Oldest Homo sapiens fossils ever found push humanity's birth back to 300,000 years. Digging on a hilltop in the Sahara Desert, scientists have found the most ancient known members of our own species, undermining longstanding ideas about the origins of humanity. Source 5o.
Considering how little remains after merely a millennia, I'm surprised archaeologists were able find anything identifiable as human. That being said, this evidence gives more proof of our long-term residency on this planet. 4 billion years old, Earth might have had many sentient life forms on it, that lived, died and all evidence was destroyed. Wouldn't it be interesting if we found a half million year old vault that contained records from some species from long ago?