In about 500 years, after we've long since outsmarted ourselves into nothingness and Aliens come checkout what's left of planet Earth - they'll find Google's data centers.
Whatever security and encryption measures Google put in place to protect the data, they'll find amusing for the second or two that it takes to override them. The Aliens are smart like that. They managed to fly to Earth, afterall. They managed not to outsmart themselves in to nothingness.
It will take the Aliens another couple of seconds to sort out the data and process the yottabytes of emails, blogs, photos, videos, and whatever else we've come up with. From this information, they'll glean a mildly useful picture of who were were. Silly, cute baby videos. Flame wars. Dubious email forwards.
That will be our legacy to the Aliens.
I hope we confuse them so much, their buggy eyes pop.
Or... maybe the robots will have already deleted all human data:
