Global Environmental Crisis of 42,000 Years Ago Linked to Breakdown in Earth’s Magnetic Field
Earth's polarity is not a constant. Unlike a classic bar magnet, or the decorative magnets on your refrigerator, Earth's magnetic field moves around. Geophysicists are pretty sure that the reason Earth has a magnetic field is because its solid iron core is surrounded by a fluid ocean of hot, liquid metal. This process can also be modeled with supercomputers. Ours is, without hyperbole, a dynamic planet. The flow of liquid iron in Earth's core creates electric currents, which in turn create the magnetic field. So while parts of Earth's outer core are too deep for scientists to measure directly, we can infer movement in the core by observing changes in the magnetic field. The magnetic north pole has been creeping northward – by more than 600 miles (1,100 km) – since the early 19th century, when explorers first located it precisely. It is moving faster now, actually, as scientists estimate the pole is migrating northward about 40 miles per year, as opposed to about 10 miles per year in the early 20th century. (Image Credit: Peter Reid, University of Edinburgh)
Global Environmental Crisis of 42,000 Years Ago Linked to Breakdown in Earth’s Magnetic Field
Scientists understand that Earth's magnetic field has flipped its polarity many times over the millennia. In other words, if you were alive about 800,000 years ago, and facing what we call north with a magnetic compass in your hand, the needle would point to 'south.' This is because a magnetic compass is calibrated based on Earth's poles. The N-S markings of a compass would be 180 degrees wrong if the polarity of today's magnetic field were reversed. Many doomsday theorists have tried to take this natural geological occurrence and suggest it could lead to Earth's destruction. But would there be any dramatic effects?
Reversals are the rule, not the exception. A reversal happens over hundreds or thousands of years, and it is not exactly a clean back flip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in "recent" years, when dinosaurs walked Earth a reversal was more likely to happen only about every one million years.
Sediment cores taken from deep ocean floors can tell scientists about magnetic polarity shifts, providing a direct link between magnetic field activity and the fossil record. The Earth's magnetic field determines the magnetization of lava as it is laid down on the ocean floor on either side of the Mid-Atlantic Rift where the North American and European continental plates are spreading apart. As the lava solidifies, it creates a record of the orientation of past magnetic fields much like a tape recorder records sound.
The temporary breakdown of Earth’s magnetic field 42,000 years ago sparked major climate shifts that led to global environmental change and mass extinctions, according to a new international study co-led by the University of New South Wales (UNSW) Sydney and the South Australian Museum.
This dramatic turning point in Earth’s history – laced with electrical storms, widespread auroras, and cosmic radiation – was triggered by the reversal of Earth’s magnetic poles and changing solar winds.
The researchers dubbed this danger period the ‘Adams Transitional Geomagnetic Event’, or ‘Adams Event’ for short – a tribute to science fiction writer Douglas Adams, who wrote in The Hitchhiker's Guide to the Galaxy that ‘42’ was the answer to life, the universe, and everything.
“For the first time ever, we have been able to precisely date the timing and environmental impacts of the last magnetic pole switch,” says Chris Turney, a professor at UNSW Science and co-lead author of the study.
“The findings were made possible with ancient New Zealand kauri trees, which have been preserved in sediments for over 40,000 years.
“Using the ancient trees we could measure, and date, the spike in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field.”
While scientists already knew the magnetic poles temporarily flipped around 41-42,000 years ago (known as the ‘Laschamps Excursion’), they didn’t know exactly how it impacted life on Earth – if at all.
But the researchers were able to create a detailed timescale of how Earth’s atmosphere changed over this time by analyzing rings on the ancient kauri trees.
“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,” says co-lead Professor Alan Cooper, Honorary Researcher at the South Australian Museum.
The researchers compared the newly-created timescale with records from sites across the Pacific and used it in global climate modelling, finding that the growth of ice sheets and glaciers over North America and large shifts in major wind belts and tropical storm systems could be traced back to the Adams Event.
One of their first clues was that mega-fauna across mainland Australia and Tasmania went through simultaneous extinctions 42,000 years ago.
“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,” says Prof. Cooper.
The study suggests that the Adams Event could explain a lot of other evolutionary mysteries, like the extinction of Neanderthals and the sudden widespread appearance of figurative art in caves around the world.
“It’s the most surprising and important discovery I’ve ever been involved in,” says Prof. Cooper.
The magnetic north pole – that is, the direction a compass needle points to – doesn’t have a fixed location. It usually wobbles close to the North Pole (the northern-most point of Earth’s axis) over time due to dynamic movements within the Earth’s core, just like the magnetic south pole.
Sometimes, for reasons that aren’t clear, the magnetic poles’ movements can be more drastic. Around 41,000 to 42,000 years ago they swapped places entirely.
“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 focused on changes that happened while the magnetic poles were reversed, when the magnetic field was weakened to about 28 per cent of its present-day strength.
But according to the team’s findings, the most dramatic part was the lead-up to the reversal, when the poles were migrating across the Earth.
