This last major geomagnetic reversal has 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 stole over the tropics, solar winds generated spectacular light spectacles (auroras), arctic air poured into North America, ice sheets and glaciers rose and weather patterns have changed violently.
During these events, life on Earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna disappeared, while modern humans sought protection in caves.
The magnetic north pole – pointing to a compass needle – does not have a permanent location. Instead, it usually moves close to the geographic north pole – the point around which the Earth revolves – over time, due to movements in the core of the Earth.
For reasons that are not yet fully clear, the movements of the magnetic pole can sometimes be more extreme than a movement. One of the most dramatic of these pole migrations took place about 42,000 years ago and is known as the Laschamps Excursion – named after the village where it was discovered in the French central massif.
The Laschamps trip has been recognized around the world, most recently in Tasmania, Australia. But so far, it has not been clear whether such magnetic changes have had any impact on the climate and life on the planet. Our new paper brings together several lines of evidence that strongly suggest that the effects were indeed global and far-reaching.
Ancient trees
To investigate what happened, we analyzed New Zealand kauri trees, which have been stored in peatlands and other sediments for more than 40,000 years. Using the annual growth rings from the kauri trees, we were able to create a detailed time frame of how the Earth’s atmosphere changed during this time. The trees revealed a prolonged increase in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field as the poles switched, providing a way to accurately link geographically dispersed records.
“Kauri trees are like the Rosetta Stone, helping us to link together records of environmental changes in caves, ice cores and peatlands around the world,” said Professor Alan Cooper, who led the research project.
Using the new time scale, we were able to show that tropical rain belts in the Pacific and winds in the western South Ocean changed abruptly at the same time, bringing arid conditions to places like Australia at the same time as a range of megafauna, including giant kangaroos. . and the giant wombats are gone. Further north, the vast Laurentide ice sheet 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 power of the Sun. Importantly, during the magnetic switch, the strength of the magnetic field dropped to less than 6% of what it is today. A compass since then was even struggling to find the north.
An old log of kauri trees in Ngāwhā, New Zealand. Nelson Parker, author provided
In essence, without a magnetic field, our planet has completely lost its very effective shield against cosmic radiation and many more of these very penetrating particles from space could reach the top of the atmosphere. In addition, the Sun experienced several “high solar minima” during this period, during which time the overall solar activity was generally much smaller, but also more unstable, sending numerous massive solar flames that allowed the stronger ionizing cosmic rays to reaches Earth.
Our models showed that this combination of factors had an amplifying effect. High-energy cosmic rays from the galaxy, as well as huge bursts of cosmic rays from solar flares, managed to enter the upper atmosphere, charging particles into the air and causing chemical changes that led to the loss of stratospheric ozone.
The modeled chemical-climate simulations are consistent with the environmental changes observed in numerous archives of natural climate and environmental changes. These conditions would also have extended the dazzling light spectacles of the aurora 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 made the first humans seek refuge in caves, explaining the apparent sudden flowering of rock art around the world 42,000 years ago.
It must have seemed like the end of days.
The Adams event
Because of the coincidence of seemingly random cosmic events and 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 for the Galaxy and identified “42” in response to life, the universe and everything. Douglas Adams was really on to something big, and the mystery remains how did he know?
Chris Fogwill is a professor of glaciology and paleoclimatology, 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 at the University of Waikato.
Chris Turney is Professor of Earth Sciences and Climate Change, Director of the Center for Earth Sciences and Sustainability Research, Director of the Chronos 14Carbon-Cycle Facility and UNSW Director of the ARC Center for Excellence in Australian Biodiversity and Heritage, UNSW.
Zoë Thomas is a member of 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, Assistant Professor Ken McCracken and Dr Jonathan Palmer of the University of New South Wales, Drew Lorrey of the New Zealand National Water and Atmospheric Institute Research, Dr. Janet Willmshurst of Landcare Research and our co-authors on the published article.
Professor Alan Hogg works for Waikato University in Hamilton, New Zealand. He is an Associate Investigator in a Marsden Grant 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 CarbonScape Graphite for Clean Technologies (https://www.carbonscape.com).
Zoë Thomas receives funding from the Australian Research Council.
Reposted with permission from The Conversation.
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