[@Member 00492] Here's what I'm thinking. If gravity is the only force that applies to Peek, at the end of his episode what would happen is that he'd continue to fall through the earth, gaining velocity till he hit the center at which point his momentum would slingshot him to the surface of the opposite side of the world. He'd then sink back into the earth and the process would start again indefinitely.

Over the course of a significant period of time, say two or three years, Peek figures out how to control the vibra-space vibrations that Nabuo Taka's belt imposed on his body. He used this control when closest to the Earth's surface to drag himself up and out. He is able to control the intangibility but he is still trapped in the vibra-space state. He needs to exert a constant force of will to keep from sinking into the Earth again. Desperate both to be able to rest from his powers and to not be bright blue covered in Kirby dots he kidnaps a scientist to help with a cure and begins stealing various components needed to aid in concocting that cure. The Titans run into him during a robbery and as he blames Batman for his journey to the center of the Earth he vows to destroy Batman's hero team.