There are some questions for which the answers we may never get..not in this lifetime at least. What was God planning? God alone knows! We Muslims have a word for this "ghaib" or unknown/hidden facts that God alone knows.
As for man's existence years and years ago, of course there are evidences via fossils, texts, discoveries of ancient things, etc. No one can deny this! But exactly how long has it been since Adam(Peace be Upon Him) this is what no one can say for sure with factual evidences.. at least not yet!

Again to me this is all not as important as my wondering where and when will it all end and where will we all end up when it does!