All i keep hearing is that life cant exist without water. How do we know this? I mean just because life on THIS planet cant exist without it is not to say that life on other planets cant. I mean life on other planets may not be carbon based as we are. It may be silicone based or something else.

Isnt it really ignorant to say that no life can exist without water based on one planet that we know of (Earth) and one lifeform?.

I dont just mean intelligent life(is there such a thing?). I mean any life form be it intelligent,bacterial,microbial etc etc etc.

Paul,

I don't think anyone seriously suggests that life CAN'T exist without water, just it's a lot less likely. When you see some of the inhospitable places life exists on this planet. For example, Balbriggan, Clondalkin, Killiney?? Who'd have thought it eh? Seriously though, primitive life has been found in some really strange places like black smokers at the bottom of the dark ocean where they thrive on sulphur.

When you hear people say, oh life can;t exist there, there is no water, they are ususally referring to places in the solar system. From what we know of life at present, water is a pre-requisite. So no water makes life extremely unlikely at best.

You can speculate all you like about silicone based life forms etc, but until there is at least some science to suggest that life could take that form, there is really not a lot of point in worrying too much about it.
From what we know, life is far more likely in places with water. If you're looking for an egg, then look in a hen house:)

Seriously though, primitive life has been found in some really strange places like black smokers at the bottom of the dark ocean where they thrive on sulphur.


Thats exactly what i was thinking of when i posted.

Granted it desnt help my comment due to the fact they live in water.............but the water is not what they thrive on.............its the sulphur.

So it shows that not all life is dependent on water.

From what we know, life is far more likely in places with water. If you're looking for an egg, then look in a hen house:)

True enough but isnt that taking a very narrow minded approach? indeed isnt it restricting us from maybe finding life on other planets is we are only looking in places where water may or could exist?

No harm in widening the scope a bit and taking a chance on planets that have no water or the chance that they may have had or ever will have water.

Just because we know one way to bulid a wall................doesnt mean there are not other ways. We just have not considered them yet cuz the way we know works best for us.


Isnt a lot of science based primerily on theory? so isnt it possible in theory to assume that there can be life forms existing that are not carbon based and dependent on water?

Its free to theorize. Just dont dismiss it as theoretically impossible based on the finding of this planet.[/i]

Granted it desnt help my comment due to the fact they live in water.............but the water is not what they thrive on.............its the sulphur.

So it shows that not all life is dependent on water.

No it shows that they can get their energy by oxidising sulphur. They are still dependant on water needing water within them to oxidise the sulphur (or iron or other metals that these things 'feed' on).

Isnt a lot of science based primerily on theory? so isnt it possible in theory to assume that there can be life forms existing that are not carbon based and dependent on water?

Possible, but if life is to be anything remotely like we see on Earth the elements used will need to be able to form into large chains - an equivalent to hydrocarbons in Earth life. The best hope for this is Silicon, its in the same group in the periodic table and can form long chains.

One reason that's give that this is unlikely is a practical one. Carbon combines with oxygen in earth based life. This produces carbon dioxide which is easy to excrete since it is a gas. Silicon dioxide is a solid which would make excretion difficult.

I read somewhere once that Silicon can not produce an equivalent to carbohydrates, which would mean that organisms effectively cannot store energy.

You might find this interesting en.wikipedia.org/wiki/Alternative_biochemistry

Of course our 'first contact' if it happens may be with silicon 'life' if sci-fi theories are correct. Whatever ancient carbon civilisation that existed may have created silicon based beings and it is them that we might encounter!

True enough but isnt that taking a very narrow minded approach?

.

Paul, maybe when we've looked in all the hen houses then we can look elsewhere. But until then why go searching places where life is less likely. Up to know we haven't even gotten close to looking in all the hen houses.

Look where the water is, if you don't find any there then examine other possibilities. Just because life could form from other basic compounds like silicone does not mean that it actually does.

Why would you want to spend money sending a probe to look for life in Jupiter's clouds when most of Mars is as yet unexplored. There is likely an water ocean under the ice crust of europa. We haven't gone there yet. When we've looked in all these places then it makes sense to look in the less likely places.

Why would you want to spend money sending a probe to look for life in Jupiter's clouds when most of Mars is as yet unexplored. There is likely an water ocean under the ice crust of europa. We haven't gone there yet. When we've looked in all these places then it makes sense to look in the less likely places.

I'd rather have a close look at Venus's atmosphere before bothering with Jupiter.

Isnt a lot of science based primerily on theory?

In fact all of science is based on theory, or hypothesis. These theories are successful if they accurately describe some phenomena. The acid test however is their ability to predict future unmeasured phenomena.

Einsteins theory of relativity predicted the positions of the planets more accurately than Newtons and so superseded it. It also predicted that large massive objects would bend light. This was demonstrated during a solar eclipse where the position of stars was altered by the amount the theory predicted by the gravitational influence of the sun.

For all that, no physicist would ever say that Einstein was the final word. They would only say he has the best solution so far.

In the case of species not requiring water, there is no evidence that they exist and, as far as I know, no one has proposed a model where life could exist in such conditions. So while not ruling it out, it's not very likely.

Possible, but if life is to be anything remotely like we see on Earth the elements used will need to be able to form into large chains - an equivalent to hydrocarbons in Earth life. The best hope for this is Silicon, its in the same group in the periodic table and can form long chains.

I know but thats my point exactly.....................

WHY should life on any other planet even remotely resemble life on earth. Chances are if it exists it would be so different that we may not even recognize it AS life.

So i guess we DO need a few pointers on what to look out for really.

Paul, maybe when we've looked in all the hen houses then we can look elsewhere. But until then why go searching places where life is less likely. Up to know we haven't even gotten close to looking in all the hen houses.

Look where the water is, if you don't find any there then examine other possibilities

True enough i guess.

Chances are if it exists it would be so different that we may not even recognize it AS life.

I don't want to put too fine a point on it, but why do you say that? The evidence strongly suggests that life forms in a certain way. Earth is nothing special just another ordinary corner of the universe. WHy should life elsewhere be vastly different?

You can speculate all you like about different types of life etc, but until we know better, water is the best there is.

You are also forgetting one other VERY strong possibility. Maybe there is no life anywhere else in the universe?. You may have your views on this but based on current evidence this is a far more likely outcome than speculative silicone life forms etc.

One line you read a lot on astronomy bulletin boards is 'There must be life elsewhere in the universe'. A kind of absolutest statement. But you can't make absolutest statements without evidence to back it up. That is the scientific way. Maybe there is life, maybe not, but until we have some evidence one way or the other then the best we can say is there might be life elsewhere. I'm trying to tie that back to your statement quoted above.
At the moment the chances are that life needs water. That's based on the evidential probability of 100% of the life we have seen so far being water based.

I'm really not trying to knock your ideas Paul, on the contrary maybe one day we will find some wierd type of life. What I'm really getting at is you need to think scientifically otherwise you will always 'just be wondering' and never really getting to the heart of the matter.

WHy should life elsewhere be vastly different?


Why shouldnt it be?

WHy should life elsewhere be vastly different?


Why shouldnt it be?

Because the best available evidence says so!

Possible, but if life is to be anything remotely like we see on Earth the elements used will need to be able to form into large chains - an equivalent to hydrocarbons in Earth life. The best hope for this is Silicon, its in the same group in the periodic table and can form long chains.

I know but thats my point exactly.....................

WHY should life on any other planet even remotely resemble life on earth. Chances are if it exists it would be so different that we may not even recognize it AS life.

So i guess we DO need a few pointers on what to look out for really.

We'll recognise it as life if its there. Does it reproduce somehow? Does it react to a stimuli? Does it adapt to a change in its environment? Does it produce energy from its environment? Those answers are basically what distinguishes life from chemistry. When we look for life we are looking for basic characteristics not chemistry.

Looking around the galaxy though carbon and water rules. We find water and amino acids in nebulae for example. Given that that sort of material is 'lying around' and given that its critical for life here, I'd put money on any life we find being carbon & water based. We cant come up with a way to make silicon based amino acids theoretically (afaik) yet nature manages to mass produce it where stars are forming!

~Albert

You are also forgetting one other VERY strong possibility. Maybe there is no life anywhere else in the universe?.

The likelyhood of us being alone is miniscule but i guess possibe. How many galaxies are there in the known universe?

How many solar systems exists around a parent star in those galaxies?

The chances of Earth being the only thing in the universe with life on it is remote.

WHY..............why should one little rock like Earth be the ONLY thing in the known universe with life (in any way shape or form) on it?

Thats just silly.....................or maybe its true.

I just dont think we are alone.

Maybe i am just living in fantasy land..........................but i cant see why Earth is so damn special as to be the only place in the universe where there is life.

Til the day i die i will always believe that there is life beyond earth.............we may never know it but i strongly believe in the possibility of it.

WHY should life on any other planet even remotely resemble life on earth. Chances are if it exists it would be so different that we may not even recognize it AS life.

I doubt it, it might not have 2/4 limbs and a head, but if it is alive we'd see it.
Come to think of it why is like on Earth so similar?, it appears that there appears to be only one formula of life that works on Earth, carbon based.
There is a massive about of silicon on the Earth,
Just look a beach and yet to silicon life..

I remember a talk at the Whirlpool a few years back (I cant remember the speaker) but he basically said that nature will arrive at the same answer for an animal no matter its environment or genetics presuming life is favourable, he pointed out as an example the European sabre tooth tiger (mammal) and a sabre tooth in Australia (marsupial), they looked almost identical but were very different once you scratch the surface.

I'm convinced that there has to be life beyond this planet of ours, where is it and what it is poses a question I cannot answer, I hope there is life on Mars (microbial) and I hope it has a radically different genetic make up to us thus proving it originated completely independent of the Earth (all organisms so far discovered on Earth that use DNA use the same code book of genetic base pairs), this would go down as one of the most important discovery of all time.
If it has the same number then maybe we came from a common source or cross contamination occured (Asteroid maybe) some time in the past.

The implications and questions raised by finding life on Mars are enormous.

You are also forgetting one other VERY strong possibility. Maybe there is no life anywhere else in the universe?.

The likelyhood of us being alone is miniscule but i guess possibe. How many galaxies are there in the known universe?

How many solar systems exists around a parent star in those galaxies?

Lots. Then we narrow down the search.
How many of those stars are stable main sequence stars?
How many are in a safe part of the galaxy?
How many are in a single star system?
How many planets are there in the habitable zone?
How many of those planets have a stable orbit? (The Earth needs the Moon to keep the orbit and tilt stable)
How many are large enough to hold onto an atmosphere?
How many of those are small enough to have a low enough surface gravity?
How many have sustained their internal magnetic field?
How many have managed not to go into a runaway greenhouse system?
How many have managed not to go into a big freeze system?

The field gets narrowed down rather quickly.

And in the one system we know with life in it we've only found on one planet. The best chances for us to find life in the universe are on Mars, Venus, Titan and Europa.

DaveL, Simon Conway Morris gave the talk. Great presentation and a great book - Life’s Solution: Inevitable humans in a Lonely Universe.

~Al

Should this forum be renamed "Cosmology, physics and biology"? :?

I doubt it, it might not have 2/4 limbs and a head, but if it is alive we'd see it.
Come to think of it why is like on Earth so similar?, it appears that there appears to be only one formula of life that works on Earth, carbon based.
There is a massive about of silicon on the Earth,
Just look a beach and yet to silicon life..

I remember a talk at the Whirlpool a few years back (I cant remember the speaker) but he basically said that nature will arrive at the same answer for an animal no matter its environment or genetics presuming life is favourable, he pointed out as an example the European sabre tooth tiger (mammal) and a sabre tooth in Australia (marsupial), they looked almost identical but were very different once you scratch the surface.

I'm convinced that there has to be life beyond this planet of ours, where is it and what it is poses a question I cannot answer, I hope there is life on Mars (microbial) and I hope it has a radically different genetic make up to us thus proving it originated completely independent of the Earth (all organisms so far discovered on Earth that use DNA use the same code book of genetic base pairs), this would go down as one of the most important discovery of all time.
If it has the same number then maybe we came from a common source or cross contamination occured (Asteroid maybe) some time in the past.

The implications and questions raised by finding life on Mars are enormous.

To be honest, i think if life was discovered elsewhere most people would still be more interested in what Britney is up to this week. Id like to be proved wrong, i really would, but i think itll only be the groundbreaking event for a small percentage of Earths population. unless little green men actually land on the White House lawn (and zap georgie bush for a bonus :wink: ) i dont think itll make much of an impact. People in general just dont get excited over bacteria/bugs, even it it was proved to be extraterrestrial.

Its one reason why some people (as on this forum) look up at the sky and wonder; yet many people see whats above their heads and never give a second glance or thought to those most profound and soul-searching questions.

I think were the result of an impact of some sort ; as you said life here is eerily similar in development direction. look the the eye of the octopus ; from what ive read its disturbingly close to a human eye. why do we all (the wider animal kingdom) develop in the same general way, ie, head, 2 eyes, forelimbs, rearlimbs, etc etc. Theres a theory that goes Nature, once it finds a good way to do something, will continue to do it that way in future, like a good recipe for a cake.

So the possibility is there that life in the solar system/universe will actually be surprisingly similar to us - forward facing eyes, hands that grip, 2 arms, 2 legs. I dont know. I have a suspicion however that when life is found it may be overlooked - something like the "WOW!" signal. i think a fledging race out there in the cosmos will likely send a simple signal that will be misinterpreted by us as a neutron star / radiation / some other wave.

Hi Paul
These are excellent questions and viewpoints which seem to be a natural progression when people first become interested in astronomy and begin to appreciate how vast the Universe or indeed perhaps the Multiverse is, are we really alone in all this vastness and time? It’s an age old question that many people have tried to answer in so many different ways. Unfortunately (or fortunately depending on your point of view) there is no definite undeniable physical proof of biological material of extraterrestrial origin available that the majority of scientists could study and perform analysis on (not yet officially anyway)! All we currently know and understand, all our knowledge of life and its accepted definition is based upon one planet, as you can gather, biologists are at a severe disadvantage in this field of study if you consider hypothetically speaking another intelligent civilization elsewhere in the MilkyWay galaxy with a billion year head start in technological/social/spiritual evolution capable of studying life in all it guises /stages/evolution basically anywhere in space and time. However, our fledgling science of astrobiology has taken its first steps to perhaps one day answer many of the questions were are asking here and indeed NASA has published a document entitled “NASA ASTROBIOLOGY ROADMAP 2008” which makes for interesting reading; see: astrobiology.arc.nasa.gov/ . At the same time we are still finding new species on earth, we still have unexplored areas on earth, and we still don’t fully understand to 100% how life evolved here and our genetic coding but inroads have been made in varying degrees of discovery and success in all these fields and more.

