Nearly 42,000 years ago, when Earth’s magnetic fields reversed, it triggered major environmental changes, extinction events and long-term shifts in human behavior, a new study reports.
The findings, made possible by a new radiocarbon record derived from ancient New Zealand kauri trees, raise important questions about the evolutionary impacts of geomagnetic reversals and excursions through deeper geological records, the authors say.
“Before this work,” author Chris Turney explains in a related video, “we knew there was a lot going on in the world 42,000 years ago, but we didn’t know precisely how… For the first time, we were able to precisely date what happened during the last reversal of the Earth’s magnetic fields.
The geological record contains many instances where the magnetic poles of the planet have flipped. Today, such an event would almost certainly wreak havoc on modern electronic and satellite technology. 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 around 41,000 years ago, provides one of the best opportunities to study the potential impacts of extreme changes of the earth’s magnetic field. However, despite compelling evidence from multiple paleoenvironmental records that suggests it coincided with significant environmental and ecological changes, the ability to precisely characterize this event and determine its role – if any – in contemporary global change has been limited. by an uncertain radiocarbon calibration for the period. .
In this study, Turney, Alan Cooper and colleagues present a new, precisely dated atmospheric radiocarbon record derived from the tree rings of ancient kauri trees preserved for millennia in New Zealand wetlands. Like a missing keystone, this new record allowed the authors to better align the other world radiocarbon and ice core records with the Laschamps.
Cooper et al. identified a significant increase in atmospheric radiocarbon during the period of magnetic field weakening that preceded the polarity reversal. By modeling the consequences of this increase, they found that the geomagnetic field minimum, when the Earth’s magnetic field was estimated at only ~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 seen in other climate records that occurred around 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 sudden, anomalous 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
