A reversal in Earth magnetic field thousands of years ago, plunged the earth into an environmental crisis which can be resembled “a disaster movie“, scientists recently discovered.
Our earth’s magnetic field is dynamic and numerous-times, it’s flipped, when the magnetic North & South Poles swap places. In our electronics dependent world, such a reversal could seriously disrupt our communication networks.
But the impact might be even more serious than that, consistent with the new study. For the first-time, scientists found evidence that a polar-flip could have serious ecological repercussions.
Their investigation connects a magnetic field reversal around 42,000 years ago to climate upheaval on a global-scale, which caused extinctions & reshaped human behavior.
The Earth’s magnetosphere, the magnetic barrier surrounding the earth, which originates from the churning of hot, molten metal around its iron core. This perpetually sloshing liquid flow generates electricity which then produces magnetic field lines that curve around the earth from pole-to-pole, consistent with NASA.
Just like a protective bubble, magnetic field shields Earth from solar radiation. On the earth’s sun-facing side, constant bombardment from solar winds squishes the magnetic field, in order that the field extends to a distance not more than 10 times Earth’s radius.
However, on the other side of the earth that facing away from the sun, the field extends much farther into space, forming a huge “magnetotail“ that reaches beyond our moon, NASA says.
Marking the 2 spots on the Earth where arcing magnetic field lines converge are the magnetic North & South Pole. But while these positions are relatively stable, the poles & the magnetic field itself aren’t fixed in place.
About once every 200,000 to 300,000 years, this field weakens enough to reverse polarity completely. The process can take hundreds or even thousands of years, consistent with NASA.
Magnetic molecules preserved in volcanic deposits & other sediments, tell scientists when past reversals happened. Those molecules align with the magnetic field at the time that they were deposited, therefore they indicate the location of the magnetic north pole, said lead study author Alan Cooper, an emeritus professor in the Department of Geology at University of Otago in New Zealand.
Recently, researchers questioned whether a relatively recent & brief polarity reversal called Laschamps Excursion, which happened between 41,000 & 42,000 years ago, might be linked to other dramatic changes on Earth from that time, which hadn’t previously been attributed to activity in the magnetosphere. They suspected, during a time when our protective magnetic field was reversing and there-by weaker than normal solar & cosmic radiation exposure could affect the atmosphere enough-to impact climate, the study authors reported.
Clues in “biscuits”
Prior-studies of Greenland ice cores dating to Laschamps didn’t reveal evidence of global climate change, consistent with the study.
But this time, researchers turned their attention to a different potential source of climate-data: bog-preserved kauri trees (Agathis australis) from northern New Zealand.
They cut cross-sections or “biscuits”, from preserved trunks and checked out the changes in levels of Carbon 14, a radioactive sort of the element, over a period that included the Laschamps reversal.
Their analysis revealed the elevated levels of radioactive carbon in the atmosphere during Laschamps, when the magnetic field was weakening.
“Once we worked-out the exact timing from the kauri record, we could see that it coincided perfectly with the records of climatic & biological change all over the world,” Cooper said.
For instance, around this time, megafauna in Australia began to extinct & Neanderthals in Europe were dying-out, their decline may be accelerated by climate-related changes to their ecosystems, Cooper said.
The authors then used computer-climate models to check what may-have caused widespread climate upheaval & related extinctions.
They found, a weak magnetic field operating at about 6% of its normal strength could lead to major climate impacts, “via the ionizing radiation strongly damaging the ozone layer, letting in UV rays and altering the ways in which the sun’s energy was absorbed-by the atmosphere,” Cooper explained.
A heavily ionized atmosphere could also generate brilliant auroras around the world & produced frequent lightning storms, making skies look-like, “something similar-to a disaster movie,” Cooper said.
Another significant-shift around that time was in Homo sapiens, with cave art starting to appear in locations around the world. This included the first-examples of red ochre hand stencils, “which we suspect is really a sign of the application of sunscreen,” a practice still-seen in modern Indigenous groups in Namibia, Cooper said.
Higher UV levels from a weak magnetic field could have driven humans to-seek shelter in caves or forced-them to protect their skin with sun-blocking minerals, he said.
Scientists cannot predict precisely when the next-reversal of our magnetic field might happen.
However, some signs like the North Pole’s current migration across the Bering Sea area and the magnetic field itself weakening nearly 10 percent over the past 170 years, suggest that a flip could be closer than we expect, making-it more urgent that the researchers fully understand how big shifts in our magnetic-field could shape environmental changes on a global scale, consistent with the study.
“Overall, these findings raise important questions about–the evolutionary impacts of geomagnetic reversals & excursions throughout the deeper geological record,” the scientists wrote.
The findings were published in the journal Science.