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On earth our continents move...real...real slow. This is of course a good thing for sentient life.

I am trying to imagine/develop a world where...things move a bit faster...ok a lot faster, but in a regular pattern that doesn't generally result in two plates ramming into each other...the idea is that the plates would be in perpetual stable motion that is fast enough for a casual observer to see it moves during the course of a day.

Think of two continents that host separate nations that are in a cyclical war. Generally their lands are separated...but every time their two plates put them next to one another they have a battle royale, then after maybe a hundred years they come back in contact and do it all over again (the time frame is flexible).

I would like the plates/continents to be as large as possible while keeping the time waited between the nations coming into contact down to <250 years.

  • Could a world such as this plausibly exist?
  • How would the plates work, would the energy created make the planet uninhabitable?
  • What would the world be like at the fault lines?
  • How large could the plates/continents be and how fast would they have to move to allow the nations to battle at least every 250 years?
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  • $\begingroup$ What sort of time frame and speed are we talking about in this question? is it several miles of drift per year? Per month? $\endgroup$ – Universalerror Jun 16 '15 at 15:41
  • $\begingroup$ @Universalerror I will generally leave that up to those answering, I would like the plates to be as large as possible while making sure these two nations come into contact at least every 250 years. (I will add that in) $\endgroup$ – James Jun 16 '15 at 15:44
  • $\begingroup$ I suddenly had this image of a shifting collage of plates. Is this something like what you have in mind? $\endgroup$ – Frostfyre Jun 16 '15 at 16:04
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    $\begingroup$ To be honest, the only way I can think to have tectonic plates in motion and not running into each other would be an artificial construct. If one plate is even slightly faster or slower than an adjacent one, you're going to have either mountains or a subduction zone. And earthquakes. Lots of earthquakes. $\endgroup$ – Frostfyre Jun 16 '15 at 16:09
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    $\begingroup$ Just put them on the backs of giant turtles that have stable migration patterns with Turtle Islands $\endgroup$ – WernerCD Jun 16 '15 at 19:25
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I'd Like to improve Amziraro's answer. Since i can't comment (and it would take too many characters to explain) i'm writing a new answer

  1. The planet must be huge (i'm thinking 2-3 times, maybe even 5 times the earth), must be covered almost entirely in water and its oceans must be very deep, like 50000 meters on average (yes, that means on average it'd be 5 times the depth of the Mariana trench but there would also be places where you can see and touch the ocean floor) to allow arbitrary sized (on both width and depth) pumice islands

  2. A long time ago there was actually a true huge continent (or more than one) but got completely destroyed by some catastrophic event (asteroids/comets/meteors...mind the plural, sudden increase of volcanic activity...you name it) which completely destroyed and scattered the land. At this point the world would be covered in dust, both in the air and floating on the sea

  3. The catastrophe resulted into extremely increased volcanic activity which released tons and tons of pumice into the water, which clumped together (in alternative the catastrophe could be the volcanic activity itself)

  4. In time, dust and other materials thrown up from the continent by the catastrophe will fall to the "ground", some dust would fall on the pumice islands, adding fertile soils, minerals in the form of dust (we can assume that either there was a civilization that mined up stuff on the original continent or that the catastrophe destroyed the continent up to its inner layers, throwing even heavy elements from the crust and the lithosphere into the air), coal (floating trunks from the original continent), and fossil fuels (water life that got trapped inside the islands).
    Taking into account both the catastrophe and volcanic activity, the planet must be very hot at this point. Water life would die and float into the island, dust-heavy rain would fall in the ocean (and into the pumice islands).

