How do you know that what you know is true?

I’ve been told that every seven years, human knowledge doubles.

In researching that I also read that online information doubles every six months. And IBM claims that by 2010 the amount of digital information in the world will double every 11 hours. 

On the first day of my 7th grade history class, my professor assigned an essay with the prompt - How do you know that what you know is true? It’s difficult these days; there’s just so much noise.

Notes