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February 18, 2021
from the University of New South Wales
The temporary collapse of the Earth’s magnetic field 42,000 years ago triggered major climate changes that led to global environmental changes and mass extinctions. This is shown by a new international study jointly carried out by UNSW Sydney and the South Australian Museum.
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This dramatic turning point in Earth’s history – riddled with electrical storms, widespread aurors and cosmic rays – was triggered by the reversal of the Earth’s magnetic poles and changing solar winds.
The researchers called this period of danger the « Adams Transitional Geomagnetic Event » or « Adams Event » for short – a homage to the science fiction writer Douglas Adams, who wrote in The Hitchhiker’s Guide to the Galaxy that « 42 » is the answer to life. the universe and everything.
« For the first time we were able to accurately date the timing and environmental impact of the last magnetic pole switch, » says Chris Turney, professor at UNSW Science and co-lead author of the study.
« The results were made possible with ancient New Zealand kauri trees that have been kept in sediments for over 40,000 years.
« With the ancient trees we were able to measure and date the rise in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field. »
While scientists already knew 41-42,000 years ago that the magnetic poles were temporarily flipped (known as « Laschamp’s Excursion »), they did not know exactly how this affected life on earth – if at all.
The However, researchers were able to create a detailed timescale of how the earth’s atmosphere changed during this time by analyzing rings on the ancient kauri trees.
« The kauri trees are like the Rosetta Stone and help us bring together records of environmental changes in caves, ice cores and peat bogs around the world, « says co-director Professor Alan Cooper, honorary researcher at the South Australian Museum.
The researchers compared the newly created timescale with records of locations across the Pacific and used them for global climate modeling. They found that the growth of ice sheets and glaciers over North America and large shifts in large wind belts and tropical storm systems could be traced back to the Adams event.
One of their first indications was that the megafauna on mainland Australia and in Tasmania was simultaneously extinct 42,000 years ago.
« That never seemed right because it was long after the Aboriginal arrival, but around the same time the Australian environment shifted to the current arid state, » says Prof. Cooper .
The paper suggests that the Adams event could explain many other evolutionary mysteries, such as the Neanderthal extinction and the sudden widespread appearance of figurative art in caves around the world.
The Magnetic North Pole – ie the direction a compass needle is pointing – has no fixed position. It usually wobbles near the North Pole (the northernmost point on the Earth’s axis) over time due to dynamic movements in the Earth’s core, just like the South Magnetic Pole.
Sometimes the movements of the magnetic poles can be more drastic for unclear reasons. About 41,000 to 42,000 years ago they completely swapped places.
« The Laschamps excursion was the last time that the magnetic poles were reversed, » says Prof. Turney. “They switched places for about 800 years before changing their minds and switching back again.”
So far, scientific research has focused on changes that occurred during the reversal of the magnetic poles when the magnetic field decreased to about 28 percent Its current strength has been weakened.
However, according to the team’s findings, the most dramatic part was preparing for the reversal as the poles moved across the earth.
« The earth’s magnetic field fell to just 0 during the Adams event up to 6 percent « , says Prof. Turney.
During the magnetic field failure, the sun experienced several » Grand Solar Minima « (GSM), long-term periods of calm solar activity.
Although a GSM means less activity on the solar surface, it can the weakening of its magnetic field means that more space weather – like solar flares and galactic cosmic rays – can control the path of the earth.
« Unfiltered radiation from the world Raum tore apart air particles in the earth’s atmosphere, separated electrons and emitted light – a process that is known as ionization, « says Prof. Turney.
» The ionized air « fried » the ozone layer and triggered a global wave of climate change . «
Aurora borealis and Aurora australis, also known as Northern and Southern Lights, are caused by solar winds hitting the Earth’s atmosphere.
Usually confined to the polar northern and southern parts of the earth, the brightly colored ones would be Sights were common during the Earth’s magnetic field collapse.
« Early people around the world would have seen amazing aurors, shimmering veils and sheets across the sky, » says Prof. Cooper.
Ionized air – a great conductor for electricity – would have also increased the frequency of electrical storms.
The researchers suspect that the dramatic environmental changes could have caused early humans sought more protection. This could explain the sudden appearance of cave art around the world around 42,000 years ago.
« We believe that the sharp rise in UV levels, especially during solar flares, would suddenly turn caves into very valuable shelters, » says Prof Cooper. « The common cave art motif of red ocher handprints could indicate that it was used as a sunscreen, a technique still used by some groups today.
» The amazing images that were taken in the caves during this time are preserved, while other art in open areas has since eroded, suggesting that art suddenly began 42,000 years ago. «
These results come two years after a particularly important ancient kauri tree was discovered in Ngāwhā, Northland .
The massive tree – with a trunk over two and a half meters – lived during the Laschamps.
« Like other buried kauri trunks, the wood of the Ngāwhā tree is so well preserved that the bark still sticks », says Dr. Jonathan Palmer of UNSW, specialist in the dating of tree rings (dendrochronology). Dr. Palmer examined the cross sections of the trees in the Chronos 14Carbon-Cycle Facility of UNSW Science.
Using radiocarbon dating – a technique used to date ancient relics or events – the team tracked changes in radiocarbon levels during magnetic pole reversal. These dates were recorded alongside the trees’ annual growth rings, which act as an accurate, natural timestamp.
The new timescale helped reveal the picture of this dramatic period in Earth’s history. The team was able to reconstruct the chain of environmental and extinction events using climate models.
« The more we looked at the data, the more everything pointed to 42, » says Prof. Turney. « It was scary.
While the magnetic poles often wander, some scientists are concerned about the current rapid movement of the north magnetic pole over the northern hemisphere.
» This speed – in addition to weakening the Earth’s magnetic field by around nine percent in the last 170 years ago – could indicate an imminent reversal, « says Prof. Cooper.
» If a similar event were to occur today, the consequences for modern society would be enormous. Incoming cosmic rays would destroy our power grids and satellite networks. «
Prof. Turney says the man-made climate crisis is catastrophic enough without major solar changes or polar reversal to throw into the mix.
» Our atmosphere is already filled with carbon in a way that mankind has never seen before, « he says. » A reversal of the magnetic pole or an extreme change in solar activity would be unprecedented accelerators of climate change.
« We urgently need to reduce CO2 emissions before such a random event occurs again. »
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Ref: https://phys.org