"That's why they're called revolutions. They always come round again."
Every 1,000 years, the Powers That Be
arrange a major event. It may be The End of the World as We Know It
(and its subsequent rebuilding) or merely a threat of one, a mass mind-wipe, or it may be something that involves a Chosen One
, who is supposed to do something predefined, or the whole effort will derail.
The reasons why they do so varies greatly. It may be necessary to keep a Sealed Evil in a Can
dormant, or to uphold the Balance Between Good and Evil
or the Masquerade
(in other words, to prevent either side from winning too much or knowing too much). Alternatively, the organizers may do it purely for entertainment
, or it may "just happen" Because Destiny Says So
, with no further explanation. It doesn't necessarily have to be a precisely regular event - what's most important is the existence of a system with wide negative effects but also a good reason to be kept up, which goes unchallenged (or all challenges to it fail) until the heroes show up.
The bad news is, last time this happened was exactly 999 years and 360 days ago, and our heroes become involved, usually against their will, in the next iteration. Two outcomes can possibly occur: either they accept
(or are forced to accept
) their destiny and continue the cycle, or they reject it. The former case is risky because the audience are likely to dismiss the story as "pointless"
. In the latter, what happens next depends on the work's position on the Sliding Scale of Idealism Versus Cynicism
, which can mean either a happy ending, in which the cycle is broken for good, or a Downer Ending
. If multiple factions want a say in this process it can result in a Tournament Arc
or There Can Be Only One
Regularly Scheduled Evil
is a special case of this. Not to be confused with Cycle of Revenge
(though such a cycle is often called this, and with good reason).
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Anime & Manga
- In the comic book Mini Series Seven Soldiers, the Sheeda wait until mankind has reached a certain point of technological advancement before swooping down and harvesting their technology, effectively 'resetting' mankind and forcing them to start from scratch.
- After multiple storylines in The Mighty Thor involving someone attempting to trigger Ragnarök, it was established that Ragnarök is a cycle that has occurred multiple times in Asgard's past.
- In The Matrix trilogy, the Machines destroy Zion and (with the help of The One) reboot the Matrix every 100 years, to prevent the Zion "anomaly" from expanding uncontrollably. Neo is the first One to refuse to participate in the reboot, and later strikes a peace agreement with the Machines, saving Zion and ending the war.
- The movie The Dark Crystal had "The Great Conjunction" of the world's three suns, the time of prophecy when a destined, Last of His Kind hero is fated to restore the balance of the planet. It's noted in the film that every time a Great Conjunction rolls around, something big happens. This can be good or bad (the last Great Conjunction had the Dark Crystal being broken, thus starting everything in the movie). Eventually, the "something big" might even be the destruction of the entire world.
- The Fifth Element: an evil planet comes to life every five thousand years and attempts to collide with Earth, causing a chain reaction that would destroy all life in the universe. This can only be prevented by the use of an ancient superweapon and, in the film, The Power of Love.
- Versus: Prisoner, The Man, The Girl and the Yakuza are parties to a never-ending battle raging on through untold centuries. The main three players (The Man, Prisoner, The Girl) don't change in essence, but may change sides (the Hero may be the Villain next time and vice-versa); in all cases, the duel repeats endlessly.
- The Lord of the Isles series by David Drake. The powers are building to a thousand-year peak. Ordinary wizards find themselves with out of control powers that brought down the kingdom during the last peak. In its current shattered state another such error will destroy civilization.
- In Stephen Baxter's novel, Manifold: Space, the Galaxy works on a so-called "Reboot cycle", where life, intelligence and civilizations appear practically everywhere in some form (that is, even as lichen colonies on the surface of stars, or giant crabs living of rogue planets). These civilizations advance, and begin a bubble-expansion at increasing speed. From there, the bubbles either collide resulting in omnipresent wars, or collapse in on themselves when they hit the lightspeed barrier and can no longer sustain the expansion. These events lead to massive technological backsteps and extinction events (which is why everyone is bound by lightspeed; nobody has time to get really smart). In addition to this, each cycle ends with the Galaxy getting sterilized by colliding neutron stars releasing massive amounts of radiation, blasting everything back to pondscum.
- The protagonists actually fail to prevent the current cycle from completing, but succeed in buying some time for the next iteration of the cycle by building a massive solar sail that would stop a neutron star collision.
