Extraterrestrial Life: How Similar Would It Be to Earth's Wildlife?

[baywax]

Every time I'm out in nature looking at the birds, snails, frogs, fish, plants and other wildlife I get this 2 part question going on in my mind.

1. On a planet like our own in orbit around a sun not unlike our own.. would the wildlife have similar features? Would there be "robins" and "thrushes" and eagles... carnivores, and herbivores and would the squirrels have the same tail or would there be squirrels at all?

2. If an extraterrestrial person came to our planet, would all of our wildlife and natural environment seem familiar to them? Or would they not recognize most of what we call the "great outdoors"?

If there are some answers among you, as speculative as you like... but based on scientific observations and calculations... please enter them here! Thank you.

 

[zoobyshoe]

1. On a planet like our own in orbit around a sun not unlike our own.. would the wildlife have similar features? Would there be "robins" and "thrushes" and eagles... carnivores, and herbivores and would the squirrels have the same tail or would there be squirrels at all?

I think a better question is whether life on that planet would bear any resemblance whatever to anything that has ever existed on earth. Our fossil record shows that the forms of animal life don't stand still, they're in constant flux. There are animals that existed at various times that you don't even know about because those periods haven't been popularized. No telling what microscopic animals have existed that we'll never know about. The early simple life forms on that other planet might end up evolving along completely different lines such that the dominant kind of life for millions of years would be huge, mobile, blobby plant things that "eat" everything in their path; all the immobile, rooted plants, such that anything vaguely reptilian, birdlike, or mammalian never gets a chance to flourish and evolve larger in size, there being very little to eat in the wake of the giant cannibal plants.

 

[jackmell]

I assume you mean in the entire evolutionary history of two appropriate planets, were there ever similarities between the life forms.

Life is massively contingent and as such it's evolution is greatly affected by it's history. Our world is also massively non-linear and sensitive to initial conditions. Finally, evolution is constrained by chemical and physical laws: you can only be so heavy and be successful with wings. I believe the first two factors would cause great variation between planets and the thirid, significant chemical similarity. Personally, I do not believe non-carbon-based complex life forms is possible. Once that is assumed and starting with sufficient chemical complexity, luck, and an energy source, proteins and nucleic acids follow and ultimately the process of Natural Selection leading to life forms on other habitable planets, chemically similar to Earth life, but quite different in phenotypes because of non-linear effects.

 

[ThomasEdison]

I would place bets that at a certain point in development for all intelligent species there comes at least one fork in the road where they decide whether or not to rebuild themselves. Once that happens their original biological form is moot and not worth talking about since they could adapt to any environment their technology allowed and lose their original form altogether.

 

[baywax]

I would place bets that at a certain point in development for all intelligent species there comes at least one fork in the road where they decide whether or not to rebuild themselves. Once that happens their original biological form is moot and not worth talking about since they could adapt to any environment their technology allowed and lose their original form altogether.

Jackmell has done an excellent job of pointing out some of the parameters involved in the development and evolution of extraterrestrial species.

I know my second question involves seeing our planet's species through extraterrestrial eyes but I'm trying to stay away from the "intelligent species" idea and to focus on the differences and similarities between terrestrial and extraterrestrial flora and fauna.

Jackmell points out that a planet with a slightly different g force may either give rise to or prohibit species that can fly. Of course, as adaptable as biological life is, a flying species would either evolve a lighter body or bigger wings in some cases. These sorts of conditions and adaptations are exactly what I'd like to see discussed. Colouration and how it can define species and sub-species is another.

 

[Shalashaska]

I don't know about gross anatomy here, but I think we can expect some similar features IF a particular trait arose. What I mean, is this: No one can really say whether flying or burrowing species will evolve, but IF they did, we can then make some predictions I think:

1: Scales, Feathers, Carapace, Skin: If life as we understand it exists and it can fly, we can reasonably expect structures similar to flaps of skin, feathers, scales, or insectoid features. Even if we're talking about radically different biology, the physics of flight remain unchanged (on a similar world).

The need for defense against the elements might or might not be significant, but any complex organism is going to have a partition between itself and its environment. That might be a jellyfish's bell, or armadillo armor, or even silica plates! It doesn't matter.

If there is a contrast in light vs. darkness, it would seem impossible for it NOT to be advantageous to have means to sense that. How that's accomplished could be myriad, from something like sight, to an EM sense, or temperature senses.

