I believe Intelligent Life has visited earth already, but not sure if they're among us! 
(Just saying that so I can trust people)
There are many historical clues about Aliens coming to Earth, but I'm very sceptic when it comes to those things.
Yes, I think so too, and all the ancient wonders (that are the structures) of the world are yet to be puzzled out as to how they could be built. All of them are beyond what engineers can build in this day and age. ....(Just saying that so I can trust people)
There are many historical clues about Aliens coming to Earth, but I'm very sceptic when it comes to those things.
There is nothing on this planet that we can't design and build, and nothing here that we didn't design and build.