- In the novel Decipher, the sun reaches its peak resonance every 12 millennia, causing The End of the World as We Know It due to the solar flare from Hell. To avert it, the heroes have to reach Atlantis so it can quasi-crystallise the planet to protect against the gravity wave.
- In Stephen King's It the eponymous monster manifests itself in Derry every 27 years or so.
- In the Wheel of Time series, the eponymous Wheel is a metaphor for seven distinct ages, each of which ends after several thousand years. The last (Second) Age ended in the Breaking of the World, and the Third Age is prophesied to end similarly; presumably this happens every age. More sinisterly, Ishamael appears to have been meddling on a smaller scale this Age — about a thousand years after the Breaking, he sent the Trollocs to ravage the world, and another thousand years later he triggered the "War of the Hundred Years" by preventing Artur Hawkwing from having a living heir. (It looks as if his intent was to keep the technology level down.)
- In The Mote in God's Eye, The Moties' biology means they must have children frequently or die, this trapped them in a never ending cycle where overpopulation inevitably resulted in a world destroying war blasting them back to the stone age
- One of their enduring mythological figures is "Crazy Eddie", who is reborn (figuratively, at least) time and time again, each time attempting to bring the cycle to an end. Sometimes he's almost successful (in the sense "it would have worked but for ..."), but he's always crazy (and the "but for ..." is usually some fundamental physical constant of the universe, or at least of Motie psychology).
- In J.V. Jones's "Cavern of Black Ice," the Endlords, chaotic beings seeking to dissolve the very universe into a hell of anarchy, are locked in a dimensional prison. Every 1,000 years someone is born who, if they lose control of their mind for a moment, can unlock the prison, unless they do it in the eponymous cavern. The longer they resist the temptation to lose control, the more their body fails, until they die and in doing so unlock the prison anyway.
- Politics in Dragaera are dominated by the Cycle, a predictable sequence by which each of seventeen Dragaeran Houses takes a turn governing the Empire. Each House's members have strengths that allow it to supplant the previous one, and weaknesses which will eventually allow its successor to claim the Imperial throne in turn.
- In the Isaac Asimov short story (and subsequent novel) "Nightfall", a world with six suns, at least one of which is in the sky at all times, has five of its suns set simultaneously and the remaining one eclipsed by an otherwise-unknown moon, once per 2049 years. Since the inhabitants have never seen the stars and have no clue they even exist, the sight of the night sky causes everyone to go mad and start burning everything to generate whatever light they can, returning civilization to the stone age.
- Discworld's Death's master, Azrael, references this. "I remember when all this shall be again."
- In Frederic Brown's story "Letter to a Phoenix", the entire plot is a man telling about how humanity repeatedly destroys its own civilization and has to start anew every 30,000 years or so - therefore, while all other races reach their peaks and after that must decay and die, humanity can survive forever - thus making it the eponymous Phoenix.
- Dragonriders of Pern: The Red Star approaches Pern every 200 years and rains hungry Thread on civilization. The few occasions when it does not do this are termed Long Intervals and end up being an important clue to saving Pern from thread forever.
- Memory, Sorrow, and Thorn: The Conqueror Star is a long-period comet (at least 500 years, although it seems to vary) whose coming universally heralds the end of an empire. The story opens at the beginning of a unique cycle in which the comet will appear in three consecutive years. This is, of course, the time that the Sealed Evil in a Can Storm King chooses to make his return.
Live Action TV
- In Babylon 5, the Shadows launch a destructive war every thousand years, which the Vorlons help to put down. In the series, the protagonists object to this arrangement, and try to put a stop to it.
- Battlestar Galactica (Reimagined): "All of this has happened before, and all of it will happen again." Explained more explicitly in a few episodes as humanity creating Cylons, who rise up against them, then create organic versions who are effectively human, who then create Cylons...
- The Doctor Who audio dramas set in the Divergent Universe weave together a plot of cyclical existence: in fact, the reason the universe has no Time is because no moment has a unique existence to anchor the Time Vortex to. Or something, it's kind of convoluted.
- In the Villains And Vigilantes adventure Devil's Domain, every 666 years the Earth's dimension and Hell come close enough together for the Devil to create a bridge between them that will allow his demon horde to pour through.
