World news – The Earth’s magnetic field collapsed 42,000 years ago, causing massive, sudden climate change


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February 19, 2021

by Chris Fogwill, Alan Hogg, Chris Turney and Zoë Thomas, The Conversation

The world experienced several centuries of apocalyptic conditions 42,000 years ago, triggered by a reversal of the Earth’s magnetic poles in conjunction with changes in the behavior of the sun. This is the main finding of our new multidisciplinary study published in Science.

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This last great geomagnetic reversal sparked a series of dramatic events that have far-reaching consequences for our planet. They read like the plot of a horror movie: the ozone layer was destroyed, electric storms raged over the tropics, solar winds created spectacular light shows (aurors), arctic air streamed over North America, ice sheets and glaciers swayed, and weather patterns moved violently.

During During these events, life on earth was exposed to intense ultraviolet light, Neanderthals and giant animals known as megafauna became extinct, while modern humans sought refuge in caves.

The magnetic north pole – pointed to by a compass needle – has no permanent position. Instead, it usually wobbles over time near the geographic North Pole – the point the Earth rotates around – due to movements in the Earth’s core.

For reasons that are not yet entirely clear, magnetic pole movements can sometimes be more extreme than a wobble. One of the most dramatic of these polar migrations took place around 42,000 years ago and is known as the Laschamps excursion – named after the village in which it was discovered in the French Massif Central.

The Laschamps excursion was recognized around the world, most recently in Tasmania, Australia. However, until now it was not clear whether such magnetic changes had an impact on the climate and life on the planet. Our new work summarizes several lines of evidence that strongly suggest that the effects were indeed global and far-reaching.

To investigate what happened, we analyzed ancient New Zealand kauri trees that have been in peat bogs for more than 40,000 years other sediments. With the help of the annual growth rings in the kauri trees, we were able to create a detailed time scale of how the earth’s atmosphere changed during this time. The trees showed a prolonged rise in atmospheric radiocarbon levels, caused by the collapse of the Earth’s magnetic field when the poles switched, and enabled precise linking of widely distributed records.

« The Kauri trees are like the Rosetta Stone and help us to bring together records of environmental changes in caves, ice cores and peat bogs around the world, « says Professor Alan Cooper, who leads this research project.

With the help of the newly created time scale, we were able to show that the tropical Pacific rainbelts and the westerly winds of the Southern Ocean simultaneously abruptly relocated and brought arid conditions to places like Australia at the same time as a number of megafauna, including giant kangaroos, and giant wombats became extinct. Further north, the huge Laurentide ice sheet in the eastern United States and Canada was growing rapidly, while in Europe the Neanderthals were threatened with extinction.

In collaboration with a computer program that simulated the global interactions between chemistry and climate, we investigated the effects a weaker magnetic field and changes in solar strength. It is important that during the magnetic switch the strength of the magnetic field dropped to less than 6% of today’s value. A compass would have difficulty finding north at all.

Since our planet has essentially no magnetic field, it has completely lost its very effective protective shield against cosmic rays, and many more of these very penetrating particles from space could appear get to the top of the atmosphere. In addition, during this period the sun experienced several « large solar minima » during which total solar activity was generally much lower, but also more unstable, and emitted numerous massive solar flares that allowed more powerful ionizing cosmic rays to reach Earth / p> Our models showed that this combination of factors had a reinforcing effect. The galaxy’s energetic cosmic rays, as well as enormous bursts of cosmic rays from solar flares, were able to penetrate the upper atmosphere, charging up particles in the air and causing chemical changes that caused the loss of stratospheric ozone.

The modeled chemistry-climate simulations are consistent with the environmental shifts observed in many archives for natural climate and environmental change. Those conditions would also have prolonged the dazzling light shows of the Aurora around the world – sometimes the nights would have been as bright as during the day. We suggest that the dramatic changes and unprecedented high UV levels led early humans to seek shelter in caves, which explains the apparent sudden bloom of cave art around the world 42,000 years ago.

Seemingly random due to the coincidence of cosmic events and extreme environmental changes around the world 42,000 years ago, we have referred to this time as the « Adams Event » – a tribute to the great science fiction writer Douglas Adams, who The Hitchhiker’s Guide to the Galaxy, identified « 42 » as Answer to life, the universe and everything. Douglas Adams was really up to something big, and the remaining mystery is how did he know?

This article is republished by The Conversation under a Creative Commons license. Read the original article.

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