1.Why does Bostrom say that discovering the fossil of a complex animal on Mars would be, in his words, "a crushing blow"?
2.According to the essay, what exactly is the Great Filter?
3.Someone argues: "Intelligent life arose here on Earth, so it must arise easily on lots of planets." How does Bostrom answer this?
4.Bostrom writes that it would be "great news to find that Mars is a completely sterile planet." What does sterile mean here?
5.Why does Bostrom reject the "zoo hypothesis" — the idea that advanced aliens are watching us but deliberately staying hidden?