What kind of time frame would be required for that (and all the other evidence) to become uninterpretable - knowing we did exist, but not much more. Is there a

What kind of time frame would be required for that (and all the other evidence) to become uninterpretable - knowing we did exist, but not much more. Is there an amount of time where there'd simply be no evidence at all? Edit: Found this which I guess is our limitation at least, though perhaps not our successors. The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old! Cyanobacteria are among the easiest microfossils to recognize. http://www.ucmp.berkeley.edu/bacteria/cyanofr.html http://www.ucmp.berkeley.edu/bacteria/cyanofr.html