“Earth’s magnetic field dropped to only 0 to 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.”
During the magnetic field breakdown, the Sun experienced several ‘Grand Solar Minima’ (GSM), long-term periods of quiet solar activity.
Even though a GSM means less activity on the Sun’s surface, the weakening of its magnetic field can mean more space weather – like solar flares and galactic cosmic rays – could head Earth’s way.
“Unfiltered radiation from space ripped apart air particles in Earth’s atmosphere, separating electrons and emitting light – a process called ionisation,” says Prof. Turney.
“The ionised air ‘fried’ the Ozone layer, triggering a ripple of climate change across the globe.”
Dazzling light shows would have been frequent in the sky during the Adams Event.
Aurora borealis and aurora australis, also known as the 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 globe, the colorful sights would have been widespread during the breakdown of Earth’s magnetic field.
“Early humans around the world would have seen amazing auroras, shimmering veils, and sheets across the sky,” says Prof. Cooper.
Ionized air – which is a great conductor for electricity – would have also increased the frequency of electrical storms.
“It must have seemed like the end of days,” says Prof. Cooper.
The researchers theorize that the dramatic environmental changes may have caused early humans to seek more shelter. This could explain the sudden appearance of cave art around the world roughly 42,000 years ago.
“We think that the sharp increases in UV levels, particularly during solar flares, would suddenly make caves very valuable shelters,” says Prof. Cooper. “The common cave art motif of red ochre handprints may signal it was being used as sunscreen, a technique still used today by some groups.
“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.”
These findings come two years after a particularly important ancient kauri tree was uncovered at Ngawha, Northland in New Zealand.
The massive tree – with a trunk spanning over two and a half meters – was alive during the Laschamps.
“Like other entombed kauri logs, the wood of the Ngawha tree is so well preserved that the bark is still attached,” says UNSW’s Dr Jonathan Palmer, a specialist in dating tree-rings (dendrochronology). Dr Palmer studied cross sections of the trees at UNSW Science’s Chronos 14Carbon-Cycle Facility.
Using radiocarbon dating – a technique to date ancient relics or events – the team tracked the changes in radiocarbon levels during the magnetic pole reversal. This data was charted alongside the trees’ annual growth rings, which acts as an accurate, natural timestamp.
The new timescale helped reveal the picture of this dramatic period in Earth’s history. The team were able to reconstruct the chain of environmental and extinction events using climate modelling.
“The more we looked at the data, the more everything pointed to 42,” says Prof. Turney. “It was uncanny.
“Douglas Adams was clearly on to something, after all.”
While the magnetic poles often wander, some scientists are concerned about the current rapid movement of the north magnetic pole across the Northern Hemisphere.
“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 Carrington Event of 1859 - A Case Study of What Could Go Wrong
An 1859 solar storm known as the "Carrington Event" was named after astronomer Richard Carrington, who observed the solar flare that caused a great deal of the havoc. The solar flare electrified transmission cables, set fires in telegraph offices, and produced Northern Lights so bright that people could read newspapers by their red and green glow. Geomagnetic activity triggered by the explosion electrified telegraph lines, shocking technicians and setting their telegraph papers on fire; Northern Lights spread as far south as Cuba and Hawaii; auroras over the Rocky Mountains were so bright, the glow woke campers who began preparing breakfast because they thought it was morning. Best estimates rank the Carrington Event as 50% or more stronger than the super-storm of May 1921.
A NASA-funded report by the National Academy of Sciences prepared in 2009 found that if a similar storm occurred today, it could cause $1 to $2 Trillion in damages to society's high-tech infrastructure and require four to ten years for complete recovery.
The problem begins with the electric power grid. "Electric power is modern society's cornerstone technology on which virtually all other infrastructures and services depend," the report notes. Yet it is particularly vulnerable to bad space weather. Ground currents induced during geomagnetic storms can actually melt the copper windings of transformers at the heart of many power distribution systems. Sprawling power lines act like antennas, picking up the currents and spreading the problem over a wide area. The most famous geomagnetic power outage happened during a space storm in March 1989 when six million people in Quebec lost power for 9 hours.
"A contemporary repetition of the Carrington Event would cause... extensive social and economic disruptions," the report warns. Power outages would be accompanied by radio blackouts and satellite malfunctions; telecommunications, GPS navigation, banking and finance, and transportation would all be affected. Some problems would correct themselves with the fading of the storm: radio and GPS transmissions could come back online fairly quickly. Other problems would be lasting: a burnt-out multi-ton transformer, for instance, can take weeks or months to repair.
According to the report, power grids may be more vulnerable than ever. The problem is interconnectedness. In recent years, utilities have joined grids together to allow long-distance transmission of low-cost power to areas of sudden demand. On a hot summer day in California, for instance, people in Los Angeles might be running their air conditioners on power routed from Oregon. It makes economic sense, but not necessarily geomagnetic sense. Interconnectedness makes the system susceptible to wide-ranging "cascade failures."
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