Oil actually comes from aquatic life (mostly plankton) that sinks to the sea floor and gets buried, squeezed and heated. Oil still forms today, but it’s a process of millions of years.

Coal is formed from plants, and that does indeed require something doesn’t eat it first. Swamps, for example, help a lot, letting the fallen trees sink down where most stuff can’t eat it. Peat can also form into coal. Coal forms even slower than oil though, and it’s much rarer, but it also doesn’t require an ocean, so it’s often more accessible for us land-living humans