# Life came to Earth from comet?



## Bullgrit (Jan 30, 2014)

I often hear/read articles that mention the theory that asteroids/comets brought water or the beginnings of life to Earth in the early stages of the solar system. (I heard one just this morning on NPR, which prompted this post.) Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space? And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?

Bullgrit


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## delericho (Jan 30, 2014)

Well, how else do you explain that all the aliens look like humans with funny noses?


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## delericho (Jan 30, 2014)

But for a serious answer: no idea, sorry.


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## Janx (Jan 30, 2014)

I saw one of those articles the other day.

While I wouldn't want science to limit its thinking to presume the earth is the center of the solar stsrem or the source of all life, in the case of life itself, it seems earth is more hospitable than anywhere else in our solar system.

It seems less probable that life evolved off-planet on a pretty crappy rock, when it has oodles of water and other stuff right here on Earth.  Even allowing for our present day earth wasn't as awesome back when life first evolved, it seems it still couldn't have sucked as much as being frozen in the vaccum of space all the time.

It almost seems like wishful oppositional defiance thinking that since "everybody" assumes life began on earth, they must be proven wrong.


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## Kramodlog (Jan 30, 2014)

Comets are important because when Earth was young and a big ball of magma, the core was forming itself drawing in all the elements toward the center. At that point Earth was devoid of most elements on it's surface.

When the surfaced cooled it prevented elements from sinking to the core, so comets with elements in them, like gold, seeded the surface. 

Sounds ridiculus? Remember, when the universe and Earth were young, there was a lot more asteroid hurling in space and planets, moons, were constantly bombarded. 

This is why life might come from the stars, elements needed for life came from the stars.


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## WayneLigon (Jan 30, 2014)

Bullgrit said:


> I often hear/read articles that mention the theory that asteroids/comets brought water or the beginnings of life to Earth in the early stages of the solar system. (I heard one just this morning on NPR, which prompted this post.) Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space? And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?
> 
> Bullgrit




There are some contending theories that even a billion years or so was not enough time for the primordial molecules to assemble and make that move from inorganic to organic; these basically try to plot Moore's Law to biological systems by regressing from current complexity to the primordial state, and come up with a time-of-origin of something like 9 billion years. A problem, since our solar system is something like 4-5 billion years old at most.

Most of the theories are not really saying 'life' but 'organic primordial molecules', kind of 'pre-life'. These can form in space itself and be propagated by the solar wind, or be hardy enough to somehow survive the 'exit-travel through space-survive re-entry' cycle of a grazing collision elsewhere.

Earth's water seems to be a balance of stuff it produced naturally, and stuff it accumulated as icy bodies were drawn in. Without knowing the composition of most Kuiper Belt objects, it's difficult to say how much may have come from the solar system leftovers. 

One of the reasons that panspermia has been given an uptick in recent years is the discovery that some of our old suppositions about the formation of life - it must have sunlight, it must have water, it can only form in x-y temperatures - all that is pretty much crap due to discovering several forms of life that require none of those things and that can exist and evolve in conditions we previously thought impossible.


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## Umbran (Jan 30, 2014)

Bullgrit said:


> Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space?




Well, the entire planet is imported from space, now isn't it?  We're only quibbling over what part of space the water came from, and when.

The thing is, water isn't just water.  Hydrogen and oxygen have isotopes.  You can look at the water on Earth, and measure the ratio of isotopes in our water, and compare it to water seen in asteroids, and that seen in comets.  If the isotope ratios match one or the other, one is apt to think there's a bit of a link.

It was only in the 1980s that we started getting an idea of the isotope ratios in the water of comets.  And the results seemed to indicate that comets had notably different ratios than seen in our oceans, while water in asteroids looked a lot more like our water.  But more recent measurements (of comet Hartley 2, for example) have shown comets with rather Earthlike water.

The basic reason folks sometimes wonder if our water came from asteroids or comets is simple:  heat.  The early Earth was molten - what water we had on the surface would be forced to vapor - hot vapor.  And hot vapor has a tendency to escape into space.  So, many figure that any water we had would have boiled off, and would have needed to be replaced.  

As far as I know, there's no consensus, though.  Some think our water came from comets and/or asteroids, others think it was outgassed or created (by burning hydrogen) on Earth after it had cooled enough to hold onto liquid water.  Others think there's a mix of sources.



> And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?




Water is pretty common stuff - there's lots of it out in the Universe that we can see.  Life is less obvious...

There's a basic tenet that runs through all of science - one place in the universe is pretty much the same as any other. We are not the center of the universe, the galaxy, or the solar system.  We aren't the center of *anything*.  Earth is not really special.  So, if you think that the origin of life is an unlikely event, you have to ask if or why it happened here, specifically.


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## Tonguez (Jan 30, 2014)

The thing is Earth is special, not because of water but because of fire. It has the right conditions for stable (non-explosive) ignition of fire. Further more the confluence of the iniquely large Moon and Jupiters gravity well help maintain the stability that allowed the ignition of the primordial goo that necame life.

All praise Father Jupiter and Mother Earth, and of course Sister Moon and Grandfather Sun


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## Umbran (Jan 30, 2014)

Tonguez said:


> The thing is Earth is special, not because of water but because of fire. It has the right conditions for stable (non-explosive) ignition of fire.




Maybe you're using the word "fire" in new and interesting ways.

But, by standard definition, no, that cannot be why we have life - we have the conditions for stable, non-explosive fire (like a burning log) because we have an oxygen atmosphere.  That atmosphere was generated by living things, which began when we had a reducing atmosphere, not an oxidative one.


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## Jeremy E Grenemyer (Jan 31, 2014)

Ooh, I'm reading about this in my brand new copy of _Cosmos_ by Carl Sagan.

Everybody stop talking so I can catch up and then contribute something worthwhile.


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## Umbran (Jan 31, 2014)

sanishiver said:


> Ooh, I'm reading about this in my brand new copy of _Cosmos_ by Carl Sagan.




Wonderful book.

While it may be brand new to you, note that was written back in 1980 - that information is some 30+ years old, and we may know better about many things in there....


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## Dioltach (Jan 31, 2014)

Oooh, does this mean I married an alien?


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## Umbran (Jan 31, 2014)

We are all alien, to one another.


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## Dioltach (Jan 31, 2014)

Not me, I'm English.


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## Morrus (Jan 31, 2014)

Dioltach said:


> Not me, I'm English.




Me too!


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## Umbran (Jan 31, 2014)

Dioltach said:


> Not me, I'm English.




And if you moved to the US, they'd give you this green card that said you were an alien.  

Actually, I don't know if the physical cards are green any more.


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## Morrus (Jan 31, 2014)

Umbran said:


> And if you moved to the US, they'd give you this green card that said you were an alien.




Which makes them wrong. When I visit the US I'm surrounded by aliens.


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## Tonguez (Feb 1, 2014)

Umbran said:


> Maybe you're using the word "fire" in new and interesting ways.
> 
> But, by standard definition, no, that cannot be why we have life - we have the conditions for stable, non-explosive fire (like a burning log) because we have an oxygen atmosphere.  That atmosphere was generated by living things, which began when we had a reducing atmosphere, not an oxidative one.




Yeah I do have a broader definition of fire being any exothermic redox reactions including respiration, fire, fermentation, corrosion, digestion etc. Some archaea did utilise dissolved oxygen compounds prior to the GOE but regardless I'd argue that complex life requires the levels of oxygen present on Earth, which is rare.

In any other environment be would be stuck with archaea or viruses...


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## The_Silversword (Feb 1, 2014)

Umbran said:


> we have the conditions for stable, non-explosive fire (like a burning log) because we have an oxygen atmosphere.




I think it has more to do with the nitrogen really, if we had higher amounts of oxygen in the atmosphere a burning log would be far more combustible.