Scent is up for grabs, but anything that eats needs a way to determine what is food, and what is not. Smell, taste, sight, touch, sonar, radar, and other options still represent another sense needed to navigate the world of what is or is not food.

So, I don't know if you can say with current knowledge that a given form of life will evolve, but if it does (and we're not talking about something swimming in Jupiter's atmosphere or something equally exotic) we can probably expect basic functions to be filled.

That said, I think Zoobyshoe has the right of this, and it's more likely we wouldn't recognize alien life at all. If it followed thermodynamic processes familiar to all life on Earth (eat, excrete [heat or other]) we'd have a chance. Then again, maybe we'd conclude that the silicate equivalent of a plant was a crystalline formation?

 

[apeiron]

From the examples of convergent evolution it seems safe to say that an earth-like planet would produce a reasonably familiar story no matter how many times evolution was re-run.

http://en.wikipedia.org/wiki/List_of_examples_of_convergent_evolution

This is a standard example of the power of downward-acting global constraints in systems thinking of course.

If the global constraints are the same, local evolutionary accidents can only wander about so far in what is invisibly perhaps a constricted phase space of possible outcomes.

 

[Shalashaska]

From the examples of convergent evolution it seems safe to say that an earth-like planet would produce a reasonably familiar story no matter how many times evolution was re-run.

http://en.wikipedia.org/wiki/List_of_examples_of_convergent_evolution

This is a standard example of the power of downward-acting global constraints in systems thinking of course.

If the global constraints are the same, local evolutionary accidents can only wander about so far in what is invisibly perhaps a constricted phase space of possible outcomes.

I think it would have to be Earth, not just Earth-Like. Once you change major issue such as long-term climate patterns, and change the history of its impacts, I don't believe that convergent evolution other than (maybe) enzymatic and metabolic pathways would necessarily be similar. It isn't hard to imagine a hotter, oxygen rich "Earth" in which insects and plants dominated all other species before reptiles or mammals could evolve.

 

[apeiron]

It isn't hard to imagine a hotter, oxygen rich "Earth" in which insects and plants dominated all other species before reptiles or mammals could evolve.

But exoskeletons are such a constraint on size that endoskeletons would surely arise at some point. Then away we go.

 

[Shalashaska]

But exoskeletons are such a constraint on size that endoskeletons would surely arise at some point. Then away we go.

They are a constraint on size, based on the availability of (in the case of Earth) Oxygen. Besides, add a few more G's, and maybe being BIG isn't all it's cracked up to be. Remember, a big creature needs a big biosphere to feed on, but that might not be possible. A highly coordinated group of smaller organisms, such as ants, seems to be effective. I can see how endoskeletons would be advantageous in some forms, so I'm not saying the idea is outrageous or anything like that. I don't think it's a forgone conclusion however. If this other Earth is subject to frequent bombardment beyond what our planet is, then larger life might not be advantageous at all. If life in that planet is subject to more extreme changes in temperature, or the need to be in oceans or underground for much of the time, then endoskeletons start to look a bit unhelpful.

 

[zomgwtf]

Life is massively contingent and as such it's evolution is greatly affected by it's history. Our world is also massively non-linear and sensitive to initial conditions.

Definitely

Finally, evolution is constrained by chemical and physical laws: you can only be so heavy and be successful with wings.

Yup, so maybe organisms on other planets the size of elephants on Earth can 'fly' or maybe they can just float.

I believe the first two factors would cause great variation between planets

Sure, no doubts here.

and the thirid, significant chemical similarity. Personally, I do not believe non-carbon-based complex life forms is possible.

Why do you make this assumption? I do not believe this is a correct or valid assumption to make from a scientific point of view. Can you back it up with sources? What about life in an NO2 atmosphere... or NH3 atmosphere. It's been shown that P-N organisms could possibly develop in these situations. So why then should we dismiss the possibility and assume that carbon based life that we know and love here on Earth is the only possible way for life to rise?

Once that is assumed and starting with sufficient chemical complexity, luck, and an energy source, proteins and nucleic acids follow and ultimately the process of Natural Selection leading to life forms on other habitable planets, chemically similar to Earth life, but quite different in phenotypes because of non-linear effects.

