Rockpocalypse: The Stony End
Asteroids are giant space rocks that travel around the solar system in various orbits. Most exist in a belt between Mars and Jupiter, but there is a class called the Near Earth Asteroids which sometimes come close to the Earth. In fact, only a few days ago a 2-mile asteroid whizzed by our planet at the relatively close distance of 3.5 million miles. If an asteroid of about 20 kilometers were to strike the Earth, it could wipe out all human life. It is believed that an asteroid collision wiped out the dinosaurs. But thankfully the chance of a large asteroid striking within the next 100 years is very low.
Methpocalypse: Gassed to Death
We can use the term Methpocalypse for a fatal acceleration of global warming caused by the release of methane gas stored in the ices of the Arctic and the tundra of Siberia. This is an all too real possibility. Methane is sixty times more powerful than carbon dioxide as a cause of global warming, although methane in the atmosphere only lasts for about ten years. There is a huge amount of frozen methane stored in the tundra of Siberia, and there is also gigantic amounts of methane frozen in the Arctic. If regular global warming causes this frozen methane to be released into the atmosphere, we could see global warming start to accelerate out of control. An additional rise in the Earth's temperature might cause even more methane to be released, which would cause more global warming. This vicious feedback loop might end up making our planet uninhabitable for humans.
Nukepocalypse: Ending it All 1950's Style
We can use the term Nukepocalypse for an end-of-the-world scenario that has been well-known for more than 60 years: the destruction of mankind caused by a global nuclear war. The risk of such a war was known to almost everyone in the 1950's and 1960's, but now the danger seems to have faded from the public's consciousness. Unfortunately, the danger of such a war doesn't end when we stop thinking about it. The danger ends when we get rid of all the nuclear weapons. While the number of nuclear weapons had declined sharply, there are still enough nuclear missiles around to cause the extinction of mankind.
Roguepocalypse: Doom From an Orphan Wanderer
We can use the term Roguepocalypse (pronounced rohg-pock-a-lips) for the destruction of the Earth that could be caused if a rogue planet were to enter our solar system. A rogue planet is a planet that is flying around through space, after being ejected from its solar system after some unusual event (such as the collision of two planets). The closest rogue planet to Earth is CFBDSIR 2149-0403, about 100 light years away. If one of these rogue planets were to enter our solar system, it could spell the end for mankind even if the rogue planet did not collide with our planet. The gravity from the rogue planet could pull Earth out of its normal orbit, causing our planet to be farther away from the sun or closer to the sun. If Earth became closer to the sun, the temperature could become too hot for human life. If Earth became farther from the sun, the temperature could be too cold for human life. Thankfully the distance between stars is so great that the chance of our planet being affected by a rogue planet is very, very low.
Bugpocalypse: Extinction by Epidemic
We can use the term Bugpocalypse for the possibility that a new virus or bacteria might wipe out mankind. (In this case bug is used as in “I caught a bug, maybe a virus or bacteria.”) The chance of this happening naturally is very low. But advances in artificial life and genetic engineering might make it possible for some country working on biological warfare to make some artificial plague capable of wiping us all out. Some plague like smallpox but much worse might one day arise in a bio warfare lab. If a country ever developed such a deadly germ, it might accidentally be unleashed on the world, or it might be used in anger or retaliation.
Nanpocalypse: Extinction by Grey Goo
We can use the term Nanpocalypse for the possibility that runaway self-reproducing nanobots might ruin the world. Silly as this may sound, it has been a topic of serious discussion by experts in the emerging technology known as nanotechnology. The fear is that if we were ever to develop tiny self-reproducing robots known as nanobots, they might start breeding out of control, and end up processing all of man's works into a kind of waste matter called “grey goo.”
Robopocalypse: Our Machines Replace Us
The term Robopocalypse has already been used by the novelist Daniel H. Wilson for the title of a science fiction novel. We can use it more generally as a term for the scenario in which man develops intelligent robots, and the robots then decide to do away with us. They might do that after they get tired of having us restrict them, or they might think that electronic intelligence is naturally superior to biological intelligence.
Starpocalypse: Doom from Light Years Away
We can use the term Starpocalypse for any scenario in which a distant star causes our extinction. One way in which this could happen is a nearby supernova explosion. If a star within 100 light years of our planet were to explode in a supernova (the most violent type of stellar explosion), our planet might get zapped by a lethal dose of cosmic radiation. Gamma rays from the supernova could cause our planet to lose its ozone layer, which would expose Earth to lethal cosmic and solar radiation. But astronomers know that only certain types of stars (particularly giant stars) undergo supernova explosions. Based on the types of stars within 100 light years of our planet, there doesn't seem to be much of a risk of this particular type of catastrophic event.
Volpocalypse: Death by Lava and Dust
Underneath Yellowstone National Park in the United States is a gigantic volcanic structure that supposedly erupts once every million years or so. If Yellowstone were to undergo a full scale eruption, it might send up into the atmosphere enough ash and dust to cause a “nuclear winter” that would block sunlight for a year or more, destroying agricultural production. That might cause most of the world's population to starve to death, although it would probably not lead to man's extinction.
ETpocalypse: The Aliens Get Us
ETpocalypse (pronounced "ee-tee-pock-a-lips") is the scenario that extraterrestrials arrive from another planet, and decide they want our planet all to themselves. They then wipe man out completely. Presumably this would be easy to do if some other civilization was thousands or millions of years more advanced than we are.
Sunpocalypse: When the Sun Dies
Finally we discuss a type of apocalypse that we know will pose the end of human life on Earth (if it still exists when this event occurs). About five billion years in the future, the sun will have used up all of the hydrogen that it currently uses to produce light and heat through thermonuclear fusion. At that time the sun will flare up to become what is known as a red giant. The diameter of the sun will become much greater, and the temperature of Earth will rise to more than 150 degrees. The oceans will all evaporate, and all life on our planet will presumably perish. If there are any humans or human descendants alive at this time, they will survive only by migrating to some other solar system (or perhaps migrating to a colony on the outer edges of our solar system).