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## Dioltach (Feb 1, 2014)

Morrus said:


> Which makes them wrong. When I visit the US I'm surrounded by aliens.




As George Mikes says,


> It was like this. Some years ago I spent a lot of time with a young lady who was very proud and conscious of being English. Once she asked me - to my great surprise - whether I would marry her. 'No,' I replied, I will not. My mother would never agree to my marrying a foreigner.' She looked at me a little surprised and irritated, and retorted: I, a foreigner? What a silly thing to say. I am English. You are the foreigner. And your mother, too.' I did not give in. 'In Budapest, too?' I asked her. 'Everywhere,' she declared with determination. 'Truth does not depend on geography. What is true in England is also true in Hungary and in North Borneo and Venezuela and everywhere.'


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## Janx (Feb 1, 2014)

Dioltach said:


> As George Mikes says,




Sounds like a good reason not to marry her snobby arse.


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## Nellisir (Feb 2, 2014)

Tonguez said:


> Yeah I do have a broader definition of fire being any exothermic redox reactions including respiration, fire, fermentation, corrosion, digestion etc. Some archaea did utilise dissolved oxygen compounds prior to the GOE but regardless I'd argue that complex life requires the levels of oxygen present on Earth, which is rare.
> 
> In any other environment be would be stuck with archaea or viruses...




If complex life requires oxygen, but it takes complex life to make oxygen....I mean, plants don't need oxygen.  They need carbon dioxide, which they then split apart and make oxygen by accident.  Oxygen typically isn't available because it's bound up in things like carbon dioxide, oxidation, and so forth. Venus has plenty of oxygen, it's just all tied up in CO2, isn't it?


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## Mustrum_Ridcully (Feb 2, 2014)

Nellisir said:


> If complex life requires oxygen, but it takes complex life to make oxygen....I mean, plants don't need oxygen.  They need carbon dioxide, which they then split apart and make oxygen by accident.  Oxygen typically isn't available because it's bound up in things like carbon dioxide, oxidation, and so forth. Venus has plenty of oxygen, it's just all tied up in CO2, isn't it?




Plants don't make oxygen by accident. They need oxygen just like we do, they just use photosynthesis and CO2 to get to the oxygen.


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## Nellisir (Feb 2, 2014)

Mustrum_Ridcully said:


> Plants don't make oxygen by accident. They need oxygen just like we do, they just use photosynthesis and CO2 to get to the oxygen.



And I've learned my new thing for the day today.


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## Tonguez (Feb 2, 2014)

Nellisir said:


> If complex life requires oxygen, but it takes complex life to make oxygen....I mean, plants don't need oxygen.  They need carbon dioxide, which they then split apart and make oxygen by accident.  Oxygen typically isn't available because it's bound up in things like carbon dioxide, oxidation, and so forth. Venus has plenty of oxygen, it's just all tied up in CO2, isn't it?




Yes precisely and thats what makes Earth unique, it has the perfect conditions to encourage stable fire. Venus has an atmosphere similar to pre-Oxygen cataclysm Earth and thus too much CO2 thus fires are suppressed. Something unique happened on Earth so our oxygen levels are just right...


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## Morrus (Feb 2, 2014)

Tonguez said:


> Yes precisely and thats what makes Earth unique, it has the perfect conditions to encourage stable fire. Venus has an atmosphere similar to pre-Oxygen cataclysm Earth and thus too much CO2 thus fires are suppressed. Something unique happened on Earth so our oxygen levels are just right...




What's fire got to do with it?  I mean... fish?

Do you not think we'll find anything in places like the seas of Europa?


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## Umbran (Feb 2, 2014)

Mustrum_Ridcully said:


> Plants don't make oxygen by accident. They need oxygen just like we do, they just use photosynthesis and CO2 to get to the oxygen.




It is perhaps more accurate to say that plants don't need *free* (or molecular) oxygen like we do - they can get it from carbon dioxide.


