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143 votes

A 40km diameter alien saucer is floating 2km above the ocean for a long time. What are the effects on the sea ecosytem below?

The ocean is a dynamic and very large place, so it's unlikely to have many large-scale effects unless humans overreact. I'll focus on the local, immediate effects of this saucer from a physical, ...
Dubukay's user avatar
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92 votes
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What if a portal is opened from the Mariana trench to the Sahara desert?

The climate of Earth has been roughed up quite a bit last century. But it has no idea what it's got coming with this portal of yours. Earth turns into Venus. Update: As R.M. pointed out, the amount of ...
Swier's user avatar
  • 2,593
85 votes

Could a person scuba diving take off his air tank and use it to propel himself?

My question is, would it be physically possible to do that with the air tank? No. Source: Tried it. We've actually been taught to breathe off a tank without a regulator. You can do so by ...
Therac's user avatar
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80 votes

If there are water oceans, must there be oxygen in the atmosphere?

will the presence of large volumes of water inevitably result in some of the oxygen making its way into the atmosphere? No The Earth has oxygen in its atmosphere because of cyanobacteria which ...
IEW's user avatar
  • 1,485
76 votes
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Could a submarine built during the cold war maintain pressure underwater for 50 years?

It's even conceivable that all ballast tanks, vents and control systems were completely compromised, and so the sub sank with no attitude controls (bow planes & stern planes completely ...
GerardFalla's user avatar
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59 votes
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Is it possible for an ocean to have a river flowing from it into a lake?

Normally, a lake will have a fresh water river flowing into it from higher ground, and a river flowing out of it to the sea. ...
Schwern's user avatar
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54 votes
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Could a person scuba diving take off his air tank and use it to propel himself?

Here is a way to bypass the issue Our hero removes his air tank, points it away from himself and starts fumbling to undo the top. It's not working! He's never opened one of these things himself let ...
Daron's user avatar
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54 votes
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What would it take for an island to sink and rise yearly and naturally

Give your planet two moons with different orbits, and once a year for about 30-60 days they align on the sides of the planet perpendicular to the twin islands. The tidal forces draw enough water away ...
Clay Deitas's user avatar
  • 4,262
53 votes

Is it possible to bind multiple ships together on open water?

You can do it if the sea conditions are favourable (read dead flat calm), otherwise having the ships that close together, tied or not, is a danger to all concerned. Banging hulls weighing tens to ...
Ash's user avatar
  • 44.8k
48 votes

Why build underwater outposts, rather than ocean-surface settlements?

Waves, on Earth wave height is, in large part, constrained by the fact that waves meet land relatively quickly in most of our oceans. On a water world there's very few chances for surface waves to ...
Ash's user avatar
  • 44.8k
48 votes
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Could human civilization live 150 years in a nuclear-powered aircraft carrier colony without resorting to mass killing/ cannibalism?

You have problems, and it isn't food Food is easy. The ocean is full of fish. So long as your story places the aircraft carriers in the right place, food is irrelevant. Your problem is nuclear ...
JBH's user avatar
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47 votes
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Could a jellyfish be bio-engineered to convert salt water into fresh water?

No. Jellyfish are osmoconformers Osmoconformers are marine organisms that maintain an internal environment that is osmotic to their external environment.[1] This means that the osmotic ...
Willk's user avatar
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46 votes
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How reflective is blood?

Consider two substances with refractive indices $n_1$ and $n_2$. The reflectivity can be calculated as $$R=\left|\frac{n_1-n_2}{n_1+n_2}\right|^2$$ For air, $n\approx1$, and for water, $n\approx1.33$. ...
HDE 226868's user avatar
  • 101k
45 votes

What would keep traders away from a specific area of the ocean?

Let's try a real world example Say that the continent shown on the map is Africa. Traders coming from Shanghai in the east going to Amsterdam in the west have the option of going through the Suez ...
AlexP's user avatar
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40 votes
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Is it biologically plausible for a land animal to drink saltwater and not drink freshwater?

In animals found on Earth, the ability to drink sea water is dependent on the ability of the kidneys to export salt without damage. Sea mammals can do it -- seals, sea lions, manatees and dugongs, ...
Zeiss Ikon's user avatar
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39 votes
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What would keep traders away from a specific area of the ocean?

