19 February 2021

Ancient relic points to a turning point in Earth’s history 42,000 years ago

The temporary breakdown of Earth’s magnetic field 42,000 years ago sparked major climate shifts that led to global environmental change and mass extinctions, a new international study involving the University of Sheffield shows.

Ancient Kauri tree log found buried underground
An ancient New Zealand kauri log. This tree is around 40,000 years old and was found buried under the ground. Photo Credit Mr Nelson Parker.

  • An international team of scientists have precisely dated the timing and environmental impacts of the last magnetic pole switch
  • New research explains what happened in the lead up to the reversal of the Earth’s poles 42,000 years ago for the first time
  • Findings show that the switch lead to major damage of the Ozone layer, triggering major climate shifts and mass extinctions

The temporary breakdown of Earth’s magnetic field 42,000 years ago sparked major climate shifts that led to global environmental change and mass extinctions, a new international study involving the University of Sheffield shows. 

This dramatic turning point in Earth’s history – laced with electrical storms, widespread auroras, and cosmic radiation – was triggered by the reversal of Earth’s magnetic poles and changing solar winds.

The researchers have dubbed this period the ‘Adams Transitional Geomagnetic Event’, or ‘Adams Event’ for short, a tribute to science fiction writer Douglas Adams, who wrote in The Hitchhiker's Guide to the Galaxy that ‘42’ was the answer to life, the universe, and everything.

The findings of the study, led by UNSW Sydney and the South Australian Museum, have been published in Science

While scientists already knew the magnetic poles temporarily flipped around 41-42,000 years ago (known as the ‘Laschamps Excursion’), they didn’t know exactly how it impacted life on Earth, if at all. 

Until now, scientific research has focused on changes that happened while the magnetic poles were reversed. But according to the team’s findings, the most dramatic part was the lead-up to the reversal, when the poles were migrating across the Earth. During this time Earth’s magnetic field dropped to only 0-6 per cent strength, leaving it with little protection from cosmic radiation. 

This unfiltered radiation from space caused ionisation in the air particles in Earth’s atmosphere, destroying the Ozone layer and triggering a ripple of climate change across the globe. 

The researchers were able to create a detailed timescale of how Earth’s atmosphere changed over this time by analysing rings in ancient kauri trees from New Zealand that were found hidden under the ground.

Using radiocarbon dating, a technique to date ancient relics or events, the team tracked the changes in radiocarbon levels during the magnetic pole reversal. This data was charted alongside the trees’ annual growth rings, which acts as an accurate, natural timestamp. 

The new timescale helped reveal the picture of this dramatic period in Earth’s history. The team were able to reconstruct the chain of environmental and extinction events using climate modelling. 

Without the Earth's geomagnetic field we would be bombarded by cosmic particles that would increase our risk of cancer and cause critical damage to many essential parts of our technological society and communications

Dr Tim Heaton

Senior Lecturer at the University of Sheffield's School of Mathematics and Statistics

Dr Tim Heaton, from the University of Sheffield’s School of Mathematics and Statistics, said: “Our geomagnetic field provides the Earth with a key shield to deflect most of the extra-terrestrial radiation that is constantly speeding towards us from the Sun and distant galaxies. Without it, we would be bombarded by cosmic particles that would increase our risk of cancer and cause critical damage to many essential parts of our technological society and communications. There would also be a lot of very confused pigeons and whales who rely on the Earth’s magnetic field to navigate.”   

Professor Chris Turney, from UNSW who co-led the study said: “For the first time ever, we have been able to precisely date the timing and environmental impacts of the last magnetic pole switch.

“The findings were made possible with ancient New Zealand kauri trees, which have been preserved in sediments for over 40,000 years.Using the ancient trees we could measure, and date, the spike in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field.”

Professor Alan Cooper, from the South Australian Museum said: “This speed – alongside the weakening of Earth’s magnetic field by around nine per cent in the past 170 years – could indicate an upcoming reversal. If a similar event happened today, the consequences would be huge for modern society. Incoming cosmic radiation would destroy our electric power grids and satellite networks.”


Additional information

Science - Full research paper

The University of Sheffield's School of Mathematics and Statistics 

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