Long before geophysicists suspected that a flip of the magnetic poles might be in progress, they began delving into a concept that startled them. It was the early 1960s. The theory of reversals was just beginning to creep into respectability. Its implications were breathtaking. Among them: Did reversals kill off or mutate species and therefore affect patterns of evolution? This suggestion went far beyond the idea that the magnetic field provides a refuge from cosmic radiation and shelters our atmosphere from solar winds that would rip it away. It was metaphysical: Did the inner machinations of the molten core help determine what lives and dies on the crust?
The first salvo, in 1963, stemmed directly from the discovery of the Van Allen belts. What would happen to all that radiation trapped in the belts when the poles reversed? Would solar wind be able to bathe the Earth in radiation, causing rampant genetic mutations? And had it done so during previous pole flips? The author of the page-and-a-half paper, Robert Uffen of the University of Western Ontario, hypothesized: yes.
“It is becoming increasingly apparent that the Earth is a heat engine the internal workings of which have controlled not only geological phenomena such as mountain building, volcanoes, and earthquakes, but also geochemical phenomena such as the development of the atmosphere and the oceans; geophysical phenomena such as the magnetic field and radiation belts; and even biological phenomena like the origin and evolution of life,” Uffen concluded.
The next step was to examine the rock record. This time, it wasn’t only to look for the magnetic memory locked in rocks, but also at its archive of fossils. It was obvious that reversals did not kill off all life, because life had persisted continuously on the planet for at least 3.6 billion years. But had previous reversals led to mass die-offs? At a first pass, there was little evidence. For one thing, the Earth had experienced just five mass extinctions. But there had been hundreds of reversals and near-reversals. Therefore, reversals didn’t cause mass extinctions, or at least not always. The logic of that line of reasoning broke down under scrutiny, though. Reversals last for perhaps a few thousand years—or less—and the paleontological record is rarely precise to that time scale. It’s hard even to find a global rock record for such a short period, much less a record of species gone missing forever within it. We have evidence of the five mass extinctions because they spanned millions of years.
As researchers dug further into the data, some peculiarities began to spring up. Two of the mass extinctions coincided with abrupt changes in the tempo of reversals. The first was the one 252 million years ago at the end of the Permian period. It is known as the Great Dying because 95 percent of species on the planet vanished. The second was the one that killed off the dinosaurs and many other species 65 million years ago at the end of the Cretaceous period. A superchron, when the Earth’s magnetic field did not change for tens of millions of years, came before each. By contrast, during those two mass extinctions, the field reversed many times. One theory was that during the superchrons, species evolved without the need to adjust to the rigors of reversals, and so when reversals came, so did pulses of extinction. That may offer a bit of comfort about the vulnerability of species to a reversal today. Ever since the dinosaurs vanished, we have been in a relatively fast-paced pulse of reversals, which may have built some level of protection into the genetic code of species now on Earth.
By 1971, the scientific exploration had turned to comparing an index of the change in the number of taxonomic animal families over the past 600 million years—a measure of rates of extinction but not mass extinction—against the timing of reversals. There was an astonishingly high correlation, the author, Ian Crain of the Australian National University in Canberra, found. But why? Did reversals foster extinction and, therefore, the emergence of new species to replace them? Pointing to lab experiments, Crain proposed that the low magnetic field itself was the killer, causing difficulty in movement and reproduction.
But perhaps there was another killing mechanism. New findings in the 1970s and 1980s were showing that the magnetic poles are important for navigation in almost every species studied, in both large and surprisingly small ways. Many use the field to find food, mates, breeding spots, and wintering areas. But, for example, radishes also align their roots according to the field and dogs prefer to urinate facing north-south rather than east-west, as long as they are off leash and not in the midst of a geomagnetic storm. What happens when the poles are reversing? Can species that rely on the poles to navigate still get where they need to go? If not, do they die en masse?
What of the perils of radiation? The long-standing belief was that the Earth’s thick atmosphere provides a physical barrier against a full blast of solar and cosmic radiation whether the magnetic shield holds or not. Exposure to radiation while you are in an airplane, for example, increases along with altitude and latitude, suggesting that the atmosphere is a filter except near the poles, where field lines converge. But what if the field were decimated? A clue came from ocean sediment records. They showed an increase in radioactive beryllium, a marker of the collision of cosmic particles with the atmosphere during the last reversal. That meant more cosmic particles were getting into the upper atmosphere before colliding and scattering damaging secondary radiation. But it was not a sign that the destructive energetic particles themselves were reaching the surface, just that secondary radiation was.
And then there was the investigation into damage not from ionizing particles but from a lack of ozone. The Dutch chemist Paul Crutzen, who won a Nobel Prize in 1995 for his work on the ozone hole, showed in 1975 that when solar protons produced ions in the stratosphere, that led, through other chemical reactions, to the widespread destruction of the ozone layer. In turn, that allowed damaging ultraviolet radiation to reach the surface of the Earth. Other investigators found that during a reversal, vast swaths of ozone would vanish, allowing greater amounts of ultraviolet B radiation to strike the surface of the Earth, especially near whatever poles there were at that time. Ultraviolet B radiation is not ionizing, but it can affect living tissue in myriad destructive ways. Skin cancer and long-term damage to the eyes and to the immune system are all linked to the rays. More recently, the French geophysicist Jean-Pierre Valet proposed that the disintegration of the ozone hole could be one factor in the final die-off of the world’s Neanderthal population. The last small populations vanished at the time of the Laschamp excursion forty thousand years ago, when the field was at one-tenth of its normal strength. Neanderthals’ tendency to be fair-skinned and redheaded suggests they were especially susceptible to ultraviolet B damage, just as modern humans with that coloration are.
