That is the prior assumption for archaeologists. For a long time, it was simply treated as "obvious" and there wasn't a well-established way to estimate tempora

That is the prior assumption for archaeologists. For a long time, it was simply treated as "obvious" and there wasn't a well-established way to estimate temporal ranges from dated finds. Now people use a technique called Optimal Linear Estimation that was originally invented by paleontologists to estimate extinction dates.