September 26, 2023

Oddities plagued the earth about 42,000 years ago. Its magnetic field collapsed. Ice sheets billowed in North America, Australasia, and the Andes. Wind belts moved across the Pacific and the South Ocean. Persistent drought hit Australia; The largest mammals on this continent became extinct. People went to caves to make ocher art. Neanderthals finally died out.

During all of this, a giant kauri tree stood tall – until after almost two millennia it died and fell into a swamp where the chemical records embedded in its flesh were flawlessly preserved. This tree, excavated near Ngawha Springs in northern New Zealand a few years ago, eventually allowed researchers to create a tight schedule for a fascinating but vaguely correlated series of events.

What if the crash of the magnetic field, the researchers say, caused the climatic changes of that time? And to think that the Ngawha Kauri tree had testified of the whole thing.

“It must have been the end of the days,” said Chris SM Turney, a geoscientist at the University of New South Wales in Sydney, Australia and part of a large team who described the results in a study published in Science Thursday. “And this tree lived through it all. Which is really amazing. “

By comparing the age data of the tree rings and the levels of radioactive carbon from this Kauri tree and three other similar vintages with the most recent dating information from two stalagmites in the Hulu Caves in China, Dr. Turney and his 32 co-authors determine exactly when The Tree Lived and Died. That gave them a so-called “calibration curve” that enabled them to convert radiocarbon from that time into calendar years.

Scientists from various disciplines said the kauri data was a dazzling addition to the radiocarbon canon and was long awaited.

“For a person with radiocarbon, the kauri records are just amazing,” said Luke C. Skinner, a paleoclimatologist at the University of Cambridge who was not involved in the study. He said the fossil kauri trees are the main way for scientists to get information about radiocarbons from so long ago.

The tree experienced a long dissolution of the magnetic field, a period known as the Laschamp excursion, when the magnetic poles tried unsuccessfully to switch places. As a result, Dr. Turney and his co-authors are using the new data to detail when this excursion took place and to keep track of what else was going on, including the bizarre climate and extinction.

“It was suddenly, my goodness, these things are actually happening all over the world at the same time, all at the same time,” said Dr. Turney. “It was just an extraordinary revelation.”

This discovery opened up a complex thought experiment. The Earth’s magnetic field, constantly being created deep in the molten outer core of the planet, protects against dangerous galactic and solar rays. Were all these particular climatic, biological, and archaeological phenomena related to the wasted magnetic field 42,000 years ago? Had his breakdown changed the course of life on earth? And what about other perturbations of the magnetic field, including the time 780,000 years ago when the magnetic poles actually changed places?

Scientists have been trying to find answers to these questions since the fact of magnetic pole reversal was established a few decades ago. As a result, this latest venture has come to an immense test.

“It’s pretty brave,” said Catherine G. Constable, a geophysicist at the Scripps Institution of Oceanography in San Diego who was not involved in the study.

Dr. Turney and his colleagues used state-of-the-art global climate model simulations that enabled chemical interactions, and tried to use the timeline generated by the kauri tree to find out what the climate was like during the excursion.

The data showed “modest but significant changes in the chemistry and climate of the atmosphere,” according to the paper. Among them: a slightly depleted ozone layer; slightly increased ultraviolet radiation, especially near the equator; a jump into tissue-damaging ionizing radiation; and aurors as close to the equator as the 40th parallel that would run through the center of the continental United States in the northern hemisphere and through the top of Australia in the south.

Adding a period of low solar activity known as Grand Solar Minima to the mix resulted in more dramatic effects. A peculiar, centuries-old series of deposits of beryllium-10 isotopes has been identified in ice cores from Greenland from the Laschamp excursion 42,000 years ago. Such isotopes are created when cosmic rays hit the upper atmosphere; In the geological record, they indicate times when the earth experienced a decreased magnetic field and sometimes solar changes.

In the more extreme computer scenario with the effects of the sun taken into account, the ultraviolet radiation increased by 10 to 15 percent compared to the norm and the ozone by about the same amount. These effects cascaded through the climate system, said Dr. Turney:

“It was basically like a perfect storm,” he said.

The simulations suggest that the weakened magnetic field caused some of the climatic changes 42,000 years ago, and that those changes may have had greater effects: the extinction of many large mammals in Australia, the acceleration of the end of the Neanderthals, and possibly the formation that the authors suggested To break out art while people hid for a long time to avoid skin-damaging ultraviolet rays.

In fact, the effects were so noticeable that the researchers renamed the years leading up to the middle of the Laschamp excursion. They call it the Adams Transitional Geomagnetic Event.

“The Adams event appears to represent an important climatic, ecological and archaeological boundary that has not yet been recognized,” the team concludes. “Overall, these results raise important questions about the evolutionary implications of geomagnetic reversals and excursions in the deeper geological records. ”

The new name pays homage to the British humorist Douglas Adams, author of “The Hitchhiker’s Guide to the Galaxy” and the book and radio series “Last Chance to See” about extinction. It is also a nod to Mr. Adams’ famous line that “the answer to life, the universe and everything” 42 is – which is what Dr. Turney said reminded him of the timing of the magnetic episode 42,000 years ago.

“It just seems scary,” he said with a laugh. “How did he know?”

The interpretation is intended to cause controversy. Some scholars who read the paper admired the breathtaking connections between the disciplines.

“One of the strengths of the paper, just from the perspective of its scientific work, not necessarily the analytical science it does, is just the degree to which it brings together all of these disparate sources of information to make its case,” he told Jason E Smerdon, a climate researcher at Columbia University’s Lamont-Doherty Earth Observatory in New York who was not involved in the study. He called it a “tour de force”.

Likewise, James ET Channell, professor emeritus of geophysics at the University of Florida, who was not involved in the study but was a peer reviewer, said that scientists had been handicapped for half a century by the question of whether a decreasing magnetic field had an impact Life. The paper opens up new research avenues.

“If we knew enough about the timing of the excursions, maybe we could look back at the problem,” he said.

However, other scientists said the comprehensive analysis asked them if there were other explanations for some of the phenomena during the Laschamp excursion.

“It opens a can of worms instead of solving a series of questions,” said Dr. Skinner.

Like several other respondents, he was concerned whether the nomenclature of the Adams event would lead to confusion in the scientific literature and whether it was necessary. But he praised the paper for the stimulating discussion.

“I’m certainly more excited about this today than yesterday,” he said.