This latest great geomagnetic reversal triggered a series of dramatic events with far-reaching consequences for our planet. They read like the plot of a horror movie: the ozone layer was destroyed, electric storms raged through the tropics, solar winds created spectacular light shows (auroras), polar air flowed through North America, ice caps and glaciers flew up and weather patterns changed dramatically.
During these events, life on Earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna became extinct, while modern humans took shelter in caves.
The magnetic north pole – to which a compass needle points – has no fixed location. Instead, it usually wobbles around near the geographic North Pole – the point around which the Earth revolves – over time due to movements in the Earth’s core.
For reasons not yet fully understood, magnetic pole movements can sometimes be more extreme than wobble. 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 the most recent in Tasmania, Australia. But until now, it was not clear whether such magnetic changes had any impact on the climate and life on the planet. Our new work brings together multiple evidence that strongly suggests that the effects were indeed global and far-reaching.
Old trees
To investigate what happened, we analyzed ancient New Zealand kauri trees preserved in peat bogs and other sediments for more than 40,000 years. Using the annual growth rings in the kauri trees, we have been able to create a detailed timetable of how the Earth’s atmosphere changed during this time. The trees revealed a protracted spike in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field as the poles alternated, providing a way to accurately link highly geographically dispersed records.
“The kauri trees are like the Rosetta Stone, helping us to bring together data on environmental changes in caves, ice cores and peatlands around the world,” said Professor Alan Cooper, who co-led this research project.
Using the newly created timescale, we were able to show that tropical Pacific rain belts and the western winds of the Southern Ocean shifted abruptly 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, died from. Further north, the vast Laurentide Ice Sheet grew rapidly in the eastern US and Canada, while in Europe, Neanderthals were facing extinction.
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 plummeted to less than 6% of what it is today. A compass from back then would have a hard time even finding north.
An old kauri tree log from Ngāwhā, New Zealand. Nelson Parker, Author provided
Because our planet had essentially no magnetic field, it completely lost its highly effective shield against cosmic rays, and many more of these highly penetrating particles from space could reach the top of the atmosphere. In addition, during this period the sun experienced several “great solar minima,” in which overall solar activity was generally much lower, but also more unstable, and emitted numerous massive solar flares that allowed more powerful ionizing cosmic rays to reach Earth.
Our models showed that this combination of factors had a reinforcing effect. The Milky Way’s high-energy cosmic rays, as well as massive bursts of cosmic rays from solar flares, were able to penetrate the upper atmosphere, recharge the particles in the air and cause chemical changes that caused the loss of ozone in the stratosphere.
The modeled chemistry-climate simulations are consistent with the environmental changes observed in many natural climate and environmental change archives. These conditions would also have spread the aurora’s dazzling light shows around the world – sometimes the nights would be just as bright as during the day. We suggest that the dramatic changes and unprecedentedly high UV levels caused early humans to seek shelter in caves, explaining the apparent sudden bloom of cave 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 dubbed 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 onto something really big, and the remaining mystery is how did he know?
Chris Fogwill is a professor of glaciology and paleoclimatology, and head of school geography, geology and 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 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 Investigator at the South Australian Museum, who co-led this study, Adjunct 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 of the published paper.
Professor Alan Hogg works for the University of Waikato in Hamilton, New Zealand. He is an assistant researcher with a Royal Society of New Zealand Marsden grant – 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 cleantech graphite company CarbonScape (https://www.carbonscape.com).
Zoë Thomas receives funding from the Australian Research Council.
Reposted with permission from The Conversation.
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