It's easy to think that as a result of the extinction of the dodo, we are now sadder and wiser, but there's a lot of evidence to suggest that we are merely sadder and better informed.
– Douglas Adams, Last Chance To See (with Mark Carwardine, 1990)

It is relatively easy for humans with normal memory and a library card to observe what historians call, technically, 'change over time'. It's harder to look at changes in prehistory, that is, before humans started writing things down. However, understanding events that happened on Planet Earth a very long time ago might be of use to those of us living now. Such knowledge could, perhaps, be vital to our survival as a species. Which is why we're talking excitedly about the Adams Event.

The Ultimate Answer? Maybe Not, But...

Fans of the Hitchhiker's Guide to the Galaxy are well aware that the 'ultimate answer' to 'Life, the Universe, and Everything'¹ is... well, 42. Author Douglas Adams chose the number for reasons of his own. Finding quasi-numinous instances of the number have become a major running joke among fans everywhere. Those fans include some dedicated scientists. So it's probably not a terrible surprise that the scientists Alan Cooper and Chris Turney, both of Australia, decided to name their discovery of a 'wide range of extinction events and major changes in the global archaeological record' the Adams Transitional Geomagnetic Event. After all, it happened 42,000 years ago.

What Happened 42,000 Years Ago, and How Do We Know About It?

The Laschamp Excursion was a major event. It would have made headlines, if there had been any in the Last Glacial Period, 41,400 years ago. The word 'excursion' refers to a shift in the magnetic poles. The magnetic poles reversed and stayed that way for about 440 years. In that time, the Earth's magnetic field strength dropped drastically. During the transition, it dropped to 5% of normal. The reversed field strength was only 25% of the normal field strength.

The magnetosphere deflects the solar wind and traps dangerous high-energy particles that are bad for living things. A drop in the magnetic field leaves Earth exposed to ultraviolet radiation, which can cause cancer in mammals like humans. A drop in the geomagnetic field in the 21st Century would have catastrophic effects on human power grids and communications satellites. 42,000 years ago, during the run-up to the Laschamp Excursion, the loss of protection in the atmosphere was an extinction-level event: scientists are blaming the Adams Event for the extinction of Neanderthals, the loss of Australian megafauna, and possibly, the beginning of cave art.

How Do We Know This?

Good question. The answer's interesting: kauri trees. Kauri, one of the Araucariaceae, is a very old species found preserved in New Zealand swamps. Samples date back to around the time of the Adams Event, and tell a riveting climate-change story. Professor Alan Cooper, co-author of the study, compared the kauri trees to 'the Rosetta Stone, helping us tie together records of environmental change in caves, ice cores and peat bogs around the world².' Studying the tree rings allowed the scientists to measure the spike in radiocarbon levels caused by the drop in atmospheric protection from the collapsed geomagnetic field.

This new information gave the researchers clues to the causes of other changes in the fossil record, such as the extinction of megafauna in Australia and Tasmania, long after the arrival of aboriginal humans. They also think the wild storms and other climate-related phenomena might have caused humans to seek shelter in caves – leading to the creation of the cave art that has been found beginning in that period. The ochre handprints on cave walls might even be evidence of prehistoric sunscreen!

What Does It All Mean?

The Adams Event provides a clue to many planet-wide changes that occurred around 42,000 years ago. It may solve some prehistoric mysteries and fill in a few blanks in our knowledge. But this information may also be of vital use to humans who live in the 21st Century. There is evidence that the magnetic poles may be getting ready to shift again. In the last 170 years, the magnetic field has weakened by around 9%. A reversal of the magnetic poles could have disastrous consequences for modern society's energy infrastructure.

So, climate change could be brought about by a naturally-occurring phenomenon such as magnetic pole reversal? That lets humans off the hook, right? We don't have to worry about human-induced climate change any longer? Wrong, say the scientists. This makes fighting manmade climate change even more urgent.

Our atmosphere is already filled with carbon at levels never seen by humanity before. A magnetic pole reversal or extreme change in Sun activity would be unprecedented climate change accelerants. We urgently need to get carbon emissions down before such a random event happens again.
– Professor Chris Turney, University of New South Wales

In other words, it's more bad news, but forewarned is forearmed.

For Further Reading

Read the abstract for the paper 'The Adams Event, a geomagnetic-driven environmental crisis 42,000 years ago' here. Or go to the Science site and read the full article, if you are willing to pay for it.

For a discussion of what the Adams Event might, or might not explain from the point of view of the scientific community, read 'A Hitchhiker's Guide to an Ancient Geomagnetic Disruption' by Alanna Mitchell in the New York Times, 18 February, 2021.

For an entertainingly illustrated explanation of the Adams Event, see this video narrated by Stephen Fry.