[Moontanman]

Is "life as we know it" common in the universe or is "life as we know it" an oddity of the Earth and it's charmed environment?

At some point the organic chemical bath of various chemical reactions, some replicating and some simply making the molecules necessary for replication came together to form a cell and these cells combined the chemical reactions that had been going on independently in the surrounding ocean and incorporated them into what we would recognize as a reproducing cell or "life as we know it". (shopping bag theory of life)

Was this first cell inevitable? Or was it the result of the Earth's environment providing an unusually long span of time for the chemical reactions of life to come together to form a cell. Or was it an oddity that seldom if ever arises on a planet. Will we find planet after planet with oceans covered only by oily organic chemical systems with nothing we would recognize as "life as we know it"?

It is my contention that the Earth was alive before the first cell as a an entire ocean of metabolizing chemicals. Also that this is the natural state of "life" and that the more advanced "cell" form of life is an oddity that may very well never come into being anywhere else.

[Boerseun]

Whether "Life as we know it" is prodiguous in the universe is, indeed, a question for the ages. And one for which we simply don't have an answer.

But we can speculate.

And I'm of the opinion, that given the complexities of organic chemistry, and the seemingly endless combinations possible with carbon, hydrogen and nitrogen, if you have an Earth-like planet roughly the same distance from a sun-like star than we are, with roughly the same mix of chemicals found on Earth, and a few billion years to play with, then, yes - life as we know it is inevitable. But that's just my opinion.

Earth-like planets are hardly the norm. Heck, look at our own solar system. The norm seems to be gas giants existing in a deep freeze. Which might make other life-forms possible based on other chemistries, totally foreign to what we are used to. Silicon might take the place of carbon, producing such strange lifeforms that we might not even recognize it as such. Which might very well mean that Earth-like life is the exception - carbon-based life might be a shortcut, coming into existance in the hectic inner regions of solar systems which are awash with plentiful energy, where species' lifetimes are measured in millions of years, whereas silicon-based lifeforms come to the fore in the more stable outer regions, where species' lifetimes are measured against the ages of stars.

I dunno, really. We can merely speculate, given the evidence. But, I'm a bit of a carbon-chauvinist, myself. And as crazy as organic chemistry appears on Earth, it'll be equally crazy and full of potential on any other planet, given the right conditions.

[Moontanman]

My point is that life doesn't have to be a cellular machine with DNA and RNA that has the potential to become complex. Life was a world wide complex of interacting chemicals, I see no reason to expect life to always or ever advance to the cellular level. a less than stable environment would be enough to cause life to remain at the less complex stage for the entire life time of a planet. so many unlikely things go into making the earth a stable environment for life as we know it I don't see any reason to expect it to happen with any regularity anywhere else.

[Donk]

Life as we know it depends first and foremost on liquid water. That gives a very narrow temperature range. But in that narrow temperature range, water on rock will give Moontanman's stew of interacting chemicals; from there it's likely that one will hit on a way of growing by absorbing nearby chemicals and then replicating itself.

Once that stage is reached, the rest becomes inevitable. At first the chemicals have an endless supply of building materials, but eventually they get used up. Then the proto-life chemicals start on each other - dismantling rivals, absorbing them, replicating. Those chemicals that do it best make more replicas. That's the start of the ongoing arms race called Life, which is continuing through us and will end who knows where?

If "life as we know it" means land life, and intelligent land life at that, it seems a lot less likely. The Earth managed for most of its history without any land life, and tool-using animals are very recent indeed. I like the theory that early land life was swept ashore on high tides and managed to learn how to survive without constant immersion in water. Without our oversized moon, there would be no tides. Life wouldn't have the same incentive to colonise the land, and it might have taken many billions more years, if ever.

[DI5STURBED]

Moontanman,
This is one of the questions I find most fascinating, seeing as there are so many different answers too it. I think a good start may be the anthropic principle, which states the we should take into account the set of constraints that can support human life. With that we can say that if there was only one universe ever made than the way it develops and the formation of planets and life for that matter was not random at all. Since the universe the anthropic principle is talking about is one that revolves around us, and why shouldn't it? We do exist.

Another way of looking at it is that all of this is completely random and that we are a fluke happening on chance alone. This may not be far from the truth, in science a lot of things are left to chance; quantum theory, probability for a chemical reaction, the weather, So why should we be so special and not just as random as everything else?

As for life on other planets I don't believe it is looking too promising since I believe only Mars and Titan have the organic compounds to support life. Although there is no reason that a different form of life that doesn’t need organic compounds to survive shouldn't exist. Personally I am an optimist and believe that there is some other form of life out there just because we haven't found life elsewhere in our little sliver of the universe we call the solar system doesn’t mean there isn’t life in this huge still expanding universe.

[Moontanman]

Originally Posted by Donk

Life as we know it depends first and foremost on liquid water. That gives a very narrow temperature range. But in that narrow temperature range, water on rock will give Moontanman's stew of interacting chemicals; from there it's likely that one will hit on a way of growing by absorbing nearby chemicals and then replicating itself.

