dstebbins

Life on other planets; is water really the primary factor?

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Everyone just ASSUMES that there's got to be life on other planets, right? I mean ... how rare can Earth actually be that it's the only planet in the whole universe with complex life on it?

Also, whenever a planet is discovered that's inside its star's "habitable zone," astromers wet their pants in excitement over the possibility oflife existing on that planet.

Here's something most people never really think about when they think about life on other planets: Even if there may be life on other planets, what makes you think they have the MEANS to travel through space like we do?

Astronomers often consider liquid water on other planets to be the holy grail of extra-terrestrial life. However, there is a difference between "life" and "civilization." Life is certainly prerequisite to civilization, but other than that, they are two completely different concepts.

For life to be sustained, we need a variety of nutrients, including liquid water, carbon, nitrogen, oxygen, and various other elements. However, there are plenty of other elements on our planet that are not edible, yet are nevertheless essential to making humans the advanced civilization we are today: Natural resources!

Resources like iron and various other metals. Combustible resources like coal and petroleum which give us a source of energy. These natural resources are not needed to support life, per se, but are all crucial to making the tools which make us the advanced civilization we are today.

Speaking of fossil feuls, that's another thing that may very well be unique to earth. Remember that fossil fuels are created from the compressed and modified corpses of dinosaurs over millions of years. That's why they're called "fossil" fuels!

In other words ... no dinosaurs, no fossil fuels!

See, here on earth, we consider humans' intelligence to be the primary factor that made us into the advanced civilization that we are. That's because, compared to every other species we've discovered up to this point, our intelligence WAS the deciding factor! The other animals on this planet had access to the same natural resources that we did, but we are the first species to figure out how to use them.

But we have no reason to assume that other planets with life on them would have the same or similar natural resources as we did to jumpstart their civilizations. Who's to say that other alien lifeforms might exist out there that have the same brainpower as us, but are still reduced to straw huts and crude stone tools because they simply lack the natural resources to do anything more advanced?

Heck, we have guys like that here on earth! They're called "third world countries." So there's definitely a precedent for life forms having the brainpower to make advanced civilizations but not having the natural resources needed to fully tap into that brainpower.

Fossil fuels alone pose a huge question mark on the ability of alien lifeforms to create civilization. Remember that the dinosaurs on our planet are not merely extinct, but were killed off in one fell swoop by an asteroid strike, giving our planet a head start on the creation of fossil fuels. Who's to say that other planets may have life on them, but they are still waiting for their dinosaurs to go extinct the old fashioned way, and THEn wait millions of years for their carcasses to be converted into fossil fuels?! That alone gives Earth a huge head start when it comes to developing a civilization, unless other planets had undergone a similar mass extinction event that killed off billions of tons of lifeforms in a very short period of time ... and did so millions of years ago, giving their carcasses enough time to be covnerted into fossil fuels for the current generation of intelligent life forms!

That, ladies and gentlemen, is just the tip of the iceberg for things that had to go almost perfectly right right down to the millimeter for this planet to not only have life, but civilization so advanced that it even CARES whether there are aliens out there!

So hold your horses, guys. Just because there's liquid water on a planet doesn't mean we should get all excited about opening up new trade routes with aliens and getting new technology and cuisine from them.

So what do you guys think?

Edited by dstebbins

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51 minutes ago, dstebbins said:

Everyone just ASSUMES that there's got to be life on other planets, right? I mean ... how rare can Earth actually be that it's the only planet in the whole universe with complex life on it?

Also, whenever a planet is discovered that's inside its star's "habitable zone," astromers wet their pants in excitement over the possibility oflife existing on that planet.

Here's something most people never really think about when they think about life on other planets: Even if there may be life on other planets, what makes you think they have the MEANS to travel through space like we do?

Astronomers often consider liquid water on other planets to be the holy grail of extra-terrestrial life. However, there is a difference between "life" and "civilization." Life is certainly prerequisite to civilization, but other than that, they are two completely different concepts.

For life to be sustained, we need a variety of nutrients, including liquid water, carbon, nitrogen, oxygen, and various other elements. However, there are plenty of other elements on our planet that are not edible, yet are nevertheless essential to making humans the advanced civilization we are today: Natural resources!

