View source for Cambrian

{{Short description|First geological period of the Paleozoic Era}}
{{hatnote group|
{{Distinguish|Cambria|Cumbria}}
{{other uses|Cambrian (disambiguation)}}
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{{Use dmy dates|date=October 2025}}
{{Infobox geologic timespan
| name                         = Cambrian
| color                        = Cambrian
| top_bar                      = 
| time_start                   = {{period start|cambrian}}
| time_start_prefix            =
| time_start_uncertainty       = {{period start error|cambrian|sign=no}}
| time_end                     = {{period end|cambrian}}
| time_end_prefix              =
| time_end_uncertainty         = {{period end error|cambrian|sign=no}}
| image_map                    = Mollweide Paleographic Map of Earth, 510 Ma.png
| caption_map                  = A map of Earth as it appeared 510 million years ago during the Cambrian Period, Series 2 epoch
| image_outcrop                =
| caption_outcrop              =
| image_art                    =
| caption_art                  =
<!--Chronology-->  
| timeline                     = Cambrian
<!--Etymology-->
| name_formality               = Formal
| name_accept_date             = 
| alternate_spellings          =
| synonym1                     =
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| synonym2                     =
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| synonym3                     =
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| nicknames                    =
| former_names                 =
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<!--Usage Information--> 
| celestial_body               = Earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
| formerly_used_by             =
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Period
| strat_unit                   = System
| proposed_by                  = [[Adam Sedgwick]], 1835
| timespan_formality           = Formal
| lower_boundary_def           = Appearance of the [[Trace fossil|Ichnofossil]] ''[[Treptichnus pedum]]''
| lower_gssp_location          = [[Fortune Head|Fortune Head section]], Newfoundland, Canada
| lower_gssp_coords            = {{Coord|47.0762|N|55.8310|W|display=inline}}
| lower_gssp_accept_date       = {{period start ratification|cambrian}}
| upper_boundary_def           = [[First appearance datum|FAD]] of the [[Conodont]] ''[[Iapetognathus fluctivagus]]''.
| upper_gssp_location          = Greenpoint section, [[Green Point, Newfoundland|Green Point]], Newfoundland, Canada
| upper_gssp_coords            = {{Coord|49.6829|N|57.9653|W|display=inline}}
| upper_gssp_accept_date       = {{period end ratification|cambrian}}
<!--Atmospheric and Climatic Data-->
| o2                           = 
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| sea_level                    = Rising steadily from 4 m to 90 m<ref>{{cite journal |last1=Haq |first1=B. U. |year=2008 |doi=10.1126/science.1161648 |title=A Chronology of Paleozoic Sea-Level Changes |journal=Science |volume=322 |pages=64–8 |pmid=18832639 |last2=Schutter |first2=SR |issue=5898 |bibcode=2008Sci...322...64H }}</ref>
}}

{{CEXNAV}}
The '''Cambrian''' ({{IPAc-en|pron|ˈ|k|æ|m|b|r|i|.|ə|n|,_|ˈ|k|eɪ|m|-}} {{respell|KAM|bree|ən|,_|KAYM|-}}) is the first [[geological period]] of the [[Paleozoic]] Era and the [[Phanerozoic Eon]].{{sfn|Howe|1911|p=86}} The Cambrian lasted 51.95 million years from the end of the preceding [[Ediacaran]] period 538.8 Ma (million years ago) to the beginning of the [[Ordovician]] Period 486.85 Ma.<ref name="ICS" />

Most of the continents were located in the southern hemisphere surrounded by the vast [[Panthalassa|Panthalassa Ocean]].<ref name="Torsvik-2017" /> The assembly of [[Gondwana]] during the Ediacaran and early Cambrian led to the development of new [[Convergent boundary|convergent plate boundaries]] and [[Volcanic arc|continental-margin arc magmatism]] along its margins that helped drive up global temperatures.<ref name="Myrow-2024" /> [[Laurentia]] lay across the equator, separated from Gondwana by the opening [[Iapetus Ocean]].<ref name="Torsvik-2017" />

The Cambrian marked a profound change in [[Life|life on Earth]]; prior to the period, the majority of living organisms were small, [[Unicellular organism|unicellular]], and poorly preserved. Complex, [[multicellular organism]]s gradually became more common during the Ediacaran, but it was not until the Cambrian that fossil diversity seems to have rapidly increased, an event known as the [[Cambrian explosion]], producing the first representatives of most modern animal [[Phylum|phyla]].<ref name="Butterfield2007">{{cite journal |last1=Butterfield |first1=N. J. |year=2007 |title=Macroevolution and macroecology through deep time |journal=Palaeontology |volume=50 |issue=1 |pages=41–55 |bibcode=2007Palgy..50...41B |doi=10.1111/j.1475-4983.2006.00613.x |doi-access=free}}</ref> The period is also unique in its unusually high proportion of [[lagerstätte]] deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells.<ref name="Orr2003">{{cite journal |last1=Orr |first1=P. J. |last2=Benton |first2=M. J. |last3=Briggs |first3=D. E. G. |year=2003 |title=Post-Cambrian closure of the deep-water slope-basin taphonomic window |journal=Geology |volume=31 |issue=9 |pages=769–772 |bibcode=2003Geo....31..769O |doi=10.1130/G19193.1}}</ref>

== Etymology and history ==
The term ''Cambrian'' is derived from a Latin version of ''[[Cymru]]'', the Welsh name for [[Wales]], where rocks of this age were first studied.<ref name="Peng-2020">{{cite book |last1=Peng |first1=S.C. |last2=Babcock |first2=L.E. |last3=Ahlberg |first3=P. |title=Geologic Time Scale 2020 |chapter=The Cambrian Period |date=2020 |pages=565–629 |doi=10.1016/b978-0-12-824360-2.00019-x |isbn=978-0-12-824360-2 }}</ref> The geological term was named by [[Adam Sedgwick]] based on work done in the summer of 1831 in [[North Wales]].<ref name=cooperjago2007>{{cite journal |last1=Cooper |first1=Barry J. |last2=Jago |first2=James B. |title=History of Cambrian Investigations in South Australia with Particular Reference to the Biostratigraphy |journal=Memoirs of the Association of Australasian Palaeontologists |date=9 November 2020 |issue=33 |pages=1–27 |url=https://search.informit.org/doi/abs/10.3316/INFORMIT.250843726882043 }}</ref> Sedgwick divided it into three groups: the Lower, Middle, and Upper Cambrian.<ref name="Peng-2020" /> He defined the boundary between the Cambrian and the overlying [[Silurian]], together with [[Roderick Murchison]], in their joint paper "''On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales''"<ref name="Davidson-2021">{{Cite book |last=Davidson |first=Nick |title=The Greywacke |publisher=Profile Books Ltd |year=2021 |isbn=978-1-78816-378-1 |edition=1st |location=London}}</ref> (1836). The proposal to label the period ''Cambrian'' was based on a segment of rock strata that represented a period  of geological time.<ref name=cooperjago2007/>

This early agreement did not last.<ref name="Davidson-2021"/> Due to the scarcity of fossils, Sedgwick used rock types to identify Cambrian strata. He was also slow in publishing further work. The clear fossil record of the Silurian, however, allowed Murchison to correlate rocks of a similar age across Europe and Russia, and on these he published extensively. As increasing numbers of fossils were identified in older rocks, he extended the base of the Silurian downwards into the Sedgwick's "Upper Cambrian", claiming all fossilised strata for "his" Silurian series. Matters were complicated further when, in 1852, fieldwork carried out by Sedgwick and others revealed an unconformity within the Silurian, with a clear difference in fauna between the two.<ref name="Sedgwick1852">{{cite journal |last=Sedgwick |first=A. |title=On the Classification and Nomenclature of the Lower Palæozoic Rocks of England and Wales |journal=Quarterly Journal of the Geological Society of London |date=February 1852 |volume=8 |issue=1–2 |pages=136–168 |doi=10.1144/GSL.JGS.1852.008.01-02.20 |bibcode=1852QJGS....8..136S }}</ref><ref name="Davidson-2021" /> This allowed Sedgwick to now claim a large section of the Silurian for "his" Cambrian and gave the Cambrian an identifiable fossil record. The dispute between the two geologists and their supporters, over the boundary between the Cambrian and Silurian, would extend beyond the life times of both Sedgwick and Murchison. It was not resolved until 1879, when [[Charles Lapworth]] proposed the disputed strata belong to its own system, which he named the [[Ordovician]].<ref name="Davidson-2021" />

The term ''Cambrian'' for the oldest period of the Paleozoic was officially agreed in 1960, at the 21st [[International Union of Geological Sciences|International Geological Congress]]. It only includes Sedgwick's "Lower Cambrian series", but its base has been extended into much older rocks.<ref name="Peng-2020" />

== Geology ==

=== Stratigraphy {{anchor|Subdivisions}} ===
[[System (stratigraphy)|Systems]], [[Series (stratigraphy)|series]] and [[Stage (stratigraphy)|stages]] can be defined globally or regionally. For global stratigraphic correlation, the ICS ratify rock units based on a [[Global Boundary Stratotype Section and Point]] (GSSP) from a single [[Geological formation|formation]] (a [[stratotype]]) identifying the lower boundary of the unit. Currently the boundaries of the Cambrian System, three series and six stages are defined by global stratotype sections and points.<ref name="ICS" />
{| class="wikitable"
! span=col| Series/epoch
! span=col| Stage/age
! span=col| Lower boundary
|-
| rowspan="3", style="background-color: {{period color|Furongian}};" | {{Colored period link|Furongian}}
|style="background-color: {{period color|Cambrian Stage 10}};" | {{Colored period link|Cambrian Stage 10}}
|{{period start|Cambrian Stage 10}} {{period start error|Cambrian Stage 10}} Ma
|-
|style="background-color: {{period color|Jiangshanian}};" | {{Colored period link|Jiangshanian}}
|{{period start|Jiangshanian}} {{period start error|Jiangshanian}} Ma
|-
|style="background-color: {{period color|Paibian}};" | {{Colored period link|Paibian}}
|{{period start|Paibian}} {{period start error|Paibian}} Ma
|-
| rowspan="3", style="background-color: {{period color|Miaolingian}}" | {{Colored period link|Miaolingian }}
|style="background-color: {{period color|Guzhangian}};" | {{Colored period link|Guzhangian}}
|{{period start|Guzhangian}} {{period start error|Guzhangian}} Ma
|-
|style="background-color: {{period color|Drumian}};" | {{Colored period link|Drumian}}
|{{period start|Drumian}} {{period start error|Drumian}} Ma
|-
|style="background-color: {{period color|Wuliuan}};" | {{Colored period link|Wuliuan}}
|{{period start|Wuliuan}} {{period start error|Wuliuan}} Ma
|-
| rowspan="2", style="background-color: {{period color|Series 2}};" | {{Colored period link|Cambrian Series 2}} 
|style="background-color: {{period color|Stage 4}};" | {{Colored period link|Cambrian Stage 4}}
|{{period start|Stage 4}} {{period start error|Stage 4}} Ma
|-
|style="background-color: {{period color|Stage 3}};" | {{Colored period link|Cambrian Stage 3}}
|{{period start|Stage 3}} {{period start error|Stage 3}} Ma
|-
| rowspan="2", style="background-color: {{period color|Terreneuvian}};" | {{Colored period link|Terreneuvian}} 
|style="background-color: {{period color|Stage 2}};" | {{Colored period link|Cambrian Stage 2}}
|{{period start|Stage 2}} {{period start error|Stage 2}} Ma
|-
|style="background-color: {{period color|Fortunian}};" | {{Colored period link|Fortunian}}
|{{period start|Fortunian}} {{period start error|Fortunian}} Ma
|}

==== Ediacaran–Cambrian boundary ====
The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by [[trilobite]]s. The recognition of [[small shelly fossils]] before the first trilobites, and [[Ediacara biota]] substantially earlier, has led to calls for a more precisely defined base to the Cambrian Period.<ref name="Geyer-2016">{{Cite journal |last1=Geyer |first1=Gerd |last2=Landing |first2=Ed |year=2016 |title=The Precambrian–Phanerozoic and Ediacaran–Cambrian boundaries: A historical approach to a dilemma |journal=Geological Society, London, Special Publications |volume=448 |issue=1 |pages=311–349 |bibcode=2017GSLSP.448..311G |doi=10.1144/SP448.10 }}</ref>