I'm not sure what you mean by 'habitable planets' I sure hope it's not another assumption about life in the universe necessarily requiring Earth-like conditions. I also don't agree that we should assume life on other planets should be chemically similar to what we have on Earth. Even assuming life elsewhere in the universe is carbon based why can't they use different amino-acids? I'm pretty sure we've even found amino-acids on meteorites... which are not (or haven't been) found on Earth...

 

[jackmell]

Other non-carbon aggregates may be possible but I do not believe they can attain any level of living complexity: containment, metabolize, reproduce, and evolve. I say that because of the chemistry of carbon:

http://www.answers.com/topic/organic-chemistry

"There are two elements noted for their ability to form long strings of atoms and seemingly endless varieties of molecules: one is carbon, and the other is silicon, directly below it on the periodic table."

http://astrobiology.nasa.gov/ask-an-astrobiologist/question/?id=144:

"Carbon is an ideal element for complicated living systems because it has four unpaired electrons enabling it to have four stable covalent bonds with other elements. With such bonding versatility, (not to mention the given abundance of carbon in the universe), carbon is able to form long chains, rings, and other complex molecules. Cabon-based molecules can take on many different forms from DNA and neurotransmitters to human hair and squid ink! No other element has yet shown the bonding versatility and stability of carbon, not to mention the property of self-replication unique to some carbon-based molecules. "

Then that means to me we have only two choices for complex life forms: carbon or silicon. But silicon-based complex life forms are unlikely:

Quote: http://www.daviddarling.info/encyclopedia/S/siliconlife.html

"Conceivably, some strange life-forms might be built from silicone-like substances were it not for an apparently fatal flaw in silicon's biological credentials. This is its powerful affinity for oxygen. When carbon is oxidized during the respiratory process of a terrestrial organism (see respiration), it becomes the gas carbon dioxide – a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of such a substance would pose a major respiratory challenge.

Life-forms must also be able to collect, store, and utilize energy from their environment. In carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. These enzymes are large, complex molecules (see proteins) which catalyze specific reactions because of their shape and "handedness." A feature of carbon chemistry is that many of its compounds can take right and left forms, and it is this handedness, or chirality, that gives enzymes their ability to recognize and regulate a huge variety of processes in the body. Silicon's failure to give rise to many compounds that display handedness makes it hard to see how it could serve as the basis for the many interconnected chains of reactions needed to support life."

Also, "different amino acids" in my opinion is similar chemistry because of the amide bonds between them.

 

[baywax]

Definitely

Yup, so maybe organisms on other planets the size of elephants on Earth can 'fly' or maybe they can just float.

Sure, no doubts here.

Why do you make this assumption? I do not believe this is a correct or valid assumption to make from a scientific point of view. Can you back it up with sources? What about life in an NO2 atmosphere... or NH3 atmosphere. It's been shown that P-N organisms could possibly develop in these situations. So why then should we dismiss the possibility and assume that carbon based life that we know and love here on Earth is the only possible way for life to rise?

I'm not sure what you mean by 'habitable planets' I sure hope it's not another assumption about life in the universe necessarily requiring Earth-like conditions. I also don't agree that we should assume life on other planets should be chemically similar to what we have on Earth. Even assuming life elsewhere in the universe is carbon based why can't they use different amino-acids? I'm pretty sure we've even found amino-acids on meteorites... which are not (or haven't been) found on Earth...

This sort of reasoning also applies to many areas with reference to the conditions created by the type of sun and resultant light.. the abundance of minerals is also a factor and how its distributed. The atmosphere, as has been pointed out, could be any of the large number of variations possible with atmospheric gases. All these factors weigh, heavily, on the form and function of the evolutionary outcome, the species. About non-carbon based life forms. I've never met one, or if I have they didn't introduce themselves as such.

 

[zomgwtf]

About non-carbon based life forms. I've never met one, or if I have they didn't introduce themselves as such.

You've been to other planets :/?

 

[baywax]

You've been to other planets :/?

Not that I know of. I'm just saying that if a pool of methane is supporting life, I haven't recognized what its supporting as life.

There are a series of questions we could work with to help understand what environmental constraints would produce what features of adaptation in extraterrestrial species. We already started this with the idea the gravity produced by each different planet will determine the sizes of the species and the form and function of any flying creatures.

What if the planet were ultra rich in iron?

What if the bedrock was pure quartz or another mineral rather than granite?


