The German Scholar Jan Assman writes, in his seminal Cultural Memory and Early Civilization: Writing, Remembrance, and Political Imagination about what he calls "the floating gap" in history: the 80-year mark. Events which happened up to 80 years ago are retained in living memory, which means that at any given point in time 80-year-old events are slipping out of it. Then there's history which is based on other things, such as documents, creating a memory which is different than living memory but less vulnerable to the passage of time.
Of course, there is no sudden break; it's not as if living memory is vibrant and strong until its 80th year at which point it abruptly ends. Indeed, as longevity grows, the 80-year gap may be inching up. Yet the concept is clear, and very plausible. When Abraham Lincoln spoke of the founding of the United States four score and ten years before his time, this was an event which had recently slipped beyond living memory; during WW2, Lincoln's war was also slipping out of it.
80 years ago today, Hitler came to power in Germany. As those of us who keep track of such matters know, this means that the dramatic events which led to that moment are mostly no longer living memory; over the next decade or so, WW2 itself, along with the Shoah, will inexorably pass from living memory to history. Living memory of the context of the creation of the State of Israel is already eroding. Some time next decade it, too, will end.
Archives don't create history, yet they do offer one of the most reliable tools for doing history beyond the 80-year floating gap.