A recent international study co-led by UNSW Sydney and the South Australian Museum shows that the temporary collapse of the Earth's magnetic field 42,000 years ago caused massive climate changes that led to global environmental change and mass extinctions.
The reversal of the Earth's magnetic poles and shifting solar winds caused this drastic turning point in Earth's history, connected with electric storms, widespread auroras, and cosmic radiation.
The researchers called this dangerous time the 'Adams Transitional Geomagnetic Event' or 'Adams Event' for short, a tribute to science fiction author Douglas Adams, who wrote that '42' was the key to life, the cosmos, and all in The Hitchhiker's Guide to the Galaxy.
The results are being published in Science today.
We were able to reliably date the timing and environmental consequences of the last magnetic pole switch for the first time ever, "For the first time ever, we have been able to precisely date the timing and environmental impacts of the last magnetic pole switch,"
Ancient New Zealand kauri trees, which have been preserved in sediments for over 40,000 years, made the findings possible.
"Using the ancient trees, the measurement, the date, the spike in the atmospheric radiocarbon levels caused by the collapse of the Earth's magnetic field can be calculated."
Although scientists already understood that the magnetic poles flipped briefly around 41-42,000 years ago (known as the 'Laschamps Excursion'), they didn't know exactly how life on Earth was affected, if at all.
But by examining rings on the ancient kauri trees, the researchers were able to establish a comprehensive timescale of how the Earth's atmosphere changed over this period.
Co-lead Professor Alan Cooper, Honorary Researcher at the South Australian Museum, says, "The kauri trees are like the Rosetta Stone, helping us tie together records of environmental change in caves, ice cores and peat bogs around the world,"
The researchers compared the newly developed time scale with records from locations around the Pacific and used it in global climate modeling, finding that the Adams Event could be traced back to the formation of ice sheets and glaciers across North America and significant changes in major wind belts and tropical storm systems.
One of their first hints was that 42,000 years ago, megafauna in mainland Australia and Tasmania went through simultaneous extinctions.
This never seemed right, because it was a long time after the arrival of Aboriginal people, but at around the same time the Australian climate shifted to the present arid state, "This had never seemed right because it was long after Aboriginal people arrived, but around the same time that the Australian environment shifted to the current arid state,"
The paper indicates that many other evolutionary mysteries, such as the disappearance of the Neanderthals and the sudden widespread emergence of figurative art in caves around the world, maybe explained by the Adams Case.
"It's the most surprising and important discovery I've ever been involved in," Prof. Cooper says.
The ideal (cosmic) storm
There is no fixed position for the magnetic north pole, i.e., the direction a compass needle points to. Due to complex motions inside the center of the Planet, it typically wobbles near to the North Pole (the northern-most point of the Earth's axis) over time, much like the magnetic South Pole.
Sometimes, for reasons which are not apparent, the motions of the magnetic poles may be more dramatic. Around 41,000-42,000 years ago, they absolutely switched locations.
"The Laschamps Excursion was the last time the magnetic poles flipped," says Prof. Turney. "They swapped places for about 800 years before changing their minds and swapping back again."
Until now, scientific research has concentrated on changes that occurred when the magnetic poles were inverted when the magnetic field was reduced to around 28 percent of its present-day strength.
But the most dramatic aspect was the lead-up to the reversal when the poles were migrating around the Planet, according to the team's results.
"Earth's magnetic field dropped to only 0-6 percent strength during the Adams Event," says Prof. Turney.
"We essentially had no magnetic field at all—our cosmic radiation shield was totally gone."
The Sun encountered many 'Grand Solar Minima' (GSM), long-term cycles of quiet solar activity, during the collapse of the magnetic field.
Although a GSM means less activity on the surface of the Sun, the weakening of its magnetic field will lead to more space weather, such as solar flares and cosmic galactic rays.
Through the caverns
At the Adams Case, sparkling light shows would have been frequent in the sky.
Solar winds entering the Earth's atmosphere are caused by Aurora borealis and aurora australis, also known as the northern and southern lights.
The colorful sights would have been common during the collapse of the Earth's magnetic field, typically limited to the polar northern and southern parts of the globe.
"Early humans around the world would have seen amazing auroras, shimmering veils and sheets across the sky," says Prof. Cooper.
The frequency of electric storms will also be enhanced by ionized air, which is a great electricity conductor.
It must have seemed like the end of a day, "It must have seemed like the end of days,"
The researchers theorize that early humans may have been caused to seek more shelter by drastic environmental changes. This may explain the sudden discovery of cave art about 42,000 years ago across the planet.
"We think that the sharp increases in UV levels, particularly during solar flares, would suddenly make caves very valuable shelters," says Prof. Cooper. The popular motif of red ochre handprints in cave art may suggest that it was being used as sunscreen, a technique some groups still use today.
"The amazing images created in the caves during this time have been preserved, while other art out in open areas has since eroded, making it appear that art suddenly starts 42,000 years ago."
Ancient Hints Uncovering
These results come two years after the discovery at Ngāwhā, Northland, of an especially significant ancient kauri tree.
During Laschamps, the huge tree was alive with a trunk stretching over two and a half meters.
"Like other entombed kauri logs, the wood of the Ngāwhā tree is so well preserved that the bark is still attached," says Dr. Jonathan Palmer of UNSW, a specialist in dating tree-rings (dendrochronology). At UNSW Science's Chronos 14Carbon-Cycle Plant, Dr. Palmer analyzed cross sections of the trees.
The team tracked the shifts in radiocarbon levels during the magnetic pole reversal using radiocarbon dating, a technique to date ancient artifacts or occurrences. In addition to the annual growth rings of the trees, this data was charted, which serves as an accurate, natural timestamp.
The new timescale has helped expose the image of this dramatic moment in the history of the World. The team was willing, using climate modeling, to recreate the sequence of environmental and extinction events.
Prof. Turney says, "The more we looked at the data, the more everything pointed to 42," "It has been uncanny.
"Douglas Adams was clearly on to something, after all."
Like no other, an accelerant
Although the magnetic poles sometimes drift, the recent rapid movement of the north magnetic pole across the Northern Hemisphere scares some scientists.
"This speed—alongside the weakening of Earth's magnetic field by around nine percent in the past 170 years—could indicate an upcoming reversal," says Prof. Cooper.
"If a similar event happened today, the consequences would be huge for modern society. Incoming cosmic radiation would destroy our electric power grids and satellite networks."
The human-induced climate crisis, Prof. Turney says, is devastating enough without throwing drastic solar shifts or a pole reversal into the mix.
"Our atmosphere is already filled with carbon at levels never seen by humanity before," he says. Unprecedented climate change accelerants will be a magnetic pole reversal or drastic change in the Sun's operation.
"We urgently need to get carbon emissions down before such a random event happens again."