Apocalyptic and post-apocalyptic fiction are genres of speculative fiction in which the Earth's civilization is collapsing or has collapsed. The apocalypse event may be climatic, such as runaway climate change; astronomical, an impact event; destructive, nuclear holocaust or resource depletion; medical, a pandemic, whether natural or human-caused; end time, such as the Last Judgment, Second Coming or Ragnarök; or any other scenario in which the outcome is apocalyptic, such as a zombie apocalypse, AI takeover, technological singularity, dysgenics or alien invasion.