="background:#EAAD43" | [[Eocene]]
 
| style="background:#EAAD43" | [[Eocene]]
| Archaic [[mammal]]s (e.g. [[Creodont]]s, [[Condylarth]]s, [[Uintatheriidae|Uintatheres]], etc) flourish and continue to develop during the epoch. Appearance of several "modern" mammal families. Primitive [[Cetacea|whales]] diversify. First grasses. Reglaciation of [[Antarctica]]; start of current ice age.
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| Archaic [[mammal]]s (e.g. Creodonts, Condylarths, Uintatheres, etc) flourish and continue to develop during the epoch. Appearance of several "modern" mammal families. Primitive [[Cetacea|whales]] diversify. First grasses. Reglaciation of [[Antarctica]]; start of current ice age.
 
| style="background:#EAAD43" | 55.8±0.2 <sup>*</sup>
 
| style="background:#EAAD43" | 55.8±0.2 <sup>*</sup>
 
|-
 
|-
 
| style="background:#EB9301" | [[Paleocene]]
 
| style="background:#EB9301" | [[Paleocene]]
| Climate tropical. Modern [[plant]]s; [[Mammal]]s diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals (up to bear or small hippo size)
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| Climate tropical. Modern [[plant]]s; [[Mammal]]s diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals (up to bear or small hippo size).
 
| style="background:#EB9301" | 65.5±0.3 <sup>*</sup>  
 
| style="background:#EB9301" | 65.5±0.3 <sup>*</sup>  
 
|-
 
|-
 
| rowspan="8" style="background:#7FAD51" | [[Mesozoic]]
 
| rowspan="8" style="background:#7FAD51" | [[Mesozoic]]
 
| rowspan="2" colspan="2" style="background:#7FC31C" | [[Cretaceous]]
 
| rowspan="2" colspan="2" style="background:#7FC31C" | [[Cretaceous]]
| style="background:#DEF197" | [[Late Cretaceous|Upper/Late]]
+
| style="background:#DEF197" | Upper/Late
| rowspan="2" | [[Flowering plant]]s appear, along with new types of insects. More modern [[teleost]] fish begin to appear. [[Ammonite]]s, [[Belemnoidea|belemnites]], [[rudist]]s, [[Echinoidea|echinoid]]s and [[Porifera|sponges]] all common. Many new types of [[dinosaur]]s (e.g. [[Tyrannosauridae|Tyrannosaurs]], [[Titanosauridae|Titanosaurs]], [[Hadrosauridae|duck bills]], and [[Ceratopsidae|horned dinosaurs]]) evolve on land, as do [[Eusuchia|modern crocodilians]]; and [[mosasaur]]s and modern sharks appear in the sea. Primitive [[Aves|birds]] gradually replace pterosaurs. [[Monotremes]], [[marsupial]]s and [[placental]] mammals appear. Break up of [[Gondwana]].
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| rowspan="2" | [[Flowering plant]]s appear, along with new types of insects. More modern [[teleost]] fish begin to appear. Ammonites, belemnites, rudists, [[Echinoidea|echinoid]]s and [[Porifera|sponges]] all common. Many new types of [[dinosaur]]s (e.g. [[Tyrannosauridae|Tyrannosaurs]], Titanosaurs, [[Hadrosauridae|duck bills]], and [[Ceratopsidae|horned dinosaurs]]) evolve on land, as do [[Eusuchia|modern crocodilians]]; and mosasaurs and modern [[shark]]s appear in the sea. Primitive [[bird]]s gradually replace pterosaurs. [[Monotremes]], [[marsupial]]s and [[placental]] mammals appear. Break up of [[Gondwana]].
 
| style="background:#DEF197" | 99.6±0.9 <sup>*</sup>
 
| style="background:#DEF197" | 99.6±0.9 <sup>*</sup>
 
|-
 
|-
| style="background:#B3DF7F" | [[Early Cretaceous|Lower/Early]]
+
| style="background:#B3DF7F" | Lower/Early
 
| style="background:#B3DF7F" | 145.5 ± 4.0
 
| style="background:#B3DF7F" | 145.5 ± 4.0
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#4DB47E" | [[Jurassic]]
 
| rowspan="3" colspan="2" style="background:#4DB47E" | [[Jurassic]]
| style="background:#CCEBC5" | [[Late Jurassic|Upper/Late]]
+
| style="background:#CCEBC5" | Upper/Late
| rowspan="3" | Gymnosperms (especially [[conifer]]s, [[Bennettitales]] and [[cycad]]s) and [[fern]]s common. Many types of [[dinosaur]]s, such as [[sauropod]]s, [[carnosaur]]s, and [[stegosaur]]s. Mammals common but small. First [[bird]]s and [[Squamata|lizards]]. [[Ichthyosaur]]s and [[plesiosaur]]s diverse. [[Bivalve]]s, [[Ammonite]]s and [[Belemnoidea|belemnites]] abundant. [[Echinoidea|Echinoid]]s very common, also [[crinoid]]s, starfish, [[Porifera|sponges]], and [[Terebratulida|terebratulid]] and [[Rhynchonellida|rhynchonellid]] [[brachiopod]]s. Breakup of [[Pangea]] into [[Gondwana]] and [[Laurasia]].
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| rowspan="3" | Gymnosperms (especially [[conifer]]s, Bennettitales, cycads) and [[fern]]s common. Many types of [[dinosaur]]s, such as [[sauropod]]s, carnosaurs, and [[stegosaur]]s. Mammals common, but small. First [[bird]]s and lizards. [[Ichthyosaur]]s and [[plesiosaur]]s diverse. [[Bivalve]]s, ammonites, and belemnites abundant. [[Echinoidea|Echinoid]]s very common, also [[crinoid]]s, starfish, [[Porifera|sponges]], and terebratulid and rhynchonellid [[brachiopod]]s. Breakup of [[Pangea]] into [[Gondwana]] and Laurasia.
 
