Minnows the Size of Blue Whales

Great Debates
1

We certainly have a diverse biosphere here on Earth, with organisms taking many forms, functions and habitats—each, through selection and vast swaths of time, adapted to exploit a vast array of terrestrial niches. The biological “size scale”, from bacteria to blue whale is quite broad and impressive. I’d like to explore the feasibility of there being an equally expansive bio size-scale on a planet elsewhere in our universe, but shifted by an order of magnitude in the direction of *really, honkin’ huge. *

As far as I know, physical and biochemical parameters dictate minimum and maximum biological size limits (scaling laws?). Our planetary conditions (e.g. size, gravity, etc.) and biological limitations (e.g. surface area/volume ratio vs. heat loss, oxygen requirements, etc.) have most likely already given us Earth’s upper and lower limits (having an atom or mountain sized organism evolve on Earth in the future is unlikely). So, we need to consider worlds with different planetary conditions than Earths’ and/or biological mechanisms utilizing different biochemical pathways than Earths biosphere. What are they?

Imagine, if you will, a planet with a similar* array of life forms to that of our own, but with minnows the size of blue whales, bean sprouts the size of Giant Sequoia and lumbering bipedal apex technophiles the size of the Sears Tower. Under the constraints of our known physical and natural laws, can we have such a Goliath-riddled world?

Questions:
Are there any known physical or natural laws that preclude a planet from developing a biosphere with a size-scale of this magnitude?

Describe the essential planetary qualities necessary for the creation and sustenance of giant life forms.

Are there any particular biochemical ingredients or pathways, different from those common on Earth, which would favor extreme gigantism (e.g. silicone vs carbon based, etc.)?

What scenario is more likely for the development of giant extraterrestrial species: hyperplasia (more cells) relative to Earth species, or hypertrophy (bigger cells)?

Even if wide variations of biological scale do exist in the universe, is there any reason to believe Earth-scale may be the norm? IOW, when we make first contact, are our green guests likely to be about our size, or will we need to build some really big (or tiny) bathroom facilities for them?

Bonus Questions:
How small do you suppose the tiniest organism in the universe is and give a reason for your limit? (Must be a single self-sufficient life form…viral-type organisms don’t count).

How big do you suppose the largest organism in the universe is and give a reason for your limit? (Discount individual organisms functioning together, robot-like—no insect hives, large algae mats, fungi colonies or the John Birch Society).

  • Similarities to terrestrial life forms: Some type of metabolic “cell” is the constituent building block (some existing singly, others as multi-cellular organisms); natural selection is their means of speciation; means of locomotion is present in most; the planet must have solid, gas and liquid habitats, each harboring life.
2

This sounds like a homework problem. :stuck_out_tongue:

-XT

3

Yes, at least for land animals. Underwater, the availability of food places some restrictions on how big animals can get.

4

The idea of silicon-based life makes good science fiction but lousy reality. There are fewer long-chain silicon molecules out there than long-chain carbon molecules, and moreover the long-chain silicon molecules are generally quite unstable. Only carbon makes the large variety of large molecules necessary for life. It’s carbon-based or it’s nothing.

5

Silicon is indeed unsuitable for organic-type polymers; it doesn’t form double or triple bonds easily, most silanes and silicones are relatively unstable (especially silanes in contact with water), and silicon dioxide, instead of being a water-soluble gas, is an insoluble solid, which would make aerobic metabolism impossible. I can’t think of any combination of physical conditions and chemical elements that would allow silicon to perform the function that carbon does.

What does it even mean to have a “minnow the size of a whale”? What would be minnow-like about it? Similarly, what does it mean to have a bean sprout the size of a giant sequoia? If it means it grows to be that size in the time it takes a bean to sprout, well – how? How big is that seed going to be, and how is it going to conduct synthesis that fast? If it means it’s herbaceous instead of woody, how little gravity would allow such a thing to happen?

6

I think he’s asking what hypothetical world would result in an organism serving the ecological role of the minnow, but would measure 100 feet from head to tail. What parameters would a planet have to fit in order to support 170-ton bait fish?

One obvious answer is that the planet would need to be pretty honkin’ big (or at least have oceans that dwarf our own). Of course, with a big planet comes higher gravity, which a whale-sized minnow might not find so survivable.

