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Let's take a different naturally-occurring type of object that has only ever been found on Earth: waterfalls. To get a waterfall, you need a set of ingredients
by saas_sam 5y ago
Let's take a different naturally-occurring type of object that has only ever been found on Earth: waterfalls. To get a waterfall, you need a set of ingredients and circumstances to occur in a particular way that a waterfall results. We've only ever seen this on Earth. They come in many forms: Niagara Falls, jungle waterfalls, small waterfalls, even frozen waterfalls and underground waterfalls. They even have different colors, chemical characteristics, and each one can be said to be very unique from all the others.
We know of no other planet that has waterfalls.
Yet, because we have seen enough waterfalls on Earth we have an evidence-based scientific belief that waterfalls cannot be Earth-specific because all that is required for one: water, erosion, gravity -- exists throughout the cosmos in very large amounts.
Life is the same. We have seen enough of it in enough variety to know that it can take on many forms, including exotic forms that are impossible on Earth but would be possible elsewhere. The abundance of the ingredients and time are all that's required.
- CorrectHorseBat 5y agoI don't think that's a good analogy, all those waterfalls developed independent of each other. As far as we know all life is related and has the same ancestor. Even on earth the emergence of life seems to be a freak accident.
- saas_sam 5y agoSigh. Analogies are hard.
- tsimionescu 5y agoI don't think this is just a limitation of the analogy, but it is the key point: for any structure where we know the process that forms it (like waterfalls or snow flakes), we can have some informed opinion about the chances of it happening elsewhere in the universe, even if we have only observed one instance of it happening. However, for structures where we have no idea of the process by which they are formed (like cells), we can't have any opinion on how likely they are to happen elsewhere, unless we see more examples.
- saas_sam 5y agoI think we know more about abiogenesis than you are giving us credit for.
- tsimionescu 5y agoWe know a few things about the formation of organic compounds that life uses from inorganic compounds, and how some specific organic compounds crucial to life appeared, but not much more than that. Nothing even close to the formation of a simple self-replicating cell, for example.
- cwkoss 5y ago> Life is the same. We have seen enough of it in enough variety to know that it can take on many forms, including exotic forms that are impossible on Earth but would be possible elsewhere. What forms of life that are impossible on earth do we know about?
- saas_sam 5y agoSilicon based for one.
- tsimionescu 5y agoThat's a conjecture, not a known form of life that couldn't occur on Earth. There is no proof that silicon based life could exist, we barely know if silicon organic chemistry could actually exist.
- sdht0 5y agohttps://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...
- tsimionescu 5y agoI understand the concept, but I don't think it applies to life specifically. Even the simplest cell is more complex than any other naturally occurring formation we have ever seen in the universe. Furthermore, unlike waterfalls, we actually have no idea how life appeared and, despite trying for many years, have been entirely unable to produce life from non-living things, and we have never observed this process occurring naturally either. Furthermore, every living thing we've ever looked at has been a relative of other living things - as far as we've been able to determine, all of the life on Earth has a single origin, a single original RNA/DNA code which must have been present in a single population of organisms, at a single location. This is a strong suggestion that the conditions that allowed life to appear on Earth may have been extraordinarily specific - otherwise, we would expect many unrelated beings sharing the planet (or at least it means that a particular for of life was overwhelmingly more adaptive and entirely wiped out all of the others). Even worse, there is another phenomenon for which we only have evidence of one instance happening in the history of the Earth: all eukaryotic life has a single common ancestor, and there are no complex multicellular organisms which are not eukaryotes. So, not only did life arise only once on the one planet we know it can thrive in, but complex life only arose once from simpler life. So, while we can't say that it's plausible life will never again arise in the universe, we can say that for any particular moment of time, it is plausible that no new life is being formed anywhere else in the universe.