It all seems to conveniant to me.
Lets assume for a minute.
Human forms inhabited a planet, say in Orion, thousands of years ago. This planets resources had been depleted. (Sound familiar).
Space travel and relocation was not only a possibility but a neccesity.
Scouts are sent out to find a possible new home, and they come across this wonderful plant, now known as earth. Its gravity is a bit strong and its
covered with neanderthals, but beggers cant be choosers.
So heres the plan.
They relocate to Earth.
Spread out across the contintents building monuments, reminders and star maps to remember the way home when they have depleted Earths resources in a
Hopefully then their origional planet will have healed its wounds and be able to sustain life again.
Clues where left around the planet to assist future generations in technological advances.
Maybe time set to be found in order at set periods in the future.
Remember if you see a sketch or drawing of something that interests you, you will try and mimic it. (Flying machines etc.)
There are periods in history that are technological explosions.
Example - Industrial revolution.
We cannot deny, even if the truth is suppresed, that there are dated artifacts that dont fit our ideals of history.
The Baghdad battery for one.
Its also strange that every advance we take in technology more resources are depleted.
This is forcing us to look for alternatives.
These alternatives will probably form the basis of new means of travel, say hyperdrives, that will allow us to explore space and find a new home.
Again sounds familiar.
Now say that the perfect planet for us to inhabit is found in Orion.
Now that would be strange.