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## Umbran (Feb 2, 2014)

Tonguez said:


> Yes precisely and thats what makes Earth unique, it has the perfect conditions to encourage stable fire. Venus has an atmosphere similar to pre-Oxygen cataclysm Earth and thus too much CO2 thus fires are suppressed. Something unique happened on Earth so our oxygen levels are just right...




The point is that our oxygen levels are a result of "fire" as you are using the term, not a cause of it!

Plants don't need free oxygen.  A high CO2 atmosphere is what plants started with.  Simply put, over the course of Earth's life, the "perfect conditions" havve not been static, perfect conditions.  They have changed dramatically over time.  And the conditions we started with are not expected to have been somehow rare or particular.


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## Nellisir (Feb 2, 2014)

Tonguez said:


> Yes precisely and thats what makes Earth unique, it has the perfect conditions to encourage stable fire. Venus has an atmosphere similar to pre-Oxygen cataclysm Earth and thus too much CO2 thus fires are suppressed. Something unique happened on Earth so our oxygen levels are just right...



But what happened, in your mind, to free up the oxygen from the CO2 and the H2O?  Oxygen binds up with  all over the place; that's why we have H2O comets, not O2 comets.


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## Nellisir (Feb 2, 2014)

Umbran said:


> It is perhaps more accurate to say that plants don't need *free* (or molecular) oxygen like we do - they can get it from carbon dioxide.



OK, this makes more sense, and yeah, it's kinda what I thought i was saying except I wasn't thinking it or saying it very well at all.


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## Nellisir (Feb 2, 2014)

Morrus said:


> What's fire got to do with it?  I mean... fish?
> 
> Do you not think we'll find anything in places like the seas of Europa?




I think he's using "fire" as some kind of weird shorthand for "chemical reaction involving free oxygen", except he's also assuming that free oxygen is somehow required to unbind CO2, or perhaps that CO2 and O2 are different beasts.


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## Nellisir (Feb 2, 2014)

Tonguez said:


> Venus has an atmosphere similar to pre-Oxygen cataclysm Earth and thus too much CO2 thus fires are suppressed.




You're going to have to explain this one a bit.

First of all, what's an "Oxygen Cataclysm"?
Second of all, are you talking about fire as in burning firewood, or fire as in "chemical reaction involving oxygen, like rusting and tarnishing"?
Third, if you took Venus's atmosphere, cooled it down, and seeded it with plant life, the plants would absorb the CO2 and release O2.  Yes or no?


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## Umbran (Feb 2, 2014)

Nellisir said:


> First of all, what's an "Oxygen Cataclysm"?




I think he's referring to what is elsewhere called the "Great Oxygenation Event", the "Oxygen Catastrophe" or the "Oxygen Crisis" - the original appearance of significant amounts of free oxygen in our atmosphere.

Note that, in all likelihood, early procaryotic and eucaryotic organisms carrying out photosynthesis predate the O2 building up in the atmosphere.  To start with, a lot of the O2 they created would have immediately bound up with iron and other minerals.  Only after much of the stuff free on the surface had oxidized would O2 start to accumulate in the air.


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## Kramodlog (Feb 2, 2014)

Morrus said:


> What's fire got to do with it?  I mean... fish?
> 
> Do you not think we'll find anything in places like the seas of Europa?



I think he means fire is what help our ancestors evolve into us. Cooking helped us cook meat, giving more energy to the brain, reducing our mastication time, harded wood, scare off beats, etc. 

He does have a point too. No other animal produces fire artificially. Some point to tools or language has what differenciates us from other animals, but tools and communication do exist in other animals, even if very primitive. Fire does not. 

Not sure what this has to do with comets or life in general.


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## Nellisir (Feb 3, 2014)

goldomark said:


> I think he means fire is what help our ancestors evolve into us. Cooking helped us cook meat, giving more energy to the brain, reducing our mastication time, harded wood, scare off beats, etc.
> 
> 
> 
> ...


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## Kramodlog (Feb 3, 2014)

It does seem to lead to intelligent life, but I agree this is anthrocentric. We have very little else to work with aside from speculation.


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## Nellisir (Feb 3, 2014)

goldomark said:


> It does seem to lead to intelligent life, but I agree this is anthrocentric. We have very little else to work with aside from speculation.



Fire or oxygen?  I don't see fire "leading" to "intelligent" life; we had it before we were homo sapiens sapiens, but we were still homo/human.

I think the more important factors are community and communication. With radical exceptions, a civilization is going to be a group of creatures that works together and can propagate learned information beyond themselves. Tigers could be really really smart, but they're never going to hang out and be sociable together.

I would also hypothesize that higher intelligence is more likely to arise in creatures that are flexible in diet and habitat and not apex predators, although they might be nearer the top than the bottom. Specialized diets lead to hardwired behavior, not learned behavior. IMO.


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## Kramodlog (Feb 3, 2014)

Nellisir said:


> Fire or oxygen?  I don't see fire "leading" to "intelligent" life; we had it before we were homo sapiens sapiens, but we were still homo/human.



Fire. 

Homo is the genus. Humans are homo, but not all homos are human. Umm... The latin thing, not folks who like same sex folk.

Did fire help us become homo sapiens sapiens instead of just being very intellegient apes? In theory it helped. More energy for the brain by cooking meat, reducing mastication time by cooking food so we have more time to do other stuff, perfect tools, etc.



> I think the more important factors are community and communication. With radical exceptions, a civilization is going to be a group of creatures that works together and can propagate learned information beyond themselves. Tigers could be really really smart, but they're never going to hang out and be sociable together.



Other animals have communities and communication. Ants, canines, other primates. None have fire. It really is a human thing.

Of course corellation doesn't mean causation.


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## Nellisir (Feb 3, 2014)

goldomark said:


> Homo is the genus. Humans are homo, but not all homos are human. Umm... The latin thing, not folks who like same sex folk.




Right. According the all-knowing wikipedia, which was all I had time to look at tonight, fire-use goes back somewhere between 200,000 and 1.2 million years, with 400K being pretty solid right now. 200K would put it out of H. sapiens, and into very late H. erectus. I forget where things are with neandertals; I think there's evidence for fire-use there.  1.2 million puts it way back into solid H. erectus; no neandertals, no sapiens.



> Other animals have communities and communication. Ants, canines, other primates. None have fire. It really is a human thing.
> Of course corellation doesn't mean causation.




Right, exactly. Is fire-use causation of humanity, or consequence? Is it a tool, or more than a tool?  Ants don't have radio either, but not many people would argue radio is our defining feature - it's a tool we use.  

I'm not saying anything with communication and socialization is a civilization; I'm saying a civilization has to have communication and socialization. So not all human-level intelligences are going to form civilizations, because not all of them will a) communicate and b) socialize.

The weird exemption may be AIs. Above a certain point, I fail to see what would keep two AIs from becoming one (it's all just code, and given sufficient processing power and storage, you can run all the code you want), at which point you might well end up with something that could reasonably be called a solar mono-intelligence, and mimic a civilization.


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## Umbran (Feb 3, 2014)

Nellisir said:


> I skipped over this before, but I fail to see the problem. Is the OP that life must be identical to life here? Why is anaerobic life automatically disqualified?




I don't have a direct link to documentation, but by my memory it has to do with energy the metabolic system can provide - this is limited by the laws of chemistry.  Things like big brains require significant levels of both energy and power (power in the scientific sense - energy per unit time), and metabolic systems that cannot provide those are, if not out of the running, at least at a significant disadvantage.


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## Dannyalcatraz (Feb 3, 2014)

From Dexy's Cosmic Runners

Come on Aliens
Fermi's Paradox means (what it means)
At this moment you'd be everywhere
But your stellar address
In space I confess
Seems so empty
Oh, come on Aliens

Edit: damn it- wrong thread...


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## The_Silversword (Feb 3, 2014)

Could be added to the song ruinier thread too, thanks alot man! I will never hear that song the same now!!!


