It's life, Jim, but not as we know it.
...or so Spock said. Apparrently.
Yesterday, for some reason, I was reading something on Wikipedia. Don't ask me what I started with, I don't remember; however, my journey through Wikipedia eventually got me to the Rare Earth hypothesis, the Principle of Mediocrity, and other related things.
Both are subjects relating to whether or not there would be life on other planets. The latter claims that this is, in fact, quite likely; the Principle of Mediocrity basically says that "Earth is a relatively ordinary planet orbiting a relatively ordinary star in a relatively ordinary galaxy which is one of countless others in a giant universe, possibly within an infinite multiverse". This is supported by a number of astronomical findings.
The contrast to that, the Rare Earth hypothesis, claims that Earth is, in fact, not a very ordinary planet. That to be able to reach a point where complex multicellular can have evolved—such as on Earth—such a high number of variables have to have the exact right value, with in many cases such low margins for errors, that while possible, the likelihood that life would exist on other planets is very low.
They were both interesting reads. However, there is one thing to which I did not find an answer: Why does it have to be Earth-like life?
As I understand the theory of our origins, life began on the Planet Earth in a relatively stable body of unclean water—known as the "Oersoep" in Dutch, though I couldn't find the English term for that—on which the sun shone; that sunshine made the elements of the "oersoep" react with eachother so that it eventually formed single-cell life, which then evolved into multi-cellular life, and so on. Even today, the sun still shines on Earth, and almost all energy in use on Earth can in some way or another be attributed to something that once received sunlight; I suspect the only exception to that is nuclear energy.
As I understand the Rare Earth hypothesis and the Principle of Mediocrity, both seem to assume the basic premise that the only way in which life could evolve is the way in which it evolved on Earth; that is, you need direct sunlight so that you can have some chemical reactions. You cannot have too much ultraviolet, gamma, or x-ray radiation, because that would kill life. You cannot have too many impacts of extraplanetarian bodies, such as comets or asteroids, because these impacts and the resulting fallout would destroy life.
I did not find any argument for that assertion, however; and what I don't see is why it would be necessary. We could define the "oersoep" as some sort of a "stable chaos": a bunch of chemical elements and a varying external influence (sunlight) means that you have a brewing and reacting bunch of matter, where the composition of the matter is constantly changing; however, at the same time, when viewed over a large amount of time, not much did in fact change. The varying external influences have a regular and stable rhythm; the sun appears in the morning and disappears in the evening. The sun shines longer in summer than it does in winter. While it is not the same all the time, there is predictability. If a number of chemical elements react with eachother in a certain way on one day, then they will react the same way again the next day. If this happens for years on end, you may have a series of reactions that is more or less reproducible, where the final result of all the chemical reactions turns out to be the original starting point again. At least almost so. Such a series of chemical reactions could be called "life", especially if it occurs within a small group of chemicals that sticks together, like a cell.
While a body of unclean water with regular sunshine certainly is one way to get to a series of repetitive chemical reactions, I fail to see why it would have to be the only possible way. If there were a planet composed mainly of Helium (rather than Hydrogen and Carbon, as on Earth) but also containing a bunch of other elements (so that they can react with eachother) with a star that sends out lots of gamma radiation and an atmosphere which blocks sunlight (I don't know whether Helium can do that, but let's assume it can), then I do not see why it would not be possible for life to evolve on such a planet which would be based on Helium rather than Carbon and Water, and which would require gamma radiation to survive but would die when brought into prolonged contact with light, just like we will die when brought into prolonged contact with gamma radiation.
Another example could be a planet where every year a comet of approximately the same composition impacts on the same place on the planet's surface. Such an impact would regularly stir up the chemical elements on this planet, and could provide the needed energy to produce the chemical reactions required to sustain life. If any life were to evolve on this planet, not only would it be able to survive such constant extraplanetary impacts, it would also require these impacts to continue in order to survive.
I haven't been able to find any information on that. It would seem that either I'm missing something very basic, or that nobody has thought of this before—and I would find that highly unlikely. So, anyone who's been thinking longer than me about this subject (that is to say, just a few hours) who could enlighten me?
Of course, one answer could be to say that God created all life, and that the evolution theory is only a theory, which is not grounded in any reality. But make a comment to that effect on my blog, and I will moderate it away. After having a good-hearted laugh at it.
The reason why scientists assume life could only emerge is earth-like conditions is that the earth is the only place where they have found life. The conditions you describe in your post all resemble at least a few other planets, comets, asteroids or moons in telescope range. Still, there are no moon-men, nor are there any martians ore Jupiterians. Scientists have pretty much looked for signs of life in every heavenly body within telescope range.
This is obviously not a stringent argument, but the scientests who create these theories are astronomers. Because of the cosmic timescales involved in astronomy, there tends to be very little data avaialble to astronomers, which is why they are known to make huge leaps of faith in their reasoning.
