By Abbydon
The previous article discussed the possibility of using soap bubbles to create small lighter than air organisms. A second possibility is more sophisticated and relies on the wonder material, graphene. It was discovered in 2004 by two scientists at the University of Manchester who were subsequently awarded a Nobel prize for their work.
Graphene is made of a flat sheet of carbon atoms, so it is a little bit like 2D diamond. It has many interesting properties but is most well-known for its high strength (100 times stronger than steel) and low density (less than 0.001 grams per square metre). An amusing illustration of this was provided in the Nobel prize paper. Imagine a one square metre graphene hammock tied between two trees. This could hold a 4 kg cat before breaking yet would only weigh as much as one of the cat’s whiskers.
As impressive as this is, recent work suggests that graphene has another property that is extremely relevant to ballonts. Graphene is also impermeable to gases. With such an amazingly low density it effectively produces a matte-black massless membrane even when a few thousand layers are used.
It would however be extremely challenging for life to produce a graphene balloon with absolutely no defects. A more robust approach is to copy the bubble foam concept and use a mass of small graphene “bubbles” instead. Conveniently, a material extremely similar to this called aerographene has been invented by scientists. It consists of a complex 3D network of graphene and carbon nanotubes where most of the volume is air. For this reason, when measured in a vacuum it has a density slightly lower than helium at 0.16 kg/m3.
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| Click to enlarge; copyright unknown; source here |
While aerographene itself is not airtight it is not inconceivable that a material like it could be produced that contains many small airtight compartments in a similar way to a bubble foam. If these compartments contained a lifting gas, then the entire structure would float. When I mention aerographene below I am actually referring to this possibility and not the real material. The chart below shows that both a 1000-layer graphene membrane and a “solid” aerographene balloon would easily enable small (or large) ballonts.
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| Click to enlarge; copyright Abbydon |
This strongly suggests that an “magic” aerographene like material could be used to enable small ballonts to exist. Since they cannot have a membrane then any aerographene produced would be an external structure grown from the bottom up, like hair, and could not be repaired only replaced. Additional graphene would be produced on the lower surface where the organism was hanging while the top surface would slowly degrade.
It is unfortunately unknown whether life could produce graphene in the first place as it does not appear to be produced naturally by life on Earth. Industrial processes for producing graphene based products typically require temperatures beyond the reach of even the most extreme of extremophiles. However, Shewanella oneidensis bacteria can be used to produce graphene from graphene oxide which is at least a start.
I am not a chemist and this is not the blog to delve deeply into the exact chemical process that life could use to produce graphene at ambient temperatures. There is some justification that it would not be implausible though. Inspired by photosynthesis the direct conversion of carbon dioxide into graphene at high temperatures has been demonstrated. A slightly different approach has even been shown to work at room temperature.
As an example of what is possible, an approximately spherical lump of dark grey aerographene with a 9 cm radius can lift about 3 g. This could support something like a praying mantis that is about 7 cm long though could perhaps be longer and thinner. A cup-like abdomen could contain the graphene and hydrogen producing organs while the four long rear legs partially surround the sphere to maintain a grip. Four independent wings could provide mobility. The long forearms would then provide good reach to gather food. Due to the benefits of aerographene this hanging mantis would be able to float even when small and could grow to a size only limited by other factors.
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| Click to enlarge; copyright Gert van Dijk. Note that the graphene 'floating body' is narrower at the tope than the bottom, because the animal grew in-between forming the early top and the more recent bottom graphene. |
The soap bubble and aerographene concepts don’t mean that the small ballont problem is solved as they are really just meant to inspire others to come up with their own ballont concepts. In the absence of any lighter-than-air organisms for comparison on Earth there are still many unanswered questions to be considered and that is all part of the fun of speculative evolution.
For example, why would an organism evolve to be lighter-than-air? Is it always lighter-than-air or is it only temporary? How does it control its movement when floating? How does it protect itself from predators? How does it feed? Can it repair or replace its balloon if punctured? How is the lifting gas generated? How fast does the lifting gas leak from the balloon?
If we were only interested in creature design then this would all be sufficient to inspire a range of organisms based on shimmering soap bubbles or black graphene. Speculative evolution requires more than that though. Demonstrating that physics supports the idea and that there is a plausible way for the organism to implement the idea are both important. To be thorough, it is also important to consider whether the proposed organism could have evolved through a series of plausible steps, rather than just spring into being fully formed.
