An Ancient Tree and the Question of Life, the Universe and Everything

The 42,000 year old kauri tree has information about Earth's magnetic field reversal at the time.

Kauri tree at Ngawha, New Zealand in 2019
Kauri tree at Ngawha, New Zealand in 2019.
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The Earth has a magnetic field that protects us from harmful solar radiation. In fact, life on the planet would not exist without it. It gives us the northern and sourthern lights, which occur when solar particles interact with it. The magnetic field also moves around and sometimes it reverses, with the north and south poles completely flipping. We know this through rock analysis, which tells us that in the last 20 million years or so, the poles have changed positions completely, many times. The trend for complete reversal is every 100,000 to 300,000 years, with the last full reversal taking place around 780,000 years ago. So, we are due for another one, but this process is unpredictable, so no one can tell for sure – the range can be 100,000 years to 50 million years. Full geomagnetic reverasals can last up to 10,000 years.

Sometimes however, the magnetic field does not flip completely. In between full reversals there are shorter disruptions known as geomagnetic excursions. These occur for shorter periods and result in temporary changes to the Earth’s magnetic field, usually lasting anywhere between a few hundred to a few thousand years. In 2019, a tree was discovered in New Zealand during the expansion of the Ngāwhā Generation geothermal power plant, which contains the record of the Laschamps magnetic field reversal. This tree – called Agathis australis – or kauri in the Maori language, was found in New Zealand’s North Island. Carbon dating indicated that it lived around 41,000 to 42,500 years ago and shows that the magnetic field almost reversed at this point though it did not do a complete flip – that is, it went through Earth’s most recent geomagnetic excursion. This excursion that occured around 42,000 years ago is known as the Laschamps excursion.

“The Laschamps Excursion was the last time the magnetic poles flipped,” explains Chris Turney, co-lead author of a landmark new study investigating this event. “They swapped places for about 800 years before changing their minds and swapping back again.”

The tree rings provide a 1,700-year record of global environmental conditions, exactly covering the period of the Laschamps Excursion. Scientists used this ancient tree and its rings to measure and date the spike in atmospheric radiocarbon levels caused by the collapse of the magnetic field. Scientists created a timeline of the Earth’s atmosphere during the Laschamp’s Excursion, then compared this with a global climate model (incorporating previously gathered data), to understand what effects the excursions had on the environment.

The new study showed dramatic environmental changes during the few hundred years leading up to the reversal, including a depleted ozone layer, higher levels of ultraviolet radiation and increased atmospheric ionization, all occuring about 42,000 years ago.

The number to note here is 42,000. Because this number reminded the scientists of Douglas Adams’ iconic book The Hitchhiker’s Guide to the Galaxy, in which the supercomputer Deep Thought calculates that the answer to the ultimate question of life, the universe and everything is “42”. In tribute, the researchers have named this specific period the “Adams Transitional Geomagnetic Event.”

The teams of scientists suggests that a number of environmental conditions would have occured during this time: auroras across the entire planet, as well as electrical storms. There are other bold assertions the study makes, which are harder to prove – such as the fact that this geomagnetic excursion led to huge progress in human cultural evolution. The team suggests that cave art thrived at this time because humans were spending a lot more time in caves to shelter from increased ultraviolet radiation. They further assert that the red ochre used in cave art was used by ancient humans as sunscreen. The study also says that the Adams Event led to the extinction of several megafauna species in Australia, as well as the end for Neanderthals.

Not everyone agrees with this however, with other scientists saying that these events do not exactly coincide with the geomagnetic excursion 42,000 years ago. Neanderthals did continue for longer and ice-cores from Greenland and Antarctica that span the past 100,000 years show no shifts 42,000 years ago.

However, the study can provide important insights into what might happen if a similar geomagnectic excursion were to occur now. The Earth’s magnetic field has weakened by almost nine percent in the past 170 years. It has also been moving east at an unusually fast pace, heading from the Canadian Arctic toward Siberia at a speed of 55 km (34 miles) per year, has although it has slowed recently to 40 km (25 miles) per year.

As Douglas Adams’/ Hitchhikers Guide fans, this is particularly exciting to us, particularly because the study, published in the journal Science is accompanied by the video by the University of New South Wales below, which talks about Hitchhiker’s Guide to the Galaxy and gives an overview of the Adams Event – narrated by Stephen Fry. Enjoy!

(How are aurors formed?)


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I am a Chartered Environmentalist from the Royal Society for the Environment, UK and co-owner of DoLocal Digital Marketing Agency Ltd, with a Master of Environmental Management from Yale University, an MBA in Finance, and a Bachelor of Science in Physics and Mathematics. I am passionate about science, history and environment and love to create content on these topics.