| style="background:#CCEBC5" | 161.2 ± 4.0
 
| style="background:#CCEBC5" | 161.2 ± 4.0
 
|-
 
|-
| style="background:#7FCA93" | [[Middle Jurassic|Middle]]
+
| style="background:#7FCA93" | Middle
 
| style="background:#7FCA93" | 175.6 ± 2.0 <sup>*</sup>
 
| style="background:#7FCA93" | 175.6 ± 2.0 <sup>*</sup>
 
|-
 
|-
| style="background:#66C292" | [[Early Jurassic|Lower/Early]]
+
| style="background:#66C292" | Lower/Early
 
| style="background:#66C292" | 199.6 ± 0.6
 
| style="background:#66C292" | 199.6 ± 0.6
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#67C3B7" | [[Triassic]]
 
| rowspan="3" colspan="2" style="background:#67C3B7" | [[Triassic]]
| style="background:#CCECE1" | [[Late Triassic|Upper/Late]]
+
| style="background:#CCECE1" | Upper/Late
| rowspan="3" | [[Archosaur]]s dominant and diverse on land, include many large forms; [[cynodont]]s become smaller and more mammal-like. First [[dinosaur]]s, [[mammal]]s, [[pterosaur]]s, and [[crocodilia]]. ''[[Dicrodium]]'' flora common on land. Many large aquatic [[temnospondyli|temnospondyl]] amphibians.   [[Ichthyosaur]]s and [[nothosaur]]s common in the seas. [[Ceratite]] ammonoids extremely common. [[Sclerractinia|Modern corals]] and [[teleost]] fish appear.
+
| rowspan="3" | Archosaurs dominant and diverse on land, include many large forms; cynodonts become smaller and more mammal-like. First [[dinosaur]]s, [[mammal]]s, [[pterosaur]]s, and [[crocodilia]]. ''Dicrodium'' flora common on land. Many large aquatic temnospondyl amphibians. [[Ichthyosaur]]s and nothosaurs common in the seas. Ceratite ammonoids extremely common. Modern corals and teleost fish appear.
 
| style="background:#CCECE1" | 228.0 ± 2.0
 
| style="background:#CCECE1" | 228.0 ± 2.0
 
|-
 
|-
| style="background:#99D7BE" | [[Middle Triassic|Middle]]
+
| style="background:#99D7BE" | Middle
 
| style="background:#99D7BE" | 245.0 ± 1.5
 
| style="background:#99D7BE" | 245.0 ± 1.5
 
|-
 
|-
| style="background:#67B39F" | [[Early Triassic|Lower/Early]]
+
| style="background:#67B39F" | Lower/Early
 
| style="background:#67B39F" | 251.0 ± 0.4 <sup>*</sup>  
 
| style="background:#67B39F" | 251.0 ± 0.4 <sup>*</sup>  
 
|-
 
|-
 
| rowspan="22" style="background:#80B5D5" | [[Paleozoic]]
 
| rowspan="22" style="background:#80B5D5" | [[Paleozoic]]
 
| rowspan="3" colspan="2" style="background:#67C6DE" | [[Permian]]
 
| rowspan="3" colspan="2" style="background:#67C6DE" | [[Permian]]
| style="background:#B3E3EE" | [[Lopingian]]
+
| style="background:#B3E3EE" | Lopingian
| rowspan="3"| Landmass unites in the supercontinent of [[Pangea]]. [[Synapsid]] [[reptile]]s become common ([[Pelycosaur]]s and [[Therapsid]]s), [[parareptile]]s and [[temnospondyli|temnospondyl]] amphibians also remain common. Carboniferous flora replaced by gymnosperms in the middle of the period. [[Coleoptera|Beetles]] and [[Diptera|flies]] evolve. Marine life flourishes in the warm shallow reefs. [[Productida|Productid]] and [[Spiriferida|spiriferid]] brachiopods, bivalves, [[foraminifera]], and ammonoids all abundant. End of Permo-carboniferous ice age. At the end of the period the [[Permian extinction]] event- 95% of life on Earth becomes extinct
+
| rowspan="3"| Landmass unites in the supercontinent of [[Pangea]]. Synapsid [[reptile]]s become common (Pelycosaurs and [[Therapsid]]s), parareptiles and temnospondyl amphibians also remain common. Carboniferous flora replaced by gymnosperms in the middle of the period. [[Beetle]]s and [[Diptera|flies]] evolve. Marine life flourishes in the warm shallow reefs. Productid and spiriferid brachiopods, bivalves, [[foraminifera]], and ammonoids all abundant. End of Permo-carboniferous ice age. At the end of the period, the [[Permian extinction]] event&mdash;95% of life on Earth becomes extinct.
| style="background:#B3E3EE" | 260.4 ± 0.7 <sup>*</sup>
+
| style="background:#B3E3EE" | 260.4 ± 0.7 <sup>*</sup>
 
|-
 
|-
| style="background:#99D8D8" | [[Guadalupian]]
+
| style="background:#99D8D8" | Guadalupian
 
| style="background:#99D8D8" | 270.6 ± 0.7 <sup>*</sup>
 
| style="background:#99D8D8" | 270.6 ± 0.7 <sup>*</sup>
 
|-
 
|-
| style="background:#80CEC9" | [[Cisuralian]]
+
| style="background:#80CEC9" | Cisuralian  
 
| style="background:#80CEC9" | 299.0 ± 0.8 <sup>*</sup>
 
| style="background:#80CEC9" | 299.0 ± 0.8 <sup>*</sup>
 
|-
 
|-
| rowspan="3" colspan="2" style="background:#689FCA" | [[Carboniferous|Carbon-<br>iferous]]<sup>4</sup> '''/'''<br>[[Pennsylvanian|Pennsyl-<br>vanian]]
+
| rowspan="3" colspan="2" style="background:#689FCA" | [[Carboniferous|Carbon-<br>iferous]]<sup>5</sup> '''/'''<br>Pennsyl-<br>vanian
| style="background:#689FCA" | [[Late Pennsylvanian|Upper/Late]]
+
| style="background:#689FCA" | Upper/Late
| rowspan="3" | Winged [[insect]]s appear and are abundant, some growing to large size. [[Tetrapod|Amphibian]]s common and diverse. First [[reptile]]s, [[coal]] forests ([[Lepidodendron]], [[Sigillaria]], [[Calamites]], [[Cordaites]], etc), very high atmospheric [[oxygen]] content. In the seas, Goniatites, brachiopods, bryozoa, bivalves, corals, etc all common.  
+
| rowspan="3" | Winged [[insect]]s appear and are abundant, some growing to large size. [[Amphibian]]s common and diverse. First [[reptile]]s, [[coal]] forests (Lepidodendron, Sigillaria, Calamites, Cordaites, etc), very high atmospheric [[oxygen]] content. In the seas, Goniatites, brachiopods, bryozoa, bivalves, corals, etc. all common.  
 
