I think you've got a minority opinion calling crystals "alive," although it does jibe with one definition of life that I heard: "any self-sustaining system that reduces internal entropy."
http://www.bbc.co.uk/earth/story/20160823-the-idea-that-life...
> Cairns-Smith found a more eager audience in science journalists and the popular press. Other scientists showed interest, too: the evