Some 30,000 years ago, before writing was invented, there was one way for people to leave a record behind for future generations. They would place their hand on cave walls and blow pigments over it, leaving behind a hand print. It was a successful strategy: Many of these haunting marks survive today.

Humans 30,000 years in the future, if they haven’t yet dragged themselves into extinction, will certainly have more information to go on about us. We have become amazingly adept at recording our lives. We have built mausoleums and libraries; we’ve written historical books and compiled sophisticated ancestry records.

Most of all, a college student named Mark Zuckerberg inadvertently developed the best tool ever developed to convey our personal histories to future generations: Facebook.

Anthropologists and social historians have always struggled to tell the stories of our everyday ancestors, even those who lived only a few generations prior. Written records offer us a great deal of insight into a handful of important people, but piecing together information about ordinary people has been more complicated.

Facebook changes all that. In a little more than a decade, Facebook’s users have contributed to a massive depository of information that documents both our reactions to events and our evolving customs with a scope and immediacy of which earlier historians could only dream.

It’s hard to understate just how incomprehensibly huge this database will be. More than 2 billion people are on Facebook, and well more than half are considered active daily users. Assuming people will continue to use the site regularly, that means most of these users will document much of their lives, leaving behind photos, friendships, their likes and dislikes, and their reactions to current events.

Today, tens of millions of dead Facebook users have left behind such digital remains, but this is set to increase exponentially in the coming decades. A new paper by Oxford University researchers estimates that if Facebook stopped growing tomorrow, the number of deceased users on the site would hit 1.4 billion by the end of the century. If the site were to continue growing as it is now, that number could reach about 5 billion users by the year 2100.

Today, these ghost accounts offer a digital place for mourning and memory. But in the future, they could be a boon to humanity. Such pages could prove invaluable to historians and social researchers, who will be able to look back and see, for example, how society reacted to the Notre Dame Cathedral catching fire. They will see Donald Trump’s election and online culture wars that facilitated and followed it. And they will see lots of the cats and puppies and “Game of Thrones” memes we used to distracted ourselves from the political grind.

For future generations, Facebook will preserve images of our lives that are vastly crisper and more nuanced than any ancestry record in existence. This will offer our descendants a thorough understanding of history and, by extension, themselves. Facebook represents, as the paper’s authors put it, our “cultural digital heritage.”

“For the first time in history, we have a chance to truly democratize history,” said Carl J. Öhman, a doctoral candidate at the Oxford Internet Institute and co-author of the paper. “Now finally we have an archive that encompasses all of us — on a global scale.”

This historical potential complicates, rather than resolves, the questions already plaguing Facebook: How much privacy do the dead deserve? And how much autonomy should we expect people to have over how their accounts are managed after they die? Who will be able to curate such data, and to what degree? How do we guarantee that those who wish to be forgotten are allowed to pursue that path?

Further, how should we go about holding Facebook accountable in maintaining this data? Does it have an obligation to make sure our “digital heritage” is preserved? Or should it hand over its historical data to an independent organization for the sake of research, as Twitter attempted to do by handing its data over to the Library of Congress in 2010?

These are not hypothetical questions. MySpace deleted users’ content, including some of the features that mourners used, in a 2013 attempt to modernize the site. What happens if Facebook similarly loses its status as a cultural behemoth? If we care about preserving the incredible breadth of human history that we’ve recorded on the site thus far, we need concrete strategies to avoid a repeat of the MySpace memory hole.

This matters because, for the first time, humans have the power to leave behind far more personalized histories than any generation before them. We don’t have to rely on the recollection of our descendants for our memory to survive, and we don’t have accept that our collective experiences will fade away with time. This is our chance to leave far more than our hand prints on the digital walls of history.

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