Despite the long recognition of its distinction from younger [[Ordovician]] rocks and older [[Precambrian]] rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at [[Fortune Head]], [[Newfoundland]], Canada, was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of ''[[Treptichnus pedum]]''.<ref name="Geyer-2016" /> Discovery of this fossil a few metres below the [[GSSP]] led to the refinement of this statement, and it is the ''T. pedum'' [[ichnofossil]] [[faunal assemblage|assemblage]] that is now formally used to correlate the base of the Cambrian.<ref name="Geyer-2016" /><ref>{{Cite journal |last1=Landing |first1=Ed |last2=Geyer |first2=Gerd |last3=Brasier |first3=Martin D. |last4=Bowring |first4=Samuel A. |year=2013 |title=Cambrian Evolutionary Radiation: Context, correlation, and chronostratigraphy—Overcoming deficiencies of the first appearance datum (FAD) concept |journal=Earth-Science Reviews |volume=123 |pages=133–172 |bibcode=2013ESRv..123..133L |doi=10.1016/j.earscirev.2013.03.008}}</ref>

This formal designation allowed [[radiometric date]]s to be obtained from samples across the globe that corresponded to the base of the Cambrian. An early date of 570 [[Megaannum|Ma]] quickly gained favour,<ref name="Geyer-2016" /> though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise analysis using modern radiometric dating yields a date of 538.8 ± 0.6 Ma.<ref name="ICS" /> The ash horizon in [[Oman]] from which this date was recovered corresponds to a marked fall in the abundance of [[carbon-13]] that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (''[[Namacalathus]]'', ''[[Cloudina]]''). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran–Cambrian boundary, but represents a [[facies]] change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 to 542 Ma, are more suitable.<ref name="Geyer-2016" />

[[File:Basal Cambrian GSSP.jpg|alt=Photograph of the layered rocks that make up the headland at Fortune Head GSSP|thumb|Ediacaran–Cambrian boundary section at [[Fortune Head]], [[Newfoundland]], [[GSSP]]]]

==== Terreneuvian ====
The [[Terreneuvian]] is the lowermost series/[[Geologic time scale|epoch]] of the Cambrian, lasting from 538.8 ± 0.6 Ma to c. 521 Ma. It is divided into two stages: the [[Fortunian]] stage, 538.8 ± 0.6 Ma to c. 529 Ma; and the unnamed Stage 2, c. 529 Ma to c. 521 Ma.<ref name="ICS" /> The name Terreneuvian was ratified by the [[International Union of Geological Sciences]] (IUGS) in 2007, replacing the previous "Cambrian Series 1". The GSSP defining its base is at Fortune Head on the Burin Peninsula, eastern Newfoundland, Canada (see Ediacaran–Cambrian boundary above). The Terreneuvian is the only series in the Cambrian to contain no trilobite fossils. Its lower part is characterised by complex, sediment-penetrating Phanerozoic-type [[trace fossil]]s, and its upper part by small shelly fossils.<ref name="Peng-2020" />

==== Cambrian Series 2 ====
The second series/epoch of the Cambrian is currently unnamed and known as [[Cambrian Series 2]]. It lasted from c. 521 Ma to c. 506.5 Ma. Its two stages are also unnamed and known as [[Cambrian Stage 3]], c. 521 Ma to c. 514.5 Ma, and [[Cambrian Stage 4]], c. 514.5 Ma to c. 506.5 Ma.<ref name="ICS" /> The base of Series 2 does not yet have a GSSP, but it is expected to be defined in [[Stratum|strata]] marking the first appearance of trilobites in [[Gondwana]]. There was a rapid diversification of [[Animal|metazoans]] during this epoch, but their restricted geographic distribution, particularly of the trilobites and [[Archaeocyatha|archaeocyaths]], have made global correlations difficult, hence ongoing efforts to establish a GSSP.<ref name="Peng-2020" />

==== Miaolingian ====
[[File:Diorama of the Burgess Shale Biota (Middle Cambrian) - sponges, arthropods (44691571505).jpg|thumb|250px|Diorama of the [[Paleobiota of the Burgess Shale|Burgess Shale Biota]]]]
The [[Miaolingian]] is the third series/epoch of the Cambrian, lasting from c. 506.5 Ma to c. 497 Ma, and roughly identical to the middle Cambrian in older literature.<ref>{{cite journal |last1=Nielsen |first1=Arne Thorshøj |last2=Ahlberg |first2=Per |title=The Miaolingian, a new name for the 'Middle' Cambrian (Cambrian Series 3): identification of lower and upper boundaries in Baltoscandia |journal=GFF |date=3 April 2019 |volume=141 |issue=2 |pages=162–173 |doi=10.1080/11035897.2019.1621374 |bibcode=2019GFF...141..162N }}</ref> It is divided into three stages: the [[Wuliuan]] c. 506.5 Ma to 504.5 Ma; the [[Drumian]] c. 504.5 Ma to c. 500.5 Ma; and the Guzhangian c. 500.5 Ma to c. 497 Ma.<ref name="ICS" /> The name replaces Cambrian Series 3 and was ratified by the IUGS in 2018.<ref name="Zhao-2019">{{Cite journal |last1=Zhao |first1=Yuanlong |last2=Yuan |first2=Jinliang |last3=Babcock |first3=Loren E. |last4=Guo |first4=Qingjun |last5=Peng |first5=Jin |last6=Yin |first6=Leiming |last7=Yang |first7=Xinglian |last8=Peng |first8=Shanchi |last9=Wang |first9=Chunjiang |last10=Gaines |first10=Robert R. |last11=Esteve |first11=Jorge |last12=Tai |first12=Tongsu |last13=Yang |first13=Ruidong |last14=Wang |first14=Yue |last15=Sun |first15=Haijing |date=1 June 2019 |title=Global Standard Stratotype-Section and Point (GSSP) for the conterminous base of the Miaolingian Series and Wuliuan Stage (Cambrian) at Balang, Jianhe, Guizhou, China |journal=Episodes Journal of International Geoscience |language=en |volume=42 |issue=2 |pages=165–184 |doi=10.18814/epiiugs/2019/019013|doi-access=free |bibcode=2019Episo..42..165Z }}</ref> It is named after the Miaoling Mountains in southeastern [[Guizhou|Guizhou Province]], South China, where the GSSP marking its base is found. This is defined by the first appearance of the [[Oryctocephalidae|oryctocephalid]] trilobite ''[[Oryctocephalus indicus]]''. Secondary markers for the base of the Miaolingian include the appearance of many [[acritarch]]s forms, a global [[marine transgression]], and the disappearance of the polymerid trilobites, ''Bathynotus'' or ''Ovatoryctocara.'' Unlike the Terreneuvian and Series 2, all the stages of the Miaolingian are defined by GSSPs''.''<ref name="Zhao-2019" />

The [[Olenelloidea|olenellids]], [[Eodiscidae|eodiscids]], and most [[Redlichiida|redlichiids]] trilobites went extinct at the boundary between Series 2 and the Miaolingian. This is considered the oldest mass extinction of trilobites.<ref name="Peng-2020" />

==== Furongian ====
The [[Furongian]], c. 497 Ma to 486.85 ± 1.5 Ma, is the fourth and uppermost series/epoch of the Cambrian. The name was ratified by the IUGS in 2003 and replaces Cambrian Series 4 and the traditional "Upper Cambrian". The GSSP for the base of the Furongian is in the [[Wuling Mountains]], in northwestern [[Hunan|Hunan Province]], China. It coincides with the first appearance of the agnostoid trilobite ''Glyptagnostus reticulatus'', and is near the beginning of a large positive [[Δ13C|δ<sup>13</sup>C]] isotopic excursion.<ref name="Peng-2020" />

The Furongian is divided into three stages: the [[Paibian]], c. 497 Ma to c. 494 Ma, and the [[Jiangshanian]] c. 494.2 Ma to c. 491 Ma, which have defined GSSPs; and the unnamed [[Cambrian Stage 10]], c. 491 Ma to 486.85 ± 1.5 Ma.<ref name="ICS" />

==== Cambrian–Ordovician boundary ====
The GSSP for the Cambrian–Ordovician boundary is at [[Green Point, Newfoundland and Labrador|Green Point]], western [[Newfoundland and Labrador|Newfoundland]], Canada, and is dated at 486.85 Ma. It is defined by the appearance of the [[conodont]] ''[[Iapetognathus fluctivagus]]''. Where these conodonts are not found the appearance of [[plankton]]ic [[graptolite]]s or the [[trilobite]] ''Jujuyaspis borealis'' can be used. The boundary also corresponds with the peak of the largest positive variation in the δ<sup>13</sup>C curve during the boundary time interval and with a global marine transgression.<ref>{{Citation |last1=Cooper |first1=R.A. |chapter=The Ordovician Period |date=2012 |title=The Geologic Time Scale |pages=489–523 |publisher=Elsevier |doi=10.1016/b978-0-444-59425-9.00020-2 |isbn=978-0-444-59425-9 |last2=Sadler |first2=P.M. |last3=Hammer |first3=O. |last4=Gradstein |first4=F.M.}}</ref>

=== Impact structures ===
Major meteorite impact structures include: the early Cambrian (c. 535 Ma) [[Neugrund crater]] in the [[Gulf of Finland]], Estonia, a complex meteorite crater about 20&nbsp;km in diameter, with two inner ridges of about 7&nbsp;km and 6&nbsp;km diameter, and an outer ridge of 8&nbsp;km that formed as the result of an impact of an asteroid 1&nbsp;km in diameter;<ref>{{Cite journal |last1=Suuroja |first1=Kalle |last2=Suuroja |first2=Sten |date=2010 |title=The Neugrund meteorite crater on the seafloor of the Gulf of Finland |journal=Baltica |volume=23 |issue=1 |pages=47–58 |url=https://baltica.gamtc.lt/administravimas/uploads/2010_vol23(1)-05_5e70963d86ee9.pdf }}</ref> the 5&nbsp;km diameter [[Gardnos crater]] (500±10 Ma) in [[Buskerud]], Norway, where post-impact sediments indicate the impact occurred in a shallow marine environment with [[Rockslide|rock avalanches]] and [[debris flow]]s occurring as the crater rim was breached not long after impact;<ref>{{cite thesis |last=Kalleson |first=Elin |date=2009 |title=The Gardnos structure: the impactites, sedimentary deposits and post-impact history |hdl=10852/33234 |hdl-access=free }}</ref> the 24&nbsp;km diameter [[Presqu'île crater|Presqu'ile crater]] (500 Ma or younger) [[Quebec]], Canada; the 19&nbsp;km diameter [[Glikson crater]] (c. 508 Ma) in Western Australia; the 5&nbsp;km diameter [[Mizarai crater]] (500±10 Ma) in Lithuania; and the 3.2&nbsp;km diameter [[Newporte crater|Newporte structure]] (c. 500 Ma or slightly younger) in [[North Dakota]], U.S.A.<ref>{{Cite web |title=Earth impact database |url=http://www.passc.net/EarthImpactDatabase/New%20website_05-2018/Agesort.html |access-date=20 September 2024 |website=www.passc.net}}</ref>

== Paleogeography ==
Reconstructing the position of the continents during the Cambrian is based on [[Paleomagnetism|palaeomagnetic]], [[Biogeography|palaeobiogeographic]], [[Tectonics|tectonic]], geological and [[Paleoclimatology|palaeoclimatic]] data. However, these have different levels of uncertainty and can produce contradictory locations for the major continents.<ref name="Keppie-2024">{{Cite journal |last1=Keppie |first1=Duncan Fraser |last2=Keppie |first2=John Duncan |last3=Landing |first3=Ed |date=23 April 2024 |title=A tectonic solution for the Early Cambrian palaeogeographical enigma |journal=Geological Society, London, Special Publications |language=en |volume=542 |issue=1 |pages=167–177 |doi=10.1144/SP542-2022-355 |doi-access=free |bibcode=2024GSLSP.542..167K }}</ref> This, together with the ongoing debate around the existence of the Neoproterozoic supercontinent of [[Pannotia]], means that while most models agree the continents lay in the southern hemisphere, with the vast [[Panthalassa]] Ocean covering most of northern hemisphere, the exact distribution and timing of the movements of the Cambrian continents varies between models.<ref name="Keppie-2024"/>
[[File:Gondwana and Laurentia.png|thumb|Approximate positions of Gondwana, Laurentia and Baltica in the middle Cambrian (c. 500 Ma). AT: Armorican terrane, CA: Carolinia, CU: Cuyania, EA: East Avalonia, FA: Famatina arc, GA: Ganderia, IB: Iberia, MX: Mixteca–Oaxaca block, WA: West Avalonia. Plate boundaries: red – subduction; white – ridges; yellow – transform.<ref name="Domeier-2016"/><ref name="Torsvik-2017" /> |alt=Paleogeographic map showing Gondwana close to the south pole, Laurentia at the equator and Baltica in between.]]

