Bittertruth you can never go back in Time. It violates the laws of Physics. It's called the grandfather paradox or butterfly effect. Time travel (in reality) is very different than what most people think it is. 
I don't believe that humans in the past were advanced. Of course they had good imagination based on what they saw and percieved at that time (Like they saw birds and thought of aeroplanes etc). Hell it was somewhere in 18th century when they found out what's was fire. Before that they thought it was one of the elements. So you are right in the sense that anything extraordinary (Like a comet or something would be percieved as something devine during ancient times) 
I agree that science is constantly evolving and for most practical purposes, the earth is round (If you look from space it is round). It's how and where you present the argument. 
Anyways going back to the topic, I don't know if there's supernatural. There could be since it's can't be disproved. But it's also possible that the mind is playing games on you. Whatever you choose to believe. But there's always an explanation to something and striving to find them is what makes humans intelligent. If you do hear a ghost, don't just run away but try to find if that's really a ghost or a racoon.