About 42,000 years ago, the earth was alien. Its magnetic field collapsed. Ice sheets have risen in North America, Australasia and the Andes. Wind belts moved across the Pacific Ocean and the Southern Ocean. Prolonged drought has hit Australia; that continent’s largest mammal became extinct. People went to caves to make art of ocher color. Neanderthals died for good.
Throughout, one giant kauri tree stood tall – until it died after nearly two millennia and fell into a swamp, where the chemical records embedded in its flesh were impeccably preserved. That tree, which was excavated near Ngawha Springs in northern New Zealand a few years ago, has finally allowed researchers to adapt a short timeline to what previously looked like an interesting but only vaguely correlated series of events.
What happens if, according to the researchers, the collapse of the magnetic field produced the climate changes of that era? And to think that the Ngawha kauri tree testified to the whole thing.
“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, who was part of a large team describing the findings in a study published Thursday in Science. “And this tree has experienced it all. Which is amazing, really. ‘
By comparing the age data of the tree ring and radioactive carbon concentrations of the kauri tree and three other similar vintages with recent dating of two stalagmites in the Hulu caves in China, dr. Turney and his 32 co-authors determine when the tree lived and died. This gave them ‘calibration curves’ that enabled them to convert radiocarbon dates from that period into calendar years.
Scientists in various disciplines have said that the kauridata is a brilliant addition to the radiocarbon cannon and that there is a long wait.
“To a radiocarbon person, the kauri plates are incredible,” said Luke C. Skinner, a paleoclimatologist at the University of Cambridge who was not involved in the study. He said the fossil kauri trees were the most important way scientists could get information about radiocarbon so long ago.
The tree experienced a long disintegration of the magnetic field, a period known as the Laschamp outing, when the magnetic poles unsuccessfully tried to change places. As a result, dr. Turney and his co-authors use the new data to describe more precisely when that excursion took place, and can trace what is still going on, including the bizarre climate and extinctions.
“It was suddenly, well, these things are actually happening all over the world at the same time, all at the same time,” said dr. Turney said. “It was just an extraordinary revelation.”
This discovery unlocked a multiple thought experiment. The Earth’s magnetic field, which is constantly generated deep inside the planet’s molten outer core, protects against dangerous galactic rays and sun rays. Are all those peculiar climatic, biological and archaeological phenomena 42,000 years ago linked to the wasted magnetic field? Did its collapse change 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 that the magnetic pole reversal was determined decades ago. Consequently, this latest attempt has shown a tremendous investigation.
“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.
Using leading global climate model simulations that made chemistry interactions possible, dr. Turney and his colleagues use the timeline generated by the kauri tree to try to figure out what the climate was like during the excursion.
According to the newspaper, the data revealed ‘modest but significant changes in atmospheric chemistry and climate’. Among them: a slightly depleted ozone layer; slightly increased ultraviolet radiation, especially near the equator; a jump in tissue damaging ionizing radiation; and auroras as close to the equator as the 40th parallel parallel, which would run through the middle of the continental United States in the Northern Hemisphere and through the lower end of Australia in the south.
The addition of a period of low solar activity, known as large solar lows, produced more dramatic effects. A peculiar, century-long series of deposits of beryllium-10 isotopes have been identified in ice cores of Greenland, dating from the Laschamp excursion 42,000 years ago. Such isotopes are created when cosmic rays occupy the upper atmosphere; in the geological report they indicate times when the earth experienced a diminished magnetic field and sometimes solar changes.
In the more extreme computer scenario, with solar power effects taken into account, ultraviolet radiation rose by 10 to 15 percent of the norm and ozone decreased by about the same amount. The consequences flowed through the climate system, said dr. Turney said:
“It was basically like a perfect storm,” he said.
The simulations suggest that the weakened magnetic field caused some of the climate changes of 42,000 years ago, and that the changes may have had wider consequences: the extinction of many large mammals in Australia, the acceleration of the end of the Neanderthals, and perhaps gave rise to cave art as people hid for a long time to avoid ultraviolet rays damaging skin, the authors suggested.
In fact, the consequences were striking that the researchers gave a new name to the years leading up to the middle of the Laschamp outing. They call it the Adams Transitional Geomagnetic Event.
‘The Adams event appears to represent an important climatic, environmental and archaeological boundary that was previously unrecognizable,’ the team writes, concluding: ‘In general, these findings raise important questions about the evolutionary impact of geomagnetic reversals and excursions through the deeper geological report. . ”
The new name is a tribute to British humorist Douglas Adams, author of ‘The Hitchhiker’s Guide to the Galaxy’ and the book and radio series ‘Last Chance to See’ on extinction. It is also a wink for mr. Douglas’s famous rule that ‘the answer to life, the universe and everything’ is 42, which, according to Dr Turney, reminded him of the timing of the magnetic episode 42,000 years ago.
“It just looks weird,” he said laughing. “How did he know?”
The interpretation is destined to create controversy. Some scientists who read the paper expressed admiration for the breathtaking link between disciplines.
“One of the strengths of the paper, just from the perspective of his scientific work, not necessarily the analytical science that does it, is just the extent to which all these diverse sources of information are put together to make his case valid,” he said. he said. Jason E. Smerdon, a climate scientist at the Lamont-Doherty Earth Observatory of Columbia University in New York, who was not involved in the study. He calls it a ‘force de force’.
Similarly, James ET Channell, an emeritus professor of geophysics at the University of Florida, who was not involved in the study but a peer reviewer, said that scholars have been stimulated for half a century by the question of a ‘declining magnetic field’. an influence has life. The paper offers new possibilities for research.
“If we know enough about the timing of excursions, we might be able to look at the problem,” he said.
But other scientists said the extensive analysis made them wonder if there were other explanations for some of the phenomena during the Laschamp outing.
“It opens a can of worms rather than solving a set of questions,” Dr Skinner said.
Like several other interviews he interviewed, he was concerned about whether or not the Adams Event designation would lead to confusion in the scientific literature. But he praised the newspaper for the stimulating discussion.
“I’m definitely more excited about this topic than I was yesterday,” he said.