There is a rather illustrative joke about an astronomer, a quantum physisist and a mathematician on a train in Scotland. The train passes a black sheep.
"Aha!," says the astronomer. "In Scotland, sheep are black."
"Nonono," says the physisist. "All we know is that there are black sheep in scotland."
"In Scotland, there is at least on sheep with at least one black side" screams the matematician.
Also, I think it was Bones, and not Spock who said 'It's life Jim, but not as we know it'.
I think the English equivalent to "oersoep" could be "Primordial Soup" or primordial stew. A hearty, warm and humid dish at any rate.
http://en.wikipedia.org/wiki/Primordial_soup
carbon can link to 4 other atoms, with enormous amount of possible chemical reactions involving carbon. helium to zero, it doesn't react, just like argon, neon, and other noble gases. there are elements similar to carbon, like silicon, but they are much more rare then carbon on the earth and probably on other planetary nebulas (funsion reactions on stars produce more lightweight elements than heavy ones). thus if there is life out there it will probably be based on carbon. sure, it doesn't rule out other elements at the base, but a lot of the constraint putted on the rare earth hypothesys makes sense.
now, we don't know how life developed here. we are not even sure life started just one time, or that life needed the sun in the beginning, there are some pretty strange bacteria and ecosystems living near underwater volcanos in the dark with very strange reactions going there. we don't even now much about viruses, how many of them are out there, how they evolved (possibly not just in parasitic forms), and many other things.
for me this just means that it is still to early to tell with a decent amount of certainty if there's life out there: the more extrasolar planets we discover and study and the more knowledge we get about life on our planet, the better our guesses will be.
I'd expected that argument
I don't think it holds, though. Mars and the moon are both dead bodies; they have a lot of rock, but not much of an atmosphere, nor do they have many fluids. There is no "stable chaos" there, since there is no chaos at all Jupiter does have an atmosphere (heck, it's a gas giant, it's probably all atmosphere), but as the Schumacker-Levy 9 comet showed us, it's not entirely clear whether it is a stable chaos, as I explained previously.
Do you have any literature you could point me to which I could read?
Right here on Earth, we have entire ecosystems that don't depend on sunlight; instead, they get their energy from breaking down hydrogen sulfide or methane released at undersea volcanic vents (so the ultimate power source is the heat of the planetary mantle). Some but not all of these do depend on oxygen produced by photosynthetic algae higher up in the ocean. Relevant Wikipedia articles: chemosynthesis, black smoker, hydrothermal vent.
Further, some people think this kind of life could exist elsewhere in the solar system, e.g. under the ice of Jupiter's moon Europa. There's not nearly enough solar input at that distance to support Earth-style photosynthesis, but there is plenty of methane.
No discussion of the origin of life on earth would be complete without the "pan spermia" hypothesis being discussed. In particular Amino acids are commonly seen in space, and so by permitting that life could have come from elsewhere, or originally generated off planet (all we need is one self reproducing molecule of common enough stuff that it can reproduce on an early earth).
Indeed it is possible such material was included in the material from which the earth was formed, so it might have started preseeded with primitive living organisms (which would explain why they appear almost as soon as the historical record suggests it is plausible for them to exist at all).
This hypothesis extends the period from the formation of the earth, back by another 10 billion years or so, and the volume of space inside which it could reasonable have occurred to a vast volume (around our sun, or its predecessors). An intriguing idea.
http://en.wikipedia.org/wiki/Panspermia
Remember "Space is big..."
One interesting remaining problem is the transition from single celled, to multicelluar organisms, whilst I suspect this is an "inevitable" step, once the process is begun ("co-operation" and "specialisation" are winning strategies in many areas), it clearly wasn't a trivial step. Not least one is competing against organisms who can usually mutate much quicker than the multicellular structures, hence requiring immune systems, or other co-operative defensive regimes.
"I'd expected that argument :-)"
Still another story relates that there is intelligent life at the bottom of Jupiters gravity well, but they haven't overcome the technical challenges of building a device to escape Jupiters gravity.
Hey it took the current human species about 40,000 years to get to the nearest moon, from a planet with a lot less gravity, atmosphere which is a lot less dense, in a spaceship that only needed to contain 1 atmospheric pressure of internal gas to keep the inhabitants comfortable. Now imagine the earths atmosphere was a thousand times thicker, and you have to launch a rocket with a capsule that can contain several million bar, through an atmosphere that is about tens times as deep as the earth diameter.
Of course the rocket engineers are going, "how hard can it be to build a rocket, when you have liquid hydrogen flowing all over the place"
We know so little about the inside of Jupiters atmosphere it is entirely possible independently evolved life forms exist at different depths throughout the atmosphere, and have yet to discover each other, let alone discover that there is a top to all those swirling clouds. Do I think it likely? Not really, I don't know where the energy comes from. Will I use the fact that the life isn't swirling around visibly in the top few kilometers as evidence it doesn't exist at all - no.