| style="background:#689FCA" | 306.5 ± 1.0
 
| style="background:#689FCA" | 306.5 ± 1.0
 
|-
 
|-
| style="background:#689FCA" | [[Middle Pennsylvanian|Middle]]
+
| style="background:#689FCA" | Middle
 
| style="background:#689FCA" | 311.7 ± 1.1
 
| style="background:#689FCA" | 311.7 ± 1.1
 
|-
 
|-
| style="background:#689FCA" | [[Early Pennsylvanian|Lower/Early]]
+
| style="background:#689FCA" | Lower/Early
 
| style="background:#689FCA" | 318.1 ± 1.3 <sup>*</sup>
 
| style="background:#689FCA" | 318.1 ± 1.3 <sup>*</sup>
 
|-
 
|-
| rowspan="3" colspan="2" style="background:#8091C.E." | [[Carboniferous|Carbon-<br>iferous]]<sup>4</sup> '''/'''<br>[[Mississippian|Missis-<br>sippian]]
+
| rowspan="3" colspan="2" style="background:#8091C.E." | [[Carboniferous|Carbon-<br>iferous]]<sup>5</sup> '''/'''<br>Missis-<br>sippian
| style="background:#8091C.E." | [[Late Mississippian|Upper/Late]]
+
| style="background:#8091C.E." | Upper/Late
| rowspan="3" | Large primitive [[tree]]s, first land [[tetrapod|vertebrate]]s, brackish water and amphibious [[eurypterid]]s; [[rhizodont]]s dominant fresh-water predators. In the seas primitive [[Chondrichthyes|sharks]] common and very diverse, [[echinoderm]]s (especially [[crinoid]]s and [[blastoid]]s) abundant, [[Coral]]s, [[bryozoa]], and brachiopods ([[Productida]], [[Spriferida]], etc) very common; [[Goniatite]]s common, [[trilobite]]s and [[nautiloid]]s in decline.   [[Glaciation]] in East [[Gondwana]].
+
| rowspan="3" | Large primitive [[tree]]s, first land [[vertebrate]]s, brackish water and amphibious eurypterids; rhizodonts dominant fresh-water predators. In the seas, primitive [[Chondrichthyes|sharks]] common and very diverse, [[echinoderm]]s (especially [[crinoid]]s and blastoids) abundant, [[Coral]]s, [[bryozoa]], and brachiopods (Productida, Spriferida, etc) very common; Goniatites common, [[trilobite]]s and [[nautiloid]]s in decline. [[Glaciation]] in East [[Gondwana]].
 
| style="background:#8091C.E." | 326.4 ± 1.6
 
| style="background:#8091C.E." | 326.4 ± 1.6
 
|-
 
|-
| style="background:#8091C.E." | [[Middle Mississippian|Middle]]
+
| style="background:#8091C.E." | Middle
 
| style="background:#8091C.E." | 345.3 ± 2.1
 
| style="background:#8091C.E." | 345.3 ± 2.1
 
|-
 
|-
| style="background:#8091C.E." | [[Early Mississippian|Lower/Early]]
+
| style="background:#8091C.E." | Lower/Early
 
| style="background:#8091C.E." | 359.2 ± 2.5 <sup>*</sup>
 
| style="background:#8091C.E." | 359.2 ± 2.5 <sup>*</sup>
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#9999C9" | [[Devonian]]
 
| rowspan="3" colspan="2" style="background:#9999C9" | [[Devonian]]
| style="background:#CBBDDC" | [[Late Devonian|Upper/Late]]
+
| style="background:#CBBDDC" | Upper/Late
| rowspan="3"| First [[clubmoss]]es and [[horsetail]]s appear, [[progymnosperm]]s (first seed bearing plants) appear, first trees ([[Archaeopteris]]). In the sea [[Strophomenida|strophomenid]] and [[Atrypida|atrypid]] [[brachiopod]]s, [[Rugosa|rugose]] and [[Tabulata|tabulate]] corals, and [[crinoid]]s are abundant. [[Goniatite]] [[ammonoid]]s are common, and [[Coleoidea|coleoids]] appear. Trilobites reduced in numbers. [[Ostracoderm]]s decline; Jawed fish ([[Placoderm]]s, [[Sarcopterygii|lobe-finned]] and [[Osteichthyes|ray-finned]] fish, and early [[Chondrichthyes|sharks]]) important life in the sea.   First [[Tetrapod|amphibian]]s (but still aquatic). "Old Red Continent" ([[Euramerica]])
+
| rowspan="3"| First clubmosses and horsetails appear, progymnosperms (first seed bearing plants) appear, first trees (Archaeopteris). In the sea, strophomenid and atrypid [[brachiopod]]s, rugose and tabulate corals, and [[crinoid]]s are abundant. Goniatite [[ammonoid]]s are common, and coleoids appear. Trilobites reduced in numbers. Ostracoderms decline; Jawed fish ([[Placoderm]]s, [[Sarcopterygii|lobe-finned]] and [[Osteichthyes|ray-finned]] fish, and early [[Chondrichthyes|sharks]]) important life in the sea. First [[amphibian]]s (but still aquatic). "Old Red Continent" (Euramerica).
 
| style="background:#CBBDDC" | 385.3 ± 2.6 <sup>*</sup>
 
| style="background:#CBBDDC" | 385.3 ± 2.6 <sup>*</sup>
 
|-
 
|-
| style="background:#9983BE" | [[Middle Devonian|Middle]]
+
| style="background:#9983BE" | Middle
 
| style="background:#9983BE" | 397.5 ± 2.7 <sup>*</sup>
 
| style="background:#9983BE" | 397.5 ± 2.7 <sup>*</sup>
 
|-
 
|-
| style="background:#807DBA" | [[Early Devonian|Lower/Early]]
+
| style="background:#807DBA" | Lower/Early
 
| style="background:#807DBA" | 416.0 ± 2.8 <sup>*</sup>
 
| style="background:#807DBA" | 416.0 ± 2.8 <sup>*</sup>
 
|-
 
|-
 
| rowspan="4" colspan="2" style="background:#B172B6" | [[Silurian]]
 
| rowspan="4" colspan="2" style="background:#B172B6" | [[Silurian]]
| style="background:#E9C7E2" | [[Pridoli]]
+
| style="background:#E9C7E2" | Pridoli
| rowspan="4"| First vascular land [[plant]]s, [[millipede]]s and [[Arthropleurida|arthropleurids]], first jawed [[fish]], as well as many types of [[ostracoderm|armoured]] [[agnatha|jawless forms]]. [[Eurypterid|sea-scorpions]] reach large size. [[Tabulata|tabulate]] and [[Rugosa|rugose]] corals, [[brachiopod]]s ([[Pentamerida]], [[Rhynchonellida]], etc), and [[crinoid]]s all abundant; [[trilobite]]s and [[mollusc]]s diverse. [[Graptolite]]s not as varied.
+
| rowspan="4"| First vascular land [[plant]]s, [[millipede]]s and arthropleurids, first jawed [[fish]], as well as many types of armoured [[agnatha|jawless forms]]. Sea-scorpions reach large size. Tabulate and rugose corals, [[brachiopod]]s (Pentamerida, Rhynchonellida, etc), and [[crinoid]]s all abundant; [[trilobite]]s and [[mollusc]]s diverse. Graptolites not as varied.
 