There are various ways that life on Earth already generates hydrogen, such as through fermentation, so that part is not unusual. The formation of chemical laced water to form longer lived bubbles is also fairly common as fish, frogs, snails and insects are already known to do this. A soap bubble based ballont as shown in the previous article therefore seems reasonably plausible.
On the other hand, the formation of graphene is more challenging to justify in a series of steps and I cannot give a solution to this. Graphene does have the ability to absorb light efficiently at all wavelengths, which is why it is black after all. A plausible evolutionary path could involve algae or plants in low light environments developing graphene for photosynthesis related reasons. Since hydrogen can be produced by algae as part of the nitrogen fixing process perhaps forests of lighter-than-air pitch black plants could feasibly evolve. That is however an idea for another time but perhaps it will eventually appear on my recently created blog. It describes the tidally locked world Khthonia, which orbits twin red dwarfs.
Finally, I am very grateful for the opportunity to share my thoughts on this matter in this blog and I hope that they inspire people to develop their own ideas in this area. Please comment to let everyone know what you think about graphene and its possibilities.
35 comments:
Another possible evolutionary path I can see would the a tough, carbonous shell of a mollusk analogue being converted into an external, gas-containing swim bladder like the Nautilus and their extinct relatives have, except spongy in structure rather than segmented. The leap to actual flight, though, is difficult, as I fail to see when being lighter than you need to be to float on water, but still too heavy to float in the air is really useful, and I'm not sure the transition from "high carbon foam" to "pure carbon aerogel" is really biologically feasible.
I think that producing a plausible route by which a graphene using organism could evolve is definitely a thorny problem. The absence of any life on Earth using graphene complicates this as there are no examples to draw on. How to combine this with hydrogen production complicates it further for sure.
I agree that the evolutionary history of a graphene ballont is not an easy thing to explain. In fact, I liked the foam idea enough to use them on Furaha, so there are now organisms that help spread their offspring by embedding minuscule larvae in a floating foam. after a day or so they come down, so we are not talking about true ballonts in the sense of lifeforms that spend most of their life aloft.
The fun part of the graphene foam is that Abbydon has pushed the limits of what is at least theoretically feasible quite a bit outwards. It's speculation...
Keavan: I agree that it is hard to think of a benefit for the mollusc to evolve a lifting envelope before it is light enough to act as a balloon. Pity...
The existance of organism that can sythesize graphene or other carbon allotropes, maybe the graphene even could be integrated to the general body mass, creating bones and other tissues stronger and ressitant, becoming bigger and lighter creatures even creating silicon carbide for shells. Itas a very interesting post, I wpuld love see more posts speking about graphene in living organisms.
I, Anthony, offer this:
Graphine, even thin, is more durable than soap bubbles, right? As low a bar as "moreso than soap bubbles" may be, perhaps thats how it starts: as something tough enough to discourage (if not defeat) predators that try to eat the eggs in the foam.
(part of me wonders if ballonts might *start* as dispersal mechanisms for larvae, and then neoteny takes over - initially to spread yet further, perhaps, or to disperse out of reach of weak-flying predators)
Great second chapter; looking forwards to more from the two of you.
unknown: nice idea. It could well be the other way around: if graphene can be manufactured by an organism, making use of its extreme weight could come secondarily.
Anthony: also a nice idea to have the graphene in there for another purpose. And thanks!
Here's an idea that may allow 'plants' (or plant analogues) to jump straight to having a larger, less problematic balloon. Kelp and select other brown algae have structures called pneumatocysts, basically just gas bladders that allow them to maintain bouyancy. These can get quite large on their own (as evidenced by the photo linked below). Now, there is a rare, but inheritable genetic defect that occurs in various vascular plants called fasciation (also linked below). A fasciated plant will have certain structures grow abnormally wide, like super wide stems, elongated fruits (like beefsteak tomatoes), or bizarre ribbon-like flowers. I know algae aren't plants, but if a structure like a pneumatocyst were to become fasciated, and if the plant filled them with a lighter than air gas, you could potentially end up with a sizeable balloon, skipping the problematic small balloon stage. Perhaps the ancestral pneumaticysts were used to disperse seeds or spouts, and the fasciated balloons allowed a greater dispersion range, or possibly allow some pioneer plants to conquer the land (depending on how far along the world is). If these were just seeds, then the balloons would probably be only a once or twice a year event, but if they were sprouts (perhaps the plant reproduces like a hyda), I could easily see some of these remaining airborne for considerable amounts of time, possibly permanently by becoming carnivorous to obtain nutrients they'd otherwise leech from the ground.