Most models show [[Gondwana]] stretching from the south polar region to north of the equator.<ref name="Torsvik-2017">{{Cite book |last1=Torsvik |first1=Trond H.  |title=Earth history and palaeogeography |last2=Cocks |first2=L. R. M. |date=2017 |publisher=Cambridge University Press |isbn=978-1-107-10532-4 |location=Cambridge, United Kingdom |oclc=968155663}}</ref> Early in the Cambrian, the south pole corresponded with the western South American sector and as Gondwana rotated anti-clockwise, by the middle of the Cambrian, the south pole lay in the northwest African region.<ref name="Keppie-2024"/>

[[Laurentia]] lay across the equator, separated from Gondwana by the [[Iapetus Ocean]].<ref name="Torsvik-2017" /> Proponents of Pannotia have Laurentia and [[Baltica]] close to the Amazonia region of Gondwana with a narrow Iapetus Ocean that only began to open once Gondwana was fully assembled c. 520 Ma.<ref>{{cite journal |last1=Dalziel |first1=Ian W. D. |last2=Dewey |first2=John F. |title=The classic Wilson cycle revisited |journal=Geological Society, London, Special Publications |date=January 2019 |volume=470 |issue=1 |pages=19–38 |doi=10.1144/SP470.1 |bibcode=2019GSLSP.470...19D }}</ref> Those not in favour of the existence of Pannotia show the Iapetus opening during the Late Neoproterozoic, with up to c. 6,500&nbsp;km (c. 4038 miles) between Laurentia and West Gondwana at the beginning of the Cambrian.<ref name="Torsvik-2017" />

Of the smaller continents, Baltica lay between Laurentia and Gondwana, the Ran Ocean (an arm of the Iapetus) opening between it and Gondwana. [[Siberia (continent)|Siberia]] lay close to the western margin of Gondwana and to the north of Baltica.<ref name="Wong Hearing-2021">{{Cite journal |last1=Wong Hearing |first1=Thomas W. |last2=Pohl |first2=Alexandre |last3=Williams |first3=Mark |last4=Donnadieu |first4=Yannick |last5=Harvey |first5=Thomas H. P. |last6=Scotese |first6=Christopher R. |last7=Sepulchre |first7=Pierre |last8=Franc |first8=Alain |last9=Vandenbroucke |first9=Thijs R. A. |date=23 June 2021 |title=Quantitative comparison of geological data and model simulations constrains early Cambrian geography and climate|journal=Nature Communications |volume=12 |issue=1 |page=3868 |doi=10.1038/s41467-021-24141-5 |pmid=34162853 |pmc=8222365 |bibcode=2021NatCo..12.3868W |hdl=1854/LU-8719399 |hdl-access=free }}</ref><ref name="Torsvik-2017" /> Annamia and [[South China craton|South China]] formed a single continent situated off north central Gondwana. The location of [[North China craton|North China]] is unclear. It may have lain along the northeast Indian sector of Gondwana or already have been a separate continent.<ref name="Torsvik-2017" />

=== Laurentia ===
During the Cambrian, Laurentia lay across or close to the equator.  It drifted south and rotated c. 20° anticlockwise during the middle Cambrian, before drifting north again in the late Cambrian.<ref name="Torsvik-2017" />

After the Late Neoproterozoic (or mid-Cambrian) [[rift]]ing of Laurentia from Gondwana and the subsequent opening of the Iapetus Ocean, Laurentia was largely surrounded by [[passive margin]]s with much of the continent covered by shallow seas.<ref name="Torsvik-2017" />

As Laurentia separated from Gondwana, a sliver of continental [[terrane]] rifted from Laurentia with the narrow [[Taconic orogeny|Taconic seaway]] opening between them. The remains of this terrane are now found in southern Scotland, Ireland, and Newfoundland. Intra-oceanic [[subduction]] either to the southeast of this terrane in the Iapetus, or to its northwest in the Taconic seaway, resulted in the formation of an [[island arc]]. This [[Accretion (geology)|accreted]] to the terrane in the late Cambrian, triggering southeast-dipping subduction beneath the terrane itself and consequent closure of the marginal seaway. The terrane collided with Laurentia in the Early Ordovician.<ref name="Domeier-2016">{{cite journal |last1=Domeier |first1=Mathew |title=A plate tectonic scenario for the Iapetus and Rheic oceans |journal=Gondwana Research |date=August 2016 |volume=36 |pages=275–295 |doi=10.1016/j.gr.2015.08.003 |bibcode=2016GondR..36..275D }}</ref>

Towards the end of the early Cambrian, rifting along Laurentia's southeastern margin led to the separation of [[Cuyania]] (now part of Argentina) from the [[Ouachita County, Arkansas|Ouachita]] embayment with a new ocean established that continued to widen through the Cambrian and Early Ordovician.<ref name="Domeier-2016" />

=== Gondwana ===
Gondwana was a massive continent, three times the size of any of the other Cambrian continents. Its continental land area extended from the south pole to north of the equator. Around it were extensive shallow seas and numerous smaller land areas.<ref name="Torsvik-2017" />

The [[craton]]s that formed Gondwana came together during the Neoproterozoic to early Cambrian. A narrow ocean separated [[Amazonian craton|Amazonia]] from Gondwana until c. 530 Ma<ref>{{cite journal |last1=Evans |first1=David A. D. |title=Pannotia under prosecution |journal=Geological Society, London, Special Publications |date=January 2021 |volume=503 |issue=1 |pages=63–81 |doi=10.1144/SP503-2020-182 |bibcode=2021GSLSP.503...63E }}</ref> and the [[Arequipa-Antofalla]] block united with the [[South America]]n sector of Gondwana in the early Cambrian.<ref name="Torsvik-2017" /> The [[Kuunga orogeny|Kuunga Orogeny]] between northern ([[Congo craton|Congo Craton]], [[Madagascar]] and [[Geology of India|India]]) and southern Gondwana ([[Kalahari craton|Kalahari Craton]] and [[East Antarctic Shield|East Antarctica]]), which began c. 570 Ma, continued with parts of northern Gondwana over-riding southern Gondwana and was accompanied by [[metamorphism]] and the [[Igneous intrusion|intrusion]] of [[granite]]s.<ref>{{cite journal |last1=Grantham |first1=Geoffrey H. |last2=Satish-Kumar |first2=M. |last3=Horie |first3=Kenji |last4=Ueckermann |first4=Henriette |title=The Kuunga Accretionary Complex of Sverdrupfjella and Gjelsvikfjella, western Dronning Maud Land, Antarctica |journal=Journal of Mineralogical and Petrological Sciences |date=2023 |volume=118 |article-number=230125 |doi=10.2465/jmps.230125 |doi-access=free }}</ref>

[[Subduction|Subduction zones]], active since the Neoproterozoic, extended around much of Gondwana's margins, from northwest Africa southwards round South America, [[South Africa]], [[East Antarctic Shield|East Antarctica]], and the eastern edge of West Australia. Shorter subduction zones existed north of [[Arabian-Nubian Shield|Arabia]] and India.<ref name="Torsvik-2017" />

The [[Famatinian orogeny|Famatinian]] [[continental arc]] stretched from central Peru in the north to central Argentina in the south. Subduction beneath this proto-[[Andean orogeny|Andean]] margin began by the late Cambrian.<ref name="Domeier-2016" />

Along the northern margin of Gondwana, between northern Africa and the [[Armorican terrane|Armorican Terranes]] of southern Europe, the continental arc of the [[Cadomian Orogeny]] continued from the Neoproterozoic in response to the [[oblique subduction]] of the Iapetus Ocean.<ref name="Murphy-2021">{{cite journal |last1=Murphy |first1=J. Brendan |last2=Nance |first2=R. Damian |last3=Cawood |first3=Peter A. |last4=Collins |first4=William J. |last5=Dan |first5=Wei |last6=Doucet |first6=Luc S. |last7=Heron |first7=Philip J. |last8=Li |first8=Zheng-Xiang |last9=Mitchell |first9=Ross N. |last10=Pisarevsky |first10=Sergei |last11=Pufahl |first11=Peir K. |last12=Quesada |first12=Cecilio |last13=Spencer |first13=Christopher J. |last14=Strachan |first14=Rob A. |last15=Wu |first15=Lei |title=Pannotia: in defence of its existence and geodynamic significance |journal=Geological Society, London, Special Publications |date=January 2021 |volume=503 |issue=1 |pages=13–39 |doi=10.1144/SP503-2020-96 |bibcode=2021GSLSP.503...13M |hdl=20.500.11937/90589 |hdl-access=free }}</ref> This subduction extended west along the Gondwanan margin and by c. 530 Ma may have evolved into a major [[transform fault]] system.<ref name="Murphy-2021" />

At c. 511 Ma the [[Flood basalt|continental flood basalts]] of the [[Kalkarindji]] [[large igneous province]] (LIP) began to erupt. These covered an area of > 2.1 million km<sup>2</sup> across northern, central and Western Australia regions of Gondwana making it one of the largest, as well as the earliest, LIPs of the Phanerozoic. The timing of the eruptions suggests they played a role in the early to middle Cambrian [[Extinction event|mass extinction]].<ref name="Murphy-2021" />

==== Ganderia, East and West Avalonia, Carolinia and Meguma Terranes ====
The terranes of [[Ganderia]], East and West [[Avalonia]], [[Carolina terrane|Carolinia]] and [[Meguma terrane|Meguma]] lay in polar regions during the early Cambrian, and high-to-mid southern [[latitude]]s by the mid to late Cambrian.<ref name="Domeier-2016" /><ref name="Keppie-2024"/> They are commonly shown as an island arc-transform fault system along the northwestern margin of Gondwana north of northwest Africa and Amazonia, which rifted from Gondwana during the Ordovician.<ref name="Domeier-2016" /> However, some models show these terranes as part of a single independent [[Continental fragment|microcontinent]], Greater Avalonia, lying to the west of Baltica and aligned with its eastern ([[Timanide Orogen|Timanide]]) margin, with the Iapetus to the north and the Ran Ocean to the south.<ref name="Keppie-2024"/>
[[File:Gondwana, China and Siberia.png|thumb|Approximate positions of Siberia, Gondwana, North and South China, Baltica and smaller terranes in the middle Cambrian (c. 500 Ma). AN: Annamia, CM: Central Mongolian terrane, JA: Japan arc, KHT: Kazakhstania terranes, MOO: Mongol-Okhotsk Ocean, NC: North China, QT: Qinling terrane, SC: South China, TA: Tarim microcontinent, VT: Variscan terranes. Plate boundaries: red – subduction; white – ridges; yellow – transform.<ref name="Torsvik-2017" /><ref name="Domeier-2018"/> |alt=Paleogeographic map showing Gondwana close to the south pole, Siberia, North and South China near the equator and Baltica to the south of Siberia.]]

