Some planets may very well be true water worlds, totally covered in water. Though some, like Gliese 581 C (a “super-earth” 50% larger than the Earth 20.5 light-years away), may have dense water—maybe a thin layer of liquid water on top of compressed water.
What sort of life would arise there? Think about it: there is no dry land, or extremely rare dry land, that is not easily flooded by storms or tides.
Life transitioning to land would not happen, at least not for large roaming life, which needs territory to grow and thrive on (digression: could high-level stationary sentient life ever evolve, I wonder?).
On Earth, life developed limbs and walked out of the seas; large tracts of land allowed for evolution to proceed in that direction. On a planet covered with one giant ocean, that direction would be blocked, unless the poles were cold enough to keep up the continued production of ice floes—then there could be an evolutionary path for living on ice floes part- or full-time.
Otherwise, any evolutionary development of limbs would go in the direction of underwater ambulation. But how useful is underwater ambulation? As useful as fins on land? And so, over millennia, higher sentient life would evolve and become totally adapted to the oceans.
I don’t think they would have just fins—it would be hard to build and use tools without some means of gripping and manipulating the physical environment.
That is not to say intelligent life needs a means to physically manipulate the environment, but that the ability to manipulate the environment does allow for greater evolution and progress of the brain, or at least makes it much easier for it to happen.
Maybe on some water world planet, a species of sentient life has evolved that cannot manipulate the environment, but they have survived for millennia and have slowly evolved to be able to do high-order abstract thinking; their art, culture, science, and theology would all be based on communication; their only tool left to them is to manipulate the mental environment.
Art would be for those that communicate via sound, vocal music, and oral literature. Science would be based largely on observation and mental experiments (of the kind that Einstein made famous but that the Greeks did to an extent as well) since they could do little experimenting (some, probably, but not much).
They would not be less likely to physically explore space, as they would not be able to leave their planet (water is extremely heavy, especially compared to air; lifting a craft full of water out into space would be extremely difficult, albeit not impossible, to do). In addition, making space suits for exploration, especially of dry surfaces, would be extremely problematic as well. Would they then be more likely to become telepathic? to astrally project themselves? Or is that too “new agey?”
A thick ocean on a large planet with several times greater gravity may have “normal” water at the surface, but the water would become denser quickly the deeper it went—water would become plastic or even solid.We have a slight inkling of that here on Earth—mountain climbers know the air gets thinner as they climb; it is a danger if ignored. Something similar may be at work for aliens from our water world.
Depending upon their evolutionary track, if they evolved as deep sea creatures, rising to the surface may be dangerous—especially if they cannot work with tools to create devices to help them breathe or deal with the pressure change.
Even sea creatures on Earth have ranges; some that live closer to the surface can dive rather deep, but they don’t live in the depths. Other deep-living creatures tend to stay in the depths, only coming near or to the surface when they are sick or dying (like giant squid)—near the surface is not a friendly environment for them to linger in.
Another thought: would, after millenia, creatures evolve to be like our flying fish? Would the air be conquered there as it has long been here by flying creatures? They would have to be creatures that feel at home surrounded by oceans and do not need land to survive.
Probably the most likely flying fish-like creatures, though it is possible that on some planets, the flying fish evolve into fish that fly more than they are fish and develop lungs; they end up spending their lives either floating on the surface (for example, when resting) or flying.
There are some sea birds on Earth that can live far out at sea and may spend much of their life out at sea. Such birds tend to glide or soar more than they use powered flight. This is because they can take advantage of the wind deflected by waves or by ground effect, which reduces drag.
Because of convergent evolution (where unrelated species tend to develop similar characteristics due to their sharing similar environments and due to the fact that the same physical laws apply to all species in the same environment), we can make educated guesses that creatures on other planets will tend to try to be efficient in adapting to their environments just like Earth life.
If deflected wind and the ground effect are still in effect on this alien water world, then flying creatures there will glide more than they will use powered flight since the latter uses more energy.
Would these fully pelagic seabird-like creatures be the ones most likely to become toolmakers? They would have, possibly, developed webbed feet, which could have an opposable digit to help them grip prey (like modern Earth birds) and which could eventually evolve to manipulate tools (as a previous blog entry noted, some birds, notably crows, are known to create and use tools and may be as smart, or even smarter, than a chimpanzee.
Or would the creatures be more like flying fish, or half bird, half fish—able to live under water (maybe to nest and breed) as well as live on the water surface and fly over it (to more easily hunt for food—flying through air is faster than flying through water—less dense, less drag)?
One disadvantage (to sentient beings) is that it would be difficult to work with metals on a water planet—to melt, smelt, and otherwise work with metal to create structures and devices that would allow them to eventually explore the stars.
Mining ore would be more problematic as well. Water is heavier than air and more dense; it takes more energy to move through it, making it probably more difficult to shore up tunnels (not only would they have the weight of the stone above, but the pressure of the water on top bearing down).
Light has a harder time penetrating water than it does gaseous atmospheres (sound, however, could travel great distances under water). Working with electricity would be harder. Building telescopes to view the heavens would be harder (though maybe on a planet with rare land, a species that could tolerate the air for short periods could build telescopes on such land—or the avian species, which would have a higher ability to tolerate the air).
On a larger planet, covered with water, how would that affect territorial issues? Such creatures would be more nomadic, especially if they never learned to farm, as there would be no need for them to settle down and build cities.
Are cities necessary for advancement? Do cities help speed up the advancement of civilization, and if they do (which it does seem like they did for humans), are they the only way? Could nomadic species find their own way to help spur on advancements in civilization? Would there be less isolation between groups if natural barriers such as mountains, oceans, ice fields, deserts, and large rivers did not exist, and thus a more “we are one” type of sentiment developed?Or would groups still develop, some adapting to colder regions, for instance? (But would this still, in the end, create fewer insulated, insular groups than is the case on Earth?) Would this create a species that would be less xenophobic?
What theology would exist for such creatures? For those on planets with rare lands, would the inhospitable land be their version of hell? Or, for deep-dwelling sentient species that cannot tolerate being near lower pressure regions in the upper regions of the sea, would the upper, more lighted, and more dynamic regions resemble hell and heaven, or the darker, heavier, and calmer pressured regions?Would they think all planets are oceans and that heaven would be a calm ocean?
They probably would have some tectonic activity—underwater volcanoes—as well as deep, dark trenches that could play roles in primitive theologies. And for the sentient species of water birds, how would their primitive ancestors first think of the world, theologically (I suppose they would love the O.T. verses that describe God as a mother hen)?
Would a water world be less susceptible to extinction-level events from meteor impacts (no dust to throw up into the air to create a long-lasting year-round winter that kills off the plant life, no cracking open part of the crust and letting out lava, etc.)?
There is an article in DVICE.com about the Focus 21 France, a hovercraft prototype that would use the ground effect to achieve helicopter speeds. It would have to fly close to the water to take advantage of the ground effect (a height equal to twice the wingspan or less). I assumed that was how sentient species in the water world would fly, at least in the beginning. Sub-orbital or low-Earth orbits are analogous to us.