I don't know if it's plausible but it's a fun thought.
Pictures:
https://commons.m.wikimedia.org/wiki/File:Algae_bladder_4290.jpg#mw-jump-to-license
https://en.m.wikipedia.org/wiki/Fasciation#:~:text=Fasciation%20(pronounced%20%2F%CB%8Cf%C3%A6,point%20and%20produces%20approximately%20cylindrical
what if ballonts could secrete foamy substance like spittlebugs and then ride their bubble like the spiders that fly on strands of silk. its only temporary and it mostly moves with limbs but can take off in danger by making new bubble at will
what if frogs could evolve into ballonts by inflating their throat sac
@Lane: That's certainly an interesting and plausible evolutionary route. The primary challenge is why would the seaweed use hydrogen initially? Algae can produce hydrogen when they fix nitrogen, so perhaps that is the source of the hydrogen. There are also some deep sea mussels that have symbiotic hydrogen oxidising bacteria. Perhaps the pneumatocysts started as some energy storage mechanism and then became water floatation aids before becoming large enough to lift into the air?
@winnie the shrew: The first part of my article covers the idea of using temporary bubbles. I mentioned froghoppers (aka spittlebugs) as a possible evolutionary route, so certainly I think that approach is plausible.
@Nancy: I do like the idea of a frog starting some chemical reaction that produces lots of hydrogen so that it inflates and starts floating. Though it does remind me of the scene in Shrek where the frog is turned into a balloon...
how would a predatory ballont work? i don't see any means of fast pursuit and it's hard to be an ambush predator when you float in plain sight. what niches might a ballont fill
i, anthony, say this:
maybe you can ambush things whose visual system relies on objects' *speed* rather than their presence...you can sneak up on them because your pace of movement is unthreatening.
I think the simplest way to allow a small ballont to become a predator is to make it nocturnal. Aerographene is extremely black so it would be very difficult to see in the dark and if bubbles were used instead they would last longer in the cool night air. To attact prey bioluminescence could be used to become an airborne anglerfish. This would be a bit like some fungus gnat larvae.
random ballont idea: an avian ballont which we shall call the "hindenburd". birds already have a complex system of internal air sacs, so one avian species, of undefined ancestry, feeds on a diet that produces lots of gaseous buildup. normally it is expelled, but the hindenburd developed the ability to store said digestive gases in a modified set of air sacs, eventually coming to use it for lift. no longer needed for propulsion, its wings become sails to catch the wind and steer, while its head becomes small and mounted on a long flexible neck like a heron's, allowing it to move its head quickly and independently of its inflated sluggish airborne body to snap up small prey down below while its large body drifts slowly overhead
The only idea for a predatory ballont I can think of would be one that dangles multiple limbs downward to catch any flying prey that blunders into them. Think something somewhat resembling a smaller version of the zerg overlord from Starcraft, or perhaps an airborne jellyfish...
Your idea deserves to exist just for the name alone. The big problem with lighter than air organisms is that they need a very large gas sac relative to their body. This makes them look quite bulbous. As you say, you can combine a kite with a balloon to get a kytoon though. There are a few other types of hybrid airships too but perhaps the most amusing one is the Airlander 10 that was often described as a "flying bum" due to its appearance!
Sorry everyone, I was busy doing other things... Lucky for me, Abbydon has jumped in. Still, here are some additional remarks. I worked my way down as I read your comments.
Lane, winnie and Nancy: Creative ideas, but you need to devise a reason for the plant/frog/whatever to produce lifting gases in the first place, and that purpose cannot be ballooning, because the reason had to be valid well before there is enough gas to form a functional balloon. Once there is, the original reason can in fact be dro9pped, if ballooning has its own rewards.
Josuge: they do not need to be active fast hunters; they can be predators in the same way that jellyfish are, or coral polyps, for that matter. They do not exactly race after their prey, but if the prey is even slower and prepared to blunder into you, you can catch it. If you do that, you are still a predator...
Anthony, that would work too, as long as the prey does not evolve a response to that.
