Lonely Life? – Is Earth the only planet with life in our galaxy?

[Jens]

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This is a much more speculative side topic to the main topic “Early Life! -- Life could only originate early or not at all.”

If you question the thesis of the main topic, read the details and post a comment in the main topic – not here.

This topic is a discussion under the assumption that the thesis in the main topic is right:

• Life could only originate early during meteorite bombardment (and not later).
• Life originated on Earth and not from another planet.

This means we cannot deduct from early emergence of life that origin of life is a likely event.

 

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Full text with all the references and details

 

Abstract

The thesis presented in ‘Early Life’ implies that life could only emerge during the meteorite bombardment and not after it ended. Typically it is assumed that life emerges on all Earth-like planets. However, the only reason for this assumption is that life emerged so early on Earth. This is taken as prove that life emerges everywhere, if the environment is suitable. If we now have to assume that life could only emerge very early on Earth and not later, this means, we cannot deduct from early emergence of life that origin of life is a likely event. In contrast the more you investigate the details of the biochemistry of metabolism, replication, transcription and translation, the more you see stunning complexity, which cannot be reduced in a simple way. Even the most primitive looking life forms are not primitive at all. With the current knowledge, we have to assume that the emergence of life is an incredibly unlikely event.

 

Life is Rare

The usual argumentation – especially in astronomy – for how likely you can find life outside Earth goes as follows:

 

Contra existence of extraterrestrial life:

A) If life has originated on every suitable planet in our galaxy, there should be some planets which have evolved intelligent life for example 100 million years before humans and should have colonized the galaxy already. So we either should already have had contact or we should not exist at all. This argument has been disputed: The evolution of complex higher life forms is unlikely and that is the reason why we do not have seen any other intelligent life elsewhere. The evolution of complex multicellular life forms requires a constant temperature range over some hundreds of millions years, which is more difficult to obtain than one might think. Indeed it looks that not only the exact distance to the sun but also a stabilizing big moon and a protecting big planet like Jupiter and roughly the right amount of mass-extinction events are needed. However, you can also argue that emergence of complex animal-like higher life forms is no issue at all since this event mainly depends on oxygen level which was reached only about 1000 million years ago. In addition the authors of Rare Earth are likely to underestimate the power of life in assuming that roughly 45°C is the upper limit for complex life. The upper limit can easily be 60°C (or more) and the only reason for not having complex life on Earth in this temperature range is that the habitats with this temperature are rather small (center of hot springs) or dry. There are for example multicellular fungi which can live in human-made piles of organic matter up to 60°C, which show that Eukarya can actually survive such temperatures. This makes it likely that given the proper large and humid environment also more complex life forms could survive temperatures much higher than 45 °C.

 

B) Even though the current knowledge in science of the biochemistry of life is already very detailed it looks actually nearly impossible that a self-replicating system can appear spontaneously (see chapter Details V below). The statement of Francis Crick ‘At present, the gap from the primal „soup“ to the first RNA system capable of natural selection looks forbiddingly wide’ is still very true!

 

Pro existence extraterrestrial life:

C) Life originated very early on Earth, this means origin of life is simple and will happen under every suitable environment.

 

In this article I try to show that emergence of life could only happen early or not at all. This in turn means that there is no prove at all that emergence of life is something that happens easily and this means also that argument C is not valid.

 

In contrast we have to take the biochemical evidence for argument B (see page 2 chapter ‘Details V: Why is the Emergence of Life an Unlikely Event’) into account, even if the result is not what we might wish. Therefore I think that:

• It is likely that Earth is the only planet with life in our galaxy.
• There will be no life found, neither on Jupiter’s moon Europa (which probably has a layer of liquid water underneath ice) nor on Mars
• We will not find extraterrestrial planets with a spectrum indicating high oxygen (O₂) concentration in the atmosphere (which in turn indicates existence of life).
• We will not be able to re-produce the origin of life in vitro

We should consider seriously that we are alone and that Earth is the only planet where we can live (without waiting some ten thousand to million years of terra-forming of another planet with liquid water). Life is a very unique thing. We simply do not realize this, since we are so used to it.

