It may. We just don’t know. That’s all I’m saying, and yes we seem to be back on track. Another helpful thing would be the link I gave to the SETI site. Nobody’s really sure exactly what to look for, much less how it might happen.
- If the panspermia hypothesis holds, water-based life here might be similar to water-based life there. (Panspermia: organic molecules or single celled organisms exist in comets, which seed planets).
But of course we don’t know whether that’s the case or not.
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Along Lib’s lines, ammonia-based soluble complex chemistry and life might be very different from the sort that’s here, even if the physics are the same. (Incidentally, ammonia is liquid across a 44 degree C range, which suggests a narrower range of planetary habitability than H2O’s 100 degrees C. Methane has a 23 degree range.)
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I wonder whether the ecosystem-destroying events on earth can tell us anything. Would dinosaurs be considered a different “form” of life? What about trilobites? If not, then we might say that life, once established, tends to displace, “other forms of life”, though it’s not clear whether “other forms” could even exist in a planet similar to ours.
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We might also wonder about complex chemistry that arises in the absence of any sort of liquid.
I would say that all life on earth that we’ve discovered belongs to one “type” of life. All living things have the same molecular machinery: the same phospholipid bilayer membranes, the same DNA triplet codons, the same ribosomes, and so on. So all Earth life including plants, animals, bacteria, fungi, protozoans, and so on all belong to one form of life.
It is true that Earth is just one test tube in the experiment of life. And we know that there are other test tubes, so in principle we can imagine that someday we can come up with some broadly applicaple rules of biology. But the obvious problem with this is that we aren’t able to examine the other test tubes at present.
The only thing we can say is that if the beginning of life on Earth was an astronomically unlikely freak accident it seems very odd that it happened so soon after liquid water formed on Earth. If the odds were that small it would seem like we would be likely to seen billions of years of an Earth with the conditions for life just sitting there lifeless. You’d expect to flip a lot of coins before you got a billion heads in a row, right? So if you start flipping coins and get a billion heads in a row right away you begin to suspect that your estimate of the probability of getting a billion heads in a row is not quite accurate.
And the trouble for the panspermia idea is that the Universe doesn’t seem to be that much older than the Earth, whatever estimates you believe it’s less than an order of magnitude. And as Sam pointed out the early universe didn’t have enough heavy elements for Life As We Know It. It’s possible to imagine a planet where life has been going for longer than Earth’s 4.5 billion years, but not much longer, at most two times longer, and three times longer seems impossible. Which means that there wasn’t all that much time to sit around waiting for that run of a billion heads even if that run didn’t happen on Earth.
Now, one potential answer to that is that in a really really really big universe of planets with flipping coins, someone somewhere is going to get an improbable run of heads, and only if those life forms evolve intelligence will they be able to marvel at the improbability of it all. But still it doesn’t seem likely that life is unlikely. With our sample set of one.
Our solar system has I guess 8 planets now, well over 100 moons, and an unknown number of dwarf planets, comets, and asteroids. We have lots of samples of where life apparently doesn’t occur.
If earth is the Brawndo of the universe “it’s got what you need” then wouldn’t you expect life on other earths to be not completely unlike ours?
Regarding that angle, it seems to me that if there is life somewhere, it is probably hard not to bump into it because of the very nature of life. Here on earth, we cannot go to places with the most extreme conditions without stepping all over all sorts of life forms. We don’t have to go all around searching for just the right spot as we do on Mars, hoping to unearth some tell-tale sign of even a single living thing. If there’s life at one spot, then it has surley spread to every nook and cranny where it can survive. So if it can survive on comets and on the moon, then signs of life on Mars should be underfoot in abundance everywhere we land if indeed the capability to sustain it is or ever has been there. Same same if we check out Enceladus or wherever.
I have hopes for Europa, a satellite of Jupiter which apparently has a subsurface liquid ocean.
Then again, the outer crust of ice is 6-20 miles deep, so any ecosystem probably wouldn’t be based upon photosynthesis. Obligatory thermal vent link.
Assuming that there are billions of intelligent species in the universe, that still works out to less than one per galaxy on average. It’s quite possible for intelligent life to be relatively common, yet have none other close enough to us for any sort of contact. If interstellar travel is difficult to impossible, intergalactic travel is orders of magnitude harder yet.
Another issue which hasn’t been touched upon so far is the difference between intelligent and technological. Many cetaceans are undoubtedly intelligent, but do not use tools at all. Chimps and bonobos seem to be about equally intelligent, but chimps use tools and bonobos don’t. Homo was tool-using, but the tool technology changed very little over 2 million years of existence until the last 100,000 years or so. The key for Homo seems to have been the development of language - a mutation which created the ability to develop and speak complex thoughts. Without this mutation, would we ever have evolved technology? A large percentage of possible intelligent species may never have evolved an equivalent to language and consequently never developed a technology beyond simple stone tools.
I have hopes for Europa too. My point though, was that we have lots of environments right here in our solar system, but as far as we (and I hope I’m wrong!) know, life hasn’t emerged in any of them but ours. From this we can conclude that if you want life, it’s going to be in an environment very much like earth, and in that case, it’s not going to be terrifically exotic.
If panspermia is true, than life everywhere could be quite similar.
Moving along, what do people mean when they say “the universe didn’t have heavy elements?” Or, “the zone of the galaxy we inhabit didn’t have sufficient heavy elements?” Doesn’t that just mean “on average?” It doesn’t mean there weren’t some areas with lots of stars exploding and making lots of elements. It’s just the overall commonality of it you’re talking about. Isn’t it possible 10 billion years ago there was an area of space with lots of the right elements?
Not really. Heavy elements only existed in trace quantities before the first generation of stars had lived out their lives and gone supernova. The percentages gradually increased as stars lived and died. With in the first couple of generations of star life, I doubt if there was enough to make it likely that rocky planets would begin to form.
It just seems to me super massive stars can live for as little as a few million years, so if you had an area giving birth to lots of super massive stars, you could get lots of heavy elements relatively early. In a galaxy the size of ours, it seems reasonable to have happened somewhere, early enough to have created an earth billions of years before our earth formed.
As I understand it, a very critical element of earth’s prototype is iron, and little if any iron was produced during the period of supermassive stars. The Iron Epoch didn’t begin until as many as 3 billion years after the formation of the galaxy.
From what I’ve read, you get the solar system’s abundance of iron from supernovae and ejection of elements from red giant stars (wiki). Both are formed from massive stars, and massive stars can have life spans of as little as few hundred thousand years (Wiki again.)
So, while our solar system is 4.6 billions years old, it theoretically only takes a few hundred thousand years to make a solar system such as ours, and that could have happened someplace, many billions of years ago.
Your link doesn’t seem to deal with the iron problem. Here’s one that discusses it: Ancients Stars Reveal Clues To Heavy Element Formation
Your link speaks of epochs, when certain elements became common. But your link also speaks of The Epoch of Very Massive Stars, with lifetimes of a few million years or less, and that epoch occurred during the earliest days of our galaxy.
The Iron Epoch introduced a lot of iron into our galactic stew, but it isn’t when the galaxy first started making iron and other heavy elements.