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A magnetic field reversal 42,000 years ago may have contributed to mass extinctions | Science News

February 22, 2021

[Posted by Chuck Almdale]

The topic of reversals of the Earth’s magnetic field has interested me for over 50 years. In the 1920’s it was discovered that some volcanic rocks were magnetized with polarity opposite to the local magnetic field. In the 1950’s, when research vessels were taking core samples of the floor of the Atlantic Ocean, they discovered that magnetic polarity of the sediments ran in north-south bands, and occasionally the polarity reversed.

This led to the theory that the sea floor is spreading out in opposite directions from the Mid-Atlantic Ridge, that “new rock” emerges at the ridge, that the earth’s crust is made of large continent-sized plates which “float” on underlying mantle rock, emerging in some places and diving under other plates in other places. The ensuing science of Plate Tectonics leapt to the forefront of geology, while the phenomenon of magnetic field reversals stayed in the background, useful for measuring crustal movements, but not much else.

When the Earth’s magnetic poles reverse, the field strength dwindles (at an unknown rate) to the zero point, then builds back up but with the north pole now at the south and vice-versa. What we currently call the “north magnetic pole” is actually the Earth’s magnetic south pole, and vice-versa for the “south magnetic pole.” Check the diagram below. I presume, but feel free to check elsewhere, that when our magnetic poles next flip, our compass needles will all point south.

For me, it’s this dwindling and zero-point of field strength which is of interest.

From Magnetic Field of the Earth

Our magnetic field protects us from incoming charged particles — cosmic rays — by deflecting them magnetically. Decrease the field and more cosmic rays come down to the surface. At the zero point of field strength, there’s only atmospheric gas molecules to stop them. In the 1960’s I learned that such charged particles are important causes of genetic changes, i.e. mutations. These protons, etc. come whizzing in from outer space, bang into our DNA molecules, knock a base pair or two around, and if it happens inside a spermatozoa or ova, the animal or plant born with that change is a mutant.

Many such mutations have no physiological affect whatsoever, causing only “genetic drift.” Many others are detrimental — with complex creatures, it’s easier for things to get worse rather than better. A few mutations bring an improvement: possibly the offspring will be stronger, faster, smarter, on any of a million other ways to “improve.” This is where natural selection comes in; the environment weeds out faulty genes and their owners, and — on average — good genes enable their owners to have more offspring. Evolution happens.

In the 1990’s, after his talk at a meeting I asked a geologist: “If huge numbers of incoming cosmic rays during these zero-point magnetic field events cause mutation rates to explode, wouldn’t a lot of animals die — from cancer, say — and greater numbers than usual of beneficial genes appear? Perhaps this has something to do with Gould and Eldredge’s theory of punctuated equilibrium? Nothing much changes for hundreds of thousands of years, then a magnetic pole reversal occurs, and suddenly new species appear and others disappear.”

“Interesting idea,” he said. “Possibly true, but I don’t know how anyone is ever going to be able to test it, or prove it, or disprove it.”

Time moves on, discoveries are made. Apparently we’re getting closer to testing and proving this idea. | Carolyn Gramling | 18 February 2021

A flip-flop of Earth’s magnetic poles between 42,000 and 41,000 years ago briefly but dramatically shrank the magnetic field’s strength — and may have triggered a cascade of environmental crises on Earth, a new study suggests.

With the help of new, precise carbon dating obtained from ancient tree fossils, the researchers correlated shifts in climate patterns, large mammal extinctions and even changes in human behavior just before and during the Laschamps excursion, a brief reversal of the magnetic poles that lasted less than a thousand years. It’s the first study to directly link a magnetic pole reversal to large-scale environmental changes, the team reports in the Feb. 19 Science.

During a reversal, Earth’s protective magnetic field, which shields the planet from a barrage of charged particles streaming from the sun, can lose strength (SN: 1/28/19). So some researchers have suggested that these flip-flops may be linked to extinction events (SN: 11/19/20).

Kauri trees (one shown) have grown in New Zealand for thousands of years. By analyzing tree rings of preserved trees in the Ngawha swampland, scientists identified evidence to suggest a magnetic pole flip around 41,000 years ago.Mark Meredith/Moment/Getty Images

Link to the original article in Science, 19 Feb 2021.

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