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I want to turn a planet fully covered in ocean into something Earth-like.

  • The planet is completely submerged in water with no land above the sea level. The ocean itself is quite deep.
  • The planet already has sea creatures and plants.
  • The average temperature is rather low, 5 to 10 degrees Celsius. This falls to -20 to -30 degrees Celsius when at the farthest point from the sun.

How to turn this planet to have islands and continents?

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    $\begingroup$ you are probably confusing something: terraforming is meant as "making the planet capable of hosting life as we know it". If it has an ocean (made of water, I assume) you don't need anything else. $\endgroup$ – L.Dutch Oct 14 '17 at 8:36
  • $\begingroup$ @L.Dutch The way I see it, terraforming means "changing a planet in any way to make it capable of hosting life" - a desert can also host life but why not terraform it to a jungle or a terran type? $\endgroup$ – SovereignSun Oct 14 '17 at 8:45
  • $\begingroup$ Sounds like you might have been playing Stellaris... I think you need to explain more what you mean by terraforming and probably by ocean planet. Are you asking how could you turn a world covered in water into an Earth-like world (with continents)? $\endgroup$ – adaliabooks Oct 14 '17 at 9:01
  • $\begingroup$ @adaliabooks Exactly. Or something similar to Earth like. $\endgroup$ – SovereignSun Oct 14 '17 at 9:14
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    $\begingroup$ Why do you want to do that? What's so special about it to use it instead of more rocky planet? Does it have atmosphere with oxygen? Active magnetic core? How is it built? except the oceanic surface, we know nothing. $\endgroup$ – Mołot Oct 14 '17 at 16:57
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Not answering this exhaustively, but pointing other ways.

You need to get ride of some water (hard) or reshape the surface (easy). If the Earth surface was flat we would have no emerged land too. The cheapest way to do this is using bombs on geological faults if the planet have a molten core. Some bombs on mantle can help too. Pointing a lot of asteroids or moons to the planet to build a mountain is other way.

Getting ride of the water can be done in the physic way, launching it on space, or in the chemical way, breaking it in hydrogen and oxygen and putting these elements in solid substances, using catalysts, atomic robots or any other method. The simplest way to turn water into rocks is to have some free carbon and sulfur and make coal, but the carbon and sulfur in the planet should already be in compounds.

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  • $\begingroup$ bind the oxygen with rock and let the hydrogen leak to space. but if you don't need the hydrogen for other thinks (like fusion-rocket-fuel) I would not throw it away, just build floating cities. $\endgroup$ – Henning M. Oct 16 '17 at 12:11
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You don't need to do anything nearly as extreme as moving the whole planet to a new orbit and boiling the oceans.

Presuming the underlying geology is already suitable (which moving the planet and boiling the oceans wouldn't fix anyway), you just need to get rid of all the excess water, somehow.

So, just launch it into space. If the planet rotates fast enough, build a space elevator and start pumping water up it. Build a lot of them if you want it to go faster. If the planet doesn't spin fast enough for that, build a Lofstrom launch loop, or an orbit ring, or whatever mass-space-launch infrastructure you prefer. How quickly you get it done depends solely on how much power you can afford to pour into the project--space-based solar arrays would help with that. And there's nothing to prevent you, and the native lifeforms, from continuing to live there throughout the entire process.

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  • $\begingroup$ Wouldn't that pump out the creatures too? I think the water will be pulled back by gravity. $\endgroup$ – SovereignSun Oct 14 '17 at 20:02
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    $\begingroup$ @SovereignSun Not if you put in the slightest bit of effort to filter the creatures out. And if gravity pulls the water back, you have clearly failed at building a suitable space launch system. Obviously you have to launch the water on an escape trajectory; otherwise, there's no point. Fortunately, that's really easy to do: give each shipment a sufficiently high energy, and every trajectory becomes an escape trajectory. We launch spacecraft on escape trajectories all the time. $\endgroup$ – Logan R. Kearsley Oct 14 '17 at 21:02
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Perhaps not entirely Earth-like, but depending on the technology available in your universe/race/story, you could do something similar to an idea taken from The Life of Pi.

Pi Martel encounters a floating, carnivorous algae island, large enough and stable enough to host a colony of Meerkats, as well as himself and a full-grown Bengal tiger. With a little bit of research, we find that this isn't too far-fetched, as stories of natural floating islands DO exist. Here's two notable examples: Cranberry Bog, Keibul Lamjao National Park. There are also explanations of large masses of peat rising from the bottom of swampy areas, stable and thick enough to support shrubs and trees.

So depending on the properties of the plant life on your world, combined with some technology and minimum (if needed) handwavium, a terrestrial ecosystem could be naturally established, or established through man-made means in a semi-natural way.

Edit for explanations: Without more detail on the flora of the planet, here are a few general ideas of how it could be achieved.