| style="background:#E9C7E2" | 418.7 ± 2.7 <sup>*</sup>
 
| style="background:#E9C7E2" | 418.7 ± 2.7 <sup>*</sup>
 
|-
 
|-
| style="background:#CAA7D1" | [[Ludlow epoch|Ludlow]]
+
| style="background:#CAA7D1" | Ludlow
 
| style="background:#CAA7D1" | 422.9 ± 2.5 <sup>*</sup>
 
| style="background:#CAA7D1" | 422.9 ± 2.5 <sup>*</sup>
 
|-
 
|-
| style="background:#B189B3" | [[Wenlock epoch|Wenlock]]
+
| style="background:#B189B3" | Wenlock
 
| style="background:#B189B3" | 428.2 ± 2.3 <sup>*</sup>
 
| style="background:#B189B3" | 428.2 ± 2.3 <sup>*</sup>
 
|-
 
|-
| style="background:#9858A8" | [[Llandovery epoch|Llandovery]]
+
| style="background:#9858A8" | Llandovery
 
| style="background:#9858A8" | 443.7 ± 1.5 <sup>*</sup>  
 
| style="background:#9858A8" | 443.7 ± 1.5 <sup>*</sup>  
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#F981A6" | [[Ordovician]]
 
| rowspan="3" colspan="2" style="background:#F981A6" | [[Ordovician]]
| style="background:#FBB4BD" | [[Late Ordovician|Upper/Late]]
+
| style="background:#FBB4BD" | Upper/Late
| rowspan="3" | [[Invertebrate]]s very diverse and include many new types. Early corals, [[Brachiopod]]s ([[Orthida]], [[Strophomenida]], etc), [[bivalve]]s, [[nautiloid]]s, [[trilobite]]s, [[ostracod]]s, [[bryozoa]], many types of [[echinoderms]] ([[Cystoidea|cystoids]], [[crinoid]]s, starfish, etc), branched [[graptolite]]s, and other taxa all common. [[Conodont]]s were primitive planktonic vertebrates that appear at the start of the Ordovician. Ice age at the end of the period. First very primitive land [[plant]]s.
+
| rowspan="3" | [[Invertebrate]]s very diverse and include many new types. Early corals, [[Brachiopod]]s (Orthida, Strophomenida, etc), [[bivalve]]s, [[nautiloid]]s, [[trilobite]]s, [[ostracod]]s, [[bryozoa]], many types of [[echinoderms]] (cystoids, crinoids, starfish, etc), branched graptolites, and other taxa all common. Conodonts were a group of eel-like vertebrates characterized by multiple pairs of bony toothplates that appear at the start of the Ordovician. Ice age at the end of the period. First very primitive land [[plant]]s.
 
| style="background:#FBB4BD" | 460.9 ± 1.6 <sup>*</sup>
 
| style="background:#FBB4BD" | 460.9 ± 1.6 <sup>*</sup>
 
|-
 
|-
| style="background:#FA9AB1" | [[Middle Ordovician|Middle]]
+
| style="background:#FA9AB1" | Middle
 
| style="background:#FA9AB1" | 471.8 ± 1.6  
 
| style="background:#FA9AB1" | 471.8 ± 1.6  
 
|-
 
|-
| style="background:#E67DA4" | [[Early Ordovician|Lower/Early]]
+
| style="background:#E67DA4" | Lower/Early
 
| style="background:#E67DA4" | 488.3 ± 1.7 <sup>*</sup>  
 
| style="background:#E67DA4" | 488.3 ± 1.7 <sup>*</sup>  
 
|-
 
|-
 
| rowspan="3" colspan="2" style="background:#FB805F" | [[Cambrian]]
 
| rowspan="3" colspan="2" style="background:#FB805F" | [[Cambrian]]
 
| style="background:#FDCDB8" | [[Furongian]]
 
| style="background:#FDCDB8" | [[Furongian]]
| rowspan="3" | Major diversification of life in the [[Cambrian Explosion]]; more than half of modern animal [[Phylum (biology)|phyla]] appear, along with a number of extinct and problematic forms. [[Archeocyatha]] abundant in the early Cambrian. [[Trilobite]]s, [[Priapulida]], [[Porifera|sponges]], inarticulate [[brachiopod]]s, and many other forms all common. First [[chordate]]s appear. [[Anomalocaris|anomalocarids]] are top predators. Edicarian animals rare, then die out.
+
| rowspan="3" | Major diversification of life in the [[Cambrian|Cambrian Explosion]]; more than half of modern animal phyla appear, along with a number of extinct and problematic forms. Archeocyatha abundant in the early Cambrian. [[Trilobite]]s, Priapulida, [[Porifera|sponges]], inarticulate [[brachiopod]]s, and many other forms all common. First [[chordate]]s appear. Anomalocarids are top predators. Edicarian animals rare, then die out.
 
| style="background:#FDCDB8" | 501.0 ± 2.0 <sup>*</sup>
 
| style="background:#FDCDB8" | 501.0 ± 2.0 <sup>*</sup>
 
|-
 
|-
| style="background:#E8AE97" | [[Middle Cambrian|Middle]]
+
| style="background:#E8AE97" | Middle
 
| style="background:#E8AE97" | 513.0 ± 2.0
 
| style="background:#E8AE97" | 513.0 ± 2.0
 
|-
 
|-
| style="background:#E77C72" | [[Early Cambrian|Lower/Early]]
+
| style="background:#E77C72" | Lower/Early
 
| style="background:#E77C72" | 542.0 ± 1.0 <sup>*</sup>  
 
| style="background:#E77C72" | 542.0 ± 1.0 <sup>*</sup>  
 
|-
 
|-
| rowspan="10" style="background:#CCD891" | [[Proterozoic|Proter-<br>ozoic]]<br><sup>5</sup>
+
| rowspan="10" style="background:#CCD891" | [[Proterozoic|Proter-<br>ozoic]]<br><sup>6</sup>
 
| rowspan="3" style="background:#CAA595" | [[Neoproterozoic|Neo-<br>proterozoic]]
 
| rowspan="3" style="background:#CAA595" | [[Neoproterozoic|Neo-<br>proterozoic]]
| colspan="2" style="background:#EAD8B.C.E." | [[Ediacaran]]
+
| colspan="2" style="background:#EAD8B.C.E." | Ediacaran
| colspan="2" | First [[metazoa|multi-celled animals]]. Edicarian fauna ([[vendobionta]]) flourish worldwide. Simple [[trace fossil]]s from worm-like animals. First [[Porifera|sponges]].
+
| colspan="2" | First [[metazoa|multi-celled animals]]. Edicarian fauna (vendobionta) flourish worldwide. Simple trace [[fossil]]s from worm-like animals. First [[Porifera|sponges]].
 
