Even as we are acquiring ever more extraordinary knowledge, we are storing it in ever more fragile and ephemeral forms. If our civilization runs into trouble, like all others before it, how much would survive? Post-catastrophe, the lack of resources -- of people, expertise, equipment -- might be a far bigger obstacle than the physical loss of data. And resources are likely to be scarce. Restarting an industrial civilization might be a lot harder the second time around, because we have used up most of the easily available resources, from oil to high-grade ores.