There are so many variables. Would the stages of evolution be similar? Would there be a distinct division between plant and animal life?... etc...

 

[Shalashaska]

Not that I know of. I'm just saying that if a pool of methane is supporting life, I haven't recognized what its supporting as life.

There are a series of questions we could work with to help understand what environmental constraints would produce what features of adaptation in extraterrestrial species. We already started this with the idea the gravity produced by each different planet will determine the sizes of the species and the form and function of any flying creatures.

What if the planet were ultra rich in iron?

What if the bedrock was pure quartz or another mineral rather than granite?


There are so many variables. Would the stages of evolution be similar? Would there be a distinct division between plant and animal life?... etc...

The biggest difference would be an element other than Nitrogen dominating our atmosphere. As it happens, undersea vents have shown bacteria which utilize methane. That said, all of this is constrained by the initial conditions of life on this planet, and the fact that methane isn't the dominant element here. A planet which was never hospitable to life based on a scaffold of carbon, filled with water, and breathing nitrogen (inert for us or not) would provide a place for those organisms to develop in more than a niche.

 

[jackmell]

Is is narrow-minded to think just carbon and similar biochemistry throughout the Universe? I'm tempted to think so just because it's so big and we're so small. But we're working with the same elements on the other side of the galaxy and other galaxies and those elements are still constrained by the same quantum mechanical properties we observe on earth.

We're familiar with Punctuated Equilibrium but what does it really mean? In our Universe change is not smooth and continuous but rather "punctuated" by events which if reached, cause abrupt and dramatic change often resulting in qualitatively different behavior. It is the existence of these "critical points" which I believe is a major driving force in evolution.

But since the universe is so non-linear, we can't expect the same sequence of event to happen in the same order anywhere in the Universe: on another planet just like ours, even after 4 billion years of evolution, there may still only be invertebrate-like creatures because events did not conspire to reach the critical points necessary for further evolution. Likewise, on still other planets, evolution may have gone further then on our planet.

Still though I believe the limiting factors of chemistry will constrain the evolution of life on other planets to follow some similar patterns found on Earth and so have some similar morphologies in their evolutionary history and quite similar biochemistry.

 

[Shalashaska]

Is is narrow-minded to think just carbon and similar biochemistry throughout the Universe? I'm tempted to think so just because it's so big and we're so small. But we're working with the same elements on the other side of the galaxy and other galaxies and those elements are still constrained by the same quantum mechanical properties we observe on earth.

We're familiar with Punctuated Equilibrium but what does it really mean? In our Universe change is not smooth and continuous but rather "punctuated" by events which if reached, cause abrupt and dramatic change often resulting in qualitatively different behavior. It is the existence of these "critical points" which I believe is a major driving force in evolution.

But since the universe is so non-linear, we can't expect the same sequence of event to happen in the same order anywhere in the Universe: on another planet just like ours, even after 4 billion years of evolution, there may still only be invertebrate-like creatures because events did not conspire to reach the critical points necessary for further evolution. Likewise, on still other planets, evolution may have gone further then on our planet.

Still though I believe the limiting factors of chemistry will constrain the evolution of life on other planets to follow some similar patterns found on Earth and so have some similar morphologies in their evolutionary history and quite similar biochemistry.

I don't think it's narrow-minded at all, even if I don't agree. It's hard to imagine some of the forms of life that exist HERE on Earth, never mind novel chemistries or a Carbon Earth. I think it's fair to say that life based on the same compounds we find on Earth would at least use similar metabolic pathways. I don't believe that holds at all for forms of life that might exist in extremes of temperatures and in elements we're simply not able to study here. I'd say this is a fine argument for more research in the lab of our solar system.

 

[baywax]

Is is narrow-minded to think just carbon and similar biochemistry throughout the Universe? I'm tempted to think so just because it's so big and we're so small. But we're working with the same elements on the other side of the galaxy and other galaxies and those elements are still constrained by the same quantum mechanical properties we observe on earth.

We're familiar with Punctuated Equilibrium but what does it really mean? In our Universe change is not smooth and continuous but rather "punctuated" by events which if reached, cause abrupt and dramatic change often resulting in qualitatively different behavior. It is the existence of these "critical points" which I believe is a major driving force in evolution.