| style="background:#EAD8B.C.E." | 630 +5/-30 <sup>*</sup>
 
| style="background:#EAD8B.C.E." | 630 +5/-30 <sup>*</sup>
 
|-
 
|-
| colspan="2" style="background:#DCABAA" | [[Cryogenian]]
+
| colspan="2" style="background:#DCABAA" | Cryogenian
| colspan="2" | Possible [[snowball Earth]] period, [[Rodinia]] begins to break up
+
| colspan="2" | Possible snowball Earth period, [[Rodinia]] begins to break up.
| style="background:#DCABAA" | 850 <sup>6</sup>
+
| style="background:#DCABAA" | 850 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#CBA46C" | [[Tonian]]
+
| colspan="2" style="background:#CBA46C" | Tonian
| colspan="2" | First [[acritarch]] radiation
+
| colspan="2" | First acritarch radiation
| style="background:#CBA46C" | 1000 <sup>6</sup>
+
| style="background:#CBA46C" | 1000 <sup>7</sup>
 
|-
 
|-
 
| rowspan="3" style="background:#DDC288" | [[Mesoproterozoic|Meso-<br>proterozoic]]
 
| rowspan="3" style="background:#DDC288" | [[Mesoproterozoic|Meso-<br>proterozoic]]
| colspan="2" style="background:#DDC288" | [[Stenian]]
+
| colspan="2" style="background:#DDC288" | Stenian
| colspan="2" | Narrow highly [[metamorphic]] belts due to [[orogeny]] as [[Rodinia]] formed.
+
| colspan="2" | Narrow highly metamorphic belts due to orogeny as [[Rodinia]] formed.
| style="background:#DDC288" | 1200 <sup>6</sup>
+
| style="background:#DDC288" | 1200 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#DDC288" | [[Ectasian]]
+
| colspan="2" style="background:#DDC288" | Ectasian
| colspan="2" | [[Platform cover]]s continue to expand
+
| colspan="2" | Platform covers continue to expand.
| style="background:#DDC288" | 1400 <sup>6</sup>
+
| style="background:#DDC288" | 1400 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#DDC288" | [[Calymmian]]
+
| colspan="2" style="background:#DDC288" | Calymmian
| colspan="2" | [[Platform cover]]s expand
+
| colspan="2" | Platform covers expand.
| style="background:#DDC288" | 1600 <sup>6</sup>
+
| style="background:#DDC288" | 1600 <sup>7</sup>
 
|-
 
|-
 
| rowspan="4" style="background:#B3B25E" | [[Paleoproterozoic|Paleo-<br>proterozoic]]
 
| rowspan="4" style="background:#B3B25E" | [[Paleoproterozoic|Paleo-<br>proterozoic]]
| colspan="2" style="background:#B3B25E" | [[Statherian]]
+
| colspan="2" style="background:#B3B25E" | Statherian
| colspan="2" | First [[Eukaryote|complex single-celled life]]. [[Columbia (supercontinent)]].
+
| colspan="2" | First [[Eukaryote|complex single-celled life (eukaryotes)]]. Columbia (supercontinent).
| style="background:#B3B25E" | 1800 <sup>6</sup>
+
| style="background:#B3B25E" | 1800 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#B3B25E" | [[Orosirian]]
+
| colspan="2" style="background:#B3B25E" | Orosirian
| colspan="2" | The [[Earth's atmosphere|atmosphere]] became [[oxygen]]ic. [[Vredefort crater|Vredefort]] and [[Sudbury Basin]] asteroid impacts. Much [[orogeny]].
+
| colspan="2" | The atmosphere became [[oxygen]]ic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny (the processes that occur during mountain-building).
| style="background:#B3B25E" | 2050 <sup>6</sup>
+
| style="background:#B3B25E" | 2050 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#B3B25E" | [[Rhyacian]]
+
| colspan="2" style="background:#B3B25E" | Rhyacian
| colspan="2" | [[Bushveld|Bushveld Formation]] formed. [[Huronian]] glaciation.
+
| colspan="2" | Bushveld Formation formed. Huronian glaciation.
| style="background:#B3B25E" | 2300 <sup>6</sup>
+
| style="background:#B3B25E" | 2300 <sup>7</sup>
 
|-
 
|-
| colspan="2" style="background:#B3B25E" | [[Siderian]]
+
| colspan="2" style="background:#B3B25E" | Siderian
| colspan="2" | [[ banded iron formation]]s formed
+
| colspan="2" | Banded iron formations formed.
| style="background:#B3B25E" | 2500 <sup>6</sup>
+
| style="background:#B3B25E" | 2500 <sup>7</sup>
 
|-
 
|-
| rowspan="4" style="background:#99ADAC" | [[Archean]]<br><sup>5</sup>
+
| rowspan="4" style="background:#99ADAC" | [[Archean]]<br><sup>6</sup>
| style="background:#CBCDC8" | [[Neoarchean]]
+
| style="background:#CBCDC8" | Neoarchean
| colspan="4" | Stabilization of most modern [[craton]]s, possible [[Mantle (geology)|mantle]] overturn event
+
| colspan="4" | Stabilization possible of most modern cratons (old, stable part of the continental crust that has survived merging and splitting of continents and supercontinents).[[Mantle (geology)|mantle]] overturn event.
| style="background:#CBCDC8" | 2800 <sup>6</sup>
+
| style="background:#CBCDC8" | 2800 <sup>7</sup>
 
|-
 
|-
| style="background:#B2B5AF" | [[Mesoarchean]]
+
| style="background:#B2B5AF" | Mesoarchean
| colspan="4" | First [[stromatolite]]s
+
| colspan="4" | First [[stromatolite]]s.
| style="background:#B2B5AF" | 3200 <sup>6</sup>
+
| style="background:#B2B5AF" | 3200 <sup>7</sup>
 
|-
 
|-
| style="background:#999791" | [[Paleoarchean]]
+
| style="background:#999791" | Paleoarchean
| colspan="4" | First known [[phototroph|oxygen producing]] [[bacteria]]
+
| colspan="4" | First known oxygen producing [[bacteria]].
| style="background:#999791" | 3600 <sup>6</sup>
+
| style="background:#999791" | 3600 <sup>7</sup>
 
|-
 
|-
| style="background:#809090" | [[Eoarchean]]
+
| style="background:#809090" | Eoarchean
| colspan="4" | [[Prokaryote|Simple single-celled life]]
+
| colspan="4" | [[Prokaryote|Simple single-celled life (prokaryote)]].
 
