42,000 years ago, the world experienced a few centuries of apocalyptic conditions caused by a reversal of the Earth’s magnetic poles combined with changes in the behavior of the Sun. That’s the key finding of our new multidisciplinary study, published in the journal Science. This latest great geomagnetic reversal set off a series of dramatic events that have far-reaching consequences for our planet. They were like the plot of a horror movie, the ozone layer was destroyed, electrical storms swept through the tropics, solar winds generated light shows (auroras), arctic air spilled over North America, the ice sheets and glaciers increased, and weather patterns changed violently.
During these events, life on Earth was exposed to intense ultraviolet light. YL Neanderthals to megafauna became extinct, while modern humans sought refuge in caves. The magnetic north pole, where a compass needle points, has no permanent location. In reality, it generally wobbles near the geographic north pole the point around which the Earth rotates over time due to motions within the planet’s core.
For reasons that are not yet entirely clear, the movements of the magnetic poles can sometimes be more extreme than a wobble. One of the most dramatic migrations from these poles took place about 42,000 years ago and is known as the Laschamps event, named after the town where it was discovered in the Massif Central of France. The Laschamps event has been recognized around the world, including recently 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 pieces of evidence strongly suggesting that the effects were global and far-reaching.
Kauri Trees
To investigate what happened, we analyzed the ancient kauri trees of New Zealand, which had been preserved 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 the Earth’s atmosphere changed during this period.
The trees revealed a prolonged rise in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field when the poles shifted. This provided a way to accurately link widely geographically dispersed records. Kauri trees are like the Rosetta Stone, helping us to piece together the records of environmental change in caves, ice cores, and peatlands around the world, says Professor Alan Cooper, who is co-leading this research project.
Using the newly created timescale, we were able to show that the rain belts of the tropical Pacific and the western winds of the Southern Ocean shifted abruptly at the same time, causing arid conditions in places like Australia. In turn, a variety of megafauna became extinct, including giant kangaroos and wombats. Further north, the vast Laurentide Ice Sheet grew rapidly in the eastern United States and Canada, while in Europe the Neanderthals 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 strength of the Sun. Importantly, during the magnetic shift, the field strength plummeted to less than 6% of what it is today. A compass back then would have a hard time finding north. Without any magnetic field, our planet completely lost its effective shield against cosmic radiation, and many penetrating particles from space entered the upper atmosphere. In addition to this, the Sun experienced several great solar minima, during which activity was much less but also more unstable sending out numerous massive solar flares that allowed 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 bursts of cosmic rays from solar flares were able to penetrate the upper atmosphere, charging the particles in the air and causing chemical changes that caused the loss of stratospheric ozone. The simulations between chemistry and climate are consistent with the environmental movements observed in many archives of natural climate change.
These conditions would also have spread dazzling aurora light shows around the world sometimes nights could 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 flowering 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 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. Adams wrote The Hitchhiker’s Guide to the Galaxy and identified 42 as the
