Editing Cambrian (section)

== 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{{dubious|reason=the sources do not make this claim|date=March 2025}} the Cambrian was a time of greenhouse climate conditions.<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 |pages=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. |date=April 2021 |title=Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years |url=http://dx.doi.org/10.1016/j.earscirev.2021.103503 |journal=[[Earth-Science Reviews]] |volume=215 |pages=103503 |bibcode=2021ESRv..21503503S |doi=10.1016/j.earscirev.2021.103503 |issn=0012-8252 |s2cid=233579194 |archive-url=https://web.archive.org/web/20210108000000/http://dx.doi.org/10.1016/j.earscirev.2021.103503 |archive-date=8 January 2021}} [https://eprints.whiterose.ac.uk/169823/ Alt URL]</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. |date=2024-05-30 |title=Life on the Edge: The Cambrian Marine Realm and Oxygenation |url=https://www.annualreviews.org/doi/10.1146/annurev-earth-031621-070316 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=52 |issue=1 |pages=109–132 |doi=10.1146/annurev-earth-031621-070316 |bibcode=2024AREPS..52..109P |hdl=10919/117422 |issn=0084-6597|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 |pages=eadl3452 |doi=10.1126/sciadv.adl3452 |issn=2375-2548 |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=2019-04-19 |title=Isotopic evidence for temperate oceans during the Cambrian Explosion |journal=Scientific Reports |language=en |volume=9 |issue=1 |pages=6330 |doi=10.1038/s41598-019-42719-4 |pmid=31004083 |pmc=6474879 |bibcode=2019NatSR...9.6330W |issn=2045-2322}}</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 |url=https://doi.org/10.1016/j.gca.2017.11.015 |journal=Geochimica et Cosmochimica Acta |volume=224 |pages=18–41 |doi=10.1016/j.gca.2017.11.015 |bibcode=2018GeCoA.224...18B |issn=0016-7037}}</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. |date=2023-05-31 |title=Evolution of Atmospheric O 2 Through the Phanerozoic, Revisited |url=https://www.annualreviews.org/doi/10.1146/annurev-earth-032320-095425 |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=51 |issue=1 |pages=253–276 |doi=10.1146/annurev-earth-032320-095425 |issn=0084-6597}}</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=2018-07-02 |title=Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing |journal=Nature Communications |language=en |volume=9 |issue=1 |pages=2554 |doi=10.1038/s41467-018-04973-4 |pmid=29967319 |pmc=6028391 |bibcode=2018NatCo...9.2554V |issn=2041-1723}}</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 |date=2019 |title=Integrated records of environmental change and evolution challenge the Cambrian Explosion |url=https://www.nature.com/articles/s41559-019-0821-6 |journal=Nature Ecology & Evolution |language=en |volume=3 |issue=4 |pages=528–538 |doi=10.1038/s41559-019-0821-6 |pmid=30858589 |bibcode=2019NatEE...3..528W |issn=2397-334X|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" />