| style="background:#809090" | 3800
 
| style="background:#809090" | 3800
 
|-
 
|-
| style="background:#809090" rowspan="4" | [[Hadean]]<br><sup>5,7</sup>
+
| style="background:#809090" rowspan="4" | [[Hadean]]<br><sup>6,8</sup>
| style="background:#809090" | [[Lower Imbrian]]
+
| style="background:#809090" | Lower Imbrian<sup>9</sup>
 
| colspan="4" | &nbsp;
 
| colspan="4" | &nbsp;
 
| style="background:#809090" | c.3850
 
| style="background:#809090" | c.3850
 
|-
 
|-
| style="background:#809090" | [[Nectarian]]
+
| style="background:#809090" | Nectarian<sup>9</sup>
 
| colspan="4" | &nbsp;
 
| colspan="4" | &nbsp;
 
| style="background:#809090" | c.3920
 
| style="background:#809090" | c.3920
 
|-
 
|-
| style="background:#809090" | [[Basin groups]]
+
| style="background:#809090" | Basin groups<sup>9</sup>
| colspan="4" | 4100 [[annum|Ma]] - Oldest known rock
+
| colspan="4" | 4100 Ma&mdash;Oldest known rock
 
| style="background:#809090" | c.4150
 
| style="background:#809090" | c.4150
 
|-
 
|-
| style="background:#809090" | [[Cryptic era|Cryptic]]<sup>8</sup>
+
| style="background:#809090" | Cryptic<sup>9</sup>
| colspan="4" | 4400 Ma - Oldest known mineral; 4570 Ma - Formation of [[Earth]]
+
| colspan="4" | 4400 Ma&mdash;Oldest known mineral; 4570 Ma&mdash;Formation of [[Earth]]
 
| style="background:#809090" | c.4570
 
| style="background:#809090" | c.4570
 
|}
 
|}
  
 
<div style="font-size:90%;">
 
<div style="font-size:90%;">
# Paleontologists often refer to [[faunal stage]]s rather than geologic periods. The stage nomenclature is quite complex.  See [http://flatpebble.nceas.ucsb.edu/cgi-bin/bridge.pl?action=startScale Harland] for an excellent time ordered list of faunal stages.
+
# Paleontologists often refer to ''faunal stages'' rather than geologic periods. The stage nomenclature is quite complex.  
# 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.
+
# 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.  
# 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.
+
# 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.
# In North America, the Carboniferous is subdivided into [[Mississippian]] and [[Pennsylvanian]] Periods.
 
# The [[Proterozoic]], [[Archean]] and [[Hadean]] are often collectively referred to as [[Precambrian|Precambrian Time]], and sometimes also as the [[Cryptozoic]].
 
# Defined by absolute age ([[Global Standard Stratigraphic Age]]).
 
# Though commonly used, the [[Hadean]] is not a formal eon and no lower bound for the Eoarchean has been agreed upon.  The Hadean has also sometimes been called the [[Priscoan]].
 
# These four era names were taken from Moon geology. Their use for Earth geology is unofficial.
 
 
# The start time for the [[Holocene]] epoch is here given as 11,430 years ago ± 130 years. For further discussion of the dating of this epoch, see [[Holocene]].
 
# The start time for the [[Holocene]] epoch is here given as 11,430 years ago ± 130 years. For further discussion of the dating of this epoch, see [[Holocene]].
 +
# In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
 +
# The [[Proterozoic]], [[Archean]] and [[Hadean]] are often collectively referred to as [[Precambrian|Precambrian Time]], and sometimes also as the Cryptozoic.
 +
# Defined by absolute age (Global Standard Stratigraphic Age).
 +
# Though commonly used, the [[Hadean]] is not a formal eon and no lower bound for the Eoarchean has been agreed upon. The Hadean has also sometimes been called the Priscoan.
 +
# These four era names were taken from Lunar geologic timescale. Their use for Earth geology is unofficial.
 +
 
</div>
 
</div>
  
 
==References==
 
==References==
* [http://www.stratigraphy.org/geowhen/ GeoWhen Database ]
+
*Amthor, J. E., J. P. Grotzinger, S. Schroder, S. A. Bowring, J. Ramezani, M. W. Martin, and A. Matter. 2003. Extinction of Cloudina and Namacalathus at the Precambrian boundary in Oman. ''Geology'' 31(5):431-434.  
* [http://www.stratigraphy.org/gssp.htm International Commission on Stratigraphy Time Scale ]
+
*Bowring, S. A., D. H. Erwin, Y. G. Jin, M. W. Martin, K. Davidek, and W. Wang. 1998. U/Pb zircon geochronology and tempo of the end-Permian mass extinction. ''Science'' 280 (5366):1039-1045.
* [http://www.chronos.org CHRONOS ]
+
*Gradstein, F. M., J. G. Ogg, and A. G. Smith. 2005. ''A Geologic Time Scale 2004''. Cambridge: Cambridge University Press.
* [http://www.chronos.org/education/educational_resources.html CHRONOS Geologic Time references ]
 
* [http://www.nmnh.si.edu/paleo/geotime/index.htm Nation Museum on Natural History Geologic Time ]
 
* [http://www.bbc.co.uk/history/games/rocky/indextime.html BBC Interactive Time Line]
 
 
 
==See also==
 
* [[Age of the Earth]]
 
* [[Fossils and the geological timescale]]
 
* [[Timeline of evolution]]
 
* [[Cosmological timeline]]
 
* [[Lunar geologic timescale]]
 
* [[Martian geologic timescale]]
 
* [[Anthropocene]]
 
* [[Logarithmic timeline]]
 
  
==External link==
 
*[http://rst.gsfc.nasa.gov/Sect2/Sect2_1b.html NASA: Geologic Time]
 
*[http://www.geosociety.org/science/timescale/timescl.htm GSA: Geologic Time Scale]
 
  
 
{{credit|31971840}}
 
{{credit|31971840}}
[[Category:Life sciences]]
+
[[Category:Life sciences]][[Category:Paleontology]][[Category:Evolution]]
 +
[[Category:Geology]]

Latest revision as of 14:44, 21 April 2015

This clock representation shows some of the major units of geological time and definitive events of Earth history.

The geologic time scale is used by geologists and other scientists to map the timing and relationships between events that have occurred during the history of the Earth.

Based on radiometric dating techniques, the Earth is estimated to be about 4,570 million years (4570 "Ma") old. The geological time scale is a means of mapping the history of the earth. It combines estimates of the age of geological formations as provided by radiometric dating techniques with the direct evidence of sequences and events in the rock record as assembled by geologists. In this way the geologic or deep time of Earth's past can be organized into various units according to events that took place in each period. Different spans of time on the time scale are usually delimited by major geologic or paleontologic events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Palaeogene period is defined by the extinction event that marked the demise of the dinosaurs and of many marine species.

