NASA scientists have made an important discovery: Earth’s magnetic field and the level of oxygen in the atmosphere are closely connected. This connection goes back over 540 million years and may change how we understand Earth’s ability to support life.

The magnetic field is created by the movement of molten iron deep inside Earth’s core. This field acts like a shield that protects the planet’s atmosphere from being blown away by strong solar winds. Scientists have always believed that this shield helps keep Earth’s air and life-supporting gases safe, but there was no direct proof—until now.

The new study looked at two sets of data. One showed the strength of Earth’s magnetic field over time, found in ancient rocks and minerals. The other tracked oxygen levels using geochemical markers. What the scientists found was surprising: when the magnetic field was strong, oxygen levels were high. When the field was weak, oxygen levels dropped. These ups and downs happened almost at the same time.

“This is the first discovery we’ve ever had to establish the link between the geomagnetic field and the oxygen level,” said study coauthor Weijia Kuang, a geophysicist at NASA’s Goddard Space Flight Center.

This discovery means that movements deep inside the Earth—like the shifting of continents or changes in the core—might affect both the magnetic field and the atmosphere. These inner-Earth processes could be important in making Earth habitable.

The study also gives scientists new clues about what to look for when studying other planets. If a planet has a magnetic field and enough oxygen, it might also be able to support life.

Still, researchers say they need more studies to fully understand how the Earth’s core affects the surface environment. This finding is just the beginning of a deeper look into Earth’s past and its ability to support life.

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