Over the last 20 years there have been approximately 270 extrasolar planets (ESPs) detected, most of them within a 300 light year radius of the Sun, considering ~10% of the milky way galaxy’s stars are sun like (similar) and that there are ~1000 stars within a radius of the sun of 100 light years that fall into this category, none unfortunately we can say has truly “Earth like” planets, this doesn’t imply that none exists, it just means we haven’t developed the technology to a level were we can easily detect possible Earth like planets with high resolution, however new space missions such as the recent European “COROT” and the “James Webb Space Telescope”, which is scheduled to be launched in a few years will addresses these problems to a certain extent and become the foundation to build upon for near future space missions such as NASA's Terrestrial Planet Finder. If we do find other earth like planets orbiting other suitable and stable stars will these planets contain life as in the definition we know it? One way of detecting life is to measure an Earth like planet transiting its parent star and therefore obtain Spectroscopic measurements to understand the planet's atmospheric composition, if there is oxygen, water vapor, methane, nitrogen etc on this Earth like planet then we should be paying very close attention to it for future exploration when we have the capabilities to do so.
In the meantime of course we have our own solar system to explore and as Dave rightly said “The implications and questions raised by finding life on Mars are enormous” I am sure we would agree that would go for life even in its simplest forms anywhere else in the solar system which leads me on to the meteorite known as “Allan Hills 84001” which was ejected from Mars and ended up on earth long ago. There was much debate regarding this rock over the intervening years but recent studies reported last month on this Mars rock shows that Mars is capable of forming organic compounds at least in its ancient past, in other words the building blocks of life. These findings have paved the way for the “Mars Science Laboratory (MSL), a nuke powered rover mission due for launch in 2009 to ascertain if Mars still holds secrets in this regard.

If we consider the possibility of intelligent life (within the definition as we currently understand) in other parts of the MilkyWay galaxy capable of least rudimentary interstellar communication like us (we have sent deliberate and powerful directional EM signals BTW to nearby target stars already, active SETI rather than passive SETI which has caused some concern for various reasons) to other peoples elsewhere capable of traveling easily between stars, then the question is where are they? Is there so few to zero other civilizations, is that why their deliberate or non intentional signals have not been detected in over 40 years, or are there many civilizations capable of communicating and interstellar travel, then the question must be asked again; where are they? Which leads us into Fermi’s paradox. The Drake equation goes someway to give a number of civilizations within the MilkyWay Galaxy capable of communication, (N). Does N=0 or N=1.0X10^6+, who knows for sure, substituting numbers into the drake equation is best guess based of current knowledge. Other investigations by scientists involved in SETV (Search for Extraterrestrial Visitation) and SETA (Search for Extraterrestrial Artifacts) have perhaps answered Fermi’s paradox in the form of other beings technological manifestations and their detection by us within our solar system including Earth, for a further treatment of these highly interesting investigations and discussions there is another thread that you might be interested in Paul: www.irishastronomy.org/boards/viewtopic.php?t=2078&start=0

“We are Made of Star Stuff”, and “We are a Way for the Universe to Know Itself”, Carl Sagan.

Clear skies
Mike

SETI: www.setileague.org/
NASA's Terrestrial Planet Finder: planetquest.jpl.nasa.gov/TPF/tpf_earths.cfm
COROT Space Telescope: smsc.cnes.fr/COROT/
NASA Planet Quest: planetquest.jpl.nasa.gov/index.cfm
Life: en.wikipedia.org/wiki/Life
Intelligence: encarta.msn.com/encyclopedia_761570026/Intelligence.html
Astrobiology: astrobiology.arc.nasa.gov/
SETV: www.daviddarling.info/encyclopedia/S/SETV.html
SETA: www.daviddarling.info/encyclopedia/S/SETV.html
Mars meteorite: www.sciencedaily.com/releases/2007/12/071211095141.htm

Hi Paul
Is there so few to zero other civilizations, is that why their deliberate or non intentional signals have not been detected in over 40 years, or are there many civilizations capable of communicating and interstellar travel, then the question must be asked again; where are they?

You have to remember that only 100 years ago we could not have been detected using radio, so in theory there is nothing prevent a pre-computer civilisation been only say 40 LYs from us.We'd need to take a spectrum of these planets to be sure, at the moment we cant even visually detect any planet in any other solar system, so a spectrum of it is a long way off yet. .

If you consider hypothetically speaking another intelligent civilization elsewhere in the MilkyWay galaxy with a billion year head start in technological/social/spiritual evolution

Mike.

