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[MetalSlimeHunt]

Yes, but when we're talking about terrestrial planets, the general assumption is that we're using Earth as the base metric.

[10ebbor10]

Then again, when talking about exoplanets the general norm is a massivegas giant, so ...

A bit of a useless discussion, as everything is small on an astronomical scale.

[MetalSlimeHunt]

I'm just saying, the significance of this exoplanet is that it is staggeringly Earthlike, and if the atmosphere is right...

Well, we might have to deal with carnivorous trees in a couple thousand years, but otherwise it's perfect.

[10ebbor10]

Doubt it actually. I mean convergent evolution will probably result in some form of photosynthetic life, but I doubt we would even have a similair chemical structure in order to serve as food.

[MetalSlimeHunt]

I was implying that it would be Earth trees turning carnivorous. If it doesn't have an ecosystem that can stop them, our plant life would utterly dominate this planet.

[Another]

I don't have links now but I saw some articles implying that the same around 20 basic amino-acids we are mostly made of are not coincidental. They kind of have the best fitness to assemble into self-replicating structures. So the chances are actually high that extraterrestrial life if it exists will be able to digest and be digested by us (at least on the bacterial level).

Sure silicon based life is theoretically possible but alternative chemistry is most likely evolutionary disfavored. (Except that left or right isomers of some molecules went one way completely arbitrary.)

[Another]

Random lifeform on Earth can also be highly toxic to humans or just inedible. The common building blocks starting point is followed by convergent evolution argument to some degree. And as I mentioned earlier there is always 50% chance to get wrong chirality.

[MetalSlimeHunt]

Something I don't see addressed often is that just because alien life can't eat us doesn't mean they won't try to eat us. Dumb animals/homicidal plants don't know they'll be fatally poisoned by trying Terran cuisine.

[Descan]

About the only times I can think where an animal wouldn't try and eat us is if it hunted/decide-to-eat by smell. Or hunted a very specific creature.

Hearing? Well we make sounds! Seeing? We reflect light. Touch? We're physical.

Taste? Well by that point you're already in a bit of a pickle.

'Course, this is all assuming they have the same senses, and also didn't have more sense that we don't/do fit in under "prey" category.

[scrdest]

'Course, this is all assuming they have the same senses, and also didn't have more sense that we don't/do fit in under "prey" category.

How likely would it be? Of billions of possible receptors, an alien race evolves to perceive the same-ish part of the electromagnetic spectrum in a same-ish way humans do, has chemical receptors that respond to similar particles in a recognizable way, has an apparatus geared for receiving and decoding acoustic waves?

And even presuming it does have all of those, that it processes them in a comprehensible to humans way? Hell, for all we know bats might perceive sound as we do light.



Oh, also, I've just read the presentation from a lecture about thermodynamic basis of life: can anyone tell me how it's not totally bullshit fitting reality to theory?

[MetalSlimeHunt]

And even presuming it does have all of those, that it processes them in a comprehensible to humans way? Hell, for all we know bats might perceive sound as we do light.

Uh, no. For one thing, bats kind of have eyes and all, so they perceive light as we do light.

And humans can echolocate if they really want to.

[Descan]

Well, yeah. The smell thing, it likely wouldn't smell anything we give off or vice-versa. The light, I don't know why we developed sight in the range we did, so I don't know what's stopping a microwave/infra-red capable ecosystem (I think there's a species of crustacean that has like, 19 different rods and cones?)

And hearing, that's mostly a matter of "Is there something here that is reflecting sound waves?" than a "I hear music!" style thing. They don't need to hear exactly what WE hear, they just need a way to perceive the vibrations in the air.

My main point: the animal only needs to perceive us in a manner that makes it willing to try and eat us. The only times it wouldn't try and eat us, if it can perceive us, is if we don't give off any phenomenon that a "prey" animal in it's ecosystem would (We can see, feel, and hear (if dropped) a rock, but I don't know of any creature that would try and eat it, thinking it's a food item) or if it only goes after a specific species that we don't resemble in whatever way it perceives things.

[Descan]

Well, regardless, if we go there then because we can't eat the shit there, we'd bring livestock and plants with us (or at least the plants, we might have artificial meat) and the creatures there would eat the plants despite it not doing anything for them.

[Helgoland]

Actually smelling them is pretty likely - the most prevalent smells are made of really simple compounds, the likes of which you'll probably find in extraterrestrial carbon-based life as well. Indeed our sense of smell is practically made for detecting any random molecule that happens to float onto our receptors...

[alway]

Sight: vision is most useful in whatever spectrum is most available in your environment and gives the most information about you environment. Visible wavelengths would likely be relatively close to the visible spectrum in Earth-life, with major variations based on their star's radiation as seen where they happen to be living. Not necessarily human-like, but probably a spectrum not too far from typical earth-fauna. Complex multicellular life would likely have some sort of eye-like structure, as it can give extremely valuable information along every step of the evolutionary chain. On earth, it ranges from simple light-sensitive skin patches to complex octopus eyes and lense apparatuses. It should be fairly simple to evolve the first steps, and is highly valuable in most plausible alien environments.

Smell/taste: these senses are both more or less molecule detectors; and would probably be quire likely to exist in some form in any relatively advanced organism, being necessary for determining usable forms of energy as compared to harmful substances, as well as being a fairly short step from cellular level mechanisms required for mono-cellular life.

So some of the basic senses would probably be somewhat related functionally in most environments