  5. Of course this means that the "surviving" pumice islands would be in such a shape that'd allow them to hold stuff inside and still float (i'm thinking plate-shaped or ship-shaped) and would need to be very big (maybe some islands would glue together to get the right shape).
    They would probably behave like icebergs (where most of the island would be underwater), and that these islands would be created millions (billions?) of years before civilizations. This might pose an issue with erosion, but we might assume that pumice would be replaced by volcanic activity

  6. Volcanic activity would stop eventually (not completely maybe, just enough to keep the pumice flow. The pumice must flow!) and the planet would cool down again and life would be allowed to thrive once more. Given enough pressure, the animals and plants trapped under the layers of dust would form coal and oil, minerals would be mixed with the soil (and if we assumed that in the earlier periods there was a lot of water on the islands too, that would generate stratification so that the heaviest elements would be in the deepest layers, effectively creating mines)

This way you'd end up with floating pumice islands that can follow the currents and support life. Some assumptions:

  • The islands never touch each other (those that did sank or merged together) as long as the currents don't change. The islands might get very close to each other, enough to be seen from a distance but not enough to touch each other. I imagine that there would be a part of the island that extends way further than the completely emerged part, creating very long and shallow shores that extend for hundreds or thousands meters

  • The islands would be "trapped" in the deepest places of the ocean since otherwise they would crash onto the ocean floor. Maybe some did and became fixed islands, while others sank

  • The pumice surrounding the islands must be very thick to prevent being destroyed by erosion and to support all the weight. Maybe someone while randomly digging managed to sunk an island by making a hole into the pumice.

  • There must be mountain ranges somewhere, or the winds generated by the Coriolis effect will devastate your planet (Dune docet), not only this, on top of that a water only world would have huge neverending waves (as seen in Interstellar), the best thing i can imagine to make things work is that this world has many oceans (communicating through underwater channels) surrounded by mountains and in these deep oceans the pumice island will float and move around in these "pools". Taking into account the long volcanic activity period, having many Mountain ranges is not that far fetched
    EDIT: You actually don't need mountain ranges to completely separate oceans, there can be few mountain ranges (just enough to block the winds and waves) and still have a fully connected and safe water world. I don't know why i didn't think of this first but yeah, that'd work too

  • Since the islands are separated you can't even assume that the civilized specie of an island is the same of the civilized specie of another island , probably the most successful civilized specie of the planet would be one that could naturally fly over long distances

I know this is still far fetched and it requires a huge amount of luck to generate such a world by chance, but well the universe is so big that it's plausible to assume something like that can happen by chance, as long as the conditions for that to happen are plausible

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  • $\begingroup$ That being said, I don't really like the "separated oceans" concept, but the answer overall is good anyway. $\endgroup$ – o0'. Jun 17 '15 at 10:49
  • $\begingroup$ Thanks (for both), I see the mountains separation as a "necessary evil" (i don't like it much either) otherwise a water world would be devastated by winds and waves. If not separation by mountains, there must be another kind of protection against these 2 issues (that is, if we want to go all scientific here, you must take into account this) $\endgroup$ – valepu Jun 17 '15 at 10:53
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    $\begingroup$ Can't you have mountain ranges on some fixed continents, without having them to completely separate the oceans? $\endgroup$ – o0'. Jun 17 '15 at 10:54
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    $\begingroup$ Yes you are right, I actually completely overlook the fact that you can have mountain ranges but they don't need to be completely closed and touch each other, there can be places where the oceans connect. My bad here. Slightly edited my answer $\endgroup$ – valepu Jun 17 '15 at 10:57
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    $\begingroup$ +1, This is a great expansion of my concept, I hope this gets accepted actually, you seem to have put more thought into this than I did! :) $\endgroup$ – Amziraro Jun 17 '15 at 11:53
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Could a world such as this plausibly exist?

Lets see...

...no. Bowlturner has the correct answer in this case. But if we do a little handwaving science based worldbuilding...

How would the plates work?

Putting on my science-handwave hat: I imagine a continental set-up very different to Earth's, in-fact, I would hesitate to call them continents. Imagine an ocean world. Almost the entire surface is covered by water except for some volcanic islands. There are hundreds, no thousands or more sub-oceanic volcanoes, which continually spew large chunks of pumice into the ocean, which float. The chunks are the size of islands By a complicated system of currents, the pumice gets carried away into two (or however many continents you want) areas of the ocean where they float together forming a huge expanse of pumice land.

At first lichens would form a cover over the bare floating rock. Later, the water will wear down the 'shore' and sand would appear. Additionally, eruptions from volcanic islands (the stationary kind) would cover the pumice land with ash, bits of rock and volcanic soil. Eventually, as birds carry seeds to the island, saltwater resistant trees (like Mangroves) would sprout and help to bind together the islands, forming a larger mass. Trees would also help for a biosphere. These would be your plates with continents.

These floating islands would get bigger and bigger, eventually becoming the size of continents. Your rival civilisations might live on each one, and the currents could shift periodically, moving closer together.

...would the energy created make the planet uninhabitable?

In this case, no. The volcanoes might be troublesome however.

What would the world be like at the fault lines?

Well, if two 'plates' met, they would probably tear chunks off each other, because they are only weakly bound by tree roots. There wouldn't be platequakes, but the jolt would probably be felt. More interestingly, if the continent floated over an active volcano the plate might tremor and split.

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    $\begingroup$ This seems far less plausible now that I have written and posted it... $\endgroup$ – Amziraro Jun 16 '15 at 16:26
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    $\begingroup$ I'd have replied saying it was impossible, you found a way to make the concept work. Good job! $\endgroup$ – Tim B Jun 16 '15 at 16:29
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    $\begingroup$ Far fetched perhaps, but I like the idea. $\endgroup$ – James Jun 16 '15 at 17:46
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    $\begingroup$ Pumice has a very low tensile strength. An island sized piece would probably break up in short order due to wave and wind action. The stuff is about as firm as a clod of dried mud. It even loses form a bit.when it gets wet, as I found with my store bought chunk of the stuff. $\endgroup$ – Oldcat Jun 16 '15 at 17:53
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    $\begingroup$ @Oldcat "saltwater resistant trees (like Mangroves) would sprout and help to bind together the islands, forming a larger mass." ;) $\endgroup$ – Amziraro Jun 16 '15 at 18:12
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The energy involved in a natural process of that speed would be immense, The energy output from a single large earthquake is terrible. So to reduce this energy generation (constantly moving at a visible pace and not shaking everything to splinters) plates would have to be pretty thin.

You wouldn't have mountains or caves more than a couple hundred feet tall and digging a basement in the wrong place might strike magma.

The crust would have to be more like melting ice in a spring lake, only the 'water' is magma. This would be a way for the continents to be able to 'float' on currents with some kind of pattern. The center of the floating islands would likely be the thickest and coolest. Larger islands would likely be thicker and cooler in the center than smaller islands. The poles might be cool enough to act as a nice temperate zone, and as the islands float out of it, fighting to get on the islands that 'behind' you might be a big deal.

Basically the planet would be 'cooling' off still. Unlikely to generate life, but a marooned colony ship might be able to survive and grow.

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    $\begingroup$ ...I sorta hate you right now in a totally respectful way because you just completely altered the world and story I was developing in my brain. $\endgroup$ – James Jun 16 '15 at 15:48
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    $\begingroup$ @James you did put the Science-based tag on it! ;) $\endgroup$ – bowlturner Jun 16 '15 at 15:52
  • $\begingroup$ How might a marooned colony ship survive if the energy involved cooks everything on the surface? $\endgroup$ – Frostfyre Jun 16 '15 at 15:55
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    $\begingroup$ On another note I guess you could always have an ocean world thats cold enough to form thick layers of ice around the poles and that has strong currents, some ice shelfs could go drifting in occasional warmer eras but retain enough of their ice until a cold era returns and you have a drifting 'ice' continent. Not sure if thats scientifically feasable but it would be an alternative $\endgroup$ – Spacemonkey Jun 16 '15 at 16:05
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    $\begingroup$ @Lohoris I had considered that, but at this point it is probably best to see how this plays out and ask a new question. $\endgroup$ – James Jun 16 '15 at 17:53
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Don't move the continents horizontally, move the sea (and the land) vertically.

A continent extends from tropical or temperate latitudes into the arctic, with the part closest to the equator covered by a shallow sea from which a few large islands protrude (much like the South China Sea, but oriented north-south rather than east-west). A short (200-year) glacial cycle (possibly caused by a remote binary companion to the main star; for example, Alpha Centauri AB orbit each other at a distance of 11-35 AU and a period of 80 years) periodically covers the mainland half of the continent in glaciers which lock water out of the ocean, causing sea levels to fall and expose a land bridge between the two largest islands.

