Almost 42,000 years ago, when Earth’s magnetic fields reversed, it triggered major environmental changes, extinction events and long-term changes in human behavior, according to a new study.

The findings, made possible by a new radiocarbon record derived from ancient New Zealand kauri trees, raise important questions about the evolutionary impacts of reversals and geomagnetic excursions in the deeper geological records, according to the authors.

“Before this work,” says author Chris Turney in a related video, “we knew there was a lot going on in the world 42,000 years ago, but we weren’t sure exactly how… To the first time, we were able to date precisely what happened during the last reversal of the Earth’s magnetic fields.

The geological records contain numerous cases where the magnetic poles of the planet have reversed. Today, such an event would almost certainly wreak havoc on modern electronic and satellite technologies. However, the potential environmental impacts of such events are virtually unknown.

The most recent major magnetic reversal, the Laschamps excursion, a relatively short-lived geomagnetic event that occurred about 41,000 years ago, offers one of the best opportunities to study the potential impacts of the changes. extremes of the earth’s magnetic field. However, despite convincing evidence from several paleoenvironmental records that suggest that it coincided with significant environmental and ecological changes, the ability to accurately characterize this event and determine its role – if any – in contemporary global changes has been limited by uncertain radiocarbon calibration for the period.

In this study, Turney, Alan Cooper and their colleagues present a new, precisely dated atmospheric radiocarbon record, derived from ancient kauri tree rings preserved for millennia in New Zealand wetlands. Like a missing keystone, this new record allowed the authors to better align other world records for radiocarbon and ice cores with the Laschamps.

Cooper et al. identified a significant increase in atmospheric radiocarbon during the period of weakening of the magnetic field that preceded the polarity reversal. By modeling the consequences of this increase, they found that the geomagnetic field minimum, while the Earth’s magnetic field was estimated to be only about 6% of current levels, triggered substantial changes in the concentration and circulation of atmospheric ozone. .

These changes may have caused synchronous global climate and environmental changes observed in other climate records that occurred approximately 42,000 years ago. The discovery that fluctuations in the geomagnetic field can affect atmospheric temperature and circulation on a global scale provides a model for understanding abnormal and sudden paleoenvironmental changes, the authors say.

Reference: “A Global Environmental Crisis 42,000 Years Ago” by Alan Cooper, Chris SM Turney, Jonathan Palmer, Alan Hogg, Matt McGlone, Janet Wilmshurst, Andrew M. Lorrey, Timothy J. Heaton, James M. Russell, Ken McCracken, Julien G. Anet, Eugene Rozanov, Marina Friedel, Ivo Suter, Thomas Peter, Raimund Muscheler, Florian Adolphi, Anthony Dosseto, J. Tyler Faith, Pavla Fenwick, Christopher J. Fogwill, Konrad Hughen, Mathew Lipson, Jiabo Liu, Norbert Nowaczyk, Eleanor Rainsley, Christopher Bronk Ramsey, Paolo Sebastianelli, Yassine Souilmi, Janelle Stevenson, Zoë Thomas, Raymond Tobler and Roland Zech, February 19, 2021, Science.
DOI: 10.1126 / science.abb8677


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