I think there is almost certainly something like that left. A low hanging fruit that we will be able to point to and go see that that explains this big big thing. But we just have no possible idea of what it is. Same as the average person couldn't have 300 years ago looked at those rocks and gone "Yes geological plate theory" we cannot ever comprehend what that "Oh of course" thing is gonna be. If I had a prediction it gonna be something to do with trees but that just cause I like Trees and forests have such complexities to them that we "see" but don't really see all the time.