Theres also a line of thought that states that a lifeform couldnt have had that kind of headstart unless they started out pretty early in the birth of the universe which they say (always 'they'?!) wouldnt have happened - it would take billions of years for it to settle down, matter being distributed, planets forming etc etc. So ive read anyway. Just goes to show - everyone has an opinion. Including the fields of cosmology/physics/astronomy. Id like to mention i have no doubt there life out there, some more advanced, some less so. some gone already, never to have shone their light upon the cosmos.

@Dave - thats true. ill live in hope - though 40LYs is still too far for a vacation.

^^^ what the hell happened to my fonts up there! :?

Hey Paul
Not sure what happened your fonts there Paul but they look impressive in my opinion! There was an interesting news release in 2003 on the oldest planet found in our MilkyWay galaxy; astoundingly it was estimated to be 13 billion years old and at a relatively nearby distance in cosmic terms of 5600 light years. OK it’s not Earth like, but it gives you some idea on how old planets may be and what may be inferred from this. Some interesting quotes from this discovery…
“The discovery suggests that the universe was quite efficient at making planets very early in its history, despite the fact that the "construction material" for planets was rare. The heavier elements needed to make at least the cores of planets weren't abundant until the first "star factories" began forging oxygen, silicon, nitrogen, etc., in their nuclear-fusion furnaces. This discovery implies that our galaxy is abundant in planets. And, where there are planets there could be life”.

“If this planet were inhabited it would be home for conceivably one of the oldest civilizations in our galaxy. Its life forms would have been far evolved by the time the very first primitive cells were assembling in Earth's primeval oceans. However, this planet is a gas giant like Jupiter, and so has no solid surface for life as we know it to arise. But if the planet has rocky moons, like the satellites of Jupiter, they might be abodes for life”.
hubblesite.org/newscenter/archive/releases/2003/19/

Dave, I agree with your rationale to some degree for detection based on technological evolution in the way you described. However we must also keep in mind that even if civilizations exist that are below or well below our current technological achievements say a 100 light years distant from us we cannot rule out the possibility of a more highly advanced type III civilisation based on the Kardashev classification (we would be considered below type I, ~0.7) sending out very highly advanced intelligent self replicating and self sustaining robotic probes in positions throughout the galaxy where stable stars and associated planets may be monitored for such artificial EM leakage and deliberate signals, hypothetically we may then receive a reply from one of these probes 100 light years distant after a period of time of evaluation even if it is positioned only 2 light years distant from another civilization below our current level of technology.
Or perhaps the probe may alert its parent civilization to our presence immediately by some means that we do not currently understand in which we would be evaluated by “them” in whatever ever methods, protocols and means deemed necessary over a period of time! These are just my thoughts and opinions that may be of no value; I personally find them fascinating simply because of the possibilities and implications.

Clear skies
Mike

Kardashev classification: www.daviddarling.info/encyclopedia/K/Kardashevciv.html

Von Neumann Probes: www.daviddarling.info/encyclopedia/V/vonNeumannprobe.html

^^^ what the hell happened to my fonts up there! :?

I fixed them

^^^ what the hell happened to my fonts up there! :?

Must've been the aliens

Even the simplest life so far discovered is immensly complex - chemically speaking (chemical complexity seems to be a pre-requisite for life). The only element available in the required quantites that can form the complexity of life is carbon, and all carbon based life requires water. This is not to say that all life has to be carbon based - but nature generally takes the easy way out - why struggle to make a silicon based lifeform when carbon works much more easily and where there is silicon you can be assured that carbon is already available in suitable quantities. If silicon life were possible I think we would have seen it here on our own planet already. The only silicon 'life' on this planet is man-made. Perhaps there is Silicon Life out there made by long dead carbon-based civilisations and it has advanced to being self aware and self perpetuating. Follow the water is a good modus, as it is relatively easily detected, and a pre-requisite for life "as we know it".

Lets just hope that if and when we make contact with an advanced ET life that they are VEGETARIANS !!!