Changing research disciplines during Graduate school I am about to start a masters on track to phd program at a graduate school in the US. I study archaeology and intend to focus my masters on a geoarchaeological research project. My archaeological background is focused primarily on geochemical studies of lithic assemblages and as such i have developed a foundation in geology and chemistry (although haven't had any formal training) alongside my archaeological knowledge.
However, my interest in earth sciences, particular planetary science, has recently grown and i am wondering if it is possible to swap disciplines furthur down my grad school career. At the moment i want to see through my archaeological training but want to know if it is possible to skew my research towards planetary science/geology for my phd if the interests still persist.
It's certainly possible, at least in the universities I'm acquainted with, to apply to a Ph.D. program in a field different from your masters degree. But to be accepted into such a program, you'll have to convince an admissions committee (or the professor with whom you want to work) that you have the necessary background. You mentioned that you have relevant background but not formal training, so this may present a problem. If you can take some relevant courses while you're in the masters program, or if you can get recommendation letters attesting to your background knowledge, that would help. If that's not possible, then you may need to take some classes after you get your masters degree and before you apply to Ph.D. programs.