Scientists discover strong, unexpected link between Earth's magnetic field and oxygen levels

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Earth's magnetic field and oxygen levels are inextricably linked, new research suggests.
The strength of the geomagnetic field has gone up in lockstep with the percentage of oxygen in Earth's atmosphere over the past 540 million years, a new study finds — but it remains unclear if one of these influences the other, or whether other unknown factors explain the link.
"This is the first discovery we've ever had to establish the link between the geomagnetic field and the oxygen level," lead author Weijia Kuang, a senior scientist in the Geodesy and Geophysics Laboratory at NASA's Goddard Space Flight Center, told Live Science.
Earth's magnetic field and oxygen levels have increased more or less in parallel since the start of the Cambrian period (541 million to 485.4 million years ago), and both factors spiked between 330 million and 220 million years ago, the results indicate.
The research could help to narrow down requirements for life on other planets, Kuang and study co-author Ravi Kopparapu, a planetary scientist at the NASA Goddard Space Flight Center, said in a joint video interview.
It may be that the geomagnetic field controls oxygen levels, or vice versa — but there is another possible scenario, which is that both factors are related to a third geochemical or geophysical process that the researchers haven't yet pinpointed, Kuang said.
For the new study, scientists used two independent datasets spanning the past 540 million years. One of the datasets showed atmospheric oxygen, derived from multiple indicators such as the abundance in sediments of fossilized charcoal, which remains after wildfires and gives clues about how much oxygen was available at a given time. The other dataset showed the strength of the geomagnetic field, derived from magnetic information that is recorded in ancient rocks and sediments. The researchers plotted these datasets against each other and found there was a strong correlation between them.
If the geomagnetic field controls oxygen levels, its influence would likely be due to the protection it offers Earth's atmosphere against space weather. Previous research indicates that the geomagnetic field can prevent or reduce the escape or erosion of atmospheric molecules. The magnetic field also shields life on the planet, including plants that produce oxygen, from X-ray and extreme ultraviolet radiation.
If, in contrast, atmospheric oxygen levels dictate the strength of Earth's magnetic field, then plate tectonics would play a central role. Plate tectonics is the process that continuously recycles Earth's crust into the mantle, which is the planetary layer that covers Earth's liquid outer core.
Earth's geomagnetic field originates from currents in the outer core, so it's possible that the recycling of crustal material and oxygen into the mantle could impact the lower mantle, which could then affect the geomagnetic field, Kuang said.
Related: Did plate tectonics give rise to life? Groundbreaking new research could crack Earth's deepest mystery.
"Plate tectonics [...] will definitely impact the thermal and the dynamical conditions at the base of the mantle where it borders the liquid outer core," he said. "On the other hand, plate tectonics also impacts the cycling of chemicals and other elements from the interior to the surface, which certainly will impact oxygenation, or the production of oxygen."
It's more likely that the geomagnetic field affects oxygen levels, rather than the other way round, Kuang said. That's because scientists know the geomagnetic field originates deep inside the planet and propagates to Earth's surface and into space. "The other direction is less well understood," he said.
The third possible scenario is that another, separate process is pushing the geomagnetic field and oxygen levels in the same direction over time. The study's authors don't know what that process might be yet, but a spike that exists in both datasets may hold the answer.
The spike coincides with the existence of the ancient supercontinent Pangaea, which formed about 320 million years ago and broke up about 195 million years ago. Due to the massive tectonic rearrangements involved, supercontinents might be the missing link between Earth's magnetic field and oxygen levels — but the evidence for this is still very tentative at this point, Kuang and Kopparapu cautioned.
"This is one of the conjectures we didn't really put out strongly in our paper, but it is something we think is a very enticing mechanism for us to pursue," Kuang said. The reason the researchers held back with this idea is that they have robust data for only one supercontinent — Pangaea — and not the ones that came before, he said.
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"There seems to be some eye-sight correlation between oxygen and magnetic field and all the other supercontinents," Kopparapu said. "However, we don't have reliable data for oxygen [going farther back] than 540 million years, and so we are unable to make that kind of a conclusion for [farther back in time] and past supercontinents."
The researchers are already working on the next step, which is to search for other geophysical and geochemical factors that might link to the geomagnetic field and oxygen levels. For this, the authors say communication and collaboration between scientists is of paramount importance.
"One single mind cannot comprehend the whole system of the Earth," Kopparapu said. "We're like kids playing with Legos, with each of us having a separate Lego piece. We're trying to fit all of it together and see what's the big picture."