A New Dark Age?

Any good writing on history will include a mention of what sources the author had available and what sources are missing or destroyed.  History has been plagued by these lost sources. 

An accurate portrayal of Robin Hood?

Were Robin Hood, King Arthur or Jesus real people? Composites of a few people? Entirely made up? Historians have no real idea because no definitive sources.  There are sources written afterwards, sources that contradict each other, sources written by people with clear agendas to make these people seem like heroes or villains.
One of the first things many family or friends did upon the death of a person was to burn any documents that could prove embarrassing to their memory.  Anne Frank's father edited her diaries before publishing them, luckily he kept the original manuscript and a complete version was published in 1950 but thousands and thousands of documents weren't that lucky.
Many documents simply don't survive the ravages of time, I just finished reading a book about the search of the Northwest Passage which ended with a description of the search for Franklin's lost expedition which cost over a hundred men their lives.  We still know very little about his last trip because the documents didn't survive, ship's logs were meticulously written and usually guarded by captains with their lives however in the end Franklin's were destroyed by weather, or perhaps were given to Inuit children as toys.

I could go on and on but I haven't mentioned the actual reason I started writing this.  It is something that I wonder about occasionally.  We have so much information floating around, some of it important, some of it utterly banal.  You may think this would be a boon for the historians of the future but maybe not so much.  Lets say you had put a touching letter to your grandchild on a floppy disk and buried it in a time capsule so they could read it on their wedding day, would they be able to open it? Would they even know what it was? 
One of the reasons we call the Dark Ages the Dark Ages is because we know so little about that time, we picture it as a backwards time where people were poor and miserable and dirty but they fact is we don't know what their lives were really like.  A lot of people were illiterate and a lot of what was written down is missing.

What will the historians of the future know about us? What will the have access to? What will survive? What judgments will they make about us with the information they have? I wonder if a future historian will pour over my twitters and try to make sense of what the world was like? God help them.