anthat caris rioactive. and that carbon emits a beta particle. could you tell me what is left? some people can. some people can't. most of you, of course-- begins with a c. can't. the shorter version of c. check your neighbor. what are the numbers gonna be, gang? what's the number gonna be over here? - seven. - seven? - is it seven? - yeah. - if it's seven, does it check? - yeah. seven minus one is six. what's seven? - nitrogen. - nitrogen. - what do we got for up here? - 14. what goes around comes around. nature is cyclic, gang. you started of nitrogen, ick, boo you end up with nitrogen. but not right away. not right away. the half-life of that reaction is 5,730 years. t, the radioactive half-life is 5,730 years for carbon 14 to decay back into nitrogen. that means this. everyone take a breath. well, you don't have to. it's all right. come on, here we go. ah, you know what you breathe in? - air. - some co2. now, you think all that co2 is c12, right? beginning with a w. some carbon 12. so as soon as you take a breath-- [makes sound] --you blow right back out again, right? but i