Apocalyptic and post-apocalyptic fiction is a subgenre of science fiction, science fantasy, dystopia or horror in which the Earth's (or another planet’s) civilization is collapsing or has collapsed. The apocalypse event may be climatic, such as runaway climate change; astronomical, such as an impact event; destructive, such as nuclear holocaust or resource depletion; medical, such as a pandemic, whether natural or human-caused; end time, such as the Last Judgment, Second Coming or Ragnarök; or more imaginative, such as a zombie apocalypse, cybernetic revolt, technological singularity, dysgenics or alien invasion.