But since the universe is so non-linear, we can't expect the same sequence of event to happen in the same order anywhere in the Universe: on another planet just like ours, even after 4 billion years of evolution, there may still only be invertebrate-like creatures because events did not conspire to reach the critical points necessary for further evolution. Likewise, on still other planets, evolution may have gone further then on our planet.

Still though I believe the limiting factors of chemistry will constrain the evolution of life on other planets to follow some similar patterns found on Earth and so have some similar morphologies in their evolutionary history and quite similar biochemistry.

All in all I think your first statements are correct in comparison to later in your post... since the universe is non-linear there is nothing that says evolution would unfold in the same manner it has on earth. However, the only evidence of extraterrestrial species we have to date suggests that the beginning stages resemble what has occurred here on earth... when we look at the (proposed) fossil record of the planet mars.

[PLAIN]http://blog.everythingdinosaur.co.uk/meteorite_mars_life.jpg

Again, however, Mars is subject to the same radiation as Earth from the same sun, and is probably composed of similar minerals, being from the same solar system.

 

[Shalashaska]

All in all I think your first statements are correct in comparison to later in your post... since the universe is non-linear there is nothing that says evolution would unfold in the same manner it has on earth. However, the only evidence of extraterrestrial species we have to date suggests that the beginning stages resemble what has occurred here on earth... when we look at the (proposed) fossil record of the planet mars.

[PLAIN]http://blog.everythingdinosaur.co.uk/meteorite_mars_life.jpg

Again, however, Mars is subject to the same radiation as Earth from the same sun, and is probably composed of similar minerals, being from the same solar system.

That's a fair statement, which is yet another good reason to start firing probes to return samples sooner rather than later.

 

[zomgwtf]

That's a fair statement.

Agreed. Although, I stand by my original statement that it is far too early in the bioastronomy game to definitively say organisms can only be carbon based.

 

[Shalashaska]

Agreed. Although, I stand by my original statement that it is far too early in the bioastronomy game to definitively say organisms can only be carbon based.

I agree with that as well, and in fact I'm in you camp when it comes to belief that while carbon based life is possible, so is life based on other chemistry. The nature of their primary, their orbit, and initial conditions for life would be VERY critical. If life based on our scaffolding can't exist on a given planet, but another chemistry COULD dominate, not having to compete with ours changes matters.

From the standpoint of evidence however, baywax has it.

 

[baywax]

I agree with that as well, and in fact I'm in you camp when it comes to belief that while carbon based life is possible, so is life based on other chemistry. The nature of their primary, their orbit, and initial conditions for life would be VERY critical. If life based on our scaffolding can't exist on a given planet, but another chemistry COULD dominate, not having to compete with ours changes matters.

From the standpoint of evidence however, baywax has it.

Here's an answer from NASA to a grade 10 student who asked if life could exist on Europa (where the rain on the plain is methane).

Scientists have occasionally speculated that life could be based on an element other than carbon. Silicon, being the lightest element with an electronic structure analogous to that of carbon (having a half-filled outer shell with 4 unpaired electrons), is the most likely candidate mentioned. However, carbon's tendency to form the long chains and rings that form the basis for organic compounds that at some level of complexity begin to self-replicate is unique. Also, because older stars naturally produce carbon, along with nitrogen and oxygen (its neighbors on the periodic table), it is relatively abundant in the universe. Many astrophysicists who study the spectra of stars believe that complex chains and even rings of carbon appear in such unlikely places as stellar envelopes (e.g., in the form of PAHs, polycyclic aromatic hydrocarbons). When such compounds reach cooler regions of space where they can bond with readily available hydrogen, organic compounds as we know them are naturally formed.
Although other elements may form complex, covalently bonded structures, none has the rich molecular variety of carbon. It is the chemistry of carbon that allows us to consider the possibility of life "as we know it" in other parts of the Galaxy and the Universe beyond. We do not know whether Earth-like conditions exist elsewhere; but if they do, it is highly likely that life forms, if they exist, will be based on carbon.

One more point: The organic types of structures appearing in stellar envelopes are very hot and probably stripped of hydrogen, so that they are not themselves alive; it is only when carried off to a more hospitable environment, such as a much cooler planet 100 million miles away or so, that the kind of chemistry required by life becomes possible on a scale large enough to allow for stable development and replication. Water is also a factor, causing the hydrophobic proteins to clump together at all, and serving as a medium a conduit for new material, protection from temperature changes and harmful stellar radiation, etc.

