The Earth’s magnetic field is one of the most mysterious forces that shape life on our planet. It is likely powered by the solidification of Earth’s iron core and appeared more than 3 billion years ago as the planet cooled. That’s our best guess – the field’s age and origin are still not fully understood.
The geomagnetic field plays many crucial functions. It is well known that it helps us tell the sides of the world by directing the compass needle. It may be a bit less known that, much more importantly, it acts as a shield that reflects cosmic radiation that could destroy our atmosphere.
However, its impact on climate remains another scientific mystery to solve.
Some 42,000 years ago, Earth went through several centuries of dramatic climate change and environmental chaos. The weather patterns went wild and shifted violently, with cold snaps commonly spreading from the Arctic over North America. The ozone layer was likely destroyed, and electrical storms created auroras even in the tropics. Neanderthals and some impressive representatives of megafauna went extinct. Strangely, amidst all the destruction, there was a boom of the surviving Homo sapiens cave art.
It was long argued that these events were all caused by sudden and massive climate change. But, what kind of climate change?
Now, scientists have an interesting guess at it. It may be that the well-documented magnetic drift called the Laschamps Excursion was behind it.
What is Geomagnetic Excursion?
Although we look at Earth’s poles as a constant, the truth is that they wobble all the time, moving around trajectories close to the pole’s center (the geographic pole). However, from time to time, the wobble gets dramatic and turns into pole migration – a reversal of poles that results in the weakening of the entire magnetic field.
One of the most dramatic known geomagnetic excursions occurred about 42,000 years ago. The first geologic proof of the event was discovered in the 1960s in the Laschamps lava flows, near the town of Clermont-Ferrand in the French Massif Central. Hence, it was named the Laschamp event, or the Laschamps excursion. Subsequently, more geologic cues (the change in natural magnetic particles such as the iron mineral magnetite, plus specific cosmogenic isotopes beryllium-10 and carbon-14) were found in various other locations around the world.
Up until recently, the full impact of the geomagnetic variability was unclear. Now, the new study powered by detailed modeling that included multiple lines of evidence implies that the magnetic excursion had a global influence on climate and life on our planet.
The magnetic field flip was also “recorded” in the fossil remains of New Zealand’s giant Kauri trees. The Kauri trees were alive during the event and had been used in the study for radiocarbon dating.
The Adams Event
So, what happened on Earth during the Laschamps excursion?
We know that during the magnetic switch, the geomagnetic field weakened – it had only 6% of the strength it has today. That resulted in the appearance of the aforementioned cosmogenic isotopes – the result of cosmic radiation being able to penetrate the atmosphere and all the way to the Earth’s surface.
As if that wasn’t troublesome enough already, the Sun went through several periods of minimal solar activity through this period. That resulted in lower temperatures, but also much more ionizing radiation due to massive solar flares that are also characteristic of grand solar minima.
The global chemistry climate modeling performed for this study was consistent with the comprehensive radiocarbon-dated and glacial sequences. The newly-modeled timescale shows that there were some significant shifts in weather and climate patterns, synchronous across the mid to low latitudes.
For example, in the Southern hemisphere, the tropical rain belts and the Southern Ocean westerly winds shifted at around the same time. As a consequence, arid conditions started to dominate Australia, and representatives of Australian megafauna such as giant kangaroos and giant wombats went extinct.
In the Northern hemisphere, the Laurentide Ice Sheet had trapped the eastern parts of North America. At the same time, Neanderthals disappeared from Europe. While there is no direct evidence that the demise of the Neandertal was all due to the Laschamps excursion, it is a coincidence that is worth exploring.
From the geologic point of view, the excursion and its consequences were short-living. The whole period was estimated to last for about 500 years, with additional 250 years needed for the transition from the normal field. In combination with the grand solar minima, this entire period makes for a new chapter in the history of our planet. The story of naming it will be a treat for science fiction fans.
As we’ve already learned, the event took place around 42 thousand years ago, and, although there are several theories, there is still no definitive scientific answer to why magnetic drifts occur. Because of this seeming randomness, plus the involvement of the number 42, the research team had an instant association to Douglas Adams and his most famous work, The Hitchhiker’s Guide to the Galaxy. In the Hitchhiker’s Guide, the number 42 is represented as “Answer to the Ultimate Question of Life, The Universe, and Everything”.
To pay tribute to the writer, and possibly imply the influence which the geomagnetic excursion and the related phenomena could have had on life as we know it today, they have named the entire period The Adams Event. In their The Conversation article, the research team concludes: “Douglas Adams really was onto something big, and the remaining mystery is how he knew?”
Cooper, A., et al. 2021. A global environmental crisis 42,000 years ago. Science. 19 Feb 2021: Vol. 371, Issue 6531, pp. 811-818 DOI: 10.1126/science.abb8677
Voosen, P. 2021. Kauri trees mark magnetic flip 42,000 years ago. Science. 19 Feb 2020: Vol. 371, Issue 6531, pp. 766 DOI: 10.1126/science.371.6531.766
Earth’s magnetic field broke down 42,000 years ago and caused massive sudden climate change. The Conversation. 18 February 2021. https://theconversation.com/earths-magnetic-field-broke-down-42-000-years-ago-and-caused-massive-sudden-climate-change-155580
We found the first Australian evidence of a major shift in Earth’s magnetic poles. It may help us predict the next. The Conversation. 25 February 2021 https://theconversation.com/we-found-the-first-australian-evidence-of-a-major-shift-in-earths-magnetic-poles-it-may-help-us-predict-the-next-155040
Origins of Earth’s magnetic field remain a mystery. MIT News. 8 April 2020 https://news.mit.edu/2020/origins-earth-magnetic-field-mystery-0408