. >> stephen: inhabitable mantle. >> if you take a slice that's the whole thing, it would be something like 10 to the 23rd kilogram. the whole rert is something to the 24th. >> stephen: i was very close. i had 10 to 292nd. >> yeah, but-- . >> stephen: right there, okay. >> but. >> stephen: all right, that's good enough. i know you don't mean to educate us. but could you incidentally through humor and through your drawing, could you incidentally educate like quides about science and math? >> yeah, well that's actually how i got started doing this was i taught a class at mit for a weekend and they have a program where you can come in and teach a bunch of high-school students on any subject you're interested in. there's no like checking credentials or anything. and so -- . >> stephen: really, and they just trust high school aged children with men who come in with no credentials. >> yeah, i had a couple friends teaching class, one doing operating system design, another root beer taste. and i said i will teach a class on the fisks of energy. because that was something i had been studying an