[wetwater]

Its not. Here is the paper. https://www.science.org/doi/10.1126/sciadv.adu8826

[JumpCrisscross]

To summarise, photosynthesis increases the amount of molecular oxygen in the atmosphere. It doesn’t create oxygen atoms. Those come, in the recent geological era, from inside the earth in the form of volcanic oxides. The paper suggests that something about the magnetic field influences the rate at which those oxides are belched into the atmosphere.