In the end, the evidence of how past reversals had affected past life—and therefore how it would affect life during a future reversal—was slender, largely theoretical, and inconclusive. The German physicists Karl-Heinz Glassmeier and Joachim Vogt, who did an extensive review of the relevant studies in 2010, concluded, “It is yet too early to decide in which way magnetic field driven bio-chemical effects influence evolution on Earth.” The implication is that they do.
I chatted with Baker about these ideas in his expansive office in Boulder, sitting at a large table overlooking the mountains, a wall of books behind us. A Hollywood casting agent would assign him the role of four-star general. He is tall and broad-shouldered with straw-straight, gingery hair. He has learned how to sit stock-still, as if conserving energy for battle. He has testified before the US Congress about the near miss of 2012, and you can see the authority his presence would wield there. You could even conclude that he’s solemn, except that from time to time that prairie-dry wit breaks through and a rare smile creeps across his face. He’s unusual among scientists. There are those who spend their whole careers looking at a single thing. One might examine coral reefs. Another, the chemistry of plastic polymers. Yet another, the physics of how to create primordial atomic particles. Baker’s passion is to put things together across disciplines. He is a synthesizer. There are the leaf inspectors and then there are the forest rangers, is how he puts it. He is the latter. And when he assembles the evidence, he finds a more declarative story about what will happen to life on Earth during a reversal.
Unquestionably, more potentially deadly solar energetic particles will reach closer to the Earth, he said. That access will be episodic rather than continual. In places, these damaging particles will be able to reach the Earth’s surface right down to where humans live. It’s the same story with galactic cosmic rays, which are a continual threat. The atmosphere will deflect only the slower, less dangerous particles.
The atmosphere will be a double-edged sword when it comes to radiation; it will both protect and harm. As high-energy particles hit the Earth’s atmosphere, some will splinter into secondary particles, producing an additional shower of damaging radiation, akin to what the beryllium marker from the last excursion showed. An unanswered question is how well the Earth’s atmosphere will withstand the violence of solar wind during the few thousand years or so of a reversal. The general agreement is that a reversal is too short-lived for much atmospheric corrosion to take place. But Baker thinks of Mars. Over time, the relentless solar wind and radiation tore away its atmosphere when that planet’s internal magnetic field died. He would like to see scientists do a closer analysis of how the Earth’s atmosphere will fare.
He wants to be clear that he does not envision a world with no protection from the terrestrial magnetic field. Instead, the weak multi-pole magnetic field of the reversal will protect parts of the Earth in complex asymmetric bands. They will not follow latitudinal lines. Some mid-latitude portions of the Earth—where humans tend to congregate—will be less protected than others. On the other hand, whole longitudinal lines could be free of any magnetic shield at all. That means there could be radiation hot spots, just as there are ozone hot spots today from holes in the atmosphere’s ozone layer. And not just radiation hot spots, but also lethal patches of intense ultraviolet B radiation from an ozone layer chemically abraded by increased upper-atmosphere solar and cosmic radiation.
“To me it’s a very real possibility that parts of the planet will not be habitable,” he said.
For him, examining the past for clues about the next reversal has its limits. The next reversal will be fundamentally different from any that preceded it for one crucial reason: The world the shield protects today is different from what it was the last time the poles succeeded in reversing 780,000 years ago, or tried to 40,000 years ago. For one thing, there are 7.5 billion humans on it, twice as many as in 1970. Last time the poles reversed, human ancestors were here in small numbers. “It completely changes the game,” Baker said.
We have cut down forests, plowed the lands, hunted creatures for meat and sport, changed the chemistry of the air and the ocean through the burning of fossil fuels, built industries and cities and networks of roads. As of 2012, nearly one-third of species that the World Conservation Union had assessed were under threat of extinction. And it’s hard for animals to move freely to and find new living spaces not already taken by human civilization and industry. Humans are driving the Earth system, just as geological forces, such as volcanoes, have done in the past. At the same time, the magnetic field, independent of human action and impossible to control, is plotting insurrection. It speaks to Baker of the possibility of a malignant confluence of effects. Of tipping points. Even if in previous times a reversal was not accompanied by widespread destruction, today it might be. When multiple hazards conflate, the result can be unimaginably worse than a single event. What if the magnetic shield is down and a solar storm erupts and there happens to be a giant earthquake?
But in addition to the biological hazards connected to a reversal, there are the dangers to the vast cyber-electric cocoon we have encased ourselves in, stretching from the depths of the ocean into space. It is the central processing system of modern civilization. And particles don’t have to reach the surface to do damage. The Earth’s atmosphere is populated with satellites, the International Space Station, and airplanes filled with crew and passengers. Solar energetic particles can rip through their sensitive, miniaturized electronics. Telluric currents produced by cosmic plasma–generated magnetic oscillations in the atmosphere can blast the transformers needed for the electrical grid. And satellite timing systems governing the grids could be knocked out, which would unravel the electric and electronic infrastructure. Because the electrical system is so extraordinarily connected, a failure in just one part of it will spread like wildfire across the globe. Never, in the history of the world, has there been this combination of systems that respond so dramatically to the changing magnetic field.
“We are sitting ducks,” Baker said.