Realistically, in the right context you may use the two words interchangeably because they mean the same thing… it’s often a matter of personal preference. I’m a native English speaker from South Africa but currently based in Sweden, if you want to practice English please feel free to take a look at my profile and perhaps book a lesson :)

Period is like a moment in time that could be a decade but era is like a thousand years. That's what I like to believe. As I never call the 80s or 90s an era.