- The Aurora in Magic: The Gathering's Lorwyn and Shadowmoor settings, which changes one world to the other (and the minds of those within). Its eventually revealed to be a magically slowed down day/night cycle. A side effect of it being slowed down is the transformation into a world epitomizing the light of day and the darkness of night, respectively
- Dungeons & Dragons
- Planescape setting. Every 289 years (17 cycles of the gears of Mechanus) the Great Modron March starts. It consists of a horde of modrons traveling around the Great Ring, causing devastation as they pass.
- Supplement Treasure Maps, adventure "Sign of the Times". Every 700 years during a specific astrological conjunction of planets, moons and stars the king of a desert empire will fall ill and die, and his son will take his place. The new king will become evil and cruel, raising taxes and invading other countries. Natural disasters (famine, pestilence and drought) will ravage the land.
- In the Forgotten Realms setting, the ancient elves overcame the dragons by creating the Dracorage Mythal, a work of high magic that caused all dragons on Toril to go into a primitive rampage every couple thousand years or so. The dragons losing their intelligence made them easier to beat in combat. Unfortunately in 1373 DR the lich Sammaster modified the mythal to make the rage permanent, in order to convince the evil dragons to become dracoliches (which were immune). A group of adventurers solves the problem by destroying the mythal entirely.
- Before Sammaster's meddling, the Dracorage Mythal invoked ominious astrological signs of the coming disaster — rather than simply keying the Mythal to go into active mode at regular intervals, the elves that created it keyed it to the light of a periodally returning and rather striking comet.
- In Earthdawn and Shadowrun, the Horrors return to Earth from astral space to torment and ravage its living creatures every few thousand years.
- Yu-Gi-Oh!: Sophia the goddess of rebirth created a never ending cycle of reincarnation of creation and destruction. To escape from this cycle, Sombres (Gem Knight Lazuli fused with the Constellar) and Kerykeion (Constellar Raselhague fused with the Evilswarm-infected Ice Barrier Dragons) attacked Sophia.
- The Warhammer 40,000 galaxy seems forever doomed to be ruled by a seemingly invincible empire, have it suffer a self-inflicted catastrophe which shrinks it into a shadow of its former self, and have the leftovers of that time period stick around to menace the galaxy's new caretakers. It happened with the Necrontyr, then the Eldar, then humanity's first empire, and the "modern" timeline depicts this happening to the Imperium of Man.
- Shin Megami Tensei is very big on this, given the emphasis on the Order Versus Chaos setting, the instability of Neutrality, and the constant reminder that Humans Are Flawed. Particular examples include the Conception in Shin Megami Tensei III: Nocturne, the Schwartzwelt in Shin Megami Tensei: Strange Journey, and the constant rise and fall of several of the series' gods. It's a bitter reminder that Order Versus Chaos cannot be anything except a Forever War.
- It's also a major problem for the Neutral alignment, which vows to protect the potential of mankind, as well as freedom and self-empowerment... all of which brought the End of the World as We Know It in the first place, although the natural tendency for belief to unknowingly fuel civilization-crushing supernatural entities doesn't exactly help.
- Dark Gaia of Sonic Unleashed gathers energy over millions of years, then rises and destroys the planet. This is counterbalanced by Light Gaia, who puts it all back together. Dr. Eggman's attempt to harness the energy of Dark Gaia ends up causing a smaller scale version of this in that the planet is split into floating continents, due to Dark Gaia not being at full strength thanks to the early awakening.
- In the Phantasy Star series, the Dark Force attacks the planets of the Algol system every 1,000 years. In Phantasy Star IV, this is revealed to be because an even worse entity, the Profound Darkness, is sealed behind the solar system itself, and Dark Force, the avatar of said entity, is attempting to free it. Not only that, the destruction of Parma has weakened the seal on the Profound Darkness, so now there are three Dark Forces attempting to free it.
- In Final Fantasy I the Four Fiends send the fallen knight Garland through time to become the immensely powerful archdemon Chaos. Following Chaos into the past, the Warriors discover it was Chaos who had sent the Four Fiends into the future, creating a time loop paradox. Defeating Chaos in the past breaks the time loop and the Warriors are sent back to the present, but having altered the time line nobody in the new time line has any memories of the events.
- Final Fantasy X has Sin, whose cycle is a little flexible - when destroyed, he rises again in a few years, but the amount of time he's active depends on how long it takes a summoner to perform the "Final Summoning" and defeat him. Near the end of the game, the heroes discover that the method of defeating Sin is what perpetuates the cycle - the "Final Aeon" called by the Final Summoning becomes the next Sin. This is because Yu Yevon, the local deity, uses Sin as his vehicle; destroying him breaks the cycle for good.