A. Masses of entangled plants could be detached from the seabed. Depending on their composition and entanglement pattern, they may need some buoyancy help, or none at all. The rigidity of the floating mass would also help shape architecture of any humanoid life on the planet.

B. Plant life suited for colder environments that has certain features causing it to be buoyant and stable could be brought in from other ecosystems and stimulated in the new environment. Ideally the plants would be able to form some sort of symbiotic relationship with some of the local fauna.

C. Reaching a little more far-fetched here, a species of plant that is known to have rather massive growth could be planted in areas of the ocean where said species of plant will be capable of breaching the surface and fanning out. That species of plant would either need to be capable of growing underwater, or would have to be planted in a specialized man-made environment until it was fully matured. The specialized environment could either be built on-site, and removed once the plant matured, or could be built off-site, and transported and transplanted.

D. Branching out (haha. sorry.) from plants towards my most far-fetched idea is floating sponge islands. To maintain the buoyancy, the humanoid race that I assume is going to be living there could run a system of pipes through the sponge, drawing water out of the sponge layer and eject it back into the ocean. Since I don't know much about your planet's location relevant to any nearby star or it's atmosphere, I'm going to assume it's cold due to lack of sunlight, so you'll have to reconcile the obvious power costs of such a system somehow.

Hope these help!

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    $\begingroup$ Welcome to Worldbuilding! Is it possible to give some idea of how this might be achieved? $\endgroup$ – Mithrandir24601 Oct 16 '17 at 20:33
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    $\begingroup$ Sure, since my response will be lengthy, I'll put it in an edit. $\endgroup$ – Utaru Oct 16 '17 at 20:38
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Any planetary engineering of this sort is going to require a massive amount of advanced technology and powers that are many orders of magnitude beyond what we currently have. So it depends on what sort of powers are available. Assuming very capable advanced hi-tech, it might work like this:

Take breeding colonies of all the life forms you want to keep and store them off planet somewhere safe. Next move your planet into a very close orbit around the sun and allow it to cook in the heat. Before long it should be converted into a Venus like world. Keep the world boiling away until lots of the oceans have boiled away and a lot of the atmosphere has been blasted off by the sun.

You must be careful not to overdo it, but with advanced tech it should be possible to determine when it’s “done”. At that point move it back out into a more distant orbit to cool off. If you’ve judged it right there will be a lot less water now but still enough to form Earth like oceans. Bombard the planet with a whole load of comets to help trigger plate tectonics and wait for it to settle down.

Reintroduce your living creatures, starting with those capable of producing oxygen, allow oxygen to build up and then introduce the rest. Alternatively just introduce whatever life you want to take hold

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  • $\begingroup$ That's really interesting. I hope the life forms can have a good vacation off-planet. But wouldn't such 'cooking' spoil the atmosphere and the water and make the planet inhabitable? $\endgroup$ – SovereignSun Oct 14 '17 at 18:36
  • $\begingroup$ Yes the atmosphere would be ruined, that’s why I suggest introducing oxygen generating species to help renew the atmosphere. The cooking is just a way to drive off excess water the atmospheric loss is “collateral damage”. The smaller amount of water that remained would condense again when the planet cooled down sufficiently. $\endgroup$ – Slarty Oct 14 '17 at 18:56
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Just some thoughts.

1) Pump the water to the poles and freeze it there. Ice is rather reflective so it would keep itself from melting for some time. You'll have to worry about possible cough climate change cough in this case.

2) Genetically engineer algae to produce buoyant organic remnants. There must be a lot of CO2 stored in this huge ocean, enough to produce "platforms" capable of sustaining a civilization. You'll have to dive for metals/minerals, though.

And also there can be methane/oil captured on the seabed. This can be turned to floating substance, too.

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  • $\begingroup$ As pointed in the question the planet is cold. There are already huge floating ice capes on poles. So, you would need to freeze ir directly in the seabed and add layer above leayer of ice. As the water grows when freezed, until the ice reaches the ice cap the sea level will rise. After reaching, you need to pump water to surface of this new ice continet, to produce a huge mountain. Big engouth mountains will lower the sea leval. $\endgroup$ – Cochise Oct 16 '17 at 20:03
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Everyone is saying to get rid of the water.

This is incorrect.

Our lovely Earth (particularly its dry land) could be entirely submerged by the water existing upon it, were it not mountainous and trenched. (If all land was equidistant from the centre.)

All you need is tectonic activity, subduction, lift, convergence, volcanism. Rifting and trenching. You will generate deeper oceans to hold the (same amount of) water, and uplifts which become the dry land.

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  • $\begingroup$ This is what I was thinking hah, surprised nobody +1'd this. Guess you were late to the party? $\endgroup$ – Magic Octopus Urn Oct 17 '18 at 2:03

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