=== Baltica ===
During the Cambrian, Baltica rotated more than 60° anti-clockwise and began to drift northwards.<ref name="Domeier-2016" /> This rotation was accommodated by major strike-slip movements in the Ran Ocean between it and Gondwana.<ref name="Torsvik-2017" />

Baltica lay at mid-to-high southerly latitudes, separated from Laurentia by the Iapetus and from Gondwana by the Ran Ocean. It was composed of two continents, [[Baltic Shield|Fennoscandia]] and [[Sarmatian craton|Sarmatia]], separated by shallow seas.<ref name="Torsvik-2017" /><ref name="Domeier-2016" /> The [[sediment]]s deposited in these [[Unconformity|unconformably]] overlay Precambrian [[Basement (geology)|basement]] rocks. The lack of coarse-grained sediments indicates low lying [[topography]] across the centre of the craton.<ref name="Torsvik-2017" />

Along Baltica's northeastern margin subduction and arc magmatism associated with the Ediacaran [[Timanide Orogen|Timanian Orogeny]] was coming to an end. In this region the early to middle Cambrian was a time of non-deposition and followed by late Cambrian rifting and sedimentation.<ref name="Domeier-2018">{{Cite journal |last=Domeier |first=Mathew |date=2018 |title=Early Paleozoic tectonics of Asia: Towards a full-plate model |journal=Geoscience Frontiers |volume=9 |issue=3 |pages=789–862 |doi=10.1016/j.gsf.2017.11.012 |bibcode=2018GeoFr...9..789D |hdl=10852/71215 |hdl-access=free }}</ref>

Its southeastern margin was also a [[convergent boundary]], with the accretion of island arcs and microcontinents to the craton, although the details are unclear.<ref name="Torsvik-2017" />

=== Siberia ===
Siberia began the Cambrian close to western Gondwana and north of Baltica. It drifted northwestwards to close to the equator as the Ægir Ocean opened between it and Baltica.<ref name="Torsvik-2017" /><ref name="Wong Hearing-2021" /> Much of the continent was covered by shallow seas with extensive [[Archaeocyatha|archaeocyathan reefs]]. The then northern third of the continent (present day south; Siberia has rotated 180° since the Cambrian) adjacent to its convergent margin was mountainous.<ref name="Torsvik-2017" />

From the Late Neoproterozoic to the Ordovician, a series of island arcs accreted to Siberia's then northeastern margin, accompanied by extensive arc and [[Back-arc region|back-arc]] volcanism. These now form the [[Altai-Sayan region|Altai-Sayan]] terranes.<ref name="Torsvik-2017" /><ref name="Domeier-2018" /> Some models show a convergent plate margin extending from Greater Avalonia, through the Timanide margin of Baltica, forming the Kipchak island arc offshore of southeastern Siberia and curving round to become part of the Altai-Sayan convergent margin.<ref name="Keppie-2024"/>

Along the then western margin, Late Neoproterozoic to early Cambrian rifting was followed by the development of a passive margin.<ref name="Domeier-2018" />

To the then north, Siberia was separated from the Central Mongolian terrane by the narrow and slowly opening [[Mongol-Okhotsk Ocean]]. The Central Mongolian terrane's northern margin with the Panthalassa was convergent, whilst its southern margin facing the Mongol-Okhotsk Ocean was passive.<ref name="Torsvik-2017" />

=== Central Asia ===
During the Cambrian, the terranes that would form [[Kazakhstania]] later in the Paleozoic were a series of island arc and [[Accretionary wedge|accretionary complexes]] that lay along an intra-oceanic convergent plate margin to the south of North China.<ref name="Domeier-2018" />

To the south of these the Tarim microcontinent lay between Gondwana and Siberia.<ref name="Torsvik-2017" /> Its northern margin was passive for much of the Paleozoic, with thick sequences of [[Carbonate platform|platform carbonates]] and [[Fluvial sediment processes|fluvial]] to marine sediments resting unconformably on Precambrian basement. Along its southeast margin was the [[Altyn-Tagh|Altyn]] Cambro–Ordovician accretionary complex, whilst to the southwest a subduction zone was closing the narrow seaway between the North West [[Kunlun Mountains|Kunlun]] region of Tarim and the South West Kunlun terrane.<ref name="Domeier-2018" />

=== North China ===
[[File:Life on the platform margin of the Miaolingian sea, North China.png|thumb|250px|Life reconstruction of the Linyi Lagerstätte in Northern China]]
North China lay at equatorial to tropical latitudes during the early Cambrian, although its exact position is unknown.<ref name="Wong Hearing-2021" /> Some models show that it lies below the equatorial latitudes.<ref>{{cite book |last1=Torsvik |first1=Trond H. |last2=Cocks |first2=L. Robin M. |chapter=Cambrian |pages=85–100 |doi=10.1017/9781316225523.006 |title=Earth History and Palaeogeography |date=2016 |isbn=978-1-316-22552-3 }}</ref> Much of the craton was covered by shallow seas, with land in the northwest and southeast.<ref name="Torsvik-2017" />

Northern North China was a passive margin until the onset of subduction and the development of the Bainaimiao arc in the late Cambrian. To its south was a convergent margin with a southwest dipping subduction zone, beyond which lay the North Qinling terrane (now part of the [[Qinling orogenic belt|Qinling Orogenic Belt]]), together with Qilian-Qaidam, Altyn belts, and South West Kunlun terranes.<ref name="Domeier-2018" />

=== South China and Annamia ===
[[File:Haikouichthys4.png|thumb|right|''[[Haikouichthys]]'' is an extinct [[Evolution of fish|fish]]-like [[Vertebrate|craniate]] that lived in what is now China approximately 518 million ago]]
South China and Annamia formed a single continent. Strike-slip movement between it and Gondwana accommodated its steady drift northwards from offshore the Indian sector of Gondwana to near the western Australian sector. This northward drift is evidenced by the progressive increase in [[limestone]]s and increasing [[fauna]]l diversity.<ref name="Torsvik-2017" />

The northern margin South China, including the South Qinling block, was a passive margin.<ref name="Torsvik-2017" />

Along the southeastern margin, lower Cambrian volcanics indicate the accretion of an island arc along the Song Ma suture zone. Also, early in the Cambrian, the eastern margin of South China changed from passive to active, with the development of oceanic volcanic island arcs that now form part of the [[Geology of Japan|Japanese terrane]].<ref name="Torsvik-2017" />

== Climate ==
The distribution of climate-indicating sediments, including the wide latitudinal distribution of tropical carbonate platforms, archaeocyathan reefs and [[bauxite]]s, and arid zone [[evaporite]]s and [[Caliche|calcrete]] deposits, show the Cambrian was a time of greenhouse climate conditions.<ref name="Torsvik-2017" /><ref name="AnEarlyCambrianGreenhouseClimate">{{cite journal |last1=Hearing |first1=Thomas W. |last2=Harvey |first2=Thomas H. P. |last3=Williams |first3=Mark |last4=Leng |first4=Melanie J. |last5=Lamb |first5=Angela L. |last6=Wilby |first6=Philip R. |last7=Gabbott |first7=Sarah E. |last8=Pohl |first8=Alexandre |last9=Donnadieu |first9=Yannick |date=9 May 2018 |title=An early Cambrian greenhouse climate |journal=[[Science Advances]] |volume=4 |issue=5 |article-number=eaar5690 |bibcode=2018SciA....4.5690H |doi=10.1126/sciadv.aar5690 |pmc=5942912 |pmid=29750198}}</ref><ref name="ChristopherScotese">{{cite journal |last1=Scotese |first1=Christopher R. |last2=Song |first2=Haijun |last3=Mills |first3=Benjamin J.W. |last4=van der Meer |first4=Douwe G. |title=Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years |journal=Earth-Science Reviews |date=April 2021 |volume=215 |article-number=103503 |doi=10.1016/j.earscirev.2021.103503 |bibcode=2021ESRv..21503503S }}</ref> During the late Cambrian the distribution of [[trilobite]] provinces also indicate only a moderate pole-to-equator temperature gradient.<ref name="ChristopherScotese" /> There is evidence of glaciation at high latitudes on Avalonia. However, it is unclear whether these sediments are early Cambrian or actually late Neoproterozoic in age.<ref name="AnEarlyCambrianGreenhouseClimate" />

Calculations of global average temperatures (GAT) vary depending on which techniques are used. Whilst some measurements show GAT over c. {{convert|40|°C|°F|abbr=on}} models that combine multiple sources give GAT of c. {{convert|20|-|22|C|F}} in the Terreneuvian increasing to c. {{convert|23|-|25|C|F}} for the rest of the Cambrian.<ref name="ChristopherScotese" /><ref name="Pruss-2024">{{cite journal |last1=Pruss |first1=Sara B. |last2=Gill |first2=Benjamin C. |title=Life on the Edge: The Cambrian Marine Realm and Oxygenation |journal=Annual Review of Earth and Planetary Sciences |date=23 July 2024 |volume=52 |issue=1 |pages=109–132 |doi=10.1146/annurev-earth-031621-070316 |bibcode=2024AREPS..52..109P |hdl=10919/117422 |hdl-access=free }}</ref> The warm climate was linked to elevated atmospheric [[carbon dioxide]] levels. Assembly of Gondwana led to the reorganisation of the tectonic plates with the development of new convergent plate margins and continental-margin arc magmatism that helped drive climatic warming.<ref name="Pruss-2024" /><ref name="Myrow-2024">{{Cite journal |last1=Myrow |first1=Paul M. |last2=Goodge |first2=John W. |last3=Brock |first3=Glenn A. |last4=Betts |first4=Marissa J. |last5=Park |first5=Tae-Yoon S. |last6=Hughes |first6=Nigel C. |last7=Gaines |first7=Robert R. |title=Tectonic trigger to the first major extinction of the Phanerozoic: The early Cambrian Sinsk event |journal=Science Advances |date=2024 |volume=10 |issue=13 |article-number=eadl3452 |doi=10.1126/sciadv.adl3452 |pmid=38552008 |pmc=10980278 |bibcode=2024SciA...10L3452M }}</ref> The eruptions of the Kalkarindji LIP [[basalt]]s during Stage 4 and into the early Miaolingian, also released large quantities of carbon dioxide, [[methane]] and [[Sulfur dioxide|sulphur dioxide]] into the atmosphere leading to rapid climatic changes and elevated sea surface temperatures.<ref name="Myrow-2024" />

There is uncertainty around the maximum sea surface temperatures. These are calculated using [[Δ18O|δ<sup>18</sup>O]] values from marine rocks, and there is an ongoing debate about the levels δ<sup>18</sup>O in Cambrian seawater relative to the rest of the Phanerozoic.<ref name="ChristopherScotese" /><ref name="Wotte-2019">{{Cite journal |last1=Wotte |first1=Thomas |last2=Skovsted |first2=Christian B. |last3=Whitehouse |first3=Martin J. |last4=Kouchinsky |first4=Artem |date=19 April 2019 |title=Isotopic evidence for temperate oceans during the Cambrian Explosion |journal=Scientific Reports |language=en |volume=9 |issue=1 |page=6330 |doi=10.1038/s41598-019-42719-4 |pmid=31004083 |pmc=6474879 |bibcode=2019NatSR...9.6330W }}</ref> Estimates for tropical sea surface temperatures vary from c. {{convert|28|-|32|C|F}},<ref name="ChristopherScotese" /><ref name="Wotte-2019" /> to c. {{convert|29|-|38|C|F}}.<ref>{{Cite journal |last1=Bergmann |first1=Kristin D. |last2=Finnegan |first2=Seth |last3=Creel |first3=Roger |last4=Eiler |first4=John M. |last5=Hughes |first5=Nigel C. |last6=Popov |first6=Leonid E. |last7=Fischer |first7=Woodward W. |date=2018 |title=A paired apatite and calcite clumped isotope thermometry approach to estimating Cambro-Ordovician seawater temperatures and isotopic composition |journal=Geochimica et Cosmochimica Acta |volume=224 |pages=18–41 |doi=10.1016/j.gca.2017.11.015 |bibcode=2018GeCoA.224...18B }}</ref><ref name="AnEarlyCambrianGreenhouseClimate" /> Modern average tropical sea surface temperatures are {{convert|26|°C|°F|abbr=on}}.<ref name="ChristopherScotese" />

Atmospheric oxygen levels rose steadily rising from the Neoproterozoic due to the increase in [[photosynthesis]]ing organisms. Cambrian levels varied between c. 3% and 14% (present day levels are c. 21%). Low levels of atmospheric oxygen and the warm climate resulted in lower dissolved oxygen concentrations in marine waters and widespread [[Anoxic waters|anoxia]] in deep ocean waters.<ref name="Pruss-2024" /><ref name="Mills-2023">{{cite journal |last1=Mills |first1=Benjamin J.W. |last2=Krause |first2=Alexander J. |last3=Jarvis |first3=Ian |last4=Cramer |first4=Bradley D. |title=Evolution of Atmospheric {{chem|O|2}} Through the Phanerozoic, Revisited |journal=Annual Review of Earth and Planetary Sciences |date=31 May 2023 |volume=51 |issue=1 |pages=253–276 |doi=10.1146/annurev-earth-032320-095425 }}</ref>

