Mysterious link between Earth’s magnetism and oxygen baffles scientists

The abundance of oxygen in Earth’s atmosphere seems to be linked with the strength of the planet’s magnetic field. Over the past 540 million years, the two appear to have risen and fallen in tandem, though it is unclear whether they directly influence one another, or are both controlled by a third factor. Explaining the link could help to reveal fundamental trends in the evolution of life on Earth — and could show astronomers the most promising places to look for signs of complex life on other planets.