In the 70s we thought we had pumped out the Texas oil fields. By the 1990s they were 2/3s full again. The oil seeps to the crust, and the left weeps.
I have a hard time believing dinosaurs lived thousands of feet below the surface under thousands of feet of ocean. They also lived underground beneath the polar icecap.
What the earth does have deep underground is carbon, hydrogen, heat and pressure.
EC