I'm by no means a physicist theoretical or otherwise, so please do excuse any things that I may be ignorant of (likely a very long list).
If by whatever mechanism a traveller were able to travel back in time from a point on the earth and say you were able to travel back 100 years in time.
Would there be anything to observe at all? Would the earth even still exist at that place as an event in space and time ? Not that it would disappear or vanish mind you but would it be somewhere else assuming that the traveller is the one moving back in time and not everything in the universe? If there was nothing observable , would it be the result of only having moved to that point in space where the earth was 100 years ago relative to where it would be today?
User John Rennie informed me that:
In physics time travel means a closed timelike curve, and while most of us believe these do not exist there's no reason why following one would make the Earth disappear.