Having now officially completed my astronomy course (i.e. received final grades and all) I can now post the second and final dissertation I wrote for the course (I posted the first one some months ago). Given the theme, this time it was much harder for me to ‘keep the philosophy at bay’ and to write a proper scientific review. Together with theoretical cosmology (and in some ways even more than that) astrobiology is a field which is very much open to cooperation between scientists and philosophers. So again, I hope someone might find it interesting.