Maybe 100 billion years ago a day on earth was 25 hours?

Do you know how long the earth has "been" around?

Agreed, my dearest friend Bacon. What if the universe as we know it was created by a bratty Japanese high school girl three seconds ago? It may seem as if it were long existing to us, but how do we know this for sure? According to Descartesian logic, "we think, therefore we are"; but how do we confirm everything we see before us is real and true? Could the memories of our long past have all been fabrications, and the world was set into motion only just now? And exactly how do we know we aren't just clowns wandering around the edge of a cliff?