Of course those statements cannot be proven yet and cannot be deducted without doubt based on current data. However, even under scientists it has become so common to state that there must be life on every suitable planet, that I feel a strong statement against this is necessary to keep the focus on the currently known facts. We should do so even if we (including myself) might which it were different.

Since it is quite possible that in our galaxy life is unique on Earth we should consider investing more in protecting this heritage by any means (protecting habitats, seed banks, genetic libraries, and taxonomy research projects of higher organisms and especially in microbiology).

Edited December 21, 2012 by Jens

[Moontanman]

Are you saying that life is rare or complex life is rare?

[Jens]

I am saying life as such is rare.

 

(because the early origin was the only possibility: see topic http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/ )

 

I do not think that complex life is rare (once there is life at all).

 

However, as mentioned above: This is really very speculative .

Edited December 22, 2012 by Jens

[Moontanman]

I see no reason what so ever to assume your basic premise of life being rare is correct nor do i see any reason to think that complex life is likely to arise if simple life arises.

 

You have created a false delima, not only are both your premises ad hoc, with a data point of one neither can be extrapolated with any assurance of accuracy

[Jens]

No, I did not want to make ad hoc assumptions.

To avoid a chaotic discussion I have split my thoughts into two discussions topics (both in this forum):

 

1)

http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/

 

2)

this topic

 

This topic here is very speculative.

The topic 1 is more serious (and is my main topic). There I claim that life could only emerge early or not at all. Please have a look at it. You can start discussion there.

 

Here I wanted to discuss the consequences:

 

Is extraterrestrial life still probable, even if we assume that early emergence of life does not indicate anything?

(because life could only originate under the conditions of early earth.)

 

looking forward to your comments

Jens

Edited December 25, 2012 by Jens

[Moontanman]

Thomas Gold speculated, somewhat controversially, that life is a naturally occurring chemical process that all nearly all planets develop at some point but generally becomes extinct as chemical processes change as the planet changes.

[pratibha_sharma08]

Hi Jens

 

I just read the topic and want to ask if your question or discussion is concentrated on the topic that existence of life on any other planet or existence of life without oxygen is possible or not

 

Thanks for sharing knowledgeable material above

 

Regards,

Pratibha

[Jens]

I just read the topic and want to ask if your question or discussion is concentrated on the topic that existence of life on any other planet or existence of life without oxygen is possible or not

 

Existence of life without oxygen is possible. Life started on earth without oxygen and there are still today many Bacteria and especially Archaea which live under oxygen-free environment. Photosynthesis made it possible to take electrons from water (and thereby producing oxygen) to reduce CO₂ for production of biomolecules. So photosynthesis reduced the dependency of life from its environment dramatically (since light, water and CO2 are easy available) but definitely is not the first step of life. It evolved actually much later. It is a very complex "invention" by cyanobacteria which happened only once on earth and then was brought into some Eukaryotes (the plants) by using cyanobacteria a cell organelles (the chloroplasts). So life produced oxygen and not the inverse.

 

Thomas Gold speculated, somewhat controversially, that life is a naturally occurring chemical process that all nearly all planets develop at some point but generally becomes extinct as chemical processes change as the planet changes.

 

Hi,

as written above I like to discuss this in the other topic in this forum:

http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/

I have posted my answer and comments there.

thanks, Jens

[Moontanman]

No, I did not want to make ad hoc assumptions.

To avoid a chaotic discussion I have split my thoughts into two discussions topics (both in this forum):

 

1)

http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/

 

2)

this topic

 

This topic here is very speculative.

The topic 1 is more serious (and is my main topic). There I claim that life could only emerge early or not at all. Please have a look at it. You can start discussion there.

 

Here I wanted to discuss the consequences:

 

Is extraterrestrial life still probable, even if we assume that early emergence of life does not indicate anything?

(because life could only originate under the conditions of early earth.)

 

looking forward to your comments

Jens

 

 

Exactly how long are you assuming the conditions for the origin of life lasted on the Earth?

[CarbonCopy]

Maybe we are being too narrow minded in our definition of life. There might be living things out there that we cannot even imagine of, that use some exotic type of biochemistry, maybe something other than carbon. They could use arsenic instead of phosphorus. There could be life forms floating in Jupiter living happily in the extreme conditions there.

On the other hand, life as WE know it could be quite rare, given the multitude of conditions required for earth like life.