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## Kramodlog (Feb 3, 2014)

Nellisir said:


> Right, exactly. Is fire-use causation of humanity, or consequence? Is it a tool, or more than a tool?  Ants don't have radio either, but not many people would argue radio is our defining feature - it's a tool we use.



But did we manage to come up with the radio because way back when some smart ape mastered fire?

Burnng stuff is still very much at the heart of humanity. We're the fire obsess ape. What do we do with petroleum, natural gas, coal, if not burn a lot of them? I'll let the phys heads decide if fission is similar to "burning".



> The weird exemption may be AIs. Above a certain point, I fail to see what would keep two AIs from becoming one (it's all just code, and given sufficient processing power and storage, you can run all the code you want), at which point you might well end up with something that could reasonably be called a solar mono-intelligence, and mimic a civilization.



A sense of individuality? In other words selfishness.


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## Mustrum_Ridcully (Feb 3, 2014)

goldomark said:


> But did we manage to come up with the radio because way back when some smart ape mastered fire?
> 
> Burnng stuff is still very much at the heart of humanity. We're the fire obsess ape. What do we do with petroleum, natural gas, coal, if not burn a lot of them? I'll let the phys heads decide if fission is similar to "burning".
> 
> A sense of individuality? In other words selfishness.




The key thing of "fire" might be that it is a way to generate energy. Fission might not be burning, but it has the same goal - getting energy.*

I suppose that is somethnig that every type of civilization needs, whether it has to start with fire, I am not sure. Probably is a good method for carbon-based life. Maybe there could be some kind of weird group of chemicals at an high-energetic environment (say, a brown dwarf or even a star) that doesn't use fire but some other process that generates extra energy to do whatever needs to be done. (Maybe a Sci-Fi writer might now get the idea of creating an alien lifeform that actually needs something to get rid of energy/heat, though i am not sure that such a tale would stand up to thermodyanmic considerations). That said, the problem with "weird group of chemicals" is - chances are good these elements are more rare than carbon, oxygen and hydrogen, and thus life of that sort is less likely. 

*) Isn't that also a reason why we cook food? Are we not able to bring the necessary energy to process raw meat? Or is it somethnig else?


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## Umbran (Feb 3, 2014)

YOu know, all this mention of "fire" might be better replaced with "fire" when we are talking about the tool humans use and "oxidation reaction" when we are talking about the chemistry going on in our cells.



Mustrum_Ridcully said:


> Maybe there could be some kind of weird group of chemicals at an high-energetic environment (say, a brown dwarf or even a star) that doesn't use fire but some other process that generates extra energy to do whatever needs to be done.




Well, Robert L Forward has written "Dragon's Egg", which discusses life on the surface of a neutron star.  If I recall correctly, those creatures don't have a "biochemistry", as on the surface of the neutron star, what we think of as chemicals and molecules do not exist.  



> (Maybe a Sci-Fi writer might now get the idea of creating an alien lifeform that actually needs something to get rid of energy/heat, though i am not sure that such a tale would stand up to thermodyanmic considerations).




You already do - if your body did not shed excess heat, you would bake and die.  Why do you think the summer is uncomfortable, and why do you think you sweat?



> That said, the problem with "weird group of chemicals" is - chances are good these elements are more rare than carbon, oxygen and hydrogen, and thus life of that sort is less likely.




Well, silicon has similar chemistry to carbon, and seems to be pretty common.  However, while similar, it is somewhat less varied in what compounds it will make.  Boron has even more varied chemical properties than carbon, but boron seems to be pretty rare in the universe.  But, you could at least imagine a silicon-based life form, instead of carbon based.

Not all Earthly life forms need oxygen for energy. But, systems that have an appropriate agent like oxygen to accept electrons at the end of the metabolic path are typically able to get more energy out of the same sources.  It may be possible to substitute another chemical - like chlorine - to do the job.  But, again, chlorine seems to be less common out in the universe, and chlorine has a stronger tendency to be bound up in minerals (salts, mostly), meaning it is tougher to build it up in an atmosphere.

