Europa or Enceladus

[kerbiloid]

There is NO 2d at all in this universe. All objects are 3d.

Plus, you're using Europa's surface, not the sunken area.

Earth life in concentrated in a room with area = 510 mln km2 and height ~= 200 m. Doesn't matter: sunken or not.

On land: 100 m between tree top and tree roots.

In ocean: 100 m below surface (where photosynthesis) and, say, 100m on the bottom (where eyeless creatures are eating sunken organic wastes).

Between them - a dark thick layer of water (where only rare whales are hunting lurking calmars. Because fishes need plankton: either at surface, either at bottom).

So if you imagine an Earth surface like a floor of room 10x10 meters, all living space would be a 0.5 micrometers thick.

As there are no stores from top to bottom (where organics could concentrate between surface and bottom), I think that you can treat this as a 2d distribution.

All things would float down until they become buoyant. So, in the middle, in a nice three dimensional area.

Yes. With no food, no hot water, no light.

There's not a hundred times more places for life to appear...

I mean, life had to form either in a hotspring or near geothermal vents...

Europa has a lot more water, and more sources of heat...

And more of Europa's ocean is warm.

(Yes, I presumed that all Europa ocean is a nice warm water.)

Seems to me, that the Early Earth (when life appeared) had hundred times more hot volcanic vents than Europa has now.

Even now, the Earth tectonical activity is still enough to move whole continents, which we can hardly see on Europa.

Lot more water - that is great, but what to do with it if there's nothing to eat?

And the food is produced only on the bottom - and stays mostly there, because who stays near the kitchen gets the most portion of food.

So, in Europa warm ocean:

100 m near the bottom: more or less rich with organics and gases. If there is life, its champions live there.

Say, 100-200 m: cheerleaders. Getting something to eat, too.

50000 m above: rare hungry loosers float aimlessly through the darkness, from time to time getting a molecula or two.

[AngelLestat]

Those erroneous thoughts were not scientific, but religious or philosophical, so your arguments fails in its beginning.

Also, silicon based life has never been proven (and is also unsound, giving the poor capabilities of such molecules), and the whole arsenic genome bacteria thing was proven to be a case of faster mouths than brains. Check your sources.

Oh, I am sorry, I feel some resentment from your part, I wonder why it will be?

If you are not open to the possibilities of different life, how it will be possible you find it?

You can have life in front of your rover camera and you will never notice it because you only search for dna.

About the arsenic in that particular bacteria, you are right, it was disproven, but the computer simulations points that is possible to remplace phosphorous with arsenic.

Is also mentioned in the "selfish gen" book, that to get evolution and complexity, you only need a not perfect replicator in a enviroment to allow such complexity. This can be anything, even things that are not material.

The problem with saying how life will be is like the problem of the theory of everythibg: Lack of DATA. Not the android, but empirical evidence.

Life is pretty well defined, actually...

The only thing defined is "life as we know it..."

http://www.nasa.gov/vision/universe/starsgalaxies/life's_working_definition.html

Read all, but I just want to quote something:

"But in order to formulate a general theory of living systems, one needs more than a single example of life. As revealed by its remarkable biochemical and microbiological similarities, life on Earth has a common origin. Despite its amazing morphological diversity, terrestrial life represents only a single case. The key to formulating a general theory of living systems is to explore alternative possibilities for life. I am interested in formulating a strategy for searching for extraterrestrial life that allows one to push the boundaries of our Earth-centric concepts of life."

[Tweety]

Life as we know it could exist everywhere or nowhere. Life as we don't know it, again could live everywhere or nowhere. There are FAR FAR too many assumptions into what 'alien' life is comprised of. I'm convinced there is life out there but I refrain from making judgements or assumptions on its compositions or how it came to be purely because our only data set for life is Earth.

You simply can't say it will be carbon based and oxygen breathing that must have formed at this depth of ocean with this radiation magnitude just because we are assuming it must be like the only life forms we know now.

On that note, give NASA and ESA more funding to prove there is life and its composition then let the debate begin

Tweety

[lajoswinkler]

Life as we know it could exist everywhere or nowhere. Life as we don't know it, again could live everywhere or nowhere. There are FAR FAR too many assumptions into what 'alien' life is comprised of. I'm convinced there is life out there but I refrain from making judgements or assumptions on its compositions or how it came to be purely because our only data set for life is Earth.

