41,000 years ago, the Earth’s magnetic shield collapsed. What do geophysicists say about this event?

Sometimes, the shield weakens and oscillates, allowing cosmic rays to enter the atmosphere, creating a stream of particles that scientists say could wreak havoc on the biosphere. This has happened many times in the history of our planet, including 41,000 years ago, during the so-called Lashamsa event..

Cosmic rays are high-energy particles, usually protons or atomic nuclei, that move through space at high speeds. Generally, are deflected into space and away from the Earth by the planet’s magnetic shield. However, this shield is a natural phenomenon and its strength fluctuates, as does its orientation. When this happens, cosmic rays impact the Earth’s atmosphere.

“During the last major reversal, called the Lashamsa event, radiocarbon dates show that around 41,500 years ago the magnetic field weakened significantly and the poles reversed, only to reverse again about 500 years later.” https://t.co/sMLxhiNkco. pic.twitter.com/e2Lzl3qH1Z

— Avni Erbey (@AvniErbey) April 3, 2023

This creates a stream of secondary particles called cosmogenic radionuclides. These isotopes are included in sediments and ice cores and even in the structure of living things such as trees.. There are different types of these isotopes, including calcium 41 and carbon 14.

Some isotopes are stable, others are radioactive. Radioactive substances have a half-life of only 20 minutes. (carbon 11) and 15.7 million years (xenon 129).

The lifespan of radioactive isotopes ranges from 20 minutes to 15.7 million years.

As Earth’s shield weakens, more of these isotopes reach the planet’s surface. and accumulate in sediments and ice. By studying these cores and deposits, scientists will be able to determine the history of the magnetic shield.

Changes in the Earth’s magnetic shield

Observations of this magnetic shield indicate that a geomagnetic reversal occurred on Earth 41,000 years ago. It is called excursion or The Lachamps event honors the Lachamps lava flows in France, where geomagnetic anomalies revealed their occurrence..

Every few hundred thousand years, the Earth’s magnetic poles switch places.. North becomes South and vice versa. In between these larger events there are smaller ones called excursions. During excursions, the poles move for some time without changing places .

The excursions weaken the Earth’s shield and can last from several thousand to tens of thousands of years. When this happens more cosmic rays reach the atmosphere, creating more radionuclides that fall to Earth.

In paleomagnetic studies, scientists often focus on a specific radioactive isotope. Beryllium-10 has a relatively long half-life (1.36 million years) and tends to accumulate on soil surfaces..

What do scientists tell us about Lachamp’s last expedition?

Sanja Panovska is a researcher at GFZ Potsdam, Germany, studying geomagnetism. At the recent 2024 General Assembly of the European Geosciences Union (EGU), Panovska presented new research on the Lachamps excursion. He discovered that during an excursion to Lachamp, Be-10 production was twice as much as usual..

Unpacking an Amazing Taonga with Jonathan Palmer – The Entry of the Ancient Cowries into @niwa_nz There’s this huge cross-section of Ngawa Springs in the archives. He lived about 42,000–41,000 years ago during the Adams event and the Lachams geomagnetic weakening/reversal. #14C pic.twitter.com/Z7RnkCR8Mf

— Drew Lorrey (@DLorrey) April 26, 2023

To better understand Lachamp, excursion to Panovska combined cosmogenic radionuclides and paleomagnetic data to reconstruct the Earth’s magnetic field at that time.. He also discovered that when the intensity of the field decreases, it also contracts.

The transition from a normal field to an inverted field took about 250 years and remained inverted for about 440 years.. During the transition, Earth’s shield was reduced to only 5% of its normal strength. When fully inverted, his strength was approximately 25% of his normal strength. This is weakening allowed more Be 10 and other cosmogenic radionuclides to reach the Earth’s surface..

These radionuclides not only accumulate in sediments and ice: some of them are radioactive. The weakening of the shield also weakened the ozone layer, allowing more ultraviolet radiation to reach the Earth’s surface.. The high-altitude atmosphere also cooled, changing wind flows. This could cause sudden changes on the Earth’s surface.

For these reasons, The Lachamps Event is associated with the extinction of the Neanderthals, the disappearance of Australian megafauna, and even the appearance of cave paintings.. These connections haven’t stood up to scientific scrutiny, but that doesn’t mean events like Lashams aren’t dangerous. If they happened now, they would destroy the power grid. and the equatorial region of the Earth will be illuminated by polar lights.

Scientists are learning that the magnetic shield is not static. There are anomalies. One of them is the South Atlantic Anomaly, a region where the magnetic field near the Earth is weakest.. When satellites pass through this region, they are exposed to higher levels of ionizing radiation.

“Understanding these extreme events is important for their future occurrence, for space weather forecasts, and for assessing impacts on the environment and the Earth system.”
Sanja Panovska, researcher at GFZ Potsdam.

This anomaly is likely caused by the deposition of dense rock deep beneath the Earth, illustrating the complexity of the magnetic shield. Scientists aren’t sure what effect cosmic rays have on life when the magnetic shield is weak.

It is tempting to link extinctions to events such as the Lachamps excursion when they coincide in time. But the poles have changed, weakened and changed places many times, and life is still here and continues to thrive..

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Link to news:
Panovska S. Long-term changes in the geomagnetic field: recent advances, problems and applications. YSU General Assembly 2024.