I wouldn't go as far to say that. Anthropology is a very inaccurate science. According to anthropologists we were only literate and building cities 10,000 years ago but within this decade we've found even older ancient cities that disprove everything we learned in the first chapter of ancient history. And in the big picture, when we look at nature's capacity to decay man made material, we can't find evidence to prove we lived 50,000 years ago but in that time, even a city like New York could be completely reduced to biodegrading material in that time frame.