- Tales of Symphonia has a similar situation, although it isn't clear if it's quite as regularly timed as most others.
- It's supposed to be. The Chosen is sent on his/her journey to supposedly reawaken the sleeping Goddess; doing so will revive the land and banish the evil Desians. What it's really doing is controlling the distribution of the remaining mana and preventing anyone's technology from getting to the point of large-scale, advanced war. It's supposed to happen at a fairly regular rate, but thanks to the Renegades killing a Chosen before the journey was completed, Tethe'alla's technology was allowed to get far more advanced than it should have.
- That world has a larger scale vicious cycle going as well. First, magitechnology is developed. Then, they develop a Mana Cannon. Use of the cannon uses up so much mana that supplies run low, chaos ensues, war escalates due to the combination of scarce resources and advanced weaponry, and humanity is thrust back to the dark ages, often with the help of an external force (usually malicious angels, although at least one meteor). Then, after a thousand years or two, people exploring ruins begin finding out about this neat thing called "magitechnology"...
- The latest story intel on the Starcraft series (mainly the "Dark Templar" book trilogy) posits that the Xel'Naga are not merely a superadvanced civilization whose experiments with creating the Zerg and Protoss failed miserably leading to their extinction. Rather, both the Protoss and Zerg are exactly what they were required to be, and in time the two species would have come together to create the new iteration of the (essentially godlike, "star-forging") Xel'Naga, as part of a cosmic cycle stretching back to the dawn of time. The current cycle never came to completion as intended, however, because someone interfered with the Zerg's genetic programming, making them savage and all-consuming, as a first step to breaking the cycle and ending the Universe.
- The eponymous castle of the Castlevania series of video games, as well as its lord, Count Dracula, reappears every 100 years in a different form. In fact, one of the major plot points of Castlevania: Symphony of the Night is that Castlevania's latest appearance is way ahead of schedule.
- Castlevania II Simons Quest revolves around the player having to revive Dracula ahead of schedule in order to kill him again, in order to break a curse he put on Simon Belmont for defeating him.
- And the there's Castlevania: Aria of Sorrow and Castlevania: Dawn of Sorrow, where Dracula was finally killed for good. But apparently the world needs a Dark Lord, so now all sorts of lunatics are trying their damnedest to become the new Dracula.
- Castlevania: Portrait of Ruin is another one that interrupts the vicious cycle. With the onset of World War II, a squatter named Brauner used all the hatred and torment felt by those killed in the War to call forth Castlevania and usurp its power for his own misanthropic needs. Because of this, the Belmont Family isn't even allowed to touch the sacred Vampire Killer whip until its next scheduled appearance in 1999.
- The four Sinistrals, villains of the Lufia series, are reborn every 100 years... a cycle which can only be broken if Erim, Mistress of Death, is the last one killed. In the first game (second chronologically) she's your childhood friend. Guess what you don't do when she's the last one standing? Cue Lufia 3.
- Mass Effect's plot revolves around this. Archaeologist Liara T'Soni talks about clues she has found during her research that indicate that every time a civilization has reached a certain level of technological development, it has been violently destroyed, and the next civilization has been founded on technology scavenged from the ruins. Commander Shepard eventually discovers that mechanical Eldritch Abominations known only as the Reapers show up every 50,000 years or so to "harvest" the galaxy's sentient life into extinction. Sovereign, the vanguard of the next Reaper invasion, tells Shepard that they have done this more than once. The game's storyline revolves around Shepard's efforts to prevent the cycle from recurring again.
- It gets even more frightening in Mass Effect 2 as Shepard finds out that the cycle is basically the Reapers' method of reproduction, melting down organics into an organic metal to create more Reapers.. And to make things even worse, we also find out that they've been doing this for AT LEAST 37 million years and almost definitely longer than that. In other words the cycle has repeated itself around at least 740 times.
- Many of the abandoned/uncolonised planets in the game have flavour text. In quite a few of them, it will say: There is evidence that sentient life once inhabited this planet. They were obliterated by a sustained, organised and totally destructive orbital bombardment. Every one has the estimated date of the destruction as a multiple of 50,000 years.