[Jens]

Maybe we are being too narrow minded in our definition of life. There might be living things out there that we cannot even imagine of, that use some exotic type of biochemistry, maybe something other than carbon. They could use arsenic instead of phosphorus. There could be life forms floating in Jupiter living happily in the extreme conditions there.

On the other hand, life as WE know it could be quite rare, given the multitude of conditions required for earth like life.

 

There are some contraints, however:

Liquid phase seems to be necessary to allow enough chemical reactions in a volume. Most important you need to have the possiblity to have an near endless amount of possibilities of defined 3D structures, so that specific catalysis is possible. The only system which seem to allow for this is a liquid with hydrogen bonds. Given the relative abondance of atoms this means either liquid H₂O or liquid NH₃. Huge part of the known biochemistry is based on reactions with carbon making double bounds to O, N, C. (Atoms in the next period like Si, P, S cannot do this). So there are some reasons about life beeing based on carbon molecules in water.

 

Exactly how long are you assuming the conditions for the origin of life lasted on the Earth?

Those conditions are given between the time liquid water was present and after the last impact which heated the surface of the whole earth to temparatures higher than lets say 150°C and the time stable oceans have been formed.

 

Since I think only under conditions of permament concentration and dilution cycles abiogenesis can happen.

[Moontanman]

 

 

There are some contraints, however:

Liquid phase seems to be necessary to allow enough chemical reactions in a volume. Most important you need to have the possiblity to have an near endless amount of possibilities of defined 3D structures, so that specific catalysis is possible. The only system which seem to allow for this is a liquid with hydrogen bonds. Given the relative abondance of atoms this means either liquid H₂O or liquid NH₃. Huge part of the known biochemistry is based on reactions with carbon making double bounds to O, N, C. (Atoms in the next period like Si, P, S cannot do this). So there are some reasons about life beeing based on carbon molecules in water.

 

I think Boron has some possibilities, it's chemistry is at least as complex as carbon, it does suffer from rarity..

 

Those conditions are given between the time liquid water was present and after the last impact which heated the surface of the whole earth to temparatures higher than lets say 150°C and the time stable oceans have been

Again, it seems a bit unlikely there would have been a time when multiple impacts would have allowed the specific conditions required by your idea. you are assuming that impacts would have been smaller and smaller as time went on. I see no reason to assume this...

Since I think only under conditions of permament concentration and dilution cycles abiogenesis can happen.

 

 

This seems unlikely to happen in the required order...

 

Sorry for the weird quote, seems to be a problem...

[too-open-minded]

The kepler telescope has pretty recently been put into action. It is the first telescope put in space who's sole objective is to find earth-like life friendly planets in our galaxy.

 

I like to think that life is just highly transformed and evolved energy.

[Jens]

Again, it seems a bit unlikely there would have been a time when multiple impacts would have allowed the specific conditions required by your idea. you are assuming that impacts would have been smaller and smaller as time went on. I see no reason to assume this...

(Sorry for late answer, I was one week on a business trip and needed to recover from jet lag...)

 

I am not implying something special: Take the many millions of years of time during that the oceans of earth formed. I am talking about the time were liquid water formed on earth in bigger quantities but still huge amount of water was in the atmosphere. At that time the surface of earth was still very hot and locally there was an enourmous amount of vulcanic activity as well as a lot of meteorite impacts. This is like a giant chemical cooking laboratory in which energy rich molecules are formed all the time and diluted again. This way you create a huge energy gradient necessary for origin of life basically everywhere on the complete surface of earth. And plenty of different molecules emerging life could use. Especially of course huge amounts of condensated phosphates (which autocondensate, it is just a question of concentration and temperature) which can easily be used as energy source. Even though these are conditions like "hell" for current life they are optimal for abiogenesis. Over time replicating molecules became less and less dependent on other molecules in their environment and finally become autotrophic.

The best environment for quick evolution (both in nature and in laboratory) is not a constant environment but repeated cycles of proliferation, killing / cleaning, and again colonize empty habitats. This is exactly what earth was providing in the beginning (and not later when all oceans were already settled down).

 

So I think abiogenesis happened on Earth (see http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/)

So I think abiogenesis had to happen early or not at all.