The earth history mapped on the geologic time scale contrasts with that mapped by young-earth creationists, which see the earth as only thousands of years old.

Terminology

In the geological time scale, the largest defined unit of time is the eon, which is further divided successively into eras, periods, epochs, and stages. Overlaid on this general pattern developed by geologists is a complementary mapping by paleontologists who have defined a system of faunal stages of varying lengths, based on changes in the observed fossil assemblages. In many cases, such faunal stages have been adopted in building the geologic nomenclature, though in general there are far more recognized faunal stages than defined geologic time units.

Geologists tend to talk in terms of Upper/Late, Lower/Early, and Middle parts of periods and other units—for example, "Upper Jurassic", "Middle Cambrian". Because geologic units occurring at the same time but from different parts of the world can often look different and contain different fossils, there are many examples where the same period was historically given different names in different locales. For example, in North America the Early Cambrian is referred to as the Waucoban series, which is then subdivided into zones based on trilobites. The same time span is split into Tommotian, Atdabanian, and Botomian stages in East Asia and Siberia. It is a key aspect of the work of the International Commission on stratigraphy to reconcile this conflicting terminology and define universal horizons that can be used around the world.

History of the time scale

Nicholas Steno laid down the principles underlying geologic time scales in the late seventeenth century. Steno argued that rock layers (strata) are laid down in succession, and that each represents a “slice” of time. He also formulated the principle of superposition, which states that any given stratum is probably older than those above it and younger than those below it.

Steno's principles were simple, but applying them to real rocks proved complex. During the eighteenth century, geologists came to realize that: 1) Sequences of strata were often eroded, distorted, tilted, or even inverted after deposition; 2) strata laid down at the same time in different areas could have entirely different appearances; and 3) the strata of any given area represented only part of the Earth's long history.

The first serious attempts to formulate a geological time scale that could be applied anywhere on Earth took place in the late eighteenth century. The most influential of those early attempts (championed by Abraham Werner, among others) divided the rocks of the Earth's crust into four types: primary, secondary, tertiary, and quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks." Indeed, "Tertiary" and "Quaternary" remained in use as names of geological periods well into the twentieth century.

The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, and Alexandre Brogniart in the early nineteenth century, enabled geologists to divide Earth history more finely and precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies of the strata and fossils of Europe produced between 1820 and 1850 formed the sequence of geological periods still used today.

British geologists dominated the process, and the names of the periods reflect that dominance. The "Cambrian," "Ordovician," and "Silurian" periods were named for ancient British tribes (and defined using stratigraphic sequences from Wales). The "Devonian" was named for the British county of Devon, and the name "Carboniferous" was simply an adaptation of "the Coal Measures," the old British geologists' term for the same set of strata. The "Permian," though defined using strata in Russia, was delineated and named by British geologist Roderick Murchison.

British geologists were also responsible for the grouping of periods into eras and the subdivision of the Tertiary and Quaternary periods into epochs.

When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, there was no way to determine what time scale they represented. Young earth creationists proposed dates of only a few thousand years, while others suggested large (and even infinite) ages. For over one hundred years, the age of the Earth and of the rock strata was the subject of considerable debate until advances in the latter part of the twentieth century allowed radioactive dating to provide relatively firm dates to geologic horizons. In the intervening century and a half, geologists and paleontologists constructed time scales based solely on the relative positions of different strata and fossils.

In 1977, the Global Commission on Stratigraphy (now the International Commission) started an effort to define global references (Global Boundary Stratotype Section and Points) for geologic periods and faunal stages. Their most recent work is described in the 2004 geologic time scale of Gradstein, Ogg, and Smith (2005), and used as the foundation of the table on this page. The tables of geologic periods presented here are in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geological Survey.

Graphical timelines

An overview of the geologic time periods. The second and third timelines are each subsections of their preceding timeline as indicated by asterisks.