There's also the potential for glacial isostasy, whereby the ice load on the arctic areas depresses the continental crust, resulting in a corresponding uplift in the tropical areas; the effect would be minor compared to the change in sea level, but still noticeable. It would have the effect of causing the local sea level to lag the climate, so that the land bridge would reach its highest level during the Long Spring (when the two nations would be engaged in competition to colonise the newly habitable mainland) rather than during the Long Winter.

Effects of post-glacial uplift in Kvarken, Finland: http://www.kvarkenworldheritage.fi/the-kvarken-archipelago/geology/the-land-uplift/
Land uplift in Kvarken, Finland

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What if the plates were actually regularly shaped "rings" around the planet (with "caps" at the poles) which when put together form the sphere that is the crust of the planet but which can move independently. Each continent would reside on one of these rings, but although they would pass each other (as they turn at different speeds), they would never collide except for maybe a minor north-south wobble.

Perhaps the gravity of a large and close satellite keeps the ones at the equator moving quickly, while the ones closer to the poles not so quick, similar to the moon and our tides? (And may be responsible for how they fell into that pattern in the first place)

I have no idea if the stress on these rings would mean they could not maintain their shape, but even if they were broken it still works as long as the parts kept moving in the same direction.

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Maybe (supposed there is enough Handwavium(TM) in your world) your continents could be on (partially submerged) plates that constantly touch but rotate around their vertical axes. Think of them like interlocking cogwheels.
If you really want, your continental plates (the cogwheels) could be on different hemispheres, touching somewhere near the equator.
That way, coriolis force might (be stretched to) explain the spinning of your continental plates.
The reason they have contact could be because their centers of gravity are not on the poles, so that the planetary spin would push them towards the equator.

Obviously, this would easiest be explained if your continental plates actually floated on the oceans, and not be connected to the planet's core.

Depending on your personal taste, the rims of your floating plates would either have been ground fairly round(ish) over the millenia, or you might get something like an uneven cogwheel-like interlocking structure.

Needless to say, in the contact region things get crushed. Nothing major, it does not really break off large chunks of the plates, but small rocks, the occasional whale or ship, might get caught inbetween the contacting surfaces and be squashed.

Assuming the circumferences of the two plates are not identical (and why would they be?), and both plates have one side submerged under the ocean, if you assume that the larger one turns once every 80 years, and the smaller one once every 50 years, you might get interesting cycles of accessibility of the landmasses from the respective opposite.

Also, the plates would be lifted up out of the water where they touch. That would periodically move the flood line of each point on the brim of each plate. Building roads or other infrastructure to try to access the enemy's plate where they don't expect it could be quite challenging, and allowing for very interesting failures.

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  • $\begingroup$ +1 for the cogwheels comment (and the rest of the answer) that is sort of what I was picturing in my head. $\endgroup$ – James Jun 17 '15 at 13:57
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The core of the planet should be mercury.

Liquid at room temperature, but heavy enough to float land on top. It's more dense than iron, lead, etc, and if there was enough of it, it would form the core of our planet, rather than iron. Iron would float on top of it.

The center would still be solid (just as ours is, due to pressure, but between the center and the crust there would be a liquid layer of mercury much closer to the surface than our iron layer, due to low temperature liquid state.

You'd need a lot of mercury, and it would poison the oceans and land, so you'd have to either have characters that were hardened to it (ie, it agrees with their biology, and if they developed on that planet it naturally would), or you'd have to have some filtering and food production methods that eliminate the mercury.

This would allow a core as hot as ours, but not so hot that the planet wouldn't support life. It would cause the crusts to be much thinner - but not necessarily so thin that they wouldn't hold together.

The movement of the crusts could be fairly fast, and could be largely defined by the movement of the liquid mercury below - once set in motion, it would have currents and patterns just as our liquid layers do. It would be stable over thousands of years, certainly, and probably longer.

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