Stand... down!
Old Man Gilliard was the one in charge of the planet core mechanism.
This old and retired Elementalist dedicated his whole life to studying the mysteries of the planet core. From the first time that he was exposed to this incredible source of power, he was amazed and enchanted by it.
The planet core was what made life possible in Planet Darvis.
It was the energy core of the planet that supplied it with energy to survive, it was the life-sustaining source of Planet Darvis.
Mana came from the planet core, so also did psionic energy.
After decades of studying it, Old Man Gilliard slowly left his ignorant status and learned a lot about the planet core. In his understanding, the planet core was a natural energy source that assimilated the natural energy of the universe.
By assimilating this natural energy from stars in space and other extraordinary phenomenon, it made it possible for super energy in a planet.