You simply can't say it will be carbon based and oxygen breathing that must have formed at this depth of ocean with this radiation magnitude just because we are assuming it must be like the only life forms we know now.

On that note, give NASA and ESA more funding to prove there is life and its composition then let the debate begin

Tweety

No, you can't make such assumptions. That's the "it's space, therefore anything is possible". It is not.

Life is governed by physical and chemical laws. They are universal. We know what some molecules can and what they can't. For example arsenic can't replace phosphorus in DNA and still be stable enough to allow hereditary information safety because the half life of its hydrolysis is too short.

Life can't exist in stars.

Life that occured here is what was the optimal solution for molecules. Don't expect much differences. Yes, some levels of organization will be radically different, but basic chemistry and body symmetry won't.

[-Velocity-]

No, you can't make such assumptions. That's the "it's space, therefore anything is possible". It is not.

Life is governed by physical and chemical laws. They are universal. We know what some molecules can and what they can't. For example arsenic can't replace phosphorus in DNA and still be stable enough to allow hereditary information safety because the half life of its hydrolysis is too short.

Life can't exist in stars.

Life that occured here is what was the optimal solution for molecules. Don't expect much differences. Yes, some levels of organization will be radically different, but basic chemistry and body symmetry won't.

I wouldn't be surprised if Earth life is the norm for naturally-occurring life forms. However, natural biological evolution cannot follow every single path of innovation. There could be radically different forms of life out there that had their genesis as artificial life created by an intelligence or intelligences. Such artificial life could even have inheritance and undergo natural selection and evolution. (And then there's a wide range of beings that could exist that could have a difficult time falling into a specific category, such as a race of intelligent machines.) Personally, I believe that at least somewhere out there in the universe, such life is likely to exist- unless we want to be racists and consider only naturally-evolved beings "true" life.

[Bill Phil]

Life has 7 criteria in the scientific world.

Homeostasis

Organization

Metabolism

Growth

Adaption

Response to stimuli

Reproduction

These are very general. All are necessary for life, and it's very likely that all extraterrestrial life follows these.

[Camacha]

All are necessary for life

Of course, they are, in the most literal sense imaginable, the definition of life. Though I am pretty sure we will need to adjust our view and definitions if and when we even encounter alien life. Some will be very obviously built along the same lines, others will quite possibly be something that we do not even recognize as life.

[Brotoro]

Reproduction is a requirement to be classified as life? So mules are not alive?

[Camacha]

Reproduction is a requirement to be classified as life? So mules are not alive?

They are viruses

[Bill Phil]

Reproduction is a requirement to be classified as life? So mules are not alive?

Their cells reproduce. But they're not a species as they can not reproduce with each other.

[lajoswinkler]

I wouldn't be surprised if Earth life is the norm for naturally-occurring life forms. However, natural biological evolution cannot follow every single path of innovation. There could be radically different forms of life out there that had their genesis as artificial life created by an intelligence or intelligences. Such artificial life could even have inheritance and undergo natural selection and evolution. (And then there's a wide range of beings that could exist that could have a difficult time falling into a specific category, such as a race of intelligent machines.) Personally, I believe that at least somewhere out there in the universe, such life is likely to exist- unless we want to be racists and consider only naturally-evolved beings "true" life.

At a biochemical level, I expect some sort of XNA with different base pairs. Some sort of stabilized coiled (saves space, low bond strain) strand (data) is to be expected. There are more than just A, C, T and G, and we use lots of others in the metabolism and genetics.

At a metabolic level we should encounter the most drastic differences. Metabolism is an enormous network and highly diverse in its parts even on Earth. It's one of the reasons why such being probably couldn't eat what we eat and vice versa. Also, the possibility of mutual infection should be very low as both sides have different nutrients and different biochemical apparatuses to deal with those. Typical enzymes from Earth would probably be useless for catalyzing breakdown of alien molecules and vice versa.

At a cellular level, basic organization of nucleus, cytoplasm and membrane is almost an axiom. Cell morphology might be radically different as the richness of our own Earth cells. Loads of shapes.

At a physiological level, basic rules of mass, surface and volume are obvious and must be respected.

At a morphological level (anatomy), basic rules apply. General rule is that what pushes itself through a fluid will have bilateral symmetry to facilitate mobility, and what stays attached and grabs food will be radially symmetric to increase the chance of predation. Variations are to be expected, of course, just like on Earth.

At a behavioral level (ecology), if the organisms have central processing units, we should expect a mixture of basic rules and great differences as we climb the organizational ladder. Simpler organisms will have expected tropisms and nastic movements, taxis and kinesis.

In the end, rules of evolution govern all of this and are unavoidable.

[Bill Phil]

Genetic material is pretty likely to have a sugar and some kind of nitrogenous base, plus something like a phosphate, if not a phosphate.

[Aanker]

It is a bit of a fallacy to claim that evolution/life always seeks the optimal solution. Just to mention two examples - for billions of years on Earth, bacteria would cyclically produce oxygen in a carbon dioxide rich environment, saturate the atmosphere with O2 and then massively kill themselves because of it. Secondly, there have been many species on Earth which defied the principle of optimal biology, with large colourful feathers or exaggerated spinal bone plates for display. Life develops in whichever ways it can develop, depending on constraints imposed by the environment.

But we should be able to speculate within reason based on what we know from life on Earth, of course. At least we know that the forms and dimensions of life we see on Earth are possible, and if we then find similar environments to these alien worls on our own planet we could imagine what scope of creatures would live there.

[Bill Phil]

Those bacteria were part of a process to be optimal, a necessary sacrifice for optimized systems. We're a part of that process, too.

Those things for display are to attract mates, hide, and plenty of other things.

[lajoswinkler]

It is a bit of a fallacy to claim that evolution/life always seeks the optimal solution. Just to mention two examples - for billions of years on Earth, bacteria would cyclically produce oxygen in a carbon dioxide rich environment, saturate the atmosphere with O2 and then massively kill themselves because of it. Secondly, there have been many species on Earth which defied the principle of optimal biology, with large colourful feathers or exaggerated spinal bone plates for display. Life develops in whichever ways it can develop, depending on constraints imposed by the environment.

But we should be able to speculate within reason based on what we know from life on Earth, of course. At least we know that the forms and dimensions of life we see on Earth are possible, and if we then find similar environments to these alien worls on our own planet we could imagine what scope of creatures would live there.

You're contradicting yourself there.

This is what evolution is all about. Optimal solution for a given problem a species is facing. Evolution has no goal, it can't predict what will happen. It's a blind process that sometimes ends in massive extinction like oxygen catastrophe. Mutations are a constant issue and the offspring which has the optimal phenotype has the best chance of survival and therefore to pass on that genetic makeup. Those bacteria had no idea oxygen will ultimatively kill their successors just like yeast has no idea it is producing ethanol that will eventually kill it.

Sometimes it's optimal to be tiny, sometimes to have large feathers, to be able to swim great distances, to eat a lot, to lose water at a very low rate, to be very social, to be as slippery as possible, to have stupidly huge eyes, to eat some of your babies, etc. There are no rules to this. Whatever is optimal has the best chance of surviving. It applies to all natural systems, whether it's complex organic molecules, butterflies, seaweed...

[Aanker]

Those bacteria were part of a process to be optimal, a necessary sacrifice for optimized systems. We're a part of that process, too.

Those things for display are to attract mates, hide, and plenty of other things.

That's the problem though - optimal for who? Certainly not for the species of bacteria which went extinct from the increased oxygen levels in the atmosphere and oceans.

The fact is, life just is: just like other phenomena of nature, it doesn't really have an end goal or purpose. Sure, an individual bacterium may seek to reproduce, but then that is hardly a process that occurs because said bacterium wants it (or has a sophisticated opinion on the matter) as much as it is a question of the right chemicals aligning in the correct amounts and patterns. I mean, I guess from a systems perspective life seeks 'balance', but then so do atmospheres, chemical cycles, orbits... it becomes a bit of a meaningless term.

[Bill Phil]

They made oxygen as a byproduct for their optimization of the local resources. Then everything died. Then new organisms used the byproduct as part of their optimization.