This last great geomagnetic inversion triggered 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, electrical storms burst into the tropics, solar winds generated spectacular light shows (auroras), Arctic air it spilled over North America, ice sheets and glaciers increased, and weather patterns changed violently. .
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, where a compass needle points, does not have a permanent location. Instead, it usually revolves near the geographic north pole (the point around which the Earth revolves) over time due to movements within the Earth’s core.
For reasons that are not yet entirely clear, the movements of the magnetic pole can sometimes be more extreme than an oscillation. One of the most spectacular migrations from this pole took place about 42,000 years ago and is known as an excursion to Laschamps, named after the village where it was discovered in the central French massif.
The excursion to Laschamps has been recognized around the world, including the most recent in Tasmania, Australia. But until now it was unclear whether these magnetic changes had any impact on the climate and life on the planet. Our new work collects multiple lines of evidence that strongly suggest that the effects were truly global and far-reaching.
Ancient trees
To investigate what happened, we looked at ancient New Zealand kauri trees that had been preserved in peatlands and other sediments for over 40,000 years. Using the annual growth rings on kauri trees, we were able to create a detailed time scale of how the Earth’s atmosphere changed over that time. The trees revealed a prolonged increase in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field as the poles changed, providing a way to accurately link widely geographically dispersed records.
“Kauri trees are like the Rosetta Stone, which helps us unite records of environmental changes in caves, ice cores and peatlands around the world,” said Professor Alan Cooper, who co-led this project. research.
Using the newly created time scale, we were able to show that the tropical rain belts of the Pacific and the westerly winds of the southern ocean changed abruptly at the same time, bringing arid conditions to places like Australia in the same. while a range of megafauna, including giant kangaroos and giant owls became extinct. Further north, the vast ice sheet of Laurentide grew rapidly in the eastern United States and Canada, while in Europe Neanderthals spiraled away.
Climate modeling
Working with a computer program that simulated the global interactions between chemistry and climate, we investigated the impact of a weaker magnetic field and changes in the strength of the Sun. It is important to note that during the magnetic switch the strength of the magnetic field fell to less than 6% of what it is today. A compass at the time would even struggle to find the north.
An ancient record of the kauri tree of Ngāwhā, New Zealand. Nelson Parker, author provided
Essentially, without any magnetic field, our planet completely lost its very effective shield against cosmic radiation and many more of these highly penetrating particles from space could access the top of the atmosphere. In addition, the Sun experienced several “large solar minima” during this period, during which general solar activity was generally much lower but also more unstable, sending numerous massive solar flares that allowed cosmic rays. more powerful ionizers would reach Earth.
Our models showed that this combination of factors had an amplifying effect. The galaxy’s high-energy cosmic rays and also huge bursts of cosmic rays from solar flares were able to penetrate the upper atmosphere, charging airborne particles and causing chemical changes that led to the loss of stratospheric ozone.
Chemical-climate modeled simulations are consistent with the environmental changes observed in many natural climate and environmental change archives. These conditions would also have extended the dazzling aurora light spectacles around the world; sometimes the nights would have been as bright as the day. We suggest that the dramatic changes and unprecedented high levels of UV caused early humans to seek refuge in caves, explaining the apparent sudden flowering of rock art around the world 42,000 years ago.
It must seem like the end of days.
The Adams event
Due to the coincidence of seemingly random cosmic events and extreme environmental changes found around the world 42,000 years ago, we have called this period the “Adams Event,” a tribute to the great science fiction writer Douglas Adams, who he wrote The Hitchhiker’s Guide to the Galaxy and identified “42” as the answer to life, the universe, and everything. Douglas Adams really had something big, and the mystery that remains is how did he know?
Chris Fogwill is a professor of glaciology and paleoclimatology and head of geography, geology and school environment and director of the Institute for Sustainable Futures at Keele University.
Alan Hogg is a professor and director of the Carbon Dating Laboratory at the University of Waikato.
Chris Turney is Professor of Earth Sciences and Climate Change, Director of the Center for Research in Earth Sciences and Sustainability, Director of the Chronos 14Carbon-Cycle Facility and Director of the UNSW of the ARC Center of Excellence in Biodiversity and Australian Heritage, UNSW.
Zoë Thomas is a member of the ARC DECRA, UNSW.
Disclosure Statements: Chris Fogwill receives funding from UKRI and the Australian Research Council. A huge thank you to Professor Alan Cooper, an honorary researcher at the South Australian Museum, who led this study, to Assistant Professor Ken McCracken and Dr Jonathan Palmer of the University of New South Wales, Drew Lorrey at the National Institute of the Water of New Zealand. and Atmospheric Research, Dr. Janet Willmshurst of Landcare Research and our co-authors on the published article.
Professor Alan Hogg works at the University of Waikato in Hamilton, New Zealand. He is an Associate Research Fellow in a Marsden Fellowship of the Royal Society of New Zealand – MFP-NIW1803: Dr. Andrew Lorrey, NIWA, Auckland, principal investigator.
Chris Turney receives funding from the Australian Research Council and is a scientific advisor to the clean technology graphite company CarbonScape (https://www.carbonscape.com).
Zoë Thomas receives funding from the Australian Research Council.
It is republished with permission from The Conversation.
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