We could also imagine life forms based on a solvent other than water - ammonia seems pretty common out there...



> Isn't that also a reason why we cook food? Are we not able to bring the necessary energy to process raw meat? Or is it something else?[/SIZE]




When we started using fire, it wasn't that we were not able to bring the necessary energy to bear.  However, use of fire has an effect we might consider... pre-digestion.  Using fire makes it easier to access nutrients and calories in a great many foods.  So, while we could bring that energy to bear, we didn't *have* to - cooking is more efficient.  By cooking, we got more out of our food than animals that didn't cook, and that's a competitive advantage.  We could get by with less food, or put forth greater effort on the same amounts of food we used to eat.

Now, humans have so adapted to cooking that we aren't really suited to eating a raw diet.  We've lost some of the machinery - our intestines are comparatively shorter than those of other primates, our teeth aren't very impressive, and so on.


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## Morrus (Feb 3, 2014)

[video=youtube;CEEPaYD5KZE]http://www.youtube.com/watch?v=CEEPaYD5KZE[/video]


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## Mustrum_Ridcully (Feb 3, 2014)

Umbran said:


> YOu know, all this mention of "fire" might be better replaced with "fire" when we are talking about the tool humans use and "oxidation reaction" when we are talking about the chemistry going on in our cells.
> 
> 
> 
> Well, Robert L Forward has written "Dragon's Egg", which discusses life on the surface of a neutron star.  If I recall correctly, those creatures don't have a "biochemistry", as on the surface of the neutron star, what we think of as chemicals and molecules do not exist.



That would be an indeed very intersting thing to speculate about. Likewise - what about the early inflationary phase after the Big Bang - you mihht think the time frames don't work for "evolution", but... that might only be true for common chemical processes on earth. Maybe entire civilizations grew up in that time, and winked out when the universe got too cold - but from their perspective, when their scientists figured out that inflation of the unvierse would lead to it cooling off too much to sustain live, but even before that, their kalaubsen* will detoriate and our peloktikus-orbitals** will eat it up, so they didn't really have to worry....



> You already do - if your body did not shed excess heat, you would bake and die.  Why do you think the summer is uncomfortable, and why do you think you sweat?



That's not what I meant, however. More like "The theoretical Gold-Fusion machine will consume enough energy to depower our entire civilization for seconds, that fixes basically all our energy problems! Unfortunately, in the past 5 picosends, scientists said the technologicaly would be commerically viable within the next 5 picosends. We may have to stick to helium fission for the forseeable future, and we still haven't found a solution for the waste disposal." 




> Well, silicon has similar chemistry to carbon, and seems to be pretty common.  However, while similar, it is somewhat less varied in what compounds it will make.  Boron has even more varied chemical properties than carbon, but boron seems to be pretty rare in the universe.  But, you could at least imagine a silicon-based life form, instead of carbon based.
> 
> Not all Earthly life forms need oxygen for energy. But, systems that have an appropriate agent like oxygen to accept electrons at the end of the metabolic path are typically able to get more energy out of the same sources.  It may be possible to substitute another chemical - like chlorine - to do the job.  But, again, chlorine seems to be less common out in the universe, and chlorine has a stronger tendency to be bound up in minerals (salts, mostly), meaning it is tougher to build it up in an atmosphere.
> 
> We could also imagine life forms based on a solvent other than water - ammonia seems pretty common out there...



Yes, the Wikipedia (?) article in this regard was pretty itnersting. For example, Silicium-based life that breathes Oxygen would probably need to operate at very different temperatures then carbon-based life, since it' difficult to devise a respiratory system using is basically sand (Silicium-Oxide). 

This could also be another aspect of why it's difficult to detect life - it might operate on different time scales simply because the (chemical) reactions it is based on have different time frames. 



*) Invented word to describe whatever a fictional primordial universe race might have in place of a sun.
**) Invented word to describe whatever a fictional primordial universe race might have in place of a planet.


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