The above question came up in conversation with Michael Vassar and some other nerds in New York City yesterday (before I went with relatives to see Gimpel Tam, an extraordinarily dark and depressing musical performed entirely in Yiddish). Look, I know a massive black hole would swallow the earth extremely quickly, and I also know that a microscopic black hole would quickly evaporate as Hawking radiation. So suppose we chose one of intermediate size so as to maximize the earth’s survival time—how long a time could we achieve? (Does the answer depend on the viscosity of the magma or whatever else is in the earth’s core?) Sure, I could try to calculate an answer myself, but why bother when so many physicists read this blog? Pencils out!