Blue Reefs The southern sea is big and open. The winds can go hard and the waves high, and there is no dry land nearby. This by itself would make the journey somewhat dangerous, but not especially so. ...
Grollo's user avatar
  • 4,147
39 votes

Would oceans filled with long-lived, omnivore, intelligent Krakens make sea travel impossible?

Octopi play. source The ocean can be terrifying. More terrifying is being played with by an intelligent predator. It grabs a person then leaves. It hits the boat and then leaves. It throws a huge ...
Willk's user avatar
  • 305k
38 votes

A 40km diameter alien saucer is floating 2km above the ocean for a long time. What are the effects on the sea ecosytem below?

Why is it that in questions like this about something blocking light, everyone seems to forget that the Earth rotates? To simplify the geometry, we'll use the following assumptions: the saucer has a ...
Keith Morrison's user avatar
37 votes
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If there are water oceans, must there be oxygen in the atmosphere?

Possibly. There are two mechanisms for producing oxygen on Earth (and other similar planets) Photosynthesis. Water is split and combined with CO2 to make (roughly) CnH2nOn and O2n. Some reduced ...
Andrew Dodds's user avatar
  • 6,285
37 votes

Why build underwater outposts, rather than ocean-surface settlements?

The best reason to build submerged cities is the same reason to build subterranean cities; protection from surface threats. Specifically radiation. Water provides amazing protection from radiation. ...
Ryan_L's user avatar
  • 13.8k
37 votes

Could a submarine built during the cold war maintain pressure underwater for 50 years?

Absolutely! It's great that you said Cold War era. The Soviets actually made a submarine with a titanium-alloy hull during the Cold War era. Titanium is highly anti-corrosive, strong, light, non-...
ColonelPanic's user avatar
  • 3,022
36 votes

How would sailing be affected if seas had actually dangerous large animals?

Humans would deal with threats the way they have done throughout history: they would eradicate those animals who threaten their safety and that's the end of it. If any survive, that'll be only ...
gerrit's user avatar
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35 votes
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What is a better design for a floating ocean city - monolithic or a fleet of interconnected modules?

Source: I've actually been employed to work on this very topic before. Indeed if a floating structure is large compared to prevailing wavelengths it won't be rocked much by it, and there isn't much ...
Eelco Hoogendoorn's user avatar
33 votes
Accepted

How To Make Earth's Oceans as Brackish as Lyr's

Less land It's actually pretty easy. There are two ways to make an ocean less salty. The first way is to remove salt, and the second is to add fresh water, both of which are possible, but takes a lot ...
Halfthawed's user avatar
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33 votes
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How to cross a metallic sea?

When temperatures rises in the day it will form an ocean of liquid metal so how do they cross it? They need to pay attention Liquid gallium is denser than solid gallium, Density (near r.t.) 5.91 $g/...
L.Dutch's user avatar
  • 289k
32 votes

What if a portal is opened from the Mariana trench to the Sahara desert?

First observation: The portals as described in the question create a perpetuum mobile. Salt water under high pressure (from the ground of the Mariana trench) wells up at some point in the Sahara ...
Sir Cornflakes's user avatar
32 votes
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Given early 1800's level technology, is it feasible to extract salt and fresh water from the ocean?

I'm from Brazil, a former colony of Portugal. In history classes we learn about this. In centuries past salt was very valuable. The word salary comes from that. Portugal had been exploring salt pans ...
The Square-Cube Law's user avatar
31 votes

How reflective is blood?

I spent some time considering how you might even start forming an ocean of blood. Mammal blood is out of question because it would coagulate. It would probably end up with rocks made of blood crust ...
The Square-Cube Law's user avatar
31 votes

In a single-continent world, what could cause hydrothermal vents?

You can have tectonic plates even on a water world, that is still "land" under there, you just have enough water to cover it all. In your case, any tectonic plates carrying enough land to break ...
Amadeus's user avatar
  • 34.7k
30 votes

Is it possible for an ocean to have a river flowing from it into a lake?

If a river flows from ocean into lake, you better have another river that flows out of the lake into someplace else, otherwise that ocean is quickly going to fill the lake, the surrounding area, and ...
SRM's user avatar
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