There is a complex relationship between oxygen levels, the [[biogeochemistry]] of ocean waters, and the evolution of life. Newly evolved burrowing organisms exposed anoxic sediments to the overlying oxygenated seawater. This [[bioturbation]] decreased the burial rates of organic carbon and [[Sulfur|sulphur]], which over time reduced atmospheric and oceanic oxygen levels, leading to widespread anoxic conditions.<ref name="van de Velde-2018">{{Cite journal |last1=van de Velde |first1=Sebastiaan |last2=Mills |first2=Benjamin J. W. |last3=Meysman |first3=Filip J. R. |last4=Lenton |first4=Timothy M. |last5=Poulton |first5=Simon W. |date=2 July 2018 |title=Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing |journal=Nature Communications |volume=9 |issue=1 |page=2554 |doi=10.1038/s41467-018-04973-4 |pmid=29967319 |pmc=6028391 |bibcode=2018NatCo...9.2554V }}</ref> Periods of higher rates of continental [[weathering]] led to increased delivery of nutrients to the oceans, boosting productivity of [[phytoplankton]] and stimulating metazoan evolution. However, rapid increases in nutrient supply led to [[eutrophication]], where rapid growth in phytoplankton numbers result in the depletion of oxygen in the surrounding waters.<ref name="Pruss-2024" /><ref name="Wood-2019">{{cite journal |last1=Wood |first1=Rachel |last2=Liu |first2=Alexander G. |last3=Bowyer |first3=Frederick |last4=Wilby |first4=Philip R. |last5=Dunn |first5=Frances S. |last6=Kenchington |first6=Charlotte G. |last7=Cuthill |first7=Jennifer F. Hoyal |last8=Mitchell |first8=Emily G. |last9=Penny |first9=Amelia |title=Integrated records of environmental change and evolution challenge the Cambrian Explosion |journal=Nature Ecology & Evolution |date=11 March 2019 |volume=3 |issue=4 |pages=528–538 |doi=10.1038/s41559-019-0821-6 |pmid=30858589 |bibcode=2019NatEE...3..528W |hdl=20.500.11820/a4e98e0f-a350-40f6-9ee6-49d4f816835f |hdl-access=free }}</ref>

Pulses of increased oxygen levels are linked to increased biodiversity; raised oxygen levels supported the increasing [[Metabolism|metabolic]] demands of organisms, and increased [[ecological niche]]s by expanding habitable areas of seafloor. Conversely, incursions of oxygen-deficient water, due to changes in sea level, ocean circulation, upwellings from deeper waters and/or biological productivity, produced anoxic conditions that limited habitable areas, reduced ecological niches and resulted in extinction events both regional and global.<ref name="Mills-2023" /><ref name="van de Velde-2018" /><ref name="Wood-2019" />

Overall, these dynamic, fluctuating environments, with global and regional anoxic incursions resulting in extinction events, and periods of increased oceanic oxygenation stimulating biodiversity, drove evolutionary innovation.<ref name="van de Velde-2018" /><ref name="Pruss-2024" /><ref name="Wood-2019" />

== Geochemistry ==
During the Cambrian, variations in [[Isotopic ratio|isotope ratios]] were more frequent and more pronounced than later in the Phanerozoic, with at least 10 carbon isotope ([[Δ13C|δ<sup>13</sup>C]]) excursions (significant variations in global isotope ratios) recognised.<ref name="Peng-2020" /> These excursions record changes in the biogeochemistry of the oceans and atmosphere, which are due to processes such as the global rates of continental arc magmatism, rates of weathering and nutrients levels entering the marine environment, sea level changes, and biological factors including the impact of burrowing fauna on oxygen levels.<ref name="Pruss-2024" /><ref name="Wood-2019" /><ref name="Myrow-2024" />

=== Isotope excursions ===

==== Base of Cambrian ====
The basal Cambrian δ<sup>13</sup>C excursion (BACE), together with low [[Uranium|δ<sup>238</sup>U]] and raised [[Δ34S|δ<sup>34</sup>S]] indicates a period of widespread shallow marine anoxia, which occurs at the same time as the extinction of the Ediacaran acritarchs. It was followed by the rapid appearance and diversification of [[bilateria]]n animals.<ref name="Peng-2020" /><ref name="Pruss-2024" />

==== Cambrian Stages 2 and 3 ====
During the early Cambrian, [[Strontium|<sup>87</sup>Sr/<sup>86</sup>Sr]] rose in response to enhanced continental weathering. This increased the input of nutrients into the oceans and led to higher burial rates of organic matter.<ref name="Zhang-2020">{{Cite journal |last1=Zhang |first1=Yinggang |last2=Yang |first2=Tao |last3=Hohl |first3=Simon V. |last4=Zhu |first4=Bi |last5=He |first5=Tianchen |last6=Pan |first6=Wenqing |last7=Chen |first7=Yongquan |last8=Yao |first8=Xizhu |last9=Jiang |first9=Shaoyong |date=2020 |title=Seawater carbon and strontium isotope variations through the late Ediacaran to late Cambrian in the Tarim Basin |journal=Precambrian Research |volume=345 |article-number=105769 |doi=10.1016/j.precamres.2020.105769 |bibcode=2020PreR..34505769Z }}</ref> Over long timescales, the extra oxygen released by organic carbon burial is balanced by a decrease in the rates of [[pyrite]] (FeS<sub>2</sub>) burial (a process which also releases oxygen), leading to stable levels of oxygen in the atmosphere. However, during the early Cambrian, a series of linked δ<sup>13</sup>C and δ<sup>34</sup>S excursions indicate high burial rates of both organic carbon and pyrite in biologically productive yet anoxic ocean floor waters. The oxygen-rich waters produced by these processes spread from the deep ocean into shallow marine environments, extending the habitable regions of the seafloor.<ref name="Peng-2020" /><ref name="He-2019">{{Cite journal |last1=He |first1=Tianchen |last2=Zhu |first2=Maoyan |last3=Mills |first3=Benjamin J. W. |last4=Wynn |first4=Peter M. |last5=Zhuravlev |first5=Andrey Yu |last6=Tostevin |first6=Rosalie |last7=Pogge von Strandmann |first7=Philip A. E. |last8=Yang |first8=Aihua |last9=Poulton |first9=Simon W. |last10=Shields |first10=Graham A. |date=2019 |title=Possible links between extreme oxygen perturbations and the Cambrian radiation of animals |journal=Nature Geoscience |language=en |volume=12 |issue=6 |pages=468–474 |doi=10.1038/s41561-019-0357-z |pmid=31178922 |pmc=6548555 |bibcode=2019NatGe..12..468H }}</ref> These pulses of oxygen are associated with the radiation of the small shelly fossils and the Cambrian [[arthropod]] radiation isotope excursion (CARE).<ref name="Zhang-2020" /> The increase in oxygenated waters in the deep ocean ultimately reduced the levels of organic carbon and pyrite burial, leading to a decrease in oxygen production and the re-establishment of anoxic conditions. This cycle was repeated several times during the early Cambrian.<ref name="Peng-2020" /><ref name="He-2019" />
[[Image:Archeocyathids.JPG|thumb|[[Archeocyathid]]s from the [[Poleta formation]] in the [[Death Valley]] area]]

==== Cambrian Stage 4 to early Miaolingian ====
The beginning of the eruptions of the Kalkarindji LIP basalts during Stage 4 and the early Miaolingian released large quantities of carbon dioxide, methane and sulphur dioxide into the atmosphere. The changes these wrought are reflected by three large and rapid δ<sup>13</sup>C excursions. Increased temperatures led to a global sea level rise that flooded continental shelves and interiors with anoxic waters from the deeper ocean and drowned carbonate platforms of archaeocyathan reefs, resulting in the widespread accumulation of black organic-rich shales. Known as the [[Sinsk Event|Sinsk anoxic extinction event]], this triggered the first major extinction of the Phanerozoic, the 513–508 Ma [[End-Botomian mass extinction|Botomian–Toyonian Extinction]] (BTE), which included the loss of the archaeocyathids and [[Hyolitha|hyoliths]] and saw a major drop in biodiversity.<ref name="Myrow-2024" /><ref name="He-2019" /> The rise in sea levels is also evidenced by a global decrease in <sup>87</sup>Sr/<sup>86</sup>Sr. The flooding of continental areas decreased the rates of continental weathering, reducing the input of <sup>87</sup>Sr to the oceans and lowering the <sup>87</sup>Sr/<sup>86</sup>Sr of seawater.<ref name="Zhang-2020" /><ref name="Peng-2020" />

The base of the Miaolingian is marked by the Redlichiid–Olenellid extinction carbon isotope event (ROECE), which coincides with the main phase of Kalkarindji volcanism.<ref name="Myrow-2024" />

During the Miaolingian, orogenic events along the Australian–Antarctic margin of Gondwana led to an increase in weathering and an influx of nutrients into the ocean, raising the level of productivity and organic carbon burial. These can be seen in the steady increase in <sup>87</sup>Sr/<sup>86</sup>Sr and δ<sup>13</sup>C.<ref name="Zhang-2020" />

==== Early Furongian ====
Continued erosion of the deeper levels of the Gondwanan mountain belts led to a peak in <sup>87</sup>Sr/<sup>86</sup>Sr and linked positive δ<sup>13</sup>C and δ<sup>34</sup>S excursions, known as the [[Steptoean positive carbon isotope excursion]] (SPICE).<ref name="Myrow-2024" /> This indicates similar geochemical conditions to Stages 2 and 3 of the early Cambrian existed, with the expansion of seafloor anoxia enhancing the burial rates of organic matter and pyrite.<ref name="Zhang-2020" /> This increase in the extent of anoxic seafloor conditions led to the extinction of the marjumiid and [[Damesellidae|damesellid]] trilobites, whilst the increase in oxygen levels that followed helped drive the radiation of plankton.<ref name="Peng-2020" /><ref name="Pruss-2024" />

<sup>87</sup>Sr/<sup>86</sup>Sr fell sharply near the top of the Jiangshanian Stage, and through Stage 10 as the Gondwanan mountains were eroded down and rates of weathering decreased.<ref name="Peng-2020" /><ref name="Zhang-2020" />

=== Magnesium/calcium isotope ratios in seawater ===
The mineralogy of inorganic marine carbonates has varied through the Phanerozoic, controlled by the Mg<sup>2+</sup>/Ca<sup>2+</sup> values of seawater. High Mg<sup>2+</sup>/Ca<sup>2+</sup> result in [[calcium carbonate]] precipitation dominated by [[aragonite]] and high-magnesium [[calcite]], known as [[aragonite sea]]s, and low ratios result in [[calcite sea]]s where low-magnesium calcite is the primary calcium carbonate precipitate.<ref name="Wei-2022">{{Cite journal |last1=Wei |first1=Guang-Yi |last2=Hood |first2=Ashleigh v. S. |last3=Planavsky |first3=Noah J. |last4=Li |first4=Da |last5=Ling |first5=Hong-Fei |last6=Tarhan |first6=Lidya G. |date=2022 |title=Calcium Isotopic Constraints on the Transition From Aragonite Seas to Calcite Seas in the Cambrian |journal=Global Biogeochemical Cycles |language=en |volume=36 |issue=5 |article-number=e2021GB007235 |doi=10.1029/2021GB007235 |bibcode=2022GBioC..3607235W }}</ref> The shells and skeletons of biomineralising organisms reflect the dominant form of calcite.<ref name="Xiong-2023">{{Cite journal |last1=Xiong |first1=Yi |last2=Wood |first2=Rachel |last3=Pichevin |first3=Laetitia |date=2023 |title=The record of sea water chemistry evolution during the Ediacaran–Cambrian from early marine cements |journal=The Depositional Record |volume=9 |issue=3 |pages=508–525 |doi=10.1002/dep2.211 |bibcode=2023DepRe...9..508X |hdl=20.500.11820/3e22be46-182d-421a-a791-8a20a96c9814 |hdl-access=free }}</ref>

