About 42,000 years ago, the Earth was beset by strange things. His magnetic field collapsed. Ice caps have leapt across North America, Australasia, and the Andes. The wind belts moved across the Pacific and South Oceans. A prolonged drought has hit Australia; The largest mammals on this continent have disappeared. Humans have gone to caves to make ocher-colored art. Neanderthals are dead for good.
Through it all a giant kauri tree stood tall – until, after nearly two millennia, it died and fell into a swamp, where the chemical records embedded in its flesh were perfectly preserved. This tree, unearthed a few years ago near Ngawha Springs in northern New Zealand, finally allowed researchers to adjust a tight schedule for what previously appeared to be a series of intriguing but vaguely correlated events. .
What if, according to the researchers, the crash of the magnetic field caused the climatic changes of that time? And to think that the Ngawha kauri tree had testified to all this.
“It must have looked like the end of days,” said Chris SM Turney, a geoscientist at the University of New South Wales in Sydney, Australia, and part of a large team that described the results in a published study. Thursday in Science. “And this tree has lived through it all. Which is really amazing.
By comparing ring age data and radioactive carbon concentrations from this and three other kauri trees from the same vintage to recent dating information derived from two stalagmites in Hulu Caves in China, Dr Turney and his 32 co -authors were able to determine when the tree lived and died. This gave them what they call a “calibration curve”, allowing them to convert the radiocarbon from that period into calendar years.
Scientists from all disciplines have said the kauri data is a dazzling addition to the radiocarbon cannon and is long overdue.
“For a radiocarbon person, the kauri recordings are just amazing,” said Luke C. Skinner, a paleoclimatologist at the University of Cambridge, who was not involved in the study. He said fossil kauri were the primary way scientists got information about the radiocarbon from so long ago.
The tree experienced a long decay of the magnetic field, a period known as the Laschamp excursion, when the magnetic poles tried unsuccessfully to change places. As a result, Dr Turney and his co-authors were able to use the new data to more accurately describe when this excursion happened and trace what else was going on, including the bizarre weather and the extinctions.
“It was suddenly, my God, these things are actually happening all over the world simultaneously, all at the same time,” Dr Turney said. “It was just an amazing revelation.”
This discovery opened up a multi-faceted thought experiment. Earth’s magnetic field, which is constantly generated deep within the planet’s molten outer core, protects against dangerous galactic and solar rays. Were all these particular climatic, biological and archaeological phenomena of 42,000 years ago related to the wasted magnetic field? Had its collapse changed the course of life on Earth? And what about other disturbances in the magnetic field, including back then 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 reversals was established decades ago. Therefore, this latest attempt has attracted close scrutiny.
“It’s brave enough,” said Catherine G. Constable, a geophysicist at the Scripps Institution of Oceanography in San Diego, who was not involved in the study.
Using state-of-the-art global climate model simulations that enabled chemical interactions, Dr Turney and his colleagues used the timeline generated by the kauri tree to try to find out what the climate looked like during the excursion.
The data revealed “modest but significant changes in atmospheric chemistry and climate,” according to the article. Among them: a slightly depleted ozone layer; slightly increased ultraviolet radiation, especially near the equator; increased ionizing radiation damaging tissue; and auroras as close to the equator as the 40th parallel of latitude, which would cross the middle of the continental United States in the northern hemisphere and the lower tip of Australia in the south.
Adding a period of low solar activity, known as high solar minima, to the mix produced more dramatic effects. A particular century-old series of beryllium-10 isotope deposits has been identified in ice cores from Greenland, dating from the Laschamp excursion 42,000 years ago. Such isotopes are created when cosmic rays strike the upper atmosphere; in geological records, they indicate times when the Earth experienced a decrease in the magnetic field and, sometimes, solar changes.
In the most extreme computer scenario, with solar effects taken into account, ultraviolet radiation has increased 10-15% from the norm and ozone has decreased by roughly the same amount. These effects have rippled through the climate system, Dr Turney said:
“It was basically like a perfect storm,” he says.
Simulations suggest that the weakening of the magnetic field caused some of the climate changes of 42,000 years ago, and that these changes may have had broader impacts: causing the extinction of many large mammals in Australia, hastening the end. Neanderthals, and possibly giving birth. wall art while humans were in hiding for long periods of time to avoid skin-damaging ultraviolet rays, the authors proposed.
In fact, the effects were striking that researchers gave a new name to the years leading up to the Laschamp excursion midway. They call it the Adams transitional geomagnetic event.
“The Adams event appears to represent a major climatic, environmental and archaeological frontier that was previously ignored,” the team wrote, concluding: “Overall, these results raise important questions about the evolutionary impacts of geomagnetic reversals and excursions at through the deeper geological records. . “
The new name is a tribute to British comedian Douglas Adams, author of “The Hitchhiker’s Guide to the Galaxy” and the book and radio series “Last Chance to See” on Extinction. It’s also a nod to Mr. Douglas’ famous phrase that “the answer to life, the universe and everything” is 42 – which Dr. Turney says reminded him of the moment. of the magnetic episode of 42,000 years ago.
“It sounds strange,” he laughs. “How did he find out?
The interpretation is intended to create controversy. Some scientists who read the article expressed their admiration for the breathtaking links between the disciplines.
“One of the strengths of the article, just from the point of view of its academic work, and not necessarily the analytical science it does, is simply the extent to which it combines all of these disparate sources of information to make make their case, ”said Jason E. Smerdon, a climatologist at the Lamont-Doherty Earth Observatory at Columbia University 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 the researchers had been stuck for half a century by whether a decreasing magnetic field affects life. The document opens up new avenues of research.
“If we knew enough about the tour schedule, maybe we could come back to the problem,” he said.
But other scientists said the in-depth analysis left them wondering if there were other explanations for some of the phenomena during Laschamp’s excursion.
“It’s opening up a box of worms rather than solving a set of questions,” said Dr. Skinner.
Like several other interviewees, he questioned whether the Adams Event nomenclature would lead to confusion in the scientific literature and whether it was necessary. But he praised the document for stimulating discussion.
“I’m certainly more excited about this topic today than I was yesterday,” he said.