The Laschamp or Laschamps event[note 1] was a geomagnetic excursion (a short reversal of the Earth's magnetic field). It occurred between 42,200 and 41,500 years ago, during the end of the Last Glacial Period. It was discovered from geomagnetic anomalies found in the Laschamps lava flows in Clermont-Ferrand, France in the 1960s.[1]

The Laschamp event was the first known geomagnetic excursion and remains the most thoroughly studied among the known geomagnetic excursions.[2]

Background and effects

Since its discovery, the magnetic excursion has been demonstrated in geological archives from many parts of the world.[2] The transition from the normal field to the reversed field lasted approximately 250 years, while the magnetic field remained reversed for approximately 440 years. During the transition, Earth's magnetic field declined to a minimum of 5% of its current strength, and was at about 25% of its current strength when fully reversed. This reduction in geomagnetic field strength resulted in more cosmic rays reaching the Earth, causing greater production of the cosmogenic isotopes beryllium-10 and carbon-14, a decrease in atmospheric ozone, and changes in atmospheric circulation.[3][4]

This loss of the geomagnetic shield is claimed to have contributed to the extinction of Australian megafauna, the extinction of the Neanderthals and the appearance of cave art.[5][6][7] However, the lack of corroborating evidence of a causal link between the Laschamp event and population bottlenecks of many megafauna species, and the relatively moderate radio-isotopic changes during the event, have cast significant doubt on the real impact of the Laschamp event on global environmental changes.[8]

Because it occurred approximately 42,000 years ago, the period has been termed the Adams Event or Adams Transitional Geomagnetic Event, a tribute to science fiction writer Douglas Adams, who wrote in The Hitchhiker's Guide to the Galaxy that "42" was the answer to life, the universe and everything.[9][10]

Research

The Australian Research Council is funding research to analyze a kauri tree found in New Zealand in 2019. Radiocarbon dating reveals that the tree was alive from 42,500–41,000 years ago, within the timeframe of the event.[11][12]

See also

Notes

1. ^ The name derives from the Laschamps lava flows from which it was discovered, but appears as 'Laschamp' in most scientific literature.[13]

References

  1. ^ Bonhommet, N.; Zähringer, J. (1969). "Paleomagnetism and potassium argon age determinations of the Laschamp geomagnetic polarity event". Earth and Planetary Science Letters. 6 (1): 43–46. Bibcode:1969E&PSL...6...43B. doi:10.1016/0012-821x(69)90159-9.
  2. ^ a b Laj, C.; Channell, J.E.T. (27 September 2007). "5.10 Geomagnetic Excursions" (PDF). In Schubert, Gerald (ed.). Treatise on Geophysics. Vol. 5 Geomagnetism (1st ed.). Elsevier Science. pp. 373–416. ISBN 978-0-444-51928-3. Retrieved 18 February 2021 – via elsevier.com.
  3. ^ "An extremely brief reversal of the geomagnetic field, climate variability, and a super volcano" (Press release). Helmholtz Association of German Research Centres. 16 October 2012. Retrieved 19 October 2012.
  4. ^ Cooper, Alan; et al. (19 February 2021). "A global environmental crisis 42,000 years ago". Science. 371 (6531): 811–818. doi:10.1126/science.abb8677. ISSN 0036-8075. PMID 33602851. S2CID 231955607.
  5. ^ "NZ's ancient kauri yields major scientific discovery". The New Zealand Herald. 19 February 2021.
  6. ^ "End of Neanderthals linked to flip of Earth's magnetic poles, study suggests". The Guardian. 18 February 2021. Retrieved 19 February 2021.
  7. ^ Watson, Sara Kiley (24 February 2021). "A geomagnetic curveball 42,000 years ago changed our planet forever: The future is unpredictable—just ask the Neanderthals". Popular Science. Retrieved 25 February 2021.
  8. ^ Voosen, Paul (19 February 2021). "Kauri trees mark magnetic flip 42,000 years ago". Science. 371 (6531): 766. Bibcode:2021Sci...371..766V. doi:10.1126/science.371.6531.766. PMID 33602836. S2CID 231963027. Retrieved 8 March 2021.
  9. ^ Cooper, Alan; Turney, Chris (May 2020). "The Adams Event, a geomagnetic-driven environmental crisis 42,000 years ago". EGU General Assembly Conference Abstracts: 12314. Bibcode:2020EGUGA..2212314C. doi:10.5194/egusphere-egu2020-12314. hdl:11475/21883. S2CID 234999027.
  10. ^ Mitchell, Alanna (18 February 2021). "A Hitchhiker's Guide to an Ancient Geomagnetic Disruption". The New York Times.
  11. ^ Piper, Denise (2019). "Ancient Northland kauri tree reveals secrets of Earth's polar reversal". i.stuff.co.nz. Retrieved 29 September 2019.
  12. ^ Greenfieldboyce, Nell (18 February 2021). "Ancient trees show when the Earth's magnetic field last flipped out". Science. Weekend Edition. National Public Radio. Retrieved 18 February 2021 – via NPR.org.
  13. ^ "Changing Name for Earth's Changing Poles". Eos. 13 March 2019. Retrieved 15 November 2021.
Categories