The Laschamp event was a geomagnetic excursion (a short reversal of the Earth's magnetic field). It occurred 41,400 years ago, during the end of the Last Glacial Period. It is known from geomagnetic anomalies discovered in the 1960s in the Laschamps lava flows in Clermont-Ferrand, France.
The Laschamp event was the first known geomagnetic excursion and remains the most thoroughly studied among the known geomagnetic excursions.
Discovery and further research
The Laschamp excursion occurred 41,400 (±2,000) years ago during the end of the Last Glacial Period; it was first recognised from a geomagnetic excursion discovered c. 1969 in the Laschamps lava flows in the Clermont-Ferrand district of France.
The magnetic excursion has since been demonstrated in geological archives from many parts of the world. The magnetic field was reversed for approximately 440 years, with the transition from the normal field lasting approximately 250 years. The reversed field was 75% weaker, whereas the strength dropped to only 5% of the current strength during the transition. 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.
The Australian Research Council is funding research to analyze a kauri tree uncovered in New Zealand in 2019. According to its carbon-dating, the tree was alive during the event (41,000–42,500 years ago).
The geomagnetic field was at low levels from 42,200–41,500 years ago. This period of low magnetic field 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. During this period, Earth's magnetic field dropped to below 6% of the current level, Carbon 14 production increased, ozone levels decreased, and atmospheric circulation changed. This loss of the geomagnetic shield was also claimed to have caused the extinction of Australian megafauna, the extinction of the Neanderthals, and the appearance of cave art.
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- 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.
- 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.
- Mitchell, Alanna (18 February 2021). "A Hitchhiker's Guide to an Ancient Geomagnetic Disruption". The New York Times.
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- "NZ's ancient kauri yields major scientific discovery". The New Zealand Herald. 19 February 2021.
- "End of Neanderthals linked to flip of Earth's magnetic poles, study suggests". The Guardian. 18 February 2021. Retrieved 19 February 2021.
- 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.
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