I’ve always believed that there has to be life beyond earth simply because of the numbers. The odds are certainly in favor of life bearing, earth-like planets. Although, I’m wondering how important it is for the planet to be earth-like.
Take extremophiles for example. These are microbial life forms that live in seemingly impossible environments. Some of these can live in toxic boiling pools near volcanoes, and some are at the bottom of the ocean surviving on sulfur emissions(this is counterintuitive because sulfur is generally toxic).
I have just read an article that explains how NASA has discovered a new organism living in its “clean rooms.” This organism is not just a new species, but also a new genus. You know what NASA does to make these rooms so “clean?”
Even with a government agency trying to keep all contaminants out, an organism still finds a way to make itself at home there.
So my point is this: is Earth somehow predisposed to allowing the proliferation of life beyond it being a Goldilocks planet? Or could life, and potentially intelligent life, be easily able to exist all over the universe in ways we don’t even comprehend?
We know that there are billions of planets of roughly Earth-size, orbiting in roughly Earth-like orbits around sun-like stars.
The history of astronomy is a history of us learning that we are less special with each discovery we make. There doesn’t appear to be anything unusual about Earth in terms of the ability of life to form.
What we don’t know is how likely intelligent, tool-using civilization is. After all, Earth is full of successful animals that did not evolve high intelligence. We don’t really know how much of an outlier we are.
Also, we don’t know the odds of the chain of life existing for for the billions of years required to evolve intelligence. Between star output variation, gamma-ray bursts, supernovas, collisions with other bodies, planetary disasters like megavolcanoes or runaway greenhouses, it may be fantastically unlikely for planets to have a biosphere that survives long enough to evolve intelligent life.
My personal opinion is that life is ubiquitous throughout the universe, but intelligent civilizations with the technology required to contact us may be incredibly rare. In fact, we might be the only ones in our galaxy, or at least in our neighborhood of the galaxy.
The probability of extraterrestrial life is so great that if we are alone in the universe, it would only be a result of prevention or destruction by some sort of supreme being. So rather than “creationists,” it makes more sense to be “destructionists.”
This, pretty much. My only difference to **Sam’s **opinion is that I doubt we are so unique as intelligent life. I do, however, think that interstellar travel as a possibility is fairly remote. Even if our nearest neighbor star held life, I doubt that we would be able to tell if they even exist, much less stop by to say hello and/or conquer them mercilessly (or vice versa).
While this is all very interesting, I have a couple questions. 1) this is still a necessary variable to consider, but why do we presume that the evolution of intelligence progresses the same way everywhere?
2) Something I was trying to get at, that I should have elaborated on, is how likely is it that most planets have supported life at one time or another, or currently do. We have proof that life can exist virtually everywhere, so why not here in our own solar system? Mars is a prime candidate of course, but it seems to me that the other planets might be as well. IIRC, the organisms at the bottom of the ocean I mentioned, were actually sulfur based organisms, not carbon based. This only stands to widen the range in which life could exist.
Maybe this rare, intelligent civilization isn’t as far away or as rare as we think.
We don’t. Thing is however that we’d have a hard time recognizing intelligence much different from our own. By what criteria do you judge what life forms on Earth are “intelligent” and how intelligent they are? Is an ant colony an intelligence?
No reason that more complex lifeforms cannot form based on other than carbon and water. But no reason to assume they could. Best place to hunt to start is where we know it can and that we’d have some chance of being able to realize what we were looking at.
It’s my understand that this isn’t quite correct. All extremophiles, including those living around ocean vents, are carbon-based, having the same carbon-based proteins and DNA (or at least RNA) as us and the life forms we know best. What makes the vent-dwellers different is that their metabolism is based on a chain which depends on sulfuric compounds found at those vents. By contrast, life-forms such as carrots, dogs, and us all have a metabolism based on a chain that starts with photosynthesis.
Of course there’s no proof that all life has to be carbon-based. However, it seems a good educated guess that all life is. The reason is that among all the elements, only carbon forms a large number of large, complex molecules that are also stable. Silicon can form many different large molecules but they generally aren’t stable. The great majority of the elements can’t form long chains at all. I would guess that any life form in this universe would need to be based on the interaction of a variety of large, stable molecules, which in practice means carbon. Obviously I could be wrong, though.
I find that doubtful, even if extraterrestrial life exists. If an alien virus arrived on earth, it could only harm us if it was capable of hijacking our cell-replication mechanisms to replicate itself, the same way that terrestrial viruses do. But it’s extremely unlikely that an alien virus would have DNA/RNA and amino acids identical to ours, so it just wouldn’t be able to use our cellular mechanisms.
Then what about pathogens other than viruses? In theory, they could enter our bodies and start replicating while our immune systems would not be able to counter them. It’s a possibility, but it could only happen if those pathogens were adapted to live in our bodies, which have certain temperatures, pH, etc…
We only have one example of ambogensis and the evolution of life so its hard to get a handle on how common it is, but looking at the timeline
Of the 4.6 billion years that the earth has been orbiting the sun, there has been mono cellular life for about 80% of it, multi-cellular life for about 20%, and tool use for about 0.04% of it, language for about 0.006% and industrial capability for 0.000003%.
The fact that single celled life appeared very shortly after the earth was cool enough to support it indicates to me that it is really easy to create such life and it probably exists anywhere where conditions are remotely suited. Multi-cellular life is no where near as much of a slam dunk. It may be that this only occurs in an extremely small percentage of planets where life evolves. Of the tens of millions of species that have existed only one has evolved intelligence, language and industrialization, and has done so in the very recent history. Therefore it is likely that the vast majority of planets in which multi-celluar life exists, intelligent life does not.
Further there in no reason to believe that intelligence is evolutionarily advantageous in the long term. I may be a pessimist but I doubt that civilization will still be around in 500,000 years. So even if intelligent life evolves on a given planet it may be that if you blink in geologic time you miss it.
With this in mind, I would probably guess that in our galaxy there are probably only a relative handful of civilizations that are existing concurrent to ours, isolated by vast distances and so overall it is pretty lonely out there.
The amount of possibilities of us vs alien germ interaction is pretty much “everything medical science knows”. I mean, even if a bacteria/microbe can grow on us (which I would have to say it can, since most microbes don’t so much interact with what it’s feeding on as rip it from where it sits), it’s alien biology could be both beneficial or extremely deadly.
As a waste product, for instance, the microbe could release a lot of something like arsenic or cyanide. Perfectly fine for microbe, incredibly deadly to the human that doesn’t know he has space SARS. Or, it could release bioactive vitamin C, saving us from space scurvy.
Or, the microbe could burst out of our chests and face rape our space friends. You know, nothing’s really off the table since we have absolutely no data to even start basing this on. (Also, don’t expect to keep your friends if you end up giving them space face-rape. It’s the worst Space-bourne Transmitted Disease. )
I am running a lottery. The winning ticket gets $10,000. I will sell you a billion tickets for $10. The total number of tickets (and therefore the probability of any one ticket winning) is a secret. If an unsold ticket wins, then I keep the prize money and everyone’s entry fees.
Are you interested? It sounds like a pretty good deal, right? Even if the odds of winning are pretty low, you have a billion chances of winning, right?
Actually I will sweeten the deal. I will sell you a trillion tickets for only $20. Now your odds of winning are a thousand times better than they would have been with only a billion tickets. How can you pass on such a great deal?
We need to consider one point while looking at this argument. It’s true that extremophiles exist. However, we’ve no reason to believe that the very first life form that ever existed on earth was an extremophile. Most likely, if that first life form came about by purely random processes, it emerged in a more “normal” environment. It replicated zillions of times. Then, in some cases, those single-celled life forms wandered to more extreme environments and evolution turned them into forms that could survive extreme heat, extreme cold, extreme radiation, etc…
But if we imagine, for instance, a planet that was extremely hot always, or extremely radioactive, or otherwise extreme, the odds of life forming and starting to replicate on that planet would be much lower, because an “ordinary” life form that formed by random processes would be immediately zapped by the heat, radiation, …
Our earth has many properties that make it a good place to live: an atmosphere and magnetic field that block many types of radiation while still allowing visible light from the sun, a range of temperatures that mean liquid water exists almost everywhere, a roughly circular orbit so that temperatures don’t swing all that wildly during one revolution around the sun, a relative shortage of highly radioactive elements on earth, and so forth. While we’ve settled the question of whether planets exist around other stars–they do–we have no way of know how many of those planets share all of these nice properties.
It wouldn’t have to harm us directly, just find Earth a sufficiently rich and competitor/predator-free environment to start multiplying without limit and we’ll be crowded or starved out. It’d be rabbits in Australia, cubed.
Current speculation is that the first bacteria were extremophiles, who then evolved into what we think of as “normal” bacteria.
The first bacteria were all chemosynthetic for two billion years until the evolution of photosynthesis. But there aren’t that many sources of chemical energy available compared to the density of photons coming from the Sun. So for the first two billion years the biosphere was a lot smaller and localized around sources of chemical energy–like volcanic vents.
So it could be that bacteria had to evolve ways to live in the strange places that weren’t near-boiling sulfuric acid rather than the reverse.