Resources like iron and various other metals. Combustible resources like coal and petroleum which give us a source of energy. These natural resources are not needed to support life, per se, but are all crucial to making the tools which make us the advanced civilization we are today.

Speaking of fossil feuls, that's another thing that may very well be unique to earth. Remember that fossil fuels are created from the compressed and modified corpses of dinosaurs over millions of years. That's why they're called "fossil" fuels!

In other words ... no dinosaurs, no fossil fuels!

See, here on earth, we consider humans' intelligence to be the primary factor that made us into the advanced civilization that we are. That's because, compared to every other species we've discovered up to this point, our intelligence WAS the deciding factor! The other animals on this planet had access to the same natural resources that we did, but we are the first species to figure out how to use them.

But we have no reason to assume that other planets with life on them would have the same or similar natural resources as we did to jumpstart their civilizations. Who's to say that other alien lifeforms might exist out there that have the same brainpower as us, but are still reduced to straw huts and crude stone tools because they simply lack the natural resources to do anything more advanced?

Heck, we have guys like that here on earth! They're called "third world countries." So there's definitely a precedent for life forms having the brainpower to make advanced civilizations but not having the natural resources needed to fully tap into that brainpower.

Fossil fuels alone pose a huge question mark on the ability of alien lifeforms to create civilization. Remember that the dinosaurs on our planet are not merely extinct, but were killed off in one fell swoop by an asteroid strike, giving our planet a head start on the creation of fossil fuels. Who's to say that other planets may have life on them, but they are still waiting for their dinosaurs to go extinct the old fashioned way, and THEn wait millions of years for their carcasses to be converted into fossil fuels?! That alone gives Earth a huge head start when it comes to developing a civilization, unless other planets had undergone a similar mass extinction event that killed off billions of tons of lifeforms in a very short period of time ... and did so millions of years ago, giving their carcasses enough time to be covnerted into fossil fuels for the current generation of intelligent life forms!

That, ladies and gentlemen, is just the tip of the iceberg for things that had to go almost perfectly right right down to the millimeter for this planet to not only have life, but civilization so advanced that it even CARES whether there are aliens out there!

So hold your horses, guys. Just because there's liquid water on a planet doesn't mean we should get all excited about opening up new trade routes with aliens and getting new technology and cuisine from them.

So what do you guys think?

Good points. I will now put my personal space program on hold...:D

Seriously, I guess it is all about the assumptions we make, and how we compute the odds based on them. From what we know, or think we know, intelligent life may not be reachable by ourselves or ourselves by "them", but the more we learn the better our assumptions can potentially become. Finding hints of any life as we know it within reach, coupled with our understanding of evolution  would surely make intelligent life out there seem more plausible, given that "out there" is pretty vast and diversified.

 

Edited by J.C.MacSwell

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It makes perfect sense to look for life as we know it first. It's hard to look for something when you don't know what it is. That means looking for liquid water amongst other things. 

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1 hour ago, dstebbins said:

Everyone just ASSUMES that there's got to be life on other planets, right?

I doubt that. It's possible for there to be life but we don't know it until we know it.

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1 hour ago, dstebbins said:

Everyone just ASSUMES that there's got to be life on other planets, right? I mean ... how rare can Earth actually be that it's the only planet in the whole universe with complex life on it?

Life is expected to occur quite often around the universe. In fact a half dozen bodies in the solar system are expected to harbor life. Complex life could indeed be much more rare. 

1 hour ago, dstebbins said:

Also, whenever a planet is discovered that's inside its star's "habitable zone," astromers wet their pants in excitement over the possibility oflife existing on that planet.

Here's something most people never really think about when they think about life on other planets: Even if there may be life on other planets, what makes you think they have the MEANS to travel through space like we do?

If there is a civilization on a planet I would ask why you would think they would not? The same laws that govern our universe here that allow for space travel hold sway there as well. Possibly you are suggesting that technological civilizations might be rare? 

1 hour ago, dstebbins said:

Astronomers often consider liquid water on other planets to be the holy grail of extra-terrestrial life. However, there is a difference between "life" and "civilization." Life is certainly prerequisite to civilization, but other than that, they are two completely different concepts.

You are correct and I don't know of any astronomers that assert anything different. 

1 hour ago, dstebbins said:

For life to be sustained, we need a variety of nutrients, including liquid water, carbon, nitrogen, oxygen, and various other elements. However, there are plenty of other elements on our planet that are not edible, yet are nevertheless essential to making humans the advanced civilization we are today: Natural resources!

Resources like iron and various other metals. Combustible resources like coal and petroleum which give us a source of energy. These natural resources are not needed to support life, per se, but are all crucial to making the tools which make us the advanced civilization we are today.

I am not sure what you are getting at here, any Earth like planets should contain similar elements to Earth's just by virtue of being Earth like planets. 

1 hour ago, dstebbins said:

Speaking of fossil feuls, that's another thing that may very well be unique to earth. Remember that fossil fuels are created from the compressed and modified corpses of dinosaurs over millions of years. That's why they're called "fossil" fuels!

In other words ... no dinosaurs, no fossil fuels!

No, fossil fuels are not made of dinosaurs, that is a popular misconception, most deposits of fossil fuels resulted from the Carboniferous age. There were no dinosaurs then only huge swampy forests. Such deposits of decaying plant material is thought to be the origin of most fossil fuels. 

1 hour ago, dstebbins said:

See, here on earth, we consider humans' intelligence to be the primary factor that made us into the advanced civilization that we are. That's because, compared to every other species we've discovered up to this point, our intelligence WAS the deciding factor! The other animals on this planet had access to the same natural resources that we did, but we are the first species to figure out how to use them.

But we have no reason to assume that other planets with life on them would have the same or similar natural resources as we did to jumpstart their civilizations. Who's to say that other alien lifeforms might exist out there that have the same brainpower as us, but are still reduced to straw huts and crude stone tools because they simply lack the natural resources to do anything more advanced?

The only way i can see this being a problem is if the planet is metal poor, such a dearth of metals is not likely since planets almost by definition should contain some metals. But I see no reason to assume technology would have to take the exact same path there as it did on Earth. 

1 hour ago, dstebbins said:

Heck, we have guys like that here on earth! They're called "third world countries." So there's definitely a precedent for life forms having the brainpower to make advanced civilizations but not having the natural resources needed to fully tap into that brainpower.

I am not so sure this is a fair comparison, other factors do come into play and I see no third world countries that cannot produce the basics of civilization. 

1 hour ago, dstebbins said:

Fossil fuels alone pose a huge question mark on the ability of alien lifeforms to create civilization. Remember that the dinosaurs on our planet are not merely extinct, but were killed off in one fell swoop by an asteroid strike, giving our planet a head start on the creation of fossil fuels. Who's to say that other planets may have life on them, but they are still waiting for their dinosaurs to go extinct the old fashioned way, and THEn wait millions of years for their carcasses to be converted into fossil fuels?! That alone gives Earth a huge head start when it comes to developing a civilization, unless other planets had undergone a similar mass extinction event that killed off billions of tons of lifeforms in a very short period of time ... and did so millions of years ago, giving their carcasses enough time to be covnerted into fossil fuels for the current generation of intelligent life forms!

Again you are making assumptions that simply do not apply. Fossil fuels are not made up from dinosaurs and in fact are thought to be the remains of plant material laid down way before there were dinosaurs. 

1 hour ago, dstebbins said:

That, ladies and gentlemen, is just the tip of the iceberg for things that had to go almost perfectly right right down to the millimeter for this planet to not only have life, but civilization so advanced that it even CARES whether there are aliens out there!

So hold your horses, guys. Just because there's liquid water on a planet doesn't mean we should get all excited about opening up new trade routes with aliens and getting new technology and cuisine from them.

So what do you guys think?

I think you have made some assumptions that simply are not true.. 

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Earth is most likely unique.  Like already said, (and thank you) so many different myriad things must come together.  In the future we may, (might) find many planets with primitive life?  The common planetary default system might dictate life.  Some may even have complex life.  But only a handful will have advanced life. 

Probably none will have high tech life.  And absolutely none will have the easy means to travel between the stars?   There may have been something 2 billion years ago in a galaxy far away and there MAYBE something right now here, (US) and there might be something two billion years from now within our own galaxy. 

But for right now our blinkers dictate that we are the only ones around.  Even 1000 years from now when, (if we survive) we have surveyed scores of likely planets for possible human colonies we will not find ONE planet exactly like Earth.  Or even close.  Human suitable?  Maybe.  Hopefully.  But that lies far in the future

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6 hours ago, dstebbins said:

Everyone just ASSUMES that there's got to be life on other planets, right? I mean ... how rare can Earth actually be that it's the only planet in the whole universe with complex life on it?

Not really. What many people do know, is that the Earth is just one planet revolving around a hum drum star,  amongst 400 billion other stars, in one just galaxy among many billions of more galaxies, just in the part of the universe that is observable, and that the "stuff of life" is found where ever we have looked. Those facts lead many people to assume that life [as we know it] should arise elsewhere as conditions dictate.

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Also, whenever a planet is discovered that's inside its star's "habitable zone," astromers wet their pants in excitement over the possibility oflife existing on that planet.

Not to long ago,  most astronomers and astrophysicists assumed that our solar system with its nine planets counting Pluto, would not really be unique or special in a galaxy of 400 billion other stars, then of course as you and I know, their reasonable assumptions  were vindicated and validated by the discovery of around 3000 extra solar planets to date with many more to yet be verified. They also assume that any planet within a star's habitable zone, is a candidate for life. Since one of mankind's age old questions has always been "is Earth the only planet with life" and "are we alone", It is then reasonable for astronomers and scientists in general to get excited when that real possibility presents itself. 

 

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Here's something most people never really think about when they think about life on other planets: Even if there may be life on other planets, what makes you think they have the MEANS to travel through space like we do?

Life on other worlds is inevitable most astronomers would believe, but they also live with the knowledge that distances between life bearing planets are astronomical, and distances between life bearing planets to have life arise that approaches our own evolutionary standards of intelligence and technology to undertake space travel, are even more astronomical.eg: 4.3 L/years to the nearest star. Plus of course, even having reached our own technological advance state, we as yet have only still explored robotically, those bodies within our own system.

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Astronomers often consider liquid water on other planets to be the holy grail of extra-terrestrial life. However, there is a difference between "life" and "civilization." Life is certainly prerequisite to civilization, but other than that, they are two completely different concepts.

Of course! Water is an indication of the probability of life having arisen, which most astronomers accept as inevitable to have happened elsewhere for the reasons already stated. They also accept that only a small percentage of that life would have evolved to what you term as "civilisation" status. Nothing new there.

 

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For life to be sustained, we need a variety of nutrients, including liquid water, carbon, nitrogen, oxygen, and various other elements. However, there are plenty of other elements on our planet that are not edible, yet are nevertheless essential to making humans the advanced civilization we are today: Natural resources!

Of course! But we also know that all the elements were forged in stars that went supernova, and the heavier elements probably via other means such as collisions between Neutron stars etc. Again, nothing particularly unique about what we find in our own system. They are everywhere!

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Resources like iron and various other metals. Combustible resources like coal and petroleum which give us a source of energy. These natural resources are not needed to support life, per se, but are all crucial to making the tools which make us the advanced civilization we are today.

Of course! And there is no reason not to believe that the Earth is in any way unique in that regard.

Quote

 

Speaking of fossil feuls, that's another thing that may very well be unique to earth. Remember that fossil fuels are created from the compressed and modified corpses of dinosaurs over millions of years. That's why they're called "fossil" fuels!

In other words ... no dinosaurs, no fossil fuels!

 

??? Any reference for that? I was always of the opinion that fossil fuels were the result of decaying and long buried vegetation.

Quote

 

See, here on earth, we consider humans' intelligence to be the primary factor that made us into the advanced civilization that we are. That's because, compared to every other species we've discovered up to this point, our intelligence WAS the deciding factor! The other animals on this planet had access to the same natural resources that we did, but we are the first species to figure out how to use them.

But we have no reason to assume that other planets with life on them would have the same or similar natural resources as we did to jumpstart their civilizations. Who's to say that other alien lifeforms might exist out there that have the same brainpower as us, but are still reduced to straw huts and crude stone tools because they simply lack the natural resources to do anything more advanced?