Abbydon: being hard to see would strengthen any predator, including the passive jellyfish analogue.
'just etc.': that is a very nice idea. I wonder what the volume of air sacs in birds is compared to their total volume. The larger it is, the more would filling the air sacs with a lifting gas help reduce the mass that still has to be lifted. I will see whether I can find something on air sac volume.
SwampmOnster: the jellyfish analogue! You know what they say about great minds...
Abbydon: true... let's find out about relative air sac volumes.
I did look for information on bird density and found this. Apparently a house sparrow is 23.56 g and has a volume of 34.05 ml.
This gives a density of just under 700 kg/m3. Unfortunately, a hydrogen balloon (ignoring the membrane) only provides 1.1 kg/m3 of lift. This means the balloon has to be VERY large compared to the sparrow: 15 cm radius or around 600 times the sparrow volume.
In the same reference it is said that the air sacs in a duck or goose are about a quarter of the volume of the body. This is probably about the same for the sparrow (hence the density being about 70% of the density of water).
This again illustrates how hard it would be to evolve lighter than air flight as the balloon volume has to be absolutely massive compared to the rest of the organism before it provides a meaningful lifting benefit.
Note that on a planet like Venus where the air has higher pressure (92 atmospheres) and density (65 kg/m3) this approach becomes somewhat more feasible. There the balloon would only need to be around 12 times the volume of the body.
I, Anthony, do ask this:
But why depend on the air sacs to do all the heavy lifting, pun intended?
Aren't there ways to cheat, though? Maybe have bristles/?/hairs to help catch more of any breeze, or to static or magnets like lint (in freshly-dried clothes) or spiderlings use?
My biggest issue about ballonts is their ability to quickly generate gas for take off. If they have to descend they will have to release some gas but then they'll have to wait for their body to generate more to lift up again.
Also, how would jet propulsion work in air? I've been trying to work on an exobiology concept for a while and one of the species on the spec planet is an airborne hunter best described as a "sky shark", that has internal sacs of hydrogen to provide lift, but there are also two "ramjet engine" type structures on either side derived from offshoots of its respiratory system that inhale air through front inlets and force air out backwards, with moveable fins to control its direction. However, I've had issues with the aforementioned "hydrogen generation" problem, as well as its method of swallowing smaller flying prey whole: would a full stomach hamper its lift?
hydrogen sounds like the only gas an organism could produce (by metabolizing water) but then it's very flammable. a creature that's prone to bursting into flames doesn't sound like one suited for natural selection...
@Anthony: A hybrid ballont that isn't quite lighter than air is a perfectly reasonably idea. However, it will still look fairly similar to a "full" ballont. The reason for this is that the lift from the balloon is the volume multiplied by the density difference between the balloon and air. Therefore, even a balloon with a massless membrane containing vacuum only lifts 1.225 kg per cubic metre of balloon. Unfortunately organisms are typically about as a dense as water (1000 kg/m3) so the balloon part of the organism has to be about 800 times as large as the non-balloon part for a full ballont. Even a hybrid ballont requires a large balloon for a meaningful amount of lift.
@Denver the Last Spinosaur: Instead of venting gas, I think ballonts would use a different way to descend. Just like ocean life, very small ballonts might not quite be lighter than air. Gravity would tend to make them sink, but wind would continually lift them again. Larger organisms might be similar but would have to rely on a small amount of work (via wings or aerofoils and forward motion) to lift them up. If they stopped working they would slowly sink.
Alternatively, they could control their buoyancy in a similar way to how fish use their swim bladder. Reducing the amount of hydrogen in the balloon would decrease the lift. Possibly they could use carbon dioxide and water to just convert hydrogen to methane and back again (with hypothetical enzymes).
Another approach that is probably more feasible for large ballonts would be to use muscles to contract the balloon volume and reduce lift. Airships basically do this with ballonets inside the main envelope.
As for jet propulsion, well, that requires a lot more thought...
@Sir Cuagodont of House Serina: I suspect that in the natural world an organism probably wouldn't encounter ignition sources often enough for that to be a problem. Also, pure hydrogen can't ignite as it requires at least a small amount of oxygen to be present. As long as the membrane stays sealed and perhaps some biochemistry mops up excess oxygen its probably okay.
I, Anthony, do add this:
I fear I was not clear earlier. I did not mean a blend of balloon- and fleshy/organ-filled body; I meant a blend of balloon and other methods of remaining in the air.