So I think we cannot deduct from early emergence of life, that abiogenesis is a likely event.

So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist.

So I think once we will find the first Earth-like planet, it will show no signs of life (= no O2 in the athmosphere).

So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice).

 

However, it is not a believe (like you point out very rightly). And I will change my mind, if somebody has better arguments.

Edited January 20, 2013 by Jens

[Moontanman]

 

(Sorry for late answer, I was one week on a business trip and needed to recover from jet lag...)

 

I am not implying something special: Take the many millions of years of time during that the oceans of earth formed. I am talking about the time were liquid water formed on earth in bigger quantities but still huge amount of water was in the atmosphere. At that time the surface of earth was still very hot and locally there was an enourmous amount of vulcanic activity as well as a lot of meteorite impacts. This is like a giant chemical cooking laboratory in which energy rich molecules are formed all the time and diluted again. This way you create a huge energy gradient necessary for origin of life basically everywhere on the complete surface of earth. And plenty of different molecules emerging life could use. Especially of course huge amounts of condensated phosphates (which autocondensate, it is just a question of concentration and temperature) which can easily be used as energy source. Even though these are conditions like "hell" for current life they are optimal for abiogenesis. Over time replicating molecules became less and less dependent on other molecules in their environment and finally become autotrophic.

The best environment for quick evolution (both in nature and in laboratory) is not a constant environment but repeated cycles of proliferation, killing / cleaning, and again colonize empty habitats. This is exactly what earth was providing in the beginning (and not later when all oceans were already settled down).

 

 

I will agree that your scenario is workable.

 

 

 

So I think abiogenesis happened on Earth (see http://www.scienceforums.net/topic/71735-early-life-life-could-only-originate-early-or-not-at-all/)

So I think abiogenesis had to happen early or not at all.

 

I would have to agree with this assessment for the most part

 

 

So I think we cannot deduct from early emergence of life, that abiogenesis is a likely event.

 

I think we can agree with this as well.

 

 

So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist.

 

This assumption is one of the likely scenarios to explain the great silence but there are other more likely scenarios as well, the fact that radio signals are absorbed by the interstellar medium to the extent that even the nearest star is unlikely to be able to pick up random radio signals from us unless we beam a tight signal directly at them.

 

 

So I think once we will find the first Earth-like planet, it will show no signs of life (= no O2 in the athmosphere).

 

O2 is not a prerequisite for life.

 

 

So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice).

 

Again O2 is not a prerequisite for life.

 

 

 

However, it is not a believe (like you point out very rightly). And I will change my mind, if somebody has better arguments.

 

This is something we share.

[Jens]

(So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist.)

This assumption is one of the likely scenarios to explain the great silence but there are other more likely scenarios as well, the fact that radio signals are absorbed by the interstellar medium to the extent that even the nearest star is unlikely to be able to pick up random radio signals from us unless we beam a tight signal directly at them.

With the radio signals I agree that this might actually be really very difficult to receive them even with hypothetical advanced technology (for the reasons you mention). I assume humans will start to find Earth-like planets (with liquid water) within the next 200 years and will probably send at least space probes (without humans) within the next 300 years, which might arrive at this planet within the next 500 years. If our galaxy is full of life we have to assume that some of them had 100 million of years (and not hundreds of years) in advance to us. If there is at least one of those civilizations which behave like us, they had colonized Earth long before we had even the slightest chance to take over.

 

 

 

(So I think once we will find the first Earth-like planet, it will show no signs of life (= no O2 in the atmosphere).)

O2 is not a prerequisite for life.

This is a misunderstanding. Of course I know that O2 is no prerequisite for life. As you also know it is the other way round: life created O2. This is what I meant: The presence of bigger quantities of O2 means there is life on such a planet. So detecting O2 in the atmosphere of an Earth-like planet is probably the first way of how we can prove the existence of life in another planet without going there. So as soon as we (let's say in 50-100 years from now) are able to detect O2 in the atmosphere of extraterrestrial planets and we find many of them with water and the right temperature but no oxygen this will be an additional indicator that I am right. If on the other side, we detect O2, I am definitely wrong. Edited February 17, 2013 by Jens

[Moontanman]

(So I think we did not met other intelligent life forms (or received radio signals) in our galaxy, simply because they do not exist.)

