The Earth's core is more than just a source of the planet's magnetic field; it plays a crucial role in the long-term conditions that support complex life. For approximately 540 million years, the Earth's magnetic field and atmospheric oxygen levels have been closely linked, with both rising and falling in tandem. This relationship has been measured and confirmed by a NASA-led team, who suggest that the planet's molten core has been instrumental in creating the conditions necessary for the evolution of complex life forms.
Weijia Kuang, a geophysicist at NASA's Goddard Space Flight Center, led the research. His work focuses on understanding how the Earth's deep interior and magnetic field influence the planet's habitability. The Earth's geomagnetic field, an invisible magnetic bubble created by the motion of the planet's liquid core, extends far into space and helps steer charged particles, protecting our atmosphere and surface from harsh radiation.
The magnetic field's strength changes due to the complex flow patterns of molten iron in the outer core, rather than a steady, uniform flow. In this new study, the team compared long-term records of magnetic field strength with estimates of atmospheric oxygen levels. They found that both curves climb overall and share a peak between about 330 and 220 million years ago. When plotted together, the lines nearly trace each other exactly, suggesting a strong correlation.
The Earth's core and magnetic field are crucial in deflecting charged particles from the solar wind, which constantly crashes into the planet's magnetic bubble. This protection helps shield our atmosphere and surface from harsh radiation. Spacecraft data from Earth, Mars, and Venus shows that a magnetic field can reduce atmospheric loss while also opening escape routes near the poles. However, one analysis reported that, under certain conditions, planets with and without internal magnetic fields can lose similar amounts of gas.
The new research does not claim that a stronger magnetic field always locks in more oxygen. Instead, the authors argue that a slow, shared process inside the Earth likely drives both magnetic activity and the balance of oxygen at the surface. Rocks hold magnetic field records, with mineral grains aligning with the field as lava cools on the seafloor, preserving a frozen record of field direction for hundreds of millions of years. Scientists infer past oxygen levels from geochemical proxies, which are chemical clues in ancient rocks that respond to how oxygen was distributed in air and seawater.
The connection between oxygen-rich environments and bursts of complex life is supported by studies of past supercontinents, such as Pangea. These studies suggest that supercontinent assembly and breakup can reshape long-term climate and ocean circulation, influencing atmospheric gases by changing volcanism and weathering rates. Kuang and colleagues suggest that deep Earth processes may explain the correlation between magnetic field strength and oxygen levels over the examined span.
The Earth is the only known planet with both complex oxygen-breathing life and a strong global magnetic field. This coincidence has led scientists to consider the magnetic field as part of planetary habitability. While the new correlation does not settle how a magnetic field shields air, it strengthens the idea that a planet's interior is crucial. For rocky exoplanets, astronomers may need to consider both distance from the star and the activity of cores and plates.
Future research will explore whether similar links appear earlier in Earth's history or in other chemical cycles, such as nitrogen. For now, the results show that deep core processes have moved in step with the air we breathe. Unraveling this partnership could help explain why life on Earth endured so many upheavals and guide the search for other long-lived worlds. The study is published in Science Advances.