This act of reproduction was already going on before cells formed.

Once that stage is reached, the rest becomes inevitable. At first the chemicals have an endless supply of building materials, but eventually they get used up. Then the proto-life chemicals start on each other - dismantling rivals, absorbing them, replicating. Those chemicals that do it best make more replicas. That's the start of the ongoing arms race called Life, which is continuing through us and will end who knows where?

The chemical pathways of chemosynthesis were already present and producing ever more chemicals for other reproducing chemicals to feed on. Even photosynthesis was already present in the soup of interacting molecules. Most all the things that go on inside cells today were already present in the world wide sea of organic chemicals both dissolved and floating on the oceans of our planet.

If "life as we know it" means land life, and intelligent land life at that, it seems a lot less likely. The Earth managed for most of its history without any land life, and tool-using animals are very recent indeed. I like the theory that early land life was swept ashore on high tides and managed to learn how to survive without constant immersion in water. Without our oversized moon, there would be no tides. Life wouldn't have the same incentive to colonise the land, and it might have taken many billions more years, if ever.

"Life as we know it" in my definition is cellular life, from bacteria on.....Once the level of bacteria was reached even more "charmed" aspects of our planet come into play. what I am questioning is the idea that cellular life is inevitable once the world wide soup of living chemicals is under way.

[Moontanman]

Originally Posted by DI5STURBED

Moontanman,
This is one of the questions I find most fascinating, seeing as there are so many different answers too it. I think a good start may be the anthropic principle, which states the we should take into account the set of constraints that can support human life. With that we can say that if there was only one universe ever made than the way it develops and the formation of planets and life for that matter was not random at all. Since the universe the anthropic principle is talking about is one that revolves around us, and why shouldn't it? We do exist.

Another way of looking at it is that all of this is completely random and that we are a fluke happening on chance alone. This may not be far from the truth, in science a lot of things are left to chance; quantum theory, probability for a chemical reaction, the weather, So why should we be so special and not just as random as everything else?

As for life on other planets I don't believe it is looking too promising since I believe only Mars and Titan have the organic compounds to support life. Although there is no reason that a different form of life that doesn’t need organic compounds to survive shouldn't exist. Personally I am an optimist and believe that there is some other form of life out there just because we haven't found life elsewhere in our little sliver of the universe we call the solar system doesn’t mean there isn’t life in this huge still expanding universe.

I ascribe to the idea that life is a natural occurrence that will come about any time the correct conditions come together.

Our own solar system is probably not full of cellular life other than the Earth. Mars is too small to really retain an atmosphere capable of allowing the metabolism first hypothesis to work. If we find cellular life on Mars them my idea of a planet awash with metabolisms with out cells is obviously false.

Titan on the other had is perfect for silicon life using liquid hydrocarbons as a life fluid. Possibly when we go there we will find an entire planet awash in metabolisms but no cells. If so this would lend credence to my suggestion.

I'm sure I will not live long enough to know details about planets on other stars other than the fact they exist but the more we visit the more data points we will have on the curve.

[Donk]

Originally Posted by Moontanman

"Life as we know it" in my definition is cellular life, from bacteria on.....Once the level of bacteria was reached even more "charmed" aspects of our planet come into play. what I am questioning is the idea that cellular life is inevitable once the world wide soup of living chemicals is under way.

Once the arms race is under way, the living chemicals have a lot of different things to do: defence, attack, digestion/growth, replication. This implies a cell wall to contain and protect the different parts of the organism: hence, cellular life - voila!!

[Moontanman]

Originally Posted by Donk

Once the arms race is under way, the living chemicals have a lot of different things to do: defence, attack, digestion/growth, replication. This implies a cell wall to contain and protect the different parts of the organism: hence, cellular life - voila!!

Why does this imply cell walls? You have metabolizing chemicals producing all the raw materials the reproducing chemicals need, why bother with cell walls? What would the incentive be to cause cells to have an edge over free roaming chemicals? Cells had to figure a way to allow certain chemicals in and allow others out with out allowing the wrong ones in or out. Sounds like a lot of trouble when free roaming chemicals were already reproducing everywhere with no bounds or limits, exploiting new chemical pathways, able to be there to reap any and all necessary chemicals.

[Donk]

Originally Posted by Moontanman

Why does this imply cell walls? You have metabolizing chemicals producing all the raw materials the reproducing chemicals need, why bother with cell walls? What would the incentive be to cause cells to have an edge over free roaming chemicals? Cells had to figure a way to allow certain chemicals in and allow others out with out allowing the wrong ones in or out. Sounds like a lot of trouble when free roaming chemicals were already reproducing everywhere with no bounds or limits, exploiting new chemical pathways, able to be there to reap any and all necessary chemicals.

You're postulating a single chemical able to do all the things I posted above: defence, offence, digestion/growth, replication. I'm suggesting that a community of specialised chemicals held in place by a cell wall would be able to outcompete the single-chemical forms and would therefore supersede them over time.