With the radio signals I agree that this might actually be really very difficult to receive them even with hypothetical advanced technology (for the reasons you mention). I assume humans will start to find Earth-like planets (with liquid water) within the next 200 years and will probably send at least space probes (without humans) within the next 300 years, which might arrive at this planet within the next 500 years. If our galaxy is full of life we have to assume that some of them had 100 million of years (and not hundreds of years) in advance to us. If there is at least one of those civilizations which behave like us, they had colonized Earth long before we had even the slightest chance to take over.

 

 

You are assuming that Aliens would want to colonize planets in general much less the earth. It seems for more likely from the stand point of both resources and incompatibility of life forms from different planets that artificial space colonies would be the easiest and ultimate the most likely way aliens would colonize space. Gravity wells are quite possibly places to be avoided by aliens lloking to colonize...

 

The entire galaxy could be colonized by many different species of aliens, our own Star could house many different aliens in it's ort cloud kuiper belt areas. In fact stars with out planets but extensive asteroid belts similar to Vega might be the most desirable of stars.

 

There have reception of radio sources that closely resembled terrestrial military radars detected from space, they were transitory and originated from near the center of our galaxy. Because they were one time events they do not count as evidence but they are suggestive...

[Jens]

 

 

 

(So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice).)

Again O2 is not a prerequisite for life.

That is a misunderstanding, too. Jupiter's moon Europa will certainly not contain O2 (and I had not written this). But Europa has a lot of liquid water (and maybe some chemical activity). If we find any life form on Europa my thesis is definitely wrong. If we find nothing that will not proove much, however, it will fit into the picture I have sketched. I have mentioned Europa and the topic above (the O2 in the atmosphere) because that are (to my understanding) the first occasions to prove that my thesis is wrong.

[Jens]

You are assuming that Aliens would want to colonize planets in general much less the earth. It seems for more likely from the stand point of both resources and incompatibility of life forms from different planets that artificial space colonies would be the easiest and ultimate the most likely way aliens would colonize space.

I do not think so. This is because I view it from the biology point of view and not from the technology point of view. For the chemistry of abiogenesis a liquid phase is needed. And not an arbitrary one. You mandatory need a liquid phase in which complex molecules can form nearly arbitrary but defined (so not random for a given molecule) 3D-structures to act as catalyst for chemical reactions or have any function (actually this means life from a biochemical point of view). In water this is done by the different behaviour of hydrophilic and hydrophobic molecules. RNA, DNA and of course proteins as well as lipid membranes form a hydrophobic center. At the same time most of the other parts of the molecules form specific hydrophilic interactions. More detailed: Actually the hydrophilic interactions are hydrogen bonds and the force which bring hydrophobic parts of the molecules together is mainly the lack of being able to form hydrogen bonds. So flexible but defined 3D structures of macromolecules is linked to liquid phase and hydrogen bonds. This means: liquid water. (the only alternative is liquid NH₃). So extraterrestrial life is also bound to liquid water.

(I have no idea how likely a planet with liquid NH₃ is. I thought that Earth has more oxygen atoms than nitrogen atoms is not just pure chance, but has some systematic reasons. So for the following discussion I will assume that planets with liquid water are much more likely than planets with liquid NH₃. I have to do some literature research on this topic.) Keep in mind that hydrogen bounds can only be made by atoms of the 2nd period which are electrophil enough: So only N, O, F. F is too rare to be considered. So H₂O and NH₃ are really the only possibilities.

 

What would humans do, if we found a planet with liquid water like Earth 800 million years ago?

Of course we cannot eat any microorganisms of the extraterrestrial life, since it will definitely have another set of RNA bases and another set of amino acids, if it has amino acids or RNA bases at all. However, since the only way for life to become completely independent of volcanic activity and colonize the oceans is to use water as electron donor for reduction reactions, it is fair to assume that there is a high probability that at some point in time extra-terrestrial life will also evolve photosynthesis and produce oxygen (that is what remains, if you use water as electron donor). So what would we do? We would make an inventory of all the extra-terrestrial life forms and start bringing our own plants to this planet (maybe in closed spaces) and have a nice living there. If it is on average warmer than Earth, we will colonize at the poles where it is colder. If it is on average colder than Earth, we will colonize in the warmest regions. However, since liquid water is a prerequisite for life anyhow, the temperature cannot be so different from Earth. Only if the temperatures are everywhere let's say above 50°C, it will definitely not a nice living, so we might only have a research station there.

