This latest great geomagnetic reversal set off 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, thunderstorms swept through the tropics, solar winds generated spectacular light shows (auroras), arctic air spilled over North America, the layers of Ice 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, has no permanent location. Instead, it generally wobbles near the geographic north pole, the point around which the Earth rotates, over time due to motions within the Earth’s core.
For reasons that are not entirely clear, the movements of the magnetic poles can sometimes be more extreme than wobble. One of the most dramatic migrations from these poles took place around 42,000 years ago and is known as the Laschamps Excursion, named after the town where it was discovered in the French Massif Central.
The Laschamps Excursion has been recognized around the world, including the most recent in Tasmania, Australia . But until now, it was not clear if such magnetic changes had any impact on the climate and life on the planet. Our new work brings together multiple lines of evidence that strongly suggest that the effects were indeed global and far-reaching.
Ancient trees
To investigate what happened, we analyzed ancient New Zealand kauri trees that have been conserved in peat bogs and other sediments for more than 40,000 years. Using the annual growth rings of kauri trees, we have been able to create a detailed timescale of how Earth’s atmosphere changed during this time. The trees revealed a prolonged spike in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field when the poles shifted, providing a way to accurately link geographically widely dispersed records.
“Kauri trees are like the Rosetta Stone, helping us unite records of environmental change in caves, ice cores and peatlands around the world,” said Professor Alan Cooper, who co-led this research project. p>
Using the newly created timescale, we were able to show that the tropical Pacific rain belts and the western Southern Ocean winds changed abruptly at the same time, bringing arid conditions to places like Australia at the same time as a variety of megafauna, including kangaroos. giants and giant wombats went extinct < / a>. Further north, the vast Laurentide Ice Sheet grew rapidly in the eastern US and Canada, while in Europe Neanderthals spirally became extinct.
Climate modeling
Working with a computer program that simulated global interactions between chemistry and climate, we investigated the impact of a weaker magnetic field and changes in the Sun’s strength. Importantly, during magnetic change, the strength of the magnetic field it plummeted to less than 6% of what it is today. A compass back then would have a hard time finding north.
An ancient kauri tree trunk from Ngāwhā, New Zealand. Nelson Parker, Author Provided
Without a magnetic field essentially, our planet completely lost its very effective shield against cosmic radiation, and many more of these very pervasive particles from space could access the upper part of the atmosphere. In addition to this, the Sun experienced several “great solar minima” during this period, during which overall solar activity was generally much lower but also more unstable, sending out numerous massive solar flares that allowed more powerful ionizing cosmic rays to reach Earth. .
Our models showed that this combination of factors had an amplifying effect. High-energy cosmic rays from the galaxy and also huge cosmic ray bursts from solar flares were able to penetrate the upper atmosphere, charging the particles in the air and causing chemical changes that led to the loss of stratospheric ozone.
The modeled chemistry-climate simulations are consistent with observed environmental changes in many natural climate and environmental change files. These conditions would also have spread the dazzling aurora light shows around the world; sometimes nights would have been as bright as day. We suggest that dramatic changes and unprecedented high levels of ultraviolet radiation caused early humans to seek refuge in caves, which explains the apparent sudden flourishing of rock art around the world 42,000 years ago.
It must have seemed like the end of days.
The Adams Event
Due to the coincidence of seemingly random cosmic events and the 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 wrote The Hitchhiker’s Guide to the Galaxy and identified “42” as the answer to life, the universe, and everything. Douglas Adams really was into something big, and the remaining mystery is how he knew it.
Chris Fogwill is Professor of Glaciology and Paleoclimatology and Director of the School of Geography, Geology and Environment and Director of the Institute for Sustainable Futures at Keele University.
p >
Alan Hogg is 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 on Earth Sciences and Sustainability, Director of the Chronos 14Carbon-Cycle Facility, and UNSW Director of the ARC Center for Excellence in Biodiversity and Australian Heritage, UNSW.
Zoë Thomas is a member of ARC DECRA, UNSW.
Disclosure Statements: Chris Fogwill is funded by UKRI and the Australian Research Council. A big thank you to Professor Alan Cooper, Honorary Research Fellow at the Museum of South Australia, who co-led this study, Associate Professor Ken McCracken and Dr Jonathan Palmer from the University of New South Wales, Drew Lorrey from the National Water Institute of New Zealand. and Atmospheric Research, Dr. Janet Willmshurst of Landcare Research and our co-authors of the published paper.
Professor Alan Hogg works for the University of Waikato in Hamilton, New Zealand. He is a Research Associate in a Marsden Grant from 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 graphite clean technology company CarbonScape ( https://www.carbonscape.com ).
Zoë Thomas receives funding from the Australian Research Council.
Published with permission of The conversation a >.
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