- In Mass Effect 3, we find information that furthers this theme: The Reaper on Rannoch states that the cycle is essential to the survival of organic civilizations, and suggests that there is a higher purpose to it than Reaper reproduction. On Thessia, we find from a Prothean VI that the cycle is more profound than previously thought. Each iteration brings forth the same conflicts and notions: discovery of the mass effect from previous civilization, wars of organics vs their synthetic creations, galaxy-spanning empires, splinter groups trying to dominate the Reapers rather than destroy them, and attempts to deploy the Crucible. The Protheans concluded that these occurrences are far too common to be mere coincidence, and suggest that the Reapers, rather than perpetuating the cycle, are only the servants of a higher power.
- In the computer game Myth: The Fallen Lords and its sequels, it is stated that King Alric and Balor are nothing more but the latest puppets of the Vicious Cycle of destruction that repeated itself at least three times before. Every five hundred or thousand years (depending on what interpretation you want to believe), Mount Tharsus erupts, and the Leveller arises far in the east. He then leads the armies of darkness to lay waste on civilization. Then, after a similar period of suffering, a hero of light arises to take down the Leveller and bring about a new 500- or 1,000-years golden age of humanity, before vanishing mysteriously. Sounds bad? That's not all. In truth, every hero who managed to defeat his age's Leveller is doomed to be eventually corrupted into becoming the next Leveller, destroying everything that he created, and bringing a new age of darkness. Thankfully, the games imply that events in the previous iteration of the cycle may have allowed Alric to break the cycle for good, or that Soulblighter's actions in the sequel may have resulted in this. We don't know for certain, though.
- Sid Meier’s Alpha Centauri uses this one nicely to explain why the game ends after 500 turns. Turns out every 100 million years, Planet's native life grows into a full-fledged, planet-wide hive mind, but the growth is so explosive it ends up eating everything on Planet and thus destroying itself. When the UN Unity arrived there, it's already been 99,999,500 years since the last outgrowth, and humanity has just 500 years to stop this cycle! What a pisser! There is also some implication that the thoughts of the human colonists are playing a role in awakening Planet and pushing it towards the end of the current cycle faster than it normally would.
- The Alien Crossfire Expansion Pack introduces the descendants of the Precursors that created Planet. It is also mentioned that a previous attempt by the creators to activate the final stage of the "Flowering" on a planet in Tau Ceti resulted in The End of the World as We Know It for them, with their descendants losing much of the knowledge their ancestors had. Presumably, similar catastrophes resulted from the other four experiments. Chiron is slecifically called by the aliens "Manifold Six". One of the factions wants to use the Flowering to attain godhood at any cost, while the other one wants to maintain Planet's self-destructive cycle, avoiding another Tau Ceti disaster.
- killer7 reveals at the end that Harmon and Kun Lan play their game against each other every century or so; no matter who wins their previous match, the game starts again in due time.
- Septerra Core subverts the trope somewhat in that the prophesied date on which all of the planet's layers go into a position that allows access to the core is still many years away. Drama is provided by the antagonist destroying layers and messing with the planet's clockwork so that he can access the core during his lifetime.
- The Elder Scrolls
- The Elder Scrolls IV: Oblivion has this in the form of Sheogorath. By the time that you're at the end of the main questline of the Shivering Isles, you learn that Sheogorath, the Prince of Madness, is really the God of Order, Jyggalag. A curse was placed upon Jyggalag, turning him into Sheogorath. Sheogorath then turns into Jyggalag every 1,000 years, and Jyggalag tries to restore his realm back into order, but doesn't have enough time to. The player, however, has the chance to end this cycle forever.
- The Elder Scrolls V: Skyrim reveals that the universe itself runs on this, with Alduin eating the world and Akatosh renewing it every few thousand years. In the current kalpa, the ancient Nords disrupted the cycle by using an Elder Scroll to cast Alduin several thousand years forward in time. It's implied that this is all the player does by defeating Alduin.
- Every 60 years there's surge of death in the outside world, and since Death is The Slacker Gensokyo gets lots and lots of flowers everywhere, because the spirits have no other place to go.
- Youkai are required to attack humans and cause incidents, because youkai depend on humans fearing them and would disappear if they didn't, while of course humans defend themselves and embark on youkai exterminations to keep themselves safe and stop the incidents; it's Inherent in the System and no-one has any idea how to stop it. Fortunately in Gensokyo the Spell Card rules mean the fighting is entirely non-lethal, and the combined team of Reimu and Yukari ensure that most incidents are inconvenient instead of catastrophic.
