With 150+ years of science lots of new kinds of questions emerged that hardly anyone went deeply into. Just begin working there and make deep contributions. To make a few things clear:
* You probably won't get any academic recognition for this or probably no research funding agency will be willing to fund your research (far too experimental).
* It is quite possible that despite you being really talented your research into this will come to nothing. That is a prize one has to pay for the possibility of doing a deep contribution.
If you are looking for ideas where to start, just look around yourself and from what you see try to create a deep general theory (the more abstract and general the better IMHO) which has lots of predictive power and either allows you to formalize a theory where you can prove theorems about (my personally prefered way, since I'm mathematician) or has strong falsifiable predictions that one can in principle do experiments on.
No, the reason for this is that all the easy stuff has already been discovered. 20 years ago it was still kind of easy for a single PhD student to make enormous progress in his field, but after a dozen of PhD generstions there is just not much left which can be discovered by a si gle student.
Just look at physics, they had to build a multi-billion dollar research facility below the ground to advance our knowledge. Or the satelites for discovering gravity waves, ... All of this can not be done in the classic PhD model where a single PhD student works on a topic.
tldr: After 150+ years of science there is almost nothing left which can be discovered by a single PhD student