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, a new international study co-led by UNSW Sydney and the South Australian Museum shows.
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.
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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 41,000-42,000 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 0-6 per cent 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 colourful 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.
Ionised 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 theorise 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.”
This is confirmation of a research paper published in 2019 in the Review of Geophysics titled: "The Role of Geomagnetic Field Intensity in Late Quaternary Evolution of Humans and Large Mammals." From the plain language summary (underline added):
The strength of Earth's magnetic field in the past, recorded by rocks and sediments, provides a proxy for past flux of ultraviolet radiation (UVR) to Earth's surface due to the role of the field in modulating stratigraphic ozone. About 40,000 years ago, mammalian fossils in Australia and Eurasia record an important die‐off of large mammals that included Neanderthals in Europe. In the Americas and Europe, a large mammalian die‐off appears to have occurred ~13,000 years ago. Both die‐offs can be linked to minima in Earth's magnetic field strength implying that UVR flux variations to Earth's surface influenced mammalian evolution. For the last ~200,000 years, estimates of the timing of branching episodes in the human evolutionary tree, from modern and fossil DNA and Y chromosomes, can be linked to minima in field strength, which implies a long‐term role for UVR in human evolution. New fossil finds, improved fossil dating, knowledge of the past strength of Earth's magnetic field, and refinements in the human evolutionary tree, are sharpening the focus on a possible link between UVR arriving at the Earth's surface, magnetic field strength, and events in mammalian evolution.
These excursions and die offs occur every 12 to 13 thousand years, which means that the current weakening of the magnetic field is right on time.