Millions of Years

Table of geologic time

Eon Era Period1 Series/
Epoch
Major Events Start, Million
Years Ago2
Phane-
rozoic
Cenozoic Neogene3 Holocene End of recent glaciation and rise of modern civilization. 0.011430 ± 0.00013 4
Pleistocene Flourishing and then extinction of many large mammals (Pleistocene megafauna); Creation of fully modern humans. 1.806 ± 0.005 *
Pliocene Intensification of present ice age. Cool and dry climate; Australopithecines appear, many of the existing genera of mammals, and recent molluscs appear. 5.332 ± 0.005 *
Miocene Moderate climate; Mountain building in northern hemisphere; Modern mammal and bird families became recognizable. Grasses become ubiquitous. First hominoids appear. 23.03 ± 0.05 *
Paleogene
3
Oligocene Warm climate; Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of angiosperms. 33.9±0.1 *
Eocene 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; start of current ice age. 55.8±0.2 *
Paleocene Climate tropical. Modern plants; Mammals diversify into a number of primitive lineages following the extinction of the dinosaurs. First large mammals (up to bear or small hippo size). 65.5±0.3 *
Mesozoic Cretaceous Upper/Late Flowering plants appear, along with new types of insects. More modern teleost fish begin to appear. Ammonites, belemnites, rudists, echinoids and sponges all common. Many new types of dinosaurs (e.g. Tyrannosaurs, Titanosaurs, duck bills, and horned dinosaurs) evolve on land, as do 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. 99.6±0.9 *
Lower/Early 145.5 ± 4.0
Jurassic Upper/Late Gymnosperms (especially conifers, Bennettitales, 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. Echinoids very common, also crinoids, starfish, sponges, and terebratulid and rhynchonellid brachiopods. Breakup of Pangea into Gondwana and Laurasia. 161.2 ± 4.0
Middle 175.6 ± 2.0 *
Lower/Early 199.6 ± 0.6
Triassic Upper/Late Archosaurs dominant and diverse on land, include many large forms; cynodonts become smaller and more mammal-like. First dinosaurs, mammals, pterosaurs, and crocodilia. Dicrodium flora common on land. Many large aquatic temnospondyl amphibians. Ichthyosaurs and nothosaurs common in the seas. Ceratite ammonoids extremely common. Modern corals and teleost fish appear. 228.0 ± 2.0
Middle 245.0 ± 1.5
Lower/Early 251.0 ± 0.4 *
Paleozoic Permian Lopingian Landmass unites in the supercontinent of Pangea. Synapsid reptiles become common (Pelycosaurs and Therapsids), parareptiles and temnospondyl amphibians also remain common. Carboniferous flora replaced by gymnosperms in the middle of the period. Beetles and flies evolve. Marine life flourishes in the warm shallow reefs. Productid and spiriferid brachiopods, bivalves, foraminifera, and ammonoids all abundant. End of Permo-carboniferous ice age. At the end of the period, the Permian extinction event—95% of life on Earth becomes extinct. 260.4 ± 0.7 *
Guadalupian 270.6 ± 0.7 *
Cisuralian 299.0 ± 0.8 *
Carbon-
iferous
5 /
Pennsyl-
vanian
Upper/Late Winged insects appear and are abundant, some growing to large size. Amphibians common and diverse. First reptiles, coal forests (Lepidodendron, Sigillaria, Calamites, Cordaites, etc), very high atmospheric oxygen content. In the seas, Goniatites, brachiopods, bryozoa, bivalves, corals, etc. all common. 306.5 ± 1.0
Middle 311.7 ± 1.1
Lower/Early 318.1 ± 1.3 *
Carbon-
iferous
5 /
Missis-
sippian
Upper/Late Large primitive trees, first land vertebrates, brackish water and amphibious eurypterids; rhizodonts dominant fresh-water predators. In the seas, primitive sharks common and very diverse, echinoderms (especially crinoids and blastoids) abundant, Corals, bryozoa, and brachiopods (Productida, Spriferida, etc) very common; Goniatites common, trilobites and nautiloids in decline. Glaciation in East Gondwana. 326.4 ± 1.6
Middle 345.3 ± 2.1
Lower/Early 359.2 ± 2.5 *
Devonian Upper/Late First clubmosses and horsetails appear, progymnosperms (first seed bearing plants) appear, first trees (Archaeopteris). In the sea, strophomenid and atrypid brachiopods, rugose and tabulate corals, and crinoids are abundant. Goniatite ammonoids are common, and coleoids appear. Trilobites reduced in numbers. Ostracoderms decline; Jawed fish (Placoderms, lobe-finned and ray-finned fish, and early sharks) important life in the sea. First amphibians (but still aquatic). "Old Red Continent" (Euramerica). 385.3 ± 2.6 *
Middle 397.5 ± 2.7 *
Lower/Early 416.0 ± 2.8 *
Silurian Pridoli First vascular land plants, millipedes and arthropleurids, first jawed fish, as well as many types of armoured jawless forms. Sea-scorpions reach large size. Tabulate and rugose corals, brachiopods (Pentamerida, Rhynchonellida, etc), and crinoids all abundant; trilobites and molluscs diverse. Graptolites not as varied. 418.7 ± 2.7 *
Ludlow 422.9 ± 2.5 *
Wenlock 428.2 ± 2.3 *
Llandovery 443.7 ± 1.5 *
Ordovician Upper/Late Invertebrates very diverse and include many new types. Early corals, Brachiopods (Orthida, Strophomenida, etc), bivalves, nautiloids, trilobites, ostracods, bryozoa, many types of echinoderms (cystoids, crinoids, starfish, etc), branched graptolites, and other taxa all common. Conodonts were a group of eel-like vertebrates characterized by multiple pairs of bony toothplates that appear at the start of the Ordovician. Ice age at the end of the period. First very primitive land plants. 460.9 ± 1.6 *
Middle 471.8 ± 1.6
Lower/Early 488.3 ± 1.7 *
Cambrian Furongian Major diversification of life in the Cambrian Explosion; more than half of modern animal phyla appear, along with a number of extinct and problematic forms. Archeocyatha abundant in the early Cambrian. Trilobites, Priapulida, sponges, inarticulate brachiopods, and many other forms all common. First chordates appear. Anomalocarids are top predators. Edicarian animals rare, then die out. 501.0 ± 2.0 *
Middle 513.0 ± 2.0
Lower/Early 542.0 ± 1.0 *
Proter-
ozoic

6
Neo-
proterozoic
Ediacaran First multi-celled animals. Edicarian fauna (vendobionta) flourish worldwide. Simple trace fossils from worm-like animals. First sponges. 630 +5/-30 *
Cryogenian Possible snowball Earth period, Rodinia begins to break up. 850 7
Tonian First acritarch radiation 1000 7
Meso-
proterozoic
Stenian Narrow highly metamorphic belts due to orogeny as Rodinia formed. 1200 7
Ectasian Platform covers continue to expand. 1400 7
Calymmian Platform covers expand. 1600 7
Paleo-
proterozoic
Statherian First complex single-celled life (eukaryotes). Columbia (supercontinent). 1800 7
Orosirian The atmosphere became oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny (the processes that occur during mountain-building). 2050 7
Rhyacian Bushveld Formation formed. Huronian glaciation. 2300 7
Siderian Banded iron formations formed. 2500 7
Archean
6
Neoarchean Stabilization possible of most modern cratons (old, stable part of the continental crust that has survived merging and splitting of continents and supercontinents).mantle overturn event. 2800 7
Mesoarchean First stromatolites. 3200 7
Paleoarchean First known oxygen producing bacteria. 3600 7
Eoarchean Simple single-celled life (prokaryote). 3800
Hadean
6,8
Lower Imbrian9   c.3850
Nectarian9   c.3920
Basin groups9 4100 Ma—Oldest known rock c.4150
Cryptic9 4400 Ma—Oldest known mineral; 4570 Ma—Formation of Earth c.4570
  1. Paleontologists often refer to faunal stages rather than geologic periods. The stage nomenclature is quite complex.
  2. 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.
  3. 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.
  4. The start time for the Holocene epoch is here given as 11,430 years ago ± 130 years. For further discussion of the dating of this epoch, see Holocene.
  5. In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
  6. The Proterozoic, Archean and Hadean are often collectively referred to as Precambrian Time, and sometimes also as the Cryptozoic.
  7. Defined by absolute age (Global Standard Stratigraphic Age).
  8. Though commonly used, the Hadean is not a formal eon and no lower bound for the Eoarchean has been agreed upon. The Hadean has also sometimes been called the Priscoan.
  9. These four era names were taken from Lunar geologic timescale. Their use for Earth geology is unofficial.

References
ISBN links support NWE through referral fees

  • Amthor, J. E., J. P. Grotzinger, S. Schroder, S. A. Bowring, J. Ramezani, M. W. Martin, and A. Matter. 2003. Extinction of Cloudina and Namacalathus at the Precambrian boundary in Oman. Geology 31(5):431-434.
  • Bowring, S. A., D. H. Erwin, Y. G. Jin, M. W. Martin, K. Davidek, and W. Wang. 1998. U/Pb zircon geochronology and tempo of the end-Permian mass extinction. Science 280 (5366):1039-1045.
  • Gradstein, F. M., J. G. Ogg, and A. G. Smith. 2005. A Geologic Time Scale 2004. Cambridge: Cambridge University Press.


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