- Dragon Age II is built on the Vicious Cycle between mages and the templars meant to keep them in check. To keep them in check, the templars lock mages away in towers and generally treat them as less than human beings. To break this oppression mages turn to Blood Magic. This causes the templars to become more oppressive and by the end of the game both have reached the breaking point and the world is about ready to go to war between the mages and templars. Which side exactly started the cycle is never answered and aids the game's Grey and Gray Morality.
- The Grail War in Fate/stay night occurs every 60 years, when there is enough magical energy in Fuyuki to activate the Grail. The system was arranged many years ago by the three mage families in order to determine the Grail's possession. The thing is, the war was supposed to have ended on the fourth iteration, but it's eventually revealed that the process merely sped up, allowing the next Grail War to start fifty years early. The Grail War system was eventually dismantled in the Heaven's Feel route.
- The Legend of Zelda's Hyrule suffers this chronically, albeit not on a very tight schedule with Ganondorf/Ganon being repeatedly sealed and escaping or dying and reviving/being reborn exactly the same. Even when Ganon doesn't show up, another powerful demon will emerge to cover for him due to Demise's Curse.
- In Monster Girl Quest, the human goddess, Ilias, has forbidden sexual intercourse with monsters. Seems fair enough, right? Well, all monsters are female, so if human males follow Ilias' commandment, it's genocide. So all the surviving species have adapted to raping human males every chance they get. Which, of course, leads the humans to believe all monsters are evil, which makes them more inclined to obey the commandment.
- This is a major plot point in Dragon's Dogma. Every several hundred years, the Seneschal unleashes the Dragon, whose goal is to both bring the end of days, and to create an Arisen that has the ability to grow strong enough to face the Dragon. If the Arisen fails, the Seneschal supposedly recreates the world and begins anew. If the Arisen succeeds and the Dragon is killed, the Arisen is given the Godsbane sword and slays the Seneschal with it, effectively becoming the new Seneschal who then creates their own Dragon, and the cycle begins anew. However, when your Arisen kills the Seneschal, they instead choose to turn the Godsbane on themselves, breaking the cycle for good.
- In Dark Souls II we learn that the world have been stuck in a continuous cycle since the events of Dark Souls. Kingdoms and Empires will rise to power before the undead curse appears again, making the entire world extremely hostile. At some point after the curse appear, a chosen undead appear, and begins slaying the inhabitants of the lands. The previous monarch during was King Vendrick, who took the throne but refused to sit on it. He and his brother Aldia tried to find a way to stop the cycle permanently. It did not work as intended. When the final boss is defeated, the chosen undead sits on the throne and becomes the monarch of the next kingdom. Dialogue with Vendrick in the Memory of the King reveals that he did find a way, though by the time he did he could no longer do it himself: master the power of the First Flame and the Dark Soul.
- The calendar in Wapsi Square puts the world through cycle after cycle, resetting time every time it hits 2012. One character retains her knowledge through all cycles, and has seen over 80,000 years worth of this cycle.
- It's eventually revealed in Cucumber Quest that, while the Nightmare Knight is indeed the previously stated 50,000 years old, he's actually been revived before the current story. Like, every 5,000 years or so. As it turns out, he's just really hard to kill, and someone eventually gets around to freeing him before they can reseal him. As with most things in the comic, this is less due to the Powers That Be having some agenda of balance or being evil and more due to them being mind bogglingly incompetent.
- Whateley Universe
- A mundane version of this happens with no less then three villains! Deathmaiden dies and returns almost exactly 20 years, and Diane Castle quotes this trope.
- The Necromancer 'arranges' a death every so often, only to return under a new ID. Furthermore, Deathlist, the rival of the Principal, always pulls a Villain: Exit Stage Left, only to return an indeterminate amount of time. These two may fit another trope as well.
- Ice Ages happen every once in a while. It always brings a massive extinction wave and the birth of new species.
- The fossil record contains evidence of multiple mass extinction events which may or may not be periodic. At one time there was a theory that these were caused by a red or brown dwarf companion star dipping through the Oort butt every 26 million years or so and sending showers of comets into the inner system. (In case this is worrying you, the most recent event was about 11 million years ago, so we've got a little time yet. Also, over the past decade or so sky surveys have all but ruled out the Sun having a companion star, even a brown dwarf one.)