We would behave the same, if we find a planet which is like Earth 30 million years ago. The only difference is, that we already find bigger organisms which are autotrophic (plants) and others which behave more like parasites (animals).

What is if we find something like Earth now? This means with an intelligent life form which is about to destroy big parts of biological diversity on this planet. Either we are egoistic and simply throw this intelligent (but under developed ) life form out and keep a few examples in an open air zoo (just for curiosity). Or we are very concerned about them killing their environment and we start communicating with them. It is unlikely that we simply watch and do nothing.

 

To my point of view your assumption is only working, if you assume that all the earlier intelligent extraterrestrial life forms have found ways to construct artificial habitats in space stations which are much nicer than actually living on a planet surface and do not give a damn about under-developed intelligent species (like us) and their planets (Earth).

 

[Moontanman]

I do not think so. This is because I view it from the biology point of view and not from the technology point of view. For the chemistry of abiogenesis a liquid phase is needed. And not an arbitrary one. You mandatory need a liquid phase in which complex molecules can form nearly arbitrary but defined (so not random for a given molecule) 3D-structures to act as catalyst for chemical reactions or have any function (actually this means life from a biochemical point of view). In water this is done by the different behaviour of hydrophilic and hydrophobic molecules. RNA, DNA and of course proteins as well as lipid membranes form a hydrophobic center. At the same time most of the other parts of the molecules form specific hydrophilic interactions. More detailed: Actually the hydrophilic interactions are hydrogen bonds and the force which bring hydrophobic parts of the molecules together is mainly the lack of being able to form hydrogen bonds. So flexible but defined 3D structures of macromolecules is linked to liquid phase and hydrogen bonds. This means: liquid water. (the only alternative is liquid NH₃). So extraterrestrial life is also bound to liquid water.

(I have no idea how likely a planet with liquid NH₃ is. I thought that Earth has more oxygen atoms than nitrogen atoms is not just pure chance, but has some systematic reasons. So for the following discussion I will assume that planets with liquid water are much more likely than planets with liquid NH₃. I have to do some literature research on this topic.) Keep in mind that hydrogen bounds can only be made by atoms of the 2nd period which are electrophil enough: So only N, O, F. F is too rare to be considered. So H₂O and NH₃ are really the only possibilities.

 

What would humans do, if we found a planet with liquid water like Earth 800 million years ago?

Of course we cannot eat any microorganisms of the extraterrestrial life, since it will definitely have another set of RNA bases and another set of amino acids, if it has amino acids or RNA bases at all. However, since the only way for life to become completely independent of volcanic activity and colonize the oceans is to use water as electron donor for reduction reactions, it is fair to assume that there is a high probability that at some point in time extra-terrestrial life will also evolve photosynthesis and produce oxygen (that is what remains, if you use water as electron donor). So what would we do? We would make an inventory of all the extra-terrestrial life forms and start bringing our own plants to this planet (maybe in closed spaces) and have a nice living there. If it is on average warmer than Earth, we will colonize at the poles where it is colder. If it is on average colder than Earth, we will colonize in the warmest regions. However, since liquid water is a prerequisite for life anyhow, the temperature cannot be so different from Earth. Only if the temperatures are everywhere let's say above 50°C, it will definitely not a nice living, so we might only have a research station there.

We would behave the same, if we find a planet which is like Earth 30 million years ago. The only difference is, that we already find bigger organisms which are autotrophic (plants) and others which behave more like parasites (animals).

What is if we find something like Earth now? This means with an intelligent life form which is about to destroy big parts of biological diversity on this planet. Either we are egoistic and simply throw this intelligent (but under developed ) life form out and keep a few examples in an open air zoo (just for curiosity). Or we are very concerned about them killing their environment and we start communicating with them. It is unlikely that we simply watch and do nothing.

