"Because there's no f-ing carbon in it!"

Carbon dating isn't used, and can't be used for dating rocks. Why, you ask? Because in general, rocks contain only a trace amounts of carbon. Most carbon dating is done on plants that draw carbon directly from the atmosphere, and thus drawing upon relatively well-known reservoirs of C-12 and C-14. You can't date things older than ~60 thousand years because the half-life of radiogenic carbon is only ~5000 years. Similarly, you also can't date rocks that don't have carbon. Or as this YouTube video by Potholer54debunks so eloquently states, "Because there's no f-ing carbon in it!" An instant classic, I say.

http://www.youtube.com/user/potholer54debunks?blend=1&ob=4#p/u/10/QbvMB57evy4