During the late Ediacaran to early Cambrian increasing oxygen levels led to a decrease in ocean acidity and an increase in the concentration of calcium in sea water. However, there was not a simple transition from aragonite to calcite seas, rather a protracted and variable change through the Cambrian. Aragonite and high-magnesium precipitation continued from the Ediacaran into Cambrian Stage 2. Low-magnesium calcite skeletal hard parts appear in Cambrian Age 2, but inorganic precipitation of aragonite also occurred at this time.<ref name="Xiong-2023" /> Mixed aragonite–calcite seas continued through the middle and late Cambrian, with fully calcite seas not established until the early Ordovician.<ref name="Xiong-2023" />

These variations and slow decrease in Mg<sup>2+</sup>/Ca<sup>2+</sup> of seawater were due to low oxygen levels, high continental weathering rates and the geochemistry of the Cambrian seas. In conditions of low oxygen and high iron levels, iron substitutes for magnesium in [[Authigenesis|authigenic clay minerals]] deposited on the ocean floor, slowing the removal rates of magnesium from seawater. The enrichment of ocean waters in silica, prior to the radiation of siliceous organisms, and the limited bioturbation of the anoxic ocean floor increased the rates of deposition, relative to the rest of the Phanerozoic, of these clays. This, together with the high input of magnesium into the oceans via enhanced continental weathering, delayed the reduction in Mg<sup>2+</sup>/Ca<sup>2+</sup> and facilitated continued aragonite precipitation.<ref name="Wei-2022" />

The conditions that favoured the deposition of authigenic clays were also ideal for the formation of ''[[lagerstätten]]'', with the minerals in the clays replacing the soft body parts of Cambrian organisms.<ref name="Pruss-2024" />

== Flora ==
The Cambrian flora was little different from the Ediacaran. The principal taxa were the marine macroalgae ''[[Fuxianospira gyrata|Fuxianospira]]'', ''[[Sinocylindra]]'', and ''[[Marpolia]]''. No [[calcareous]] macroalgae are known from the period.<ref>{{cite journal |last1=LoDuca |first1=S. T. |last2=Bykova |first2=N. |last3=Wu |first3=M. |last4=Xiao |first4=S. |last5=Zhao |first5=Y. |title=Seaweed morphology and ecology during the great animal diversification events of the early Paleozoic: A tale of two floras |journal=Geobiology |date=July 2017 |volume=15 |issue=4 |pages=588–616 |doi=10.1111/gbi.12244|pmid=28603844 |bibcode=2017Gbio...15..588L |doi-access=free }}</ref>

No [[land plant]] ([[embryophyte]]) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya,{{sfn|Schieber|Bose|Eriksson|Banerjee|2007|pp=53–71}} and microbes forming microbial Earth [[ecosystem]]s, comparable with modern [[cryptobiotic soil|soil crust]] of desert regions, contributing to soil formation.<ref>{{cite journal | last1 = Retallack | first1 = G.J. | year = 2008 | title = Cambrian palaeosols and landscapes of South Australia | journal = Alcheringa | volume = 55 | issue = 8| pages = 1083–1106 | doi=10.1080/08120090802266568|bibcode = 2008AuJES..55.1083R }}</ref><ref>{{cite press release |title=Greening of the Earth pushed way back in time |url=https://phys.org/news/2013-07-greening-earth.html |work=Phys.org |publisher=University of Oregon |date=22 July 2013 }}</ref> Although molecular clock estimates suggest [[Embryophyta|terrestrial plants]] may have first emerged during the Middle or Late Cambrian, the consequent large-scale removal of the [[greenhouse gas]] CO<sub>2</sub> from the atmosphere through sequestration did not begin until the Ordovician.<ref>{{cite journal |last1=Donoghue |first1=Philip C.J. |last2=Harrison |first2=C. Jill |last3=Paps |first3=Jordi |last4=Schneider |first4=Harald |title=The evolutionary emergence of land plants |journal=Current Biology |date=October 2021 |volume=31 |issue=19 |pages=R1281–R1298 |doi=10.1016/j.cub.2021.07.038|pmid=34637740 |hdl=1983/662d176e-fcf4-40bf-aa8c-5694a86bd41d |doi-access=free |bibcode=2021CBio...31R1281D |hdl-access=free }}</ref>

[[Land plants]] may have emerged during the Cambrian, but the evidence for this is fragmentary and contested and the oldest unamibiguous evidence for land plants is from the following Ordovician.<ref>{{Cite journal |last1=Strother |first1=Paul K. |last2=Foster |first2=Clinton |date=13 August 2021 |title=A fossil record of land plant origins from charophyte algae |journal=Science |volume=373 |issue=6556 |pages=792–796 |doi=10.1126/science.abj2927 |pmid=34385396 |bibcode=2021Sci...373..792S }}</ref> [[Molecular clock]] estimates have also led some authors to suggest that arthropods colonised land during the Cambrian, but again the earliest physical evidence of this is during the following Ordovician.<ref>{{Cite journal |last1=Zong |first1=Ruiwen |last2=Edgecombe |first2=Gregory D. |last3=Liu |first3=Bingcai |last4=Wang |first4=Yi |last5=Yin |first5=Jiayi |last6=Ma |first6=Juan |last7=Xu |first7=Honghe |date=March 2023 |editor-last=Cherns |editor-first=Lesley |title=Silurian freshwater arthropod from northwest China |journal=Papers in Palaeontology |volume=9 |issue=2 |article-number=e1488 |doi=10.1002/spp2.1488 |bibcode=2023PPal....9E1488Z }}</ref>

== Oceanic life ==
{{Life timeline}}
{{Main|Cambrian explosion}}
The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time,<ref>{{cite web|url=http://www.humboldt.edu/natmus/lifeThroughTime/Cambrian.web/index.html|title=Cambrian |date = 28 October 2012|last = Paselk|first = Richard|work = Natural History Museum|publisher=Humboldt State University}}</ref> but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO<sub>3</sub>), which fossilized far more easily than the fragile [[chitin]]ous exoskeletons of other arthropods, leaving numerous preserved remains.<ref>{{Cite book |chapter=Evolving Respiratory Systems as a Cause of the Cambrian Explosion |title=Out of Thin Air: Dinosaurs, Birds, and Earth's Ancient Atmosphere |publisher=The National Academies Press|doi=10.17226/11630|year=2006|isbn=978-0-309-10061-8|last1=Ward|first1=Peter |bibcode=2006nap..book11630W |chapter-url=https://www.nationalacademies.org/read/11630/chapter/5 }}</ref>

The period marked a steep change in the diversity and composition of Earth's [[biosphere]]. The [[Ediacaran biota]] suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a [[Cambrian substrate revolution|profound and irreversible effect on the substrate]] which transformed the [[seabed]] ecosystems. Before the Cambrian, the sea floor was covered by [[microbial mat]]s. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches.<ref>{{cite web|url=http://www.sciencenews.org/view/feature/id/48630/title/As_the_worms_churn|title=As the worms churn|first=Sid|last= Perkins|date=23 October 2009|archive-url = https://web.archive.org/web/20091025115251/http://www.sciencenews.org/view/feature/id/48630/title/As_the_worms_churn |archive-date = 25 October 2009|work = ScienceNews}}</ref> Around the same time there was a seemingly rapid appearance of representatives of all the mineralized [[phylum|phyla]], including the [[Bryozoa]],<ref>{{cite journal |last1=Zhang |first1=Zhiliang |last2=Zhang |first2=Zhifei |last3=Ma |first3=J. |last4=Taylor |first4=P. D. |last5=Strotz |first5=L. C. |last6=Jacquet |first6=S. M. |last7=Skovsted |first7=C. B. |last8=Chen |first8=F. |last9=Han |first9=J. |last10=Brock |first10=G. A. |year=2021 |title=Fossil evidence unveils an early Cambrian origin for Bryozoa |journal=Nature |volume=599 |issue=7884 |pages=251–255 |doi=10.1038/s41586-021-04033-w |pmid=34707285 |pmc=8580826 |bibcode=2021Natur.599..251Z }}</ref> which were once thought to have only appeared in the Lower Ordovician.<ref name=Taylor2013>{{cite journal |last1=Taylor |first1=Paul D. |last2=Berning |first2=Björn |last3=Wilson |first3=Mark A. |title=Reinterpretation of the Cambrian 'bryozoan' Pywackia as an octocoral |journal=Journal of Paleontology |date=November 2013 |volume=87 |issue=6 |pages=984–990 |doi=10.1666/13-029 |bibcode=2013JPal...87..984T }}</ref> However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.<ref name=Budd2000>{{cite journal|last1=Budd |first1=G. E.|last2=Jensen |first2=S.|year=2000|title=A critical reappraisal of the fossil record of the bilaterian phyla|volume=75 |issue=2 |pages=253–95|journal=Biological Reviews of the Cambridge Philosophical Society|doi=10.1111/j.1469-185X.1999.tb00046.x |pmid=10881389 |bibcode=2000BioRv..75..253B }}</ref>

[[File:Margaretia dorus Reconstruction.png|thumb|150px|left|A reconstruction of ''[[Margaretia|Margaretia dorus]]'' from the [[Burgess Shale]], which were once believed to be [[green algae]], but are now understood to represent [[hemichordate]]s<ref>{{Cite journal|doi=10.1186/s12915-016-0271-4|pmid=27383414|pmc=4936055|title=Cambrian suspension-feeding tubicolous hemichordates|journal=BMC Biology|volume=14|article-number=56|year=2016|last1=Nanglu|first1=Karma|last2=Caron|first2=Jean-Bernard|last3=Conway Morris|first3=Simon|last4=Cameron|first4=Christopher B. |issue=1 |doi-access=free |bibcode=2016BMCB...14...56N }}</ref>]]

While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 Ma, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the [[speciation]] rate in many groups was reduced to between a fifth and a third of previous levels.<ref>{{Cite web |url=http://www.nuffieldfoundation.org/sites/default/files/the-ordovician-explosion-651.doc |title=The Ordovician: Life's second big bang |access-date=10 February 2013 |archive-url=https://web.archive.org/web/20181009201136/http://www.nuffieldfoundation.org/sites/default/files/the-ordovician-explosion-651.doc |archive-date=9 October 2018 }}</ref><ref>{{cite web|url=https://www.newscientist.com/article/dn19916-oxygen-crash-led-to-cambrian-mass-extinction.html|title=Oxygen crash led to Cambrian mass extinction|first=Michael|last=Marshall}}</ref> Marine life lived under low and fluctuating levels of [[oxygen]] where upwellings of [[Anoxic waters|anoxic]] deep ocean waters into shallow marine environments could push organisms over the edge into mass extinctions. Ultimately, however, these led to increased [[biodiversity]] as new ecological niches became available.<ref name="Pruss-2024" />

[[File:Artistic reconstruction of the Cambrian (Drumian) Marjum biota.png|thumb|250px|Artistic reconstruction of [[Marjum Formation|Marjum biota]], including various arthropods ([[trilobite]]s, [[Hymenocarina|hymenocarines]], and [[Radiodonta|radiodonts]]), sponges, echinoderms, and various other groups ]]
Some Cambrian organisms ventured onto land, producing the trace fossils ''[[Protichnites]]'' and ''[[Climactichnites]]''. Fossil evidence suggests that [[euthycarcinoid]]s, an extinct group of arthropods, produced at least some of the ''Protichnites''.{{sfnm|1a1=Collette|1a2=Hagadorn|1y=2010|2a1=Collette|2a2=Gass|2a3=Hagadorn|2y=2012}} Fossils of the track-maker of ''Climactichnites'' have not been found; however, fossil trackways and resting traces suggest a large, [[slug]]-like [[mollusc]].{{sfnm|1a1=Yochelson|1a2=Fedonkin|1y=1993|2a1=Getty|2a2=Hagadorn|2y=2008}}