 

To my point of view your assumption is only working, if you assume that all the earlier intelligent extraterrestrial life forms have found ways to construct artificial habitats in space stations which are much nicer than actually living on a planet surface and do not give a damn about under-developed intelligent species (like us) and their planets (Earth).

 

 

 

Your assertion is falsified by the simple fact that liquid water does not mean we could live there and not being able to eat the local wild life is the least of our worries. A few percentage points differences in the minor gas constituents from Earth normal would be a deal breaker. In fact humans couldn't have lived on the earth 800 million years ago due to the differences in atmospheric gas, liquid water may indeed be a prerequisite for life but it doesn't guarantee we could live there. Ever see the movie Avatar?

[SamBridge]

Life as we know it is likely rare for any given field of view, this planet is really good for life, yet in the 3.8 billion years life started, we have not seen any new type of base-pair life, that's how unlikely it is. Even on a perfect planet we have not seen any new life spontaneously develop after 3.8 billion years, but given that the universe is so large there must be life in at least one other planet. Given that it is indefinitely large, there could be an indefinite amount of life, but looking at probability it would still have to be spread out pretty far.

Edited February 24, 2013 by SamBridge

[Moontanman]

(So I think there will be no life found on Jupiter's moon Europa even though it contains liquid water (under several hundred meters of ice).)That is a misunderstanding, too. Jupiter's moon Europa will certainly not contain O2 (and I had not written this). But Europa has a lot of liquid water (and maybe some chemical activity). If we find any life form on Europa my thesis is definitely wrong. If we find nothing that will not proove much, however, it will fit into the picture I have sketched. I have mentioned Europa and the topic above (the O2 in the atmosphere) because that are (to my understanding) the first occasions to prove that my thesis is wrong.

 

 

The oceans of Europa could have more oxygen than earths oceans...

 

http://phys.org/news174918239.html

 

Life as we know it is likely rare for any given field of view, this planet is really good for life,

 

"Life as we know it", life has adapted to the Earth and changed the earth to suit the life that lives there. We can't draw a conclusion from one data point.

 

yet in the 3.8 billion years life started, we have not seen any new type of base-pair life, that's how unlikely it is.

 

No, it means the conditions for forming life no longer occur...

 

Even on a perfect planet we have not seen any new life spontaneously develop after 3.8 billion years,

 

The current conditions and conditions that we can deduce show that life cannot form independently on this "perfect" earth... in fact if life was completely eliminated from the earth conditions would have to change drastically for life to develop again... Then there is the fact that any new organic molecules are eaten by current life forms as soon as they form...

 

but given that the universe is so large there must be life in at least one other planet. Given that it is indefinitely large, there could be an indefinite amount of life, but looking at probability it would still have to be spread out pretty far.

 

 

Again please show this probability, with only one data point this is not a supportable assumption...

[SamBridge]

"Life as we know it", life has adapted to the Earth and changed the earth to suit the life that lives there. We can't draw a conclusion from one data point.

Yeah we can. We have no data that life can form without the definitions we have for it, which forms somewhat predictable limitation when considering how life might exist.

 

No, it means the conditions for forming life no longer occur...

Which scientifically we expect was something lie lightning strikes a pool of water containing complex chemicals. Those possible circumstances still exist on Earth. There's still the same chemicals in the oldest life form now, there's still lighting, life had 3.8 billion more years to spontaneously form on Earth again, and out of all that time it didn't.

 

 

 

The current conditions and conditions that we can deduce show that life cannot form independently on this "perfect" earth... in fact if life was completely eliminated from the earth conditions would have to change drastically for life to develop again... Then there is the fact that any new organic molecules are eaten by current life forms as soon as they form...

If you looked at data gathered by various telescopes, you would discover that obviously this planet is the most suitable for life as we know it. There are plenty of planets with chemicals toxic to us, but they are not diverse in their minerals or have too much or too little heat for complex chemicals to not be broken down to to form. We have no evidence to support that life can be made out of only the materials of a single type of rock, or plasma, or space dust. We can say that based on our knowledge there can possibly be silicon based life if not carbon based. There can't be uranium based life with the data we have.

 

Again please show this probability, with only one data point this is not a supportable assumption...

