Or far more likely than “space aliens” is a previous Earth civilization or several previous ones, all of whom left Earth for their own reasons, returning once in a while. 4.5 billion years is a long time and much could have/did happened.
Consider man’s current footprint on the earth.
Its much bigger than the black mat left by comet that ended the dinasaurs.
An earlier such civilization would have also left a footprint.
No footprint has been found.
That said, current archaelogy is placing the beginning of settled life in the middle east both before and after the big comet strike that caused the younger dryas 12k years ago. Right after the earth warmed up after the younger dryas 1000 year winter, the first big megalith was built at catalhoyuk in turkey in about 9000 BC. Anther 5 millenium passes of increasingly sophisticated village life occured before the ancient sumerians built their ziggaurats.