7

I wouldn’t be surprised if there was one somewhere that covered almost an entire planetary surface, barring exceedingly hostile regions ( live volcanoes come to mind ). Something that grows like a thick mat over the surface; like the Strata Beasts of Major Operation ( which covered a continent - each ), then extends into the oceans. Probably in two layers for the oceans; one on the seabed to extract nutrients, and another on the surface to absorb sunlight.

It would probably have to be a colonial organism to allow for evolution, but that doesn’t mean that it’s not an individual. When you get right down to it, WE are colonies of cells.

8

A 100-foot long fish wouldn’t be fullfiling the ecological role of a minnow; it would be fulfilling its own unique niche.

9

I concede that organisms may very well have reached their size limits on our planet and that the square-cube law is perhaps the prime restrictive factor. But, is it not likely that this law may be far less restrictive given ideal planetary and biological conditions? I’m no expert on either side of the coin, but with regard to planetary conditions conducive to creating and maintaining giant life forms, would not a very large planet with relatively low mass, an atmosphere hyper-saturated with whatever chemical it’s biosphere uses to stoke it’s metabolic fire and an abundance of calorie-rich food for fuel be a prime candidate? On the biological side, surely there must be a more efficient mechanism of metabolism than our fauna’s dependence on oxygen, extracted from an atmosphere only ~20% O2 rich and its flora’s dependence on carbon dioxide, from an atmosphere only 0.038% CO2 rich? And, if stronger musculature is needed to overcome the square-cube law’s reduction of strength coincidental with scaling up, can we not devise a more efficient means of locomotion than our feeble actin/myocin muscle physiology? So, I guess my questions boil down to: are there hypothetical planetary and biological conditions that can diminish the size limiting effects of the square-cube law? If so, what are those conditions and how likely are they to exist in our universe? And, all things considered, if few size limiting restrictions exist on a planet, would evolution tend to select for extremes in size?

10

I was simply trying to illustrate an alien planet with a range of life form sizes relative to ours on earth, but scale shifted larger, wherein it’s mid-sized animals (e.g. ~minnow) were the size of our largest animal (blue whale) and its largest animals were…well, really, really big. I meant not to suggest any other similarities—they need not even have fish or mammals as we know them.

11

You run into physical problems. Gravity. The inverse-square law. To have taller trees in the same gravity you need a higher atmospheric pressure which means a different atmospheric composition. Animals get more massive proportional to the cube of their size but limbs only get stronger proportional to the square of the cross-section of their limbs. A lower-gravity world could not retain the same atmosphere as the Earth, at least not at Earth temperatures.

12

Oh yes, you need to differentiate between larger and more massive (q.v. balloons).

13

No.

14

If Jupiter were in Earth’s orbit, I wonder if it could support balloon-like creatures? Large, but not particularly massive.

15

Therefore, blue whale-size may be the universal upper limit for liquid-habitat creatures and large sauropod-size may be the universal upper limit for land creatures? This is a reasonable deduction, I suppose, but still I wonder—assuming our universe is indeed teaming with life—if at least some planetary biospheres have found a way to significantly break through this barrier. I mean, it strikes me odd that conditions on our rather mundane planet just happen to be primed to harbor the largest creatures in the universe—unless most other life-bearing planets also evolve organisms that reach similar size and hit the same barrier.

16

Absolutely not. Different conditions will apply on different planets.

17

I have solved the problem.

Place the OP in a reducerizer.

Upon exit, OP is the size of an ant.

OOooOoooo everything so Biiiiiiig…

It’s all relative to you.

18

There is a terrific essayby JBS Haldane about the optimal size of animals.

19

Did you even read the article on the square-cube law? It has nothing to do with local conditions, and everything to do with basic physics. If you multiply the size of an object by a constant, the mass (which is proportional to the volume) increases by the cube of that constant, while the object’s ability to support its own weight (which is proportional to the cross-sectional area) increases by the square of that constant. At some point, the object can no longer support its own weight. There’s no biosphere that can get around that.

20

Well, yes and no. You can get around it to a degree; by changing the materials used, and by making the creature less solid; remember, the OP is asking about size, not mass. Some creature that’s mostly hollow or some sort of latticework could be much larger than a more solid creature without being crushed under its own weight. And something made of sturdier material than Earthlife uses could also obviously be bigger; and I think we can’t really answer the question “What’s the strongest material living creaures can make ?”. At least not yet.