Strange as it may seem, the Earth’s magnetic poles are not fixed. They roam around a bit and, throughout the history of the Earth, they have even completely reversed themselves. Now scientists have evidence of how these magnetic projections could affect life on Earth.
Scientists don’t know what causes magnetic upheavals, says Carolyn Gramling, a climate writer at Science News.
“What we know,” she says, “is that the Earth has a metal core. It has a liquid metal outer core and a solid metal inner core made of iron and nickel. And the interaction between these two cores and the flow of the minerals inside of them … generates an electric current that generates [magnetic] field. “
“Throughout Earth’s history, for millions and millions of years, we know that [Earth’s] poles sometimes inverted, so that the north pole becomes south and south becomes north. “
This magnetic field is similar to a “giant rod magnet in the center of the planet,” which has north and south poles, Gramling says. “And throughout Earth’s history, over millions and millions of years, we know that those poles have sometimes reversed themselves, so that the North Pole is turning south and the south is turning north.”
A fossilized tree discovered in New Zealand helped researchers date one of these magnetic launches about 41,000 years ago, a time when the Earth also saw megafauna extinctions, climate change and even an increase in cave art.
Related: The history of the world is written in tree rings
Scientists call this particular magnetic inversion the Laschamps excursion. They can date this event by studying the rock disc. “When rocks form, the tiny magnetic minerals that are inside those rocks can orient themselves to adhere to the current magnetic field, whatever the path,” Gramling explains.
Laschamps’ excursion lasted only a few hundred years, but scientists are interested in it because they think it could help them figure out how a magnetic reversal may have affected creatures living on Earth at the time.
Before a magnetic reversal, there is a period when the poles are “kind of ready to change,” Gramling says. During this period, the Earth’s magnetic field weakens, allowing more solar radiation to hit the Earth, which can affect life on the planet.
“So the great danger period was … actually about 42,000 years ago, just before the upheaval actually happened,” Gramling explains.
Scientists know that some “great charismatic animals” became extinct at this time, ”and that,“ strangely, just around this time you saw this great growth in cave art, in people painting in caves, ”says Gramling. I knew some climate change was happening around this time. But being able to link them to this event is the real trick. “
In 2019, says Gramling, a group of scientists found the “Rosette Stone” that could link all of these events: an ancient tree excavated from a peat bog in New Zealand.
Some of these ancient coniferous trees still live in New Zealand today and their antecedents have existed since the Jurassic period, millions of years ago, Gramling says. The separate trees in this peat bog date back about 50,000 years.
Many giant old trunks, some of them a few meters in diameter, are buried in these swamps and have been preserved there, Gramling says. People dig them up for selfish purposes – for example using them for table tops or pillars – but they are important for science because they contain a record of climatic events.
Related: Ancient leaves preserved under a mile of Greenland ice – and lost in a freezer for years – hold lessons on climate change
So researchers knew that if anything could possibly tell them what happened to the climate about 42,000 years ago – it might be this tree.
The researchers examined the tree’s rings for changes in the amount of carbon-14 over the years, Gramling explains. Carbon-14 is useful not only for dating things, but because the interaction of cosmic rays with molecules in the atmosphere produces a lot of it. And when the Earth has a weakened magnetic field, more cosmic rays hit the planet.
The scientists actually found a large sting of carbon-14 in the tree, which they were then able to compare with the rock disk, which indicated a magnetic reversal. Now, Gramling notes, they might say, “‘Well, we know these things were coincidental. Isn’t that interesting?'”
In addition, there is the documented growth of cave art just about 41,000-42,000 years ago, Gramling points out. Scientists have also found paintings from this time with sketched handprints made of red ocher. As is the case, some indigenous communities even today use red ocher as sunscreen.
“Is it possible that you’re getting into this extra UV radiation and suddenly you have people in caves more, doing this cave art with the red ocher paint? Is it possible that it could be because they were shielded from the increased radiation of the sun?” during that time? “
“So is it possible that you have this extra UV radiation coming in and all of a sudden you have people in caves more, making this cave art with the red ocher paint,” Gramling asks. “Is it possible that this could have happened because they took refuge from the increased radiation of the sun during that time?”
As it happens, about 40,000 years ago, Neanderthals became extinct. Could the magnetic reversal be linked with this event as well?
“With the rapidly changing climate, it can be [Homo sapiens] could compete with Neanderthals for whatever means were more scarce, ”suggests Gramling.
“And of course, there were these megafauna extinctions, especially in Australia. They notice, for example, that there was a giant kangaroo extinct around that time, and some other strange Australian animals. There was a kind of carnivorous marsupial, sometimes called a pocket lion, that became extinct, [and] a roe deer wombat that stood about 6 feet. So all of these things happened right around that same time. “
This article is based on an interview that aired on PRX’s Living on Earth