According to Wikipedia thorium is probably created from neutron stars or supernovae making it one of the rarest elements in the galaxy. But, it’s quite abundant on Earth, maybe 3x as abundant as Uranium on earths crust. Because of this abundance it is, along with Radon, the primary constituent of earths natural background radiation.

The actual journal article, since NYT didn't bother linking to it: https://www.nature.com/articles/s41586-026-11084-4

archived no paywall: https://nonograph.com/in-vienna-and-beijing-the-first-nuclea...