(I've seen spider draglines do this (before they had a chance to build up a full web) when one or both ends is severed, the dragline will ride the breeze for easily over five minutes or until there is no breeze, even if two meters in length)
hmm, that mention of a swim bladder brought an interesting idea: what if a ballont evolves from an aquatic ancestor with a swim bladder to regulate buoyancy? Eventually it starts floating at the surface, to ambush prey below with dangling appendages, and when it develops the ability to breathe atmospheric air it becomes able to leave the water entirely, drifting over the ocean's surface to snatch aquatic prey down below like some bizarre sort of pelican-niche but certainly not looking anything like one at all...
To all: Interesting discussions! Over the years, some concepts do seem to come back again when it comes to ballonts. My personal ssynthesis of it all is that ballonts, in the form of animals of sparrow size and larger, are still not at all probable on an Earth-like planet. I agree that they might work on a Venusian-style planet, but the circumstances there would differ so much form the ones we are used to that I for one would have a hard time evolving believable creatures there.
The concept that the the balloon envelope was the culprit led to the 'massless membrane', foam and graphne, thanks to Abbydon's efforts. There are creatures on Furaha now that use 'lifting foam' to disperse their young. I feel that that they are about as unlikely as small spiders using a long thread to float up. If they would not exist, would you believe in them? ;-)
Just my two cents on the gas regulation thing: what if their gas bladders housed symbiotic microbes that made the gas for them? The microbes also serve to metabolize any unwanted gases, or excrete heavier gases to help it descend (though how the ballont can control the fermentation process to rise or sink is a bit of an issue).
Pfff, Female Kayentatherium had me giggling about the "Hindenburd". I picture that since some birds have inflatable combs or wattles that they use for display the Hindenburd could use a similar growth connected to its torso, though given those volume measurements all I can imagine is this goose-sized bird attached to an inflated wattle the size of a school bus...
@Robbie: I'm certainly not saying it is impossible but the challenge for evolving lighter than air flight via a swim bladder is the huge density change from water (1000 kg/m3) to air (1.2 kg/m3). Interestingly, this becomes a lot easier on Titan if life evolved in methane oceans. Liquid methane is about half as dense as water and Titan's atmosphere is about 4.5 times more dense than on Earth. This would still be a challenging barrier to overcome but it is a smaller change than on an Earth like planet.
Yesterday Netflix released a documentary on exoplanets and speculative evolution called Alien Worlds. Interestingly, episode 1 was set on a high gravity world and featured two lighter-than-air organisms. I'd say it was certainly worth viewing but the speculative evolution design has a few flaws. They should have used graphene as a solution! Anyway, I've posted a review of the first episode on my blog as it is too long to post as a comment here, even for me.
Abbydon: I have mixed feelings about that documentary, as I was invited to participate, which I dearly wanted to, but on such a short notice that my work at the time made it impossible to do so. Very frustrating...
It's a shame that you weren't involved as I am sure it would have been an interesting experience. Perhaps next time? I've managed to quickly write articles on each of the worlds presented. Maybe you need to write one to show how you would have done things differently? Certainly there seems to be a lot of interest as my page views are about ten times higher than the normal low levels.
Abbydon: I haven't looked yet because I was very busy with other things. i will have a look after the weekend. I don't known whether I should respond to the documentary, seeing I was invited but could not contribute.
As for a high visitor count, that sounds familiar. If you add famous books or film or TV titles to your blog ytou wil get many visitors. It might be easy to exploit: 'This planet is not Tatooine!'; 'This post is not really about Dune, Avatar, Star Trek or Star Wars!'...
What about it's insulating properties?
That would be an easy answer to the "half a wing" question.
Small animals lose heat easily in cold climates, and many places can experience extreme temperature swings over the course of a day, so being able to whip up a winter coat from your own froth in five minutes would be pretty handy.
Colder air is also denser, so living in a colder climate makes ballooning that much easier.
Sockmonkey: interesting idea! I think foam could indeed be an insulator, I think. But the fluid in the foam should definitely not evaporate quickly, as evaporation would cool it. It should also be very resistant to freezing. But we are talking about a foam with interesting chemical additions anyway. I have my doubt about ballooning in cold air, when the gas inside the balloon has the same temperature as the air outside it. In that case, the liftable mass might not change; I can work that out, but not right now ;-)
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