I think Randall Munroe (the author of XKCD) spends a lot of time researching his comics, so it's probably right about the order of magnitude. In general, he li

I think Randall Munroe (the author of XKCD) spends a lot of time researching his comics, so it's probably right about the order of magnitude. In general, he likes to play with facts exactly like this one: transform some interesting science fact (speed at which tectonic plates move away from each other) into unrelated comparison just for fun. I am sure he has calculated the rough surface area between them using geological data (putting imaginary borders on top and botton), then redone it accounting for movement in say 60s, then looked at how much 12pt text fits on a page (maybe inspired by that "weight of bytes" post also appearing on HN?), and got the rate of expansion in 12pt words per second :) Being a scientist, he also only kept one significant digit proclaiming it to be 100 wps (anything else would indicate much smaller error which would be lying). If you like that kind of thing, XKCD is a lot of fun. It is a lot of fun :) Basically, this is all to say that he has probably checked this himself: don't take it as gospel, but you can likely trust it as much as anyone else without checking it yourself (or having a bunch of people independently verify it).