How the mass of a planet affects the evolution of life on that planet

[dimrous1960]

Summary:: Specifically, how Earth and life on it would have evolved if our planet was twice as massive but with the same composition of building elements?

Could humans or sentient, upright walking creatures appear in the evolutionary scale in a twice as strong gravitational field? How that would affect geophysical processes and evolution? I hypothesize it would turn them more violent and chaotic and it would render the chances of life happening much slimmer.

 

[berkeman]

Summary:: Specifically, how Earth and life on it would have evolved if our planet was twice as massive but with the same composition of building elements?

Could humans or sentient, upright walking creatures appear in the evolutionary scale in a twice as strong gravitational field? How that would affect geophysical processes and evolution? I hypothesize it would turn them more violent and chaotic and it would render the chances of life happening much slimmer.

Welcome to the PF.

We don't allow personal hypotheses or speculation here. Please see if you can find a scientific paper that covers this type of influence on evolution, then post a link here so that we can discuss it. Thanks.

 

[jedishrfu]

I moved your thread to the Science Fiction forum as it could be an interesting though not so scientific premise for a story.

With respect to your question, I don't think it would make a species more or less aggressive being raised in a heavier environment to Earth. All species strive to survive and use whatever means available to them to do so.

Some popular stories with differing gravities:
- John Carter of Mars where the lighter gravity gave John Carter superhuman abilities
- Superman also came from a heavier gravity planet

 

[BillTre]

Aspects of biophysics deal with differences in body shapes under different conditions.
As land animals get larger, their mass will increase in a somewhat cubic manner, but their supports (such as legs) will increase disproportionately because the amount of weight they can support depends on the leg cross section , an area, which works more on a square function.
Animals in the water can get larger (such as blue whales, the largest known animals ever) due to their neutral buoyancy.
Birds have to maximize light weight and therefore have much lighter and more fragile bones.

Affects upon behavior:
Large size does not necessarially have to go aggressive action.
They often don't need it. Many predators are often not a threat to large animals (although their young may be endangered) and large animals are often not predators.

The basic rules of building a functioning ecology would still have to hold. How the ecology is made would be modified to the specific situation.

 

[256bits]

it would render the chances of life happening much slimmer.

Are you basing that on substance separation by artificial means such as with a centrifuge.

 

[some bloke]

I think life would be based around a squatter, short-legged frame to reduce the need to pump blood against gravity - sort of crocodilian in nature. You wouldn't get many giraffes.
Cell structures would be different, they would probably evolve to strengthen the walls. I don't know if they might be smaller/larger t oachieve stronger bonds, or if that is even necessary in 2G.

 

[hmmm27]

If they were quadrupedes, evolving into bipeds would be less likely. Likewise avians.

So, centaurs.

 

[some bloke]

If they were quadrupedes, evolving into bipeds would be less likely. Likewise avians.

So, centaurs.

Centaurs would also necessitate the blood being pumped up the body. In high-G, I would expect any land creatures to be fairly flat and squat to reduce the amount of overcoming gravity involved.
I also think that this sort of evolution would lend itself to predators which can "get the drop" on prey, by being above them. Though the prey might have rotating eyes to see further around, that sort of thing.

 

[member 656954]

I hypothesize it would turn them more violent and chaotic

Your conclusion of violence, @dimrous1960, I don't follow. What makes you think this?

and it would render the chances of life happening much slimmer

Given we're not sure how life arises or how ubiquitous it is, I'd also be interested in why you think this. Or by 'life' are you envisioning more evolved forms, such as animals? Because I'd expect bacterial life not to be overly fussed by gravity, esp. if it's living in an aquatic environment.

I also think that this sort of evolution would lend itself to predators which can "get the drop" on prey, by being above them.

Any large animal dropping any distance is going to need to be really robust to survive impact because 19.6ms² gets you up to speed in short order! Though I guess smaller types of life - insect equivalents, for example - might use the higher gravity as you describe. And presumably, if they did, it would lead to very fast reaction times in their prey.

 

[some bloke]

Any large animal dropping any distance is going to need to be really robust to survive impact because 19.6ms² gets you up to speed in short order! Though I guess smaller types of life - insect equivalents, for example - might use the higher gravity as you describe. And presumably, if they did, it would lead to very fast reaction times in their prey.

I think that's a really good point there. everything would have a really fast reaction time, as they would need to in order to not fall over at any stumble. Slug-like creatures less so, though.

It would be very odd to see a sentient creature from this place visit earth. It would be moon-hopping everywhere, immensely strong, lightning quick reactions - like superman crossed with a kangaroo.

 

[ZapperZ]

In the meantime, the OP @dimrous1960 , does not seem interested in following up with the question and responses. I'm also not sure why this in the Sci-Fi section. No reason was given for it.

Note that one aspect that hasn't been discussed here is that if the Earth, with the same density, is twice as massive, then it would have cooled down even slower since it will have a smaller surface area to volume ratio. As a consequence, it would have been more geologically active than it is now, and certainly will affect how live evolved on it, if it even gets to a point of having life. So all these discussions about various creatures or having riots etc. might be moot if there's very little life that can be sustained by this point in the evolution of the Earth and the solar system.

That is the type of point that would have been pointed out if this were in the Astronomy forum.

Zz.

 

[Vanadium 50]

. I'm also not sure why this in the Sci-Fi section. No reason was given for it.

It was moved here. This sectioned was promised not to become a dustbin for messages that aren't appropriate anywhere else, but that's not what happened in this case. That explains why some of the messages seem to be a bit of a non sequitur - they were posted as this message was blowing through the various sections like a leaf in autumn.

As you say, the OP is gone. And while your premise is unquestionably true, I am not sure simple scaling works. buoyancy forces will be larger and differentiation will be stronger, so magma chamber formation will change. I'm not sure it will be "more" geologically active so much as "differently" geologically active.

 

[ZapperZ]

And while your premise is unquestionably true, I am not sure simple scaling works. buoyancy forces will be larger and differentiation will be stronger, so magma chamber formation will change. I'm not sure it will be "more" geologically active so much as "differently" geologically active.

I'm not saying it will be. I'm saying it's a distinct possibility within the Solar Nebular theory. It explained why Mercury and our Moon are geologically dead, even though they showed possibilities of previous scars of being geologically active in the past.

So if we extrapolate on that, with everything else being equal, the Earth should have cooled down a lot slower than what we have now, and that means that more of the interior will still be molten.

Again, I'm saying that that is just one possible scenario. There are other problems here, because within the solar system, there are no terrestrial planets of that size. The big boys are beyond the asteroid belt. What are the odds of a solar system planet this close to the sun having that big of a size?

When people propose variation such as this, they often do not think of the "chain reaction" of changes and questions that have to accompany such a scenario. Nothing is ever that simple.

Zz.

 

[member 656954]

When people propose variation such as this, they often do not think of the "chain reaction" of changes and questions that have to accompany such a scenario. Nothing is ever that simple.

Absolutely agree with that, and such sloppy thinking seems more evident in the sci-fi forum than the other forums¹, maybe because "If it's make believe, what does it matter..." Maybe, but having experts weigh in with scientifically astute comments and observations is appreciated to many of us working on being authors of science fiction, @ZapperZ, so thank you for your input

¹ And I'll sheepishly put my hand up for such thinking on topics related to my writing and to being surprised each time with a D'oh! because it is often blindingly obvious when it's pointed out and a little more research would have uncovered that