[[Sponge|Porifera]] (sponges), [[Cnidaria]] (e.g. [[jellyfish]], [[Hydrozoa]], [[sea anemone]]s and [[coral]]s) and [[Ctenophora]] (comb jellies) have an uneven fossil record in the Cambrian and are best preserved in Lagerstätten.<ref name="Zhuravlev 2018">{{cite journal |last1=Zhuravlev |first1=Andrey Yu. |last2=Wood |first2=Rachel A. |title=The two phases of the Cambrian Explosion |journal=Scientific Reports |date=9 November 2018 |volume=8 |issue=1 |article-number=16656 |doi=10.1038/s41598-018-34962-y |pmid=30413739 |pmc=6226464 |bibcode=2018NatSR...816656Z }}</ref> Their evolutionary relationships are the subject of ongoing debate.<ref name="Parry 2021">{{cite journal |last1=Parry |first1=Luke A. |last2=Lerosey-Aubril |first2=Rudy |last3=Weaver |first3=James C. |last4=Ortega-Hernández |first4=Javier |title=Cambrian comb jellies from Utah illuminate the early evolution of nervous and sensory systems in ctenophores |journal=iScience |date=September 2021 |volume=24 |issue=9 |article-number=102943 |doi=10.1016/j.isci.2021.102943 |pmid=34522849 |pmc=8426560 |bibcode=2021iSci...24j2943P }}</ref><ref name="Zhao 2019">{{cite journal |last1=Zhao |first1=Yang |last2=Vinther |first2=Jakob |last3=Parry |first3=Luke A. |last4=Wei |first4=Fan |last5=Green |first5=Emily |last6=Pisani |first6=Davide |last7=Hou |first7=Xianguang |last8=Edgecombe |first8=Gregory D. |last9=Cong |first9=Peiyun |title=Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan |journal=Current Biology |date=April 2019 |volume=29 |issue=7 |pages=1112–1125.e2 |doi=10.1016/j.cub.2019.02.036 |pmid=30905603 }}</ref><ref name="Ou 2022">{{cite journal |last1=Ou |first1=Qiang |last2=Shu |first2=Degan |last3=Zhang |first3=Zhifei |last4=Han |first4=Jian |last5=Van Iten |first5=Heyo |last6=Cheng |first6=Meirong |last7=Sun |first7=Jie |last8=Yao |first8=Xiaoyong |last9=Wang |first9=Rong |last10=Mayer |first10=Georg |title=Dawn of complex animal food webs: A new predatory anthozoan (Cnidaria) from Cambrian |journal=The Innovation |date=January 2022 |volume=3 |issue=1 |article-number=100195 |doi=10.1016/j.xinn.2021.100195 |pmid=35005675 |pmc=8717384 |bibcode=2022Innov...300195O }}</ref> Prior to about 513 Ma both [[Crown group|stem]] and [[crown group]]s were present, however, many stem groups went extinct during the Sinsk anoxic event at the end of Series 2, with crown groups diversifying afterwards.<ref name="Zhuravlev 2018" />

Porifera are divided into three main groups: [[Calcareous sponge|Calcarea]] (calcareous sponges), [[Hexactinellid]]a (silica or glass sponges), and [[Demospongia]] ([[spongin]] and/or silica sponges). Demospongia are most common in the Cambrian fossil record, Hexactiniellida and Calcarea may be present but the evidence is contested, as is evidence of Ediacaran sponges.<ref name="Antcliffe 2014">{{cite journal |last1=Antcliffe |first1=Jonathan B. |last2=Callow |first2=Richard H. T. |last3=Brasier |first3=Martin D. |title=Giving the early fossil record of sponges a squeeze |journal=Biological Reviews |date=November 2014 |volume=89 |issue=4 |pages=972–1004 |doi=10.1111/brv.12090 |pmid=24779547 }}</ref><ref name=":0">{{cite journal |last1=Botting |first1=Joseph P. |last2=Muir |first2=Lucy A. |title=Early sponge evolution: A review and phylogenetic framework |journal=Palaeoworld |date=March 2018 |volume=27 |issue=1 |pages=1–29 |doi=10.1016/j.palwor.2017.07.001 |bibcode=2018Palae..27....1B }}</ref> Many Cambrian sponge groups (e.g. [[Reticulosa]], [[Heteractinida]] and [[Protomonaxonida]]) are considered stem-groups of these major sponge lineages as they have sponge-like features, but the groups themselves are extinct.<ref name=":0" /> For example, ''[[Eiffelia]]'' (a heteractinid) has features of calcareous and siliceous sponges with spicules of both silica and calcium carbonate.<ref name="Antcliffe 2014" />

[[Archaeocyatha]] are probably related to demosponges. They first appear in the fossil record in Stage 2 of the Terreneuvian, rapidly diversifying during Stage 3 of Series 2, before going into a sharp decline during Stage 4 and going extinct during the Sinsk anoxic event.<ref name="Kershaw 2025">{{cite journal |last1=Kershaw |first1=Stephen |last2=Li |first2=Qi-Jian |title=Fossil hypercalcified sponges; types, relationships and geological history |journal=Journal of Palaeogeography |date=October 2025 |volume=14 |issue=4 |article-number=100289 |doi=10.1016/j.jop.2025.100289 |bibcode=2025JPalG..1400289K }}</ref> Archaeocyatha were [[Sessility (motility)|sessile]], [[Filter feeder|suspension feeders]] that pumped water through their porous cup-shaped calcareous skeletons.<ref name="Antcliffe 2014" /><ref name="Kershaw 2025" /> Together with [[cyanobacteria]], they were the primary reef builders in the early Cambrian, constructing the oldest known large-scale structures built by animals. The presence of cyanobacteria within the skeletal framework of Archaeocyatha suggests a [[Photosymbiosis|photosymbiotic]] relationship. Cyanobacteria and other [[calcimicrobe]]s precipitated calcium carbonate, which encrusted Archaeocyatha skeletons, binding them together to form the framework of the reef.<ref name="Gandin 2010">{{cite journal |last1=Gandin |first1=Anna |last2=Debrenne |first2=Françoise |title=Distribution of the archaeocyath-calcimicrobial bioconstructions on the Early Cambrian shelves |journal=Palaeoworld |date=December 2010 |volume=19 |issue=3–4 |pages=222–241 |doi=10.1016/j.palwor.2010.09.010 |bibcode=2010Palae..19..222G }}</ref><ref name="Stanley 2015">{{Cite book |last1=Stanley |first1=Steven |title=Earth System Science |last2=Luczaj |first2=John |publisher=W.H.Freeman and Company |year=2015 |isbn=978-1-319-15402-8 |edition=4th |location=New York|pages=304–328}}</ref> Early coral-like [[anthozoa]]ns (cnidarians) also contributed to reef building.<ref name="Stanley 2015" /><ref name="Murdock 2020">{{cite journal |last1=Murdock |first1=Duncan J. E. |title=The 'biomineralization toolkit' and the origin of animal skeletons |journal=Biological Reviews |date=October 2020 |volume=95 |issue=5 |pages=1372–1392 |doi=10.1111/brv.12614 |pmid=32447836 |bibcode=2020BioRv..95.1372M }}</ref> These died out together with Archaeocyatha during the Sinsk anoxic event.<ref name="Zhuravlev 2018" /><ref name="Stanley 2015" /> They were replaced by [[Heteroscleromorpha|lithistid]] demosponges as the principal reef building sponges for the rest of the Cambrian.<ref name="Kershaw 2025" />

Ctenophora (comb jellies) are a group of [[Pelagic zone|pelagic]], predatory animals with gelatinous, globular bodies, and comb rows (external [[Cilium|cilia]]) which are used for propulsion. The oldest undisputed ctenophore fossils are found in the lower Cambrian. Cambrian ctenophores had more comb rows, but lack paired tentacles with colloblasts, which modern ctenophores use for feeding.<ref name="Parry 2021" /><ref name="Zhao 2019" /> Stem group Ctenophora include [[Scleroctenophora]], which had paired comb rows, and organic skeleton something modern ctenophores lack.<ref name="Zhao 2019" />

[[Dinomischidae|Dinomischids]] were [[Polyp (zoology)|polyp]]-like, sessile filter feeders with organic skeletons that collected food via a crown of tentacles around their mouths. These have been assigned to both Ctenophora with the suggestion the tentacles evolved into comb rows,<ref name="Zhao 2019" /> and Cnidaria because the internal structures more closely resemble those of a sea anemone-like ancestor.<ref name="Ou 2022" />

Cnidarians are divided into two main classes; Anthozoa (sea anemones, corals), which are [[benthic]] polyps, and [[Medusozoa]] (hydroids, jellyfishes), which have alternating life cycle stages of polyps and medusae (free swimming).<ref>{{cite journal |last1=Zhao |first1=Yang |last2=Parry |first2=Luke A. |last3=Vinther |first3=Jakob |last4=Dunn |first4=Frances S. |last5=Li |first5=Yu-Jing |last6=Wei |first6=Fan |last7=Hou |first7=Xian-Guang |last8=Cong |first8=Pei-Yun |title=An early Cambrian polyp reveals a potential anemone-like ancestor for medusozoan cnidarians |journal=Palaeontology |date=January 2023 |volume=66 |issue=1 |article-number=e12637 |doi=10.1111/pala.12637 |bibcode=2023Palgy..6612637Z }}</ref> The oldest example of a jellyfish in the fossil record is ''[[Olivooides]]'' an embryonic jellyfish from the Fortunian.<ref>{{cite journal |last1=Parry |first1=Luke A. |last2=Lerosey-Aubril |first2=Rudy |last3=Coleman |first3=Robert |last4=Mouro |first4=Lucas Del |last5=Gaines |first5=Robert R. |last6=Skabelund |first6=Jacob |last7=Weaver |first7=James C. |last8=Ortega-Hernández |first8=Javier |title=The oldest diverse jellyfish fauna reinterpreted as sessile polypoid dinomischids (stem-group Ctenophora) |journal=Journal of Systematic Palaeontology |date=31 December 2025 |volume=23 |issue=1 |article-number=2545834 |doi=10.1080/14772019.2025.2545834 |bibcode=2025JSPal..2345834P }}</ref> Examples of anthozoans are found from Series 2.<ref name="Ou 2022" /> One of these, the polyp-like ''[[Nailiana|Nailiana elegans]]'' was a stem-group anthozoan. Its long, flexible tentacles were used to detect, grasp, and drag prey into its mouth in a similar manner to modern predatory sea anemones. A fossil specimen from Stage 3 (c. 520 Ma) shows the earliest known evidence of this macrophagous style of [[predation]]. The fossil preserves a brachiopod surrounded by the ''N. elegans''<nowiki />' tentacles with part of the brachiopod already within the cnidarian.<ref name="Ou 2022" />

Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of {{lang|de|[[Lagerstätte]]n}}. These include [[Sirius Passet]],<ref>{{cite journal |doi=10.1111/let.12174|title=The Sirius Passet Lagerstätte: Silica death masking opens the window on the earliest matground community of the Cambrian explosion|journal=Lethaia|volume=49|issue=4|pages=631–643|year=2016|last1=Strang|first1=Katie M.|last2=Armstrong|first2=Howard A.|last3=Harper|first3=David A. T.|last4=Trabucho-Alexandre|first4=João P.|doi-access=free}}</ref><ref>{{Cite journal |last1=Nielsen |first1=Morten Lunde |last2=Lee |first2=Mirinae |last3=Ng |first3=Hong Chin |last4=Rushton |first4=Jeremy C. |last5=Hendry |first5=Katharine R. |last6=Kihm |first6=Ji-Hoon |last7=Nielsen |first7=Arne T. |last8=Park |first8=Tae-Yoon S. |last9=Vinther |first9=Jakob |last10=Wilby |first10=Philip R. |date=1 January 2022 |title=Metamorphism obscures primary taphonomic pathways in the early Cambrian Sirius Passet Lagerstätte, North Greenland |journal=Geology |volume=50 |issue=1 |pages=4–9 |doi=10.1130/G48906.1 |bibcode=2022Geo....50....4N |doi-access=free }}</ref> the Sinsk Algal Lens,<ref name="SinskAlgalLens">{{cite journal |last1=Ivantsov |first1=Andrey Yu. |last2=Zhuravlev |first2=Andrey Yu. |last3=Leguta |first3=Anton V. |last4=Krassilov |first4=Valentin A. |last5=Melnikova |first5=Lyudmila M. |last6=Ushatinskaya |first6=Galina T. |title=Palaeoecology of the Early Cambrian Sinsk biota from the Siberian Platform |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=May 2005 |volume=220 |issue=1–2 |pages=69–88 |doi=10.1016/j.palaeo.2004.01.022 |bibcode=2005PPP...220...69I }}</ref> the [[Maotianshan Shales]],<ref>{{cite journal |last1=MacKenzie |first1=Lindsay A. |last2=Hofmann |first2=Michael H. |last3=Junyuan |first3=Chen |last4=Hinman |first4=Nancy W. |title=Stratigraphic controls of soft-bodied fossil occurrences in the Cambrian Chengjiang Biota Lagerstätte, Maotianshan Shale, Yunnan Province, China |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=February 2015 |volume=420 |pages=96–115 |doi=10.1016/j.palaeo.2014.11.006 |bibcode=2015PPP...420...96M }}</ref> the [[Emu Bay Shale]],<ref>{{cite journal |last1=Paterson |first1=John R. |last2=García-Bellido |first2=Diego C. |last3=Jago |first3=James B. |last4=Gehling |first4=James G. |last5=Lee |first5=Michael S.Y. |last6=Edgecombe |first6=Gregory D. |title=The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana |journal=Journal of the Geological Society |date=January 2016 |volume=173 |issue=1 |pages=1–11 |doi=10.1144/jgs2015-083 |bibcode=2016JGSoc.173....1P }}</ref> and the Burgess Shale.<ref name=Butterfield1990>{{cite journal |jstor = 2400788 |author = Butterfield, N.J. |journal = [[Paleobiology (journal)|Paleobiology]] |volume = 16 |issue = 3 |pages = 272–286 |year = 1990 |title=Organic Preservation of Non-Mineralizing Organisms and the Taphonomy of the Burgess Shale |doi = 10.1017/S0094837300009994 |bibcode = 1990Pbio...16..272B }}</ref><ref name="Page2008">{{cite journal |year= 2008 |doi = 10.1130/G24991A.1 |title = Ubiquitous Burgess Shale–style "clay templates" in low-grade metamorphic mudrocks |last1 = Page |first1 = Alex |last2 = Gabbott |first2 = Sarah |last3 = Wilby |first3 = Phillip R. |last4 = Zalasiewicz  |first4 = Jan A. |journal = [[Geology (journal)|Geology]] |volume = 36 |issue = 11 |pages = 855–858 |bibcode = 2008Geo....36..855P }}</ref><ref name=OrrEtAl1998>{{cite journal | doi = 10.1126/science.281.5380.1173 | pmid = 9712577 | author = Orr, Patrick J. | author2 = Briggs, Derek E. G. | author2-link = Briggs, Derek E. G. | author3 = Kearns, Stuart L. | journal = [[Science (journal)|Science]] | volume = 281 | issue = 5380 | pages = 1173–5 | year = 1998 | title = Cambrian Burgess Shale Animals Replicated in Clay Minerals | bibcode=1998Sci...281.1173O}}</ref>

==Symbol==
The United States [[Federal Geographic Data Committee]] uses a "barred capital C" {{angbr|Ꞓ}} character to represent the Cambrian Period.<ref>{{cite book
|editor=Federal Geographic Data Committee
|title=FGDC Digital Cartographic Standard for Geologic Map Symbolization FGDC-STD-013-2006
|url=https://ngmdb.usgs.gov/fgdc_gds/geolsymstd/fgdc-geolsym-all.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://ngmdb.usgs.gov/fgdc_gds/geolsymstd/fgdc-geolsym-all.pdf |archive-date=9 October 2022 |url-status=live
|access-date=23 August 2010
|date=August 2006
|publisher=U.S. Geological Survey for the Federal Geographic Data Committee
|page=A–32–1}}</ref>
The [[Unicode]] character is {{unichar|A792|LATIN CAPITAL LETTER C WITH BAR}}.<ref>{{cite web |last=Priest |first=Lorna A. |title=Proposal to Encode C WITH BAR|url=http://std.dkuug.dk/jtc1/sc2/wg2/docs/n3896.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://std.dkuug.dk/jtc1/sc2/wg2/docs/n3896.pdf |archive-date=9 October 2022 |url-status=live|access-date=6 April 2011|author2=Iancu, Laurentiu |author3=Everson, Michael |date=October 2010}}</ref><ref>[https://www.fileformat.info/info/unicode/char/A792/index.htm Unicode Character 'LATIN CAPITAL LETTER C WITH BAR' (U+A792)]. fileformat.info. Retrieved 15 June 2015</ref>

==Gallery==
<gallery mode="packed">
File:CambrianStromatolites.jpg|[[Stromatolite]]s of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada
File:Elrathia kingii growth series.jpg|[[Trilobite]]s, like these ''[[Elrathia kingii]]'' were very common arthropods during this time
File:20191203 Anomalocaris canadensis.png|''[[Anomalocaris]]'' was an early marine predator, a member of the stem-arthropod group [[Radiodonta]]
File:20191108 Opabinia regalis.png|''[[Opabinia]]'' was a bizarre stem-arthropod that possessed five stalked eyes, and a fused proboscis tipped with a claw-like appendage.
File:Protichnites, Blackberry Hill, Wisconsin, Cambrian 2.jpg|''[[Protichnites]]'' were the trackways of arthropods that walked Cambrian beaches
File:20210830 Hallucigenia sparsa diagrammatic reconstruction.png|''[[Hallucigenia|Hallucigenia sparsa]]'' was a member of the group [[lobopodia]], that is considered to be related to modern [[Onychophora|velvet worms]].
File:20200329 Cambroraster falcatus.png|''[[Cambroraster]] falcatus'' was a [[Hurdiidae|hurdiid]] radiodont that bore a large horseshoe-shaped carapace.
File:Schematic anatomical reconstruction of Pikaia.png|''[[Pikaia]]'' was a stem-chordate from the Middle Cambrian
File:Amiskwia sagittiformis restoration.png|''[[Amiskwia sagittiformis]]'' was a large bodied [[Gnathifera (clade)|gnathiferan]] from Canada and China
File:Haplophrentis.png|''[[Haplophrentis]]'' was a [[Hyolitha|hyolith]], a group of conical shelled [[lophotrochozoa]]ns that were potentially related to either [[Lophophorata|lophophorates]] or [[Mollusca|mollusks]].
File:Halkieria reconstruction.png|[[Halkieriid|''Halkieria'']] was a bizarre invertebrate that was an early member of the mollusk group
</gallery>

== See also ==
* [[Cambrian–Ordovician extinction event]] – circa 488 Ma
* [[Dresbachian]] extinction event—circa 499 Ma
* [[End-Botomian mass extinction|End Botomian]] extinction event—circa 513 Ma
* [[List of fossil sites]] ''(with link directory)''
* [[Type locality (geology)]], the locality where a particular rock type, stratigraphic unit, fossil or mineral species is first identified
{{Cambrian preservational modes}}

== References ==
{{reflist|30em}}

== Further reading ==
{{Wikisource portal|Paleozoic#Cambrian}}
* {{cite journal  | last1 = Amthor | first1 =  J. E.  | year = 2003 | title= Extinction of ''Cloudina'' and ''Namacalathus'' at the Precambrian-Cambrian boundary in Oman | journal = Geology | volume = 31 | pages = 431–434 | doi= 10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2 | last2 = Grotzinger | first2 = John P. | last3 = Schröder | first3 = Stefan | last4 = Bowring | first4 = Samuel A. | last5 = Ramezani | first5 = Jahandar | last6 = Martin | first6 = Mark W. | last7 = Matter | first7 = Albert |bibcode = 2003Geo....31..431A | issue = 5 }}
*{{cite journal |last1=Collette |first1=J. H. |last2=Gass |first2= K. C. |last3=Hagadorn |first3=J. W. |year=2012 |title=''Protichnites eremita'' unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies |journal=Journal of Paleontology |volume=86 |pages=442–454 |doi=10.1666/11-056.1 |issue=3 |bibcode=2012JPal...86..442C }}
*{{cite journal |last1=Collette |first1=J. H. |last2=Hagadorn |first2=J. W. |year=2010 |title=Three-dimensionally preserved arthropods from Cambrian Lagerstatten of Quebec and Wisconsin |journal=Journal of Paleontology |volume=84 |pages=646–667 |doi=10.1666/09-075.1 |issue=4 }}
*{{cite journal |last1=Getty |first1=P. R. |last2=Hagadorn |first2=J. W. |year=2008 |title=Reinterpretation of ''Climactichnites'' Logan 1860 to include subsurface burrows, and erection of ''Musculopodus'' for resting traces of the trailmaker |journal=Journal of Paleontology |volume=82 |pages=1161–1172 |doi=10.1666/08-004.1 |issue=6 |bibcode=2008JPal...82.1161G }}
* {{cite book |author-link=S. J. Gould |last1=Gould |first1=S. J. |title=Wonderful Life: the Burgess Shale and the Nature of Life |url=https://archive.org/details/wonderfullifebur00goul |url-access=registration |location=New York |publisher=Norton |year=1989 |isbn=978-0-393-02705-1 }}
* {{Cite EB1911|wstitle=Cambrian System|volume=05|pages=86–89|first=John Allen|last=Howe}}
* {{cite web |last=Ogg |first=J. |date=June 2004 |title=Overview of Global Boundary Stratotype Sections and Points (GSSPs) |archive-url=https://web.archive.org/web/20060423084018/http://www.stratigraphy.org/gssp.htm  |archive-date=23 April 2006 |url=http://www.stratigraphy.org/gssp.htm |access-date=30 April 2006 }}
*{{cite journal |last=Owen |first=R. |year=1852 |title=Description of the impressions and footprints of the ''Protichnites'' from the Potsdam sandstone of Canada |journal=Geological Society of London Quarterly Journal |volume=8 |issue=1–2 |pages=214–225 |doi=10.1144/GSL.JGS.1852.008.01-02.26 |bibcode=1852QJGS....8..214O |url=https://zenodo.org/record/1602923 }}
* {{cite book |last1=Peng |first1=S. |last2=Babcock |first2=L.E. |last3=Cooper |first3=R.A. |title=The Geologic Time Scale |chapter=The Cambrian Period |date=2012 |pages=437–488 |doi=10.1016/B978-0-444-59425-9.00019-6 |isbn=978-0-444-59425-9 }}
*{{cite book |last1=Schieber |first1=J. |first2=P. K. |last2=Bose |first3=P. G. |last3=Eriksson |first4=S. |last4=Banerjee |first5=S. |last5=Sarkar |first6=W. |last6=Altermann |first7=O. |last7=Catuneau |title=Atlas of Microbial Mat Features Preserved within the Clastic Rock Record |year=2007 |publisher=Elsevier |pages=53–71 |isbn=978-0-444-52859-9}}
*{{cite journal |last1=Yochelson |first1=E. L. |first2=M. A.|last2=Fedonkin |title=Paleobiology of ''Climactichnites'', and Enigmatic Late Cambrian Fossil|journal=Smithsonian Contributions to Paleobiology|volume=74|issue=74|year=1993|pages= 1–74 |doi=10.5479/si.00810266.74.1 |url=https://www.biodiversitylibrary.org/bibliography/159009 }}

== External links ==
{{commons category}}
* {{In Our Time|Cambrian period|p003k9bg|Cambrian_period}}
* [http://www.trilobites.info/biostratigraphy.htm Biostratigraphy] – includes information on Cambrian trilobite [[biostratigraphy]]
* [http://www.trilobite.info Sam Gon's trilobite pages] {{Webarchive|url=https://web.archive.org/web/20210307163105/http://www.trilobite.info/ |date=7 March 2021 }} (contains numerous Cambrian trilobites)
* [http://www.geo-lieven.com/erdzeitalter/kambrium/kambrium.htm Examples of Cambrian Fossils]
* [http://www.scotese.com/ Paleomap Project]
* [https://web.archive.org/web/20030829130602/http://www.earth-pages.com/archive/geobiology.asp Report on the web on Amthor and others from ''Geology'' vol. 31]
* [https://web.archive.org/web/20090616125244/http://www.astrobio.net/news/article251.html Weird Life on the Mats]
* [https://web.archive.org/web/20200727073140/https://ghkclass.com/ghkC.html?Cambrian Chronostratigraphy scale v.2018/08 | Cambrian]

{{Cambrian footer}}
{{Geological history|p|p|state=collapsed}}
{{Authority control}}

[[Category:Cambrian| ]]
[[Category:Geological periods]]