New research reveals that carbon made it possible for Earth’s molten core to freeze into a solid heart, stabilizing the magnetic field that protects our planet. Without it, Earth’s deep interior — and life above — might look very different.

The researchers showed that the core would need to be made of 3.8% carbon for it to have begun crystallizing. This result indicates that carbon may be more abundant in Earth’s core than previously thought, and that this element could have played a key role in how it froze, offering a rare glimpse into the processes occurring at the heart of our planet.