There's nothing to prove, it's called set theory, it's a set that is indefinitely or infinitely large, therefore no matter how small the chance is, as long as it is above 0 or does not definitely approach 0, there must be some event that happens out of an indefinite number of elements in a set, which we can see clearly on Earth as we do not observe every planet having life. Cosmologists have not discovered an observable boundary to the universe nor have they discovered consistent global curvature, therefore they consider space to extend indefinitely, which means the number of planets in the universe or stars in the universe are contained in a set that is indefinitely large. If I throw a dart at a dart board, even though there's an infinite number of infinitely small squares it can be broken down into, it has to hit at some location.

Edited February 24, 2013 by SamBridge

[Moontanman]

Yeah we can. We have no data that life can form without the definitions we have for it, which forms somewhat predictable limitation when considering how life might exist.

 

How is that relevant to this issue?

 

Which scientifically we expect was something lie lightning strikes a pool of water containing complex chemicals. Those possible circumstances still exist on Earth. There's still the same chemicals in the oldest life form now, there's still lighting, life had 3.8 billion more years to spontaneously form on Earth again, and out of all that time it didn't.

 

This is at best out dated clap trap and at worst intentional obfuscation, which is it?

 

If you looked at data gathered by various telescopes, you would discover that obviously this planet is the most suitable for life as we know it. There are plenty of planets with chemicals toxic to us, but they are not diverse in their minerals or have too much or too little heat for complex chemicals to not be broken down to to form. We have no evidence to support that life can be made out of only the materials of a single type of rock, or plasma, or space dust. We can say that based on our knowledge there can possibly be silicon based life if not carbon based. There can't be uranium based life with the data we have.

 

A simple change in the minor atmospheric gases would eliminate complex "life as we know it" on earth, you are building straw men for no apparent reason, no one is suggesting anything but carbon based water containing life...

 

There's nothing to prove, it's called mathematics, it's a set that is indefinitely or infinitely large, therefore no matter how small the chance is, as long as it is above 0, there must be some event that happens out of an indefinite number of elements in a set, which we can see clearly on Earth as we do not observe every planet having life. Cosmologists have not discovered an observable boundary to the universe nor have they discovered consistent global curvature, therefore they consider space to extend indefinitely. If I throw a dart at a dart board, even though there an infinite number of infinitely small squares it can be broken down into, it has to hit at some location.

 

 

total straw man...

Edited February 24, 2013 by Moontanman

[SamBridge]

How is that relevant to this issue?

A rock isn't a living thin. We know that based on our definitions of life, if it is living, it must be able to in some way respond to stimuli, communicate at at least a cellular level, undergo the process of evolution and grow, as well as a couple other limitations. With our data, life cannot form to meet these circumstances if it is say...xenon based, or uranium based. Only certain elements and materials will have the chemical properties unnecessary to create self-organizing systems capable of sustaining and growing in certain environments. A large amount chromium and iron and copper isn't going to do it, those chemicals have very limited bonding capabilities, so if we find a heavily metallic planet with little non-metal resources and not much heat, chances are it will not be able to form any type of life that can fit our definitions of life.

 

 

 

This is at best out dated clap trap and at worst intentional obfuscation, which is it?

 

The oldest living life form we know of is some type of algae, green algae related to it that resides in the oceans still today. We have analyzed all the chemicals in that algae, and many they need water and energy to form on their own. To form in large enough quantities at the right rations so that the quantities are not thrown off due to dynamics shifts in the equilibrium of reversible reactions, there needed to be an environment of some of the chemicals with an extreme amount of heat. It is possible that due to the lack of ozone at the time that intense UV light could have triggered some reaction, but we have not found any experiment in which life is created from intense UV light, as often UV light destroys the chemicals that comprise organic life.

 

A simple change in the minor atmospheric gases would eliminate complex "life as we know it" on earth.

And if that change happened there would likely be no life on this planet. Not every chemical can successfully deliver energy required to sustain self-organization reactions. We know of definite limitations to the chemical reactions of elements and molecules in certain various environments. We know that some are always exothermic, or always endothermic, or reversible with how their equilibrium shifts, we know that some are molecular, we know that some are ionic, and we know the patterns for elements to form these various things, and we have determined after much observation that many combinations of these chemicals and elements cannot spontaneously form life.

 

total straw man...

 

You need to seriously look up the definition of a straw-man.