I could be wrong but if you used paper from the 70s I believe the carbon dating will tell you it's from the 70s even if it was drawn yesterday. I'm less certain about pencil.Ghengis John said:I never said it could tell us the difference between 1972 and 1975, I said we could use it to tell the difference between something made in 1973 and 2011.
Even then I'm not sure if you could get a really accurate result. You could test the paper composition but all this can do is debunk the claim if it's new paper, if the paper is from the 70s it just tells you when the paper was made, not when the picture was drawn.
I've read a little about dating inks but nothing about pencil so I don't know if there are solid options here or not.