This last major geomagnetic reversal has caused a series of dramatic events that have far-reaching consequences for our planet. They read like the plot of a horror movie: the ozone layer was destroyed, electric storms raged across the tropics, solar winds produced spectacular flashes of light (auroras), North Pole sky poured over North America, ice sheets and glaciers erupted and weather patterns erupted violently. moved.
During these events, life on Earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna became extinct, while modern humans sought protection in caves.
The magnetic north pole – to which a compass needle points – does not have a permanent location. Instead, it usually oscillates near the geographic North Pole – the point around which the earth rotates – over time due to movements within the earth’s core.
For reasons that are not yet completely clear, magnetic pole motions can sometimes be more extreme than a bickering. One of the most dramatic of these pole migrations took place some 42,000 years ago and is known as the Laschamps Excursion – named after the village where it was discovered in the French Massif Central.
The Laschamps excursion has been recognized around the world, including recently in Tasmania, Australia. But so far it has not been clear whether such magnetic changes have had an effect on the climate and life on the planet. Our new work contains several pieces of evidence that strongly suggest that the consequences were indeed global and far-reaching.
Antique trees
To investigate what happened, we analyzed ancient New Zealand kauri trees that have been preserved in peat and other sediments for over 40,000 years. Using the annual growth rings in the kauri trees, we were able to compile a detailed time scale on how the earth’s atmosphere changed during this time. The trees revealed a sustained increase in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field while the poles were reversing, providing a way to accurately link widely geographically distributed records.
“The kauri trees are like the Rosetta Stone, which helps us put together records of environmental change in caves, ice cores and peat bogs around the world,” said Professor Alan Cooper, who led this research project.
Using the newly created time scale, we were able to show that the tropical Pacific rain belts and the westerly winds of the Southern Ocean suddenly shifted at the same time, bringing dry conditions to places like Australia, at the same time as a series of megafauna, including giant kangaroos. and giant wombats became extinct. Further north, the expansive Laurentide ice sheet grew rapidly across the eastern United States and Canada, while the Neanderthals in Europe became extinct.
Climate modeling
In collaboration with a computer program that mimicked the global interaction between chemistry and climate, we investigated the impact of a weaker magnetic field and changes in the strength of the sun. It is important that the strength of the magnetic field during the magnetic switch dropped to less than 6% of the current amount. A compass at the time would struggle to find even north.
An ancient kauri tree from Ngāwhā, New Zealand. Nelson Parker, author provided
With no magnetic field, our planet has lost its very effective shield against cosmic radiation, and many more of these very penetrating particles from space have been able to reach the top of the atmosphere. In addition, the sun experienced several “large solar minima” during this period, during which the overall solar activity was generally much lower, but also more unstable, and emitted numerous massive solar flares that made it possible to reach the earth with more powerful ionizing cosmic rays.
Our models have shown that this combination of factors has a reinforcing effect. The high energy cosmic rays from the galaxy and also enormous cosmic rays from solar flares could penetrate the upper atmosphere and charge the particles into the air and cause chemical changes that caused the loss of stratospheric ozone.
The modeled chemistry-climate simulations are consistent with the environmental shifts observed in many archives for natural climate and environmental change. These conditions would also have extended the aurora’s dazzling light showers around the world – sometimes the nights would have been just as bright as the day. We suggest that the dramatic changes and the unprecedented high UV levels caused early humans to seek refuge in caves, which explained the apparent sudden flourishing of cave art around the world 42,000 years ago.
It must have looked like the end of days.
The Adams Event
Because of the coincidence of seemingly random cosmic events and the extreme environmental changes found around the world 42,000 years ago, we called this period the “Adams Event” – a tribute to the great science fiction writer Douglas Adams, who wrote The Hitchhiker’s Guide to the Milky Way and identified ’42 ‘as the answer to life, the universe and everything. Douglas Adams was really doing something big, and the remaining mystery is how did he know?
Chris Fogwill is a professor of glaciology and paleoclimatology, and the head of school geography, geology and the environment and director of the Institute for Sustainable Futures, Keele University.
Alan Hogg is a professor and director of the Carbon Dating Laboratory, University of Waikato.
Chris Turney is a Professor of Earth Science and Climate Change, Director of the Earth and Sustainability Science Research Center, Director of Chronos 14Carbon-Cycle Facility, and UNSW Director of the ARC Center for Excellence in Australian Biodiversity and Heritage, UNSW.
Zoë Thomas is an ARC DECRA Fellow, UNSW.
Disclosure Statements: Chris Fogwill receives funding from UKRI and the Australian Research Council. A big thank you to Professor Alan Cooper, honorary researcher at the South Australian Museum, who led this study, Deputy Professor Ken McCracken and dr. Jonathan Palmer at the University of New South Wales, Drew Lorrey at the New Zealand National Institute of Water. and Atmospheric Research, Dr. Janet Willmshurst of Landcare Research and our co-authors on the published article.
Professor Alan Hogg works for the University of Waikato in Hamilton, New Zealand. He is a co-researcher at a Royal Society of New Zealand Marsden Award – MFP-NIW1803: Dr Andrew Lorrey, NIWA, Auckland, Principal Investigator.
Chris Turney receives funding from the Australian Research Council and is a scientific adviser to the cleaning graphite company CarbonScape (https://www.carbonscape.com).
Zoë Thomas receives funding from the Australian Research Council.
Replace with permission from The Conversation.
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