There are megalithic structures all over the earth as old as 10,000 years, but they are not in good repair. Anything less than megalithic structures would not last even that long. There wouldn't be much left of anything older than that. If something happened to be living here 100,000 years ago and didn't happen to build megalithic structures, it would all be gone back to nature. If we found some fossil bones, we might not recognize them as alien, especially if they were related to us in the first place.
Yet there are fossilized footprints (dinosaurs) and other evidence of life from the past...hmmmm
Then there are these 3 interesting claims:
A 75-foot trail of human footprints have been found in Tanzania in a layer of volcanic ash, which was dated at 3.75 million years old. T. D. White in describing the footprints said, "Make no mistake about it…they are like modern human footprints. If one were left in the sand of a California beach today, and a four-year old were asked what it was, he would instantly say that somebody had walked there. He wouldn't be able to tell it from a hundred other prints on the beach, nor would you." (D. Johanson and M. A. Edey, Lucy the Beginnings of Humankind, Simon and Schuster, New York, 1981, p. 250, as sited in Evolution: The Challenge of the Fossil Record by Duane T. Gish).
Human footprints and been found in the same strata as dinosaur prints in the Paluxy River Bed in Glen Rose, Texas. The prints are within a few yards of each other, and sometimes even cross each other. Dr. Camp from the University of California and Dr. G. Westcott of Ypsilanti, Michigan have pronounced them genuine. The human footprints continue under shale that has been bulldozed away, proving they could not have been carved in the formation. (Winkie Pratney, Creation or Evolution? The Fossil Record, Pretty Good Printing, 1982).
Two fossilized human skeletons have been found in Cretaceous sandstone at Moab, Utah. The fossils were found in strata supposedly 65-100 million years before humans were said to have evolved. (Burdick, C.L., "Discovery of human skeletons in Cretaceous Formation", Creation Research Society Quarterly, vol. 10, no. 2, September 1973, pp. 109-110.)
If you believe the evolutionary path of humanity (which I don't) we certainly shouldn't have human footprints 4,000,000+ years old that are virtually identical to human footprints of today.