Editing Brunhes–Matuyama reversal (section)

{{short description|Most recent geomagnetic reversal event}}
The '''Brunhes–Matuyama reversal''', named after [[Bernard Brunhes]] and [[Motonori Matuyama]], was a [[Geology|geologic]] event, approximately 781,000 years ago, when the [[Earth's magnetic field]] last underwent [[Geomagnetic reversal|reversal]].<ref>{{cite book|editor2-last= Ogg |editor2-first=James G. |editor3-last= Smith |editor3-first=Alan G. |editor-last=Gradstein|editor-first=Felix M. |title=A Geological Time Scale |url= https://archive.org/details/geologictimescal2004grad |url-access= limited |date=2004|publisher=Cambridge University Press|location=Cambridge |isbn=978-0521786737|page=[https://archive.org/details/geologictimescal2004grad/page/n49 28]|edition=3rd }}</ref><ref>{{cite web|title=Global chronostratigraphical correlation table for the last 2.7 million years|url=http://www.stratigraphy.org/upload/QuaternaryChart1.JPG|publisher=International Commission on Stratigraphy|accessdate=31 March 2014}}</ref> Estimations vary as to the abruptness of the reversal. A 2004 paper estimated that it took over several thousand years;<ref name="slow">{{cite journal|first=Bradford M.|last=Clement|title=Dependence of the duration of geomagnetic polarity reversals on site latitude|date=8 April 2004|journal=Nature|volume=428|pmid=15071591|issue=6983|doi=10.1038/nature02459|pages=637–40|bibcode = 2004Natur.428..637C |s2cid=4356044}}</ref> a 2010 paper estimated that it occurred more quickly,<ref name="SN090210">{{cite web|last=Witze|first=Alexandra|title=Geomagnetic field flip-flops in a flash|url=http://www.sciencenews.org/view/generic/id/62947/title/Geomagnetic_field_flip-flops_in_a_flash|publisher=ScienceNews|accessdate=3 September 2010|date=Sep 2, 2010|archive-date=27 September 2012|archive-url=https://web.archive.org/web/20120927145706/http://www.sciencenews.org/view/generic/id/62947/title/Geomagnetic_field_flip-flops_in_a_flash|url-status=dead}}</ref><ref>{{Cite journal |first1=R.S. |last1=Coe |first2=M. |last2=Prévot |first3=P. |last3=Camps |title=New evidence for extraordinarily rapid change of the geomagnetic field during a reversal |url=http://es.ucsc.edu/~rcoe/eart110c/Coeetal_Steens_Nature95.pdf |journal=Nature |volume=374 |date=20 April 1995 |pages=687 |doi=10.1038/374687a0 |issue=6524 |bibcode=1995Natur.374..687C |s2cid=4247637 |url-status=dead |archiveurl=https://web.archive.org/web/20100731030313/http://es.ucsc.edu/~rcoe/eart110c/Coeetal_Steens_Nature95.pdf |archivedate=31 July 2010 }}</ref><ref>{{Cite journal |last1=Bogue |first1=S. W. |first2=J. M. G. |last2=Glen |s2cid=129896450 |year=2010 |pages=L21308 |title=Very rapid geomagnetic field change recorded by the partial remagnetization of a lava flow |volume=37 |issue=21 |journal=Geophysical Research Letters |doi=10.1029/2010GL044286 |bibcode=2010GeoRL..3721308B}}</ref> perhaps within a human lifetime;<ref>{{cite journal
|first1=Leonardo|last1=Sagnotti
|first2=Giancarlo|last2=Scardia
|first3=Biagio|last3=Giaccio
|first4=Joseph C.|last4=Liddicoat
|first5=Sebastien|last5=Nomade
|first6=Paul R.|last6=Renne
|first7=Courtney J.|last7=Sprain
|title=Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal
|date=21 July 2014
|journal=Geophys. J. Int.
|volume=199
|issue=2
|doi=10.1093/gji/ggu287
|pages=1110–1124
|bibcode =  2014GeoJI.199.1110S
|doi-access=free
}}</ref> a 2019 paper estimated that the reversal lasted 22,000 years.<ref>{{Cite journal|last1=Singer|first1=Brad S.|last2=Jicha|first2=Brian R.|last3=Mochizuki|first3=Nobutatsu|last4=Coe|first4=Robert S.|date=August 7, 2019|title=Synchronizing volcanic, sedimentary, and ice core records of Earth's last magnetic polarity reversal|journal=Science Advances|language=en|volume=5|issue=8|pages=eaaw4621|doi=10.1126/sciadv.aaw4621|pmid=31457087|pmc=6685714|bibcode=2019SciA....5.4621S|issn=2375-2548|doi-access=free}}</ref><ref>{{Cite web|url=https://www.space.com/lava-flows-earth-magnetic-field-reversal.html|title=Earth's Last Magnetic-Pole Flip Took Much Longer Than We Thought|last1=Rabie|first1=Passant|date=2019-08-07|website=Space.com|language=en|access-date=2019-08-08|df=mdy-all}}</ref>

The apparent duration at any particular location can vary by an order of magnitude, depending on geomagnetic latitude and local effects of non-dipole components of the Earth's field during the transition.<ref name="slow" />

The Brunhes–Matuyama reversal is a marker for the [[Global Boundary Stratotype Section and Point]] (GSSP)  defining the base of the [[Chibanian]] Stage and [[Middle Pleistocene]] Subseries at the Chiba section, Japan, which was officially ratified in 2020 by the [[International Union of Geological Sciences]].<ref name="GSSP Web">{{cite web|title=Global Boundary Stratotype Section and Point|url=http://www.stratigraphy.org/GSSP/index.html|publisher=International Commission of Stratigraphy|accessdate=31 March 2014|url-status=dead|archiveurl=https://web.archive.org/web/20121115175854/http://www.stratigraphy.org/GSSP/index.html|archivedate=15 November 2012}}</ref><ref name="Head2021">{{cite journal |last1=Head |first1=Martin J. |title=Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19 |journal=Progress in Earth and Planetary Science |year=2021 |volume=8 |issue=1 |page=50 |publisher=Progress in Earth and Planetary Science (2021) 8(1): 50. |doi=10.1186/s40645-021-00439-2|pmid=34722119 |pmc=8549982 |bibcode=2021PEPS....8...50H |doi-access=free }}</ref> It is useful in dating ocean sediment cores and subaerially erupted volcanics. 

There is a highly speculative theory that connects this reversal event to the large [[Australasian strewnfield]] (c. 790,000 years ago),<ref name="Glass">Glass, B. P., Swincki, M. B., & Zwart, P. A. (1979). [http://articles.adsabs.harvard.edu/full/1979LPSC...10.2535G "Australasian, Ivory Coast and North American tektite strewnfields – Size, mass and correlation with geomagnetic reversals and other earth events"] Lunar and Planetary Science Conference, 10th, Houston, Tex., March 19–23, 1979, pp. 2535–2545.</ref> although the causes of the two are almost certainly unconnected and only coincidentally happened around the same time.{{Citation Needed|reason=this is purely conjecture that two geological events that happened millions of years ago are wholly unrelated; the previous clauses may not have provided an adequate explanation for the coinciding of the two events but claiming they are unrelated for no reason other than "they probably are" is not reliable|date=July 2021}} Adding to the data is the large African [[Lake Bosumtwi|Bosumtwi impact event]] (c. 1.07 million years ago) and the later [[Jaramillo reversal]] (c. 1 million years ago), another pair of events which has not gone unnoticed.<ref name="Glass" />