Heck, we have guys like that here on earth! They're called "third world countries." So there's definitely a precedent for life forms having the brainpower to make advanced civilizations but not having the natural resources needed to fully tap into that brainpower.

Fossil fuels alone pose a huge question mark on the ability of alien lifeforms to create civilization. Remember that the dinosaurs on our planet are not merely extinct, but were killed off in one fell swoop by an asteroid strike, giving our planet a head start on the creation of fossil fuels. Who's to say that other planets may have life on them, but they are still waiting for their dinosaurs to go extinct the old fashioned way, and THEn wait millions of years for their carcasses to be converted into fossil fuels?! That alone gives Earth a huge head start when it comes to developing a civilization, unless other planets had undergone a similar mass extinction event that killed off billions of tons of lifeforms in a very short period of time ... and did so millions of years ago, giving their carcasses enough time to be covnerted into fossil fuels for the current generation of intelligent life forms!

That, ladies and gentlemen, is just the tip of the iceberg for things that had to go almost perfectly right right down to the millimeter for this planet to not only have life, but civilization so advanced that it even CARES whether there are aliens out there!

So hold your horses, guys. Just because there's liquid water on a planet doesn't mean we should get all excited about opening up new trade routes with aliens and getting new technology and cuisine from them.

 

Obviously then your wrong assumptions re fossil fuel invalidates what you seem to be implying.

In a universe of billions of galaxies, each containing  hundreds of billions of stars, each with the possibilities of having planets orbiting each of them, with the stuff of life being everywhere we look, the chances of Earth being unique and the only planet to have evolved life, would be rather slim at best. Of course for that life to have evolved to our own standards would be somewhat less likely, but also there is that possibility that some life may have evolved to even higher more advanced states. As yet, we do not know. In fact as yet we do not have any empirical evidence to support the likelyhood of life elsewhere, although at this time, many astronomers believe we are getting close to obtaining that evidence and finely answering one of mankind's eternal questions in the affirmative. 

 

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So what do you guys think?

We were all born in the belly of stars each and every one of us, including Earth and everything on it. Just as any Alien life form off this planet was also born in the belly of other stars.

2000 odd years ago, it was believed that the Earth was the center of the universe and the Sun revolved around this fart arse little blue orb. 350 years ago, a bloke called Galileo was ridiculed and put under house arrest when he showed that this was not the case. We have come a long way since then.

Edited by beecee

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Fossil fuels is a misnomer.
Methane is classified as a 'fossil fuel'.
The biggest deposit of methane that I know of is Jupiter, which doesn't even have a solid surface, let alone plants and dinosaurs.

The habitable zone is where we expect to find life possibly similar to ours.
I.E. carbon based and dependent on liquid water.

Carbon makes a huge number of compounds ( with hydrogen, oxygen and concatenates, I think that's the right term; John or Hyper ?? ).
But so do sulfur and silicon ( remember the hot, living rocks in Star Trek: TOS ? ).
So, who's to say a different kind of life couldn't evolve based on these elements, and much closer to the parent star, at temperatures of thousands of degrees ?

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23 minutes ago, MigL said:

Carbon makes a huge number of compounds ( with hydrogen, oxygen and concatenates, I think that's the right term; John or Hyper ?? ).
But so do sulfur and silicon ( remember the hot, living rocks in Star Trek: TOS ? ).
So, who's to say a different kind of life couldn't evolve based on these elements, and much closer to the parent star, at temperatures of thousands of degrees ?

Bingo! And the reason why I near always mention "life as we know it" when talking of the possibility of ETL. 

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2 hours ago, HB of CJ said:

Earth is most likely unique.

Why do you assert this? Why would it be important? 

 

2 hours ago, HB of CJ said:

 

  Like already said, (and thank you) so many different myriad things must come together.

Please be specific, what things exactly?

2 hours ago, HB of CJ said:

  In the future we may, (might) find many planets with primitive life?  The common planetary default system might dictate life.  Some may even have complex life.  But only a handful will have advanced life. 

What is the difference between complex and advanced life? 

2 hours ago, HB of CJ said:

Probably none will have high tech life.  And absolutely none will have the easy means to travel between the stars?   There may have been something 2 billion years ago in a galaxy far away and there MAYBE something right now here, (US) and there might be something two billion years from now within our own galaxy. 

You really need to justify these assertions, all of what you assert is completely baseless. Some evidence other than you simply saying it's true needs to be presented.  

2 hours ago, HB of CJ said:

But for right now our blinkers dictate that we are the only ones around.  Even 1000 years from now when, (if we survive) we have surveyed scores of likely planets for possible human colonies we will not find ONE planet exactly like Earth.  Or even close.  Human suitable?  Maybe.  Hopefully.  But that lies far in the future

Again you make assertions without evidence other than your own claims. Why do you think these things are true? 

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53 minutes ago, Moontanman said:

Why do you assert this? Why would it be important? 

 

Please be specific, what things exactly?

What is the difference between complex and advanced life? 

You really need to justify these assertions, all of what you assert is completely baseless. Some evidence other than you simply saying it's true needs to be presented.  

Again you make assertions without evidence other than your own claims. Why do you think these things are true? 

Yep, great questions and equally great advice: Please accept my one paltry "like" !

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9 hours ago, J.C.MacSwell said:

Good points. I will now put my personal space program on hold...:D

Seriously, I guess it is all about the assumptions we make, and how we compute the odds based on them. From what we know, or think we know, intelligent life may not be reachable by ourselves or ourselves by "them", but the more we learn the better our assumptions can potentially become. Finding hints of any life as we know it within reach, coupled with our understanding of evolution  would surely make intelligent life out there seem more plausible, given that "out there" is pretty vast and diversified.

 

The distance our activities and signals, travelling at light speed, have reached out into this galaxy, let alone the universe, is pitiful. :) 

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Just found an interesting paper, which I believe is relevant.....

 

http://www.mdpi.com/2075-1729/6/3/25/htm

The Cosmic Zoo: The (Near) Inevitability of the Evolution of Complex, Macroscopic Life:

Abstract: 

Life on Earth provides a unique biological record from single-cell microbes to technologically intelligent life forms. Our evolution is marked by several major steps or innovations along a path of increasing complexity from microbes to space-faring humans. Here we identify various major key innovations, and use an analytical toolset consisting of a set of models to analyse how likely each key innovation is to occur. Our conclusion is that once the origin of life is accomplished, most of the key innovations can occur rather readily. The conclusion for other worlds is that if the origin of life can occur rather easily, we should live in a cosmic zoo, as the innovations necessary to lead to complex life will occur with high probability given sufficient time and habitat. On the other hand, if the origin of life is rare, then we might live in a rather empty universe.
 

Conclusions:

After establishing a set of preconditions needed for life, which are similar to the criteria for habitability that have been discussed extensively in the astrobiology literature, we examined the key innovations of life on Earth, and tested them for multiple occurrences. Using a consistent approach and a model toolset we find that, with the exception of the origin of life and the origin of technological intelligence, we can favour the Critical Path model or the Many Paths model in most cases. The origin of oxygenesis, may be a Many Paths process, and we favour that interpretation, but may also be Random Walk events. This implies that in any world where life has arisen and sufficient energy flux exists, we are confident that we will find complex, animal-like life. The example of Earth suggests that such complex life could evolve in a 1–10 Ga timescale. This does not mean that, as Conway-Morris argues [21], life has to end with humans or animals we are familiar with, but suggests that if we rewind the tape, the result will be same function, but different anatomy and very possibly also different chemistry.
Our conclusion has implications for the search for life on other worlds. Not only should we expect microbial biosignatures, but also the detection of signatures that depend on large, complex, multicellular organisms such as the vegetation Red Edge (if it is relevant to the physics and chemistry of the world—see [39]). In particular, this is relevant to the selection of tools we use in searching for life on planets in other solar systems. We hope that our analysis will give support to the search for such life.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
 
If I was going to ask a question of this paper, it would be on the last sentence in the Abstract...."On the other hand, if the origin of life is rare, then we might live in a rather empty universe".
 
That question is what and how does one define "rare"? A handful of planetary habitats where life has evolved per galaxy? Two or three examples per galaxy? Or if you prefer a more pessimistic number, how's about One planetary habitat per galaxy? Even in the pessimistic case we would have billions of examples in the observable universe where life has evolved. So again, how would or should one define as "rare"?

 

 

 

Edited by beecee

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Correction to Moontanman's assertion that most fossil fuels were produced in the Carboniferous era from rotting vegetation. Setting aside that if it rotted the carbon wouldn't be available, the Carboniferous produced a substantial part of the Earth's coal deposits, but oil was generated from marine deposits of plankton, primarily IIRC zooplankton. There are various sources for that oil, but most of them are post-Carboniferous. Natural gas (methane) is derived from coal, or in some cases decomposition of petroleum.

On topic, @dstebbins , you have highligted an issue with popular science. It is rarely made clear enough that when scientists speak of life they are speaking of any form of life and more often than not very simple life forms, equivalent to prokaryotes. When they speak of complex life they are generally, at most, thinking in terms of sponges, or echinoderm like entities. And if they mention advanced life they might be referencing lizards, weasels, or politicians. Intelligent, "civilised" life will likely only be in the conversation if we are talking SETI.

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Yes water is really a primary factor for life, as we know it.  There are other liquids (e.g. ammonia) but water seems best for life, whether it be a planet in the habitable zone, or moon or planet that has an interior ocean heated by gravitational flexing.

I'm not interested in stars that are over a thousand light years away.  Those are way out of our reach, except as curiosities or as reference.  How about planets with life, or Earth-like (or better) that are within a hundred light years?  That is most interesting!

Watch for the launch of TESS (Transiting Exoplanet Survey Satellite) this year.  In a few years we will have a much better idea of how common Earth-like planets are, or planets BETTER suited to life than Earth.  TESS will look at the closest 1,000 red dwarf stars as well as 500,000 other stars.  Then the James Webb will take a closer look at those.  The next few years should be very interesting, stay tuned!

https://en.wikipedia.org/wiki/Transiting_Exoplanet_Survey_Satellite

https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Edited by Airbrush

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The only advantage water has, is that its solid state is less dense than its liquid state.
Water tends to freeze from the top down, giving life a chance to survive at depth, even when the surface is frozen solid.

How big an advantage to primordial life this would be, I have no clue.

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On 05/02/2018 at 5:22 AM, beecee said:
 
That question is what and how does one define "rare"? A handful of planetary habitats where life has evolved per galaxy? Two or three examples per galaxy? Or if you prefer a more pessimistic number, how's about One planetary habitat per galaxy? Even in the pessimistic case we would have billions of examples in the observable universe where life has evolved. So again, how would or should one define as "rare"?

Rarity is normally defined on a percentage, or per capita basis. Yes, in your pessimistic case there are many billions of planets where life has evolved, but only one planet out hundreds of billions in any one galaxy has life. I think by any reasonable definition of "rare" that is "rare", if not "extremely rare". And with only one per galaxy we aren't going to have much of a conversation. For all presently discernible practical purposes rare might as well be equivalent to non-existent.

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On 2/9/2018 at 3:22 AM, Area54 said:

Correction to Moontanman's assertion that most fossil fuels were produced in the Carboniferous era from rotting vegetation. Setting aside that if it rotted the carbon wouldn't be available, the Carboniferous produced a substantial part of the Earth's coal deposits, but oil was generated from marine deposits of plankton, primarily IIRC zooplankton. There are various sources for that oil, but most of them are post-Carboniferous. Natural gas (methane) is derived from coal, or in some cases decomposition of petroleum.

On topic, @dstebbins , you have highligted an issue with popular science. It is rarely made clear enough that when scientists speak of life they are speaking of any form of life and more often than not very simple life forms, equivalent to prokaryotes. When they speak of complex life they are generally, at most, thinking in terms of sponges, or echinoderm like entities. And if they mention advanced life they might be referencing lizards, weasels, or politicians. Intelligent, "civilised" life will likely only be in the conversation if we are talking SETI.

Thanks for the correction, I should not have missed that one... 

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On 15/02/2018 at 4:19 PM, Moontanman said:

Thanks for the correction, I should not have missed that one... 

You are most welcome. It is a commonly held belief - I'm not sure how it arose. Thinking out loud, if no one has written a popular science book on The Ten Most Common Misunderstandings About Science, then someone ought to. :)

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On ‎2‎/‎12‎/‎2018 at 11:20 AM, MigL said:

The only advantage water has, is that its solid state is less dense than its liquid state.
Water tends to freeze from the top down, giving life a chance to survive at depth, even when the surface is frozen solid...

The other liquids (ammonia, methane, ethane, nitrogen, hydrogen fluoride, hydrogen sulfide, silicon dioxide, etc.) are liquid at such low temperatures that any molecular motion is S L O W.  Life would develop much slower, and complex life would be less likely, and intelligent life seems an absurd idea.  Liquid water works faster and better.  Look for the water.

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

Edited by Airbrush

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4 minutes ago, Airbrush said:

The other liquids (ammonia, methane, ethane, nitrogen, etc.) are liquid at such low temperatures that any molecular motion is S L O W.  Life would develop much slower, and complex life would be less likely, and intelligent life seems an absurd idea.  Liquid water works faster and better.  Look for the water.

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry

I disagree, while those liquids might be much colder but organic compounds that are much more fragile that the ones we use would be more stable and able to react at reasonable speeds...  

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2 minutes ago, Moontanman said:

I disagree, while those liquids might be much colder but organic compounds that are much more fragile that the ones we use would be more stable and able to react at reasonable speeds...  

How can you say "react at reasonable speeds" at such extremely low temperatures?  How does complex life evolve in such cold solutions?

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Just now, Airbrush said:

How can you say "react at reasonable speeds" at such extremely low temperatures?  How does complex life evolve in such cold solutions?

 Again, organic compounds more delicate than the ones we use, read that more unstable, would be more stable at low temps and possible react at the same speeds the ones we use do at higher temps. 

Let's not forget life much hotter as well. Sulfuric acid could be used on worlds much hotter than ours with chemicals that are too stable to be useful at our temps... Such a life form might look at the chemicals we use and say the same thing about us as we do about the colder ones.. 

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On ‎2‎/‎18‎/‎2018 at 8:51 AM, Moontanman said:

 ...organic compounds more delicate than the ones we use... would be more stable at low temps and possible react at the same speeds the ones we use do at higher temps....

You say "possibly react at the same speeds" as water-based life.  What kind of probability do you think?  My guess is a low probability, and for that reason water is really the primary factor when looking for ANY kind of life because of the higher probability.  Astronomers say "follow the water."  We may find some weird simple form of life on Titan in liquid methane, but scientists will be more busy looking for life inside of Mars, Europa, and Enceladus, and when it comes to exoplanets, they will focus attention first on planets within the habitable zone of liquid water.  They have not even planned any mission for exploring the methane lakes of Titan.

Edited by Airbrush

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31 minutes ago, Airbrush said:

You say "possibly react at the same speeds" as water-based life.  What kind of probability do you think?  My guess is a low probability, and for that reason water is really the primary factor when looking for ANY kind of life because of the higher probability.  Astronomers say "follow the water."  We may find some weird simple form of life on Titan in liquid methane, but scientists will be more busy looking for life inside of Mars, Europa, and Enceladus, and when it comes to exoplanets, they will focus attention first on planets within the habitable zone of liquid water.  We have not even planned any mission for exploring the methane lakes of Titan.

Actually low temps will slow down chemical reactions, this is a known quantity. I was just trying to be careful about what I was asserting since we don't know if these more reactive molecules can form replicating analogs to what we currently know. There is no reason to assert they cannot but it is still an unknown. Water is indeed the only data point we have in solvents for life although there are bacteria that live in oil they still need intracellular water. 

And yes some ideas about looking for life in liquid methane have been proposed from cell structures to the size and chemical respiration of those cells.

https://www.nasa.gov/feature/goddard/2017/nasa-finds-moon-of-saturn-has-chemical-that-could-form-membranes

https://www.nasa.gov/topics/solarsystem/features/titan20100603.html

http://www.telegraph.co.uk/science/2017/12/21/nasa-funds-helicopter-mission-hunt-alien-life-titan/

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