Mark Kowitt and Damian Audley
for Ask an Astrophysicist.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980221b.html

The basics for forming life as we know it seem too fundamental to try and compromise or switch and bait with. That's why I'm really more interested in the variety of life we'd see else where. The varieties and the determining factors that bring about that variety are a huge chunk to bite off... as it is

 

[zoobyshoe]

The basics for forming life as we know it seem too fundamental to try and compromise or switch and bait with. That's why I'm really more interested in the variety of life we'd see else where. The varieties and the determining factors that bring about that variety are a huge chunk to bite off... as it is

Given carbon as the sine qua non of life, the next step would be to determine how many possible initial leaps there are from that which is just chemical to that which is life. It could be there's only one possible way, which means we could go to the next step and ask to what extent variations are possible from the first thing which is life to the next step. And so on. As more branches become possible you could start eliminating the ones that were taken on Earth in order to arrive eventually at the most "alien" possible variations. In this way you could get a sketch of how very different life could be.

 

[baywax]

Given carbon as the sine qua non of life, the next step would be to determine how many possible initial leaps there are from that which is just chemical to that which is life. It could be there's only one possible way, which means we could go to the next step and ask to what extent variations are possible from the first thing which is life to the next step. And so on. As more branches become possible you could start eliminating the ones that were taken on Earth in order to arrive eventually at the most "alien" possible variations. In this way you could get a sketch of how very different life could be.

Good point Zooby... sorry I missed your first post on this thread.

With regard to the two starting points of life on a planet... abiogenisis and panspermia... I like to try and calculate the percentage of probability for each beginning of life on a planet. What are the odds for "habitable planets" to be seeded with interstellar or inter planetary viruses or megabacteria and what are the odds for the same to support the actual formation of life... from scratch?

For instance, Earth may well have been an incubator for life that simply drifted here from mars... with Mars being the site of abiogenisis... (as an hypothetical example).

 

[Shalashaska]

Good point Zooby... sorry I missed your first post on this thread.

With regard to the two starting points of life on a planet... abiogenisis and panspermia... I like to try and calculate the percentage of probability for each beginning of life on a planet. What are the odds for "habitable planets" to be seeded with interstellar or inter planetary viruses or megabacteria and what are the odds for the same to support the actual formation of life... from scratch?

For instance, Earth may well have been an incubator for life that simply drifted here from mars... with Mars being the site of abiogenisis... (as an hypothetical example).

I think the odds are pretty good were you have liquid H₂O, a decent magnetosphere to preserve that, carbon, a LOT of nitrogen, and acidic regions... you could reasonably expect that something like virions might emerge. How that translates into life, or life which can persist, GOK?!

 

[baywax]

I think the odds are pretty good were you have liquid H₂O, a decent magnetosphere to preserve that, carbon, a LOT of nitrogen, and acidic regions... you could reasonably expect that something like virions might emerge. How that translates into life, or life which can persist, GOK?!

Yes...

I'm just trying to get people to figure out

1. what percentage of life bearing planets got their life started by panspermia and

2. what percentage got life started with abiogenisis.. ?

(for the moment)

 

[zomgwtf]

The planet must also be geologically active. I don't think life can rise up on an 'unactive' planet. An important part in abiogenisis on Earth was the large about of geological activity occurring.

In regard to panspermia, I think it would be much more likely that life arises from abiogenisis.

 

[baywax]

The planet must also be geologically active. I don't think life can rise up on an 'unactive' planet. An important part in abiogenisis on Earth was the large about of geological activity occurring.

In regard to panspermia, I think it would be much more likely that life arises from abiogenisis.

Hi zomgwtf... could you please explain your bias toward abiogenisis. There has been no study that I know of that shows Earth was a site for abiogenisis. This is very hard to prove but I think there could be a study devised to show how life came to flourish on planet earth.

 

[Shalashaska]

There was a recent Sci-Am article about dating and characterizing the range and magnitude of the Earth's early magnetic field, putting the magnetopause at about 30,000 (miles or kilometers... I forget). A planet without a dynamo to produce a strong magnetic field, would have any H₂O blasted away over time. That certainly implies the need for geological activity, or something very exotic that I can't think of.

As for panspermia or abiogenisis, I could see it being either, or both. There are excellent cases made for both, and nothing even close to decisive. We need to be landing probes on asteroid, moons, and comets and taking samples if we can, not to mention Titan, and mars. I'm more inclined to look for factors which preserve water (not ice)... the rest seems doable given the odds, but without water, Earth-like chemistry is a no-go.

 

[zoobyshoe]

Good point Zooby... sorry I missed your first post on this thread.

With regard to the two starting points of life on a planet... abiogenisis and panspermia... I like to try and calculate the percentage of probability for each beginning of life on a planet. What are the odds for "habitable planets" to be seeded with interstellar or inter planetary viruses or megabacteria and what are the odds for the same to support the actual formation of life... from scratch?

For instance, Earth may well have been an incubator for life that simply drifted here from mars... with Mars being the site of abiogenisis... (as an hypothetical example).

Panspermia can be considered a form of mass extinction: all life forms that did not get ejected into space and survive are effectively extinct as far as the new environment is concerned. This throws a twist into the game: in the new environment the life will evolve differently than it would have on the home planet, not only because the environment is different, but because all it's competitors and symbiotes are gone.

As for probabilities, I have the feeling that moving from chemical to life must needs be probable. It's hard to believe it is so delicate that it only happened on one planet and spread to the rest (assuming there is, or has been, life elsewhere). Perhaps there is some strain of primitive bacteria or mold or algae or whatever so ubiquitous no one is surprised to find it in the soil here any where on earth, but, in fact, it has been generated from scratch during the last lightning storm. In other words, perhaps abiogenesis is ongoing and chronic. However, that could be ignorant raving. I'm not sure. Someone might be able to easily explain why that's impossible.

 

[DaveC426913]

I agree with that as well, and in fact I'm in you camp when it comes to belief that while carbon based life is possible, so is life based on other chemistry. The nature of their primary, their orbit, and initial conditions for life would be VERY critical. If life based on our scaffolding can't exist on a given planet, but another chemistry COULD dominate, not having to compete with ours changes matters.

This argument presupposes that there are alternate possibilities for complex chemistry / life.

But are there?

We have access to all elements here on Earth under controlled and uncontrolled conditions, and what we see is that there are precious few combinations that can (let alone might) form very complex molecules. It just doesn't happen.

Question: what is the most complex non-organic molecule known?

 

[jackmell]

I do not see a problem with abiogenisis at all and feel panspermia is unlikely unless it "rained" down continuously for thousands of years. Given a sufficiently complex chemical mixture, time, and energy, "complexification" emerges naturally. That's what I believe and is proposed by Stuart Kauffman and John Casti in the books "At Home in the Universe" and "Complexification". Two other, "Signs of Life" and my all-time-favorite, "Self-Organization in Biological Systems" convince me that life is inevitable. I believe anyone that reads those four books would find final comfort in the matter of how life may have arose on this planet starting from simple chemicals. That's what happen to me. :)

 

[Shalashaska]

This argument presupposes that there are alternate possibilities for complex chemistry / life.

But are there?

We have access to all elements here on Earth under controlled and uncontrolled conditions, and what we see is that there are precious few combinations that can (let alone might) form very complex molecules. It just doesn't happen.

Question: what is the most complex non-organic molecule known?

I don't know without using Google regarding your question, so I won't insult you with a random guess. That being said, Nitrogen, Chlorine, Sulphur, Arsenic, Phosphorus, Methane, Silicon/Silanes and more are all viable in roles that replace carbon. Given the limited scope of our "laboratory" and ongoing discoveries about the synergistic role of plants and bacteria, fungi and bacteria, and human's and viruses (which are organic, but alive?), I tend not to assume that we have a lock on biochemistry.

Question: How many different combinations does it take, especially if Planet 'B' is never hospitable to carbon-based life, and therefore P-N types never have to compete in that arena? Hell, for all I know you could have a form of life based on electromagnetic interactions within rock formations in a planet close enough to its primary. I don't really see that as likley, and I wonder if that would be life or just a thermodynamic system, but then I wonder if we're equipped to know the difference in enough cases? We have access to elements, but the conditions in which we find them and manipulate them are limited by our technology (after we have a chem lab on Venus, Mars, and Titan I'll be more inclined) and scale.

 

[zomgwtf]

P-N is also known to form rings and chains I'm pretty sure.