If the means were available, we could trace our ancestry - yours and mine - back to the first blob of life-like material that came into being on the planet.
We said, there's another second gone, there's another minute and another hour and another day, when, as a matter of fact the second or the minute or the hour was never gone. It was the same one all the time. It had just moved along and we had moved with it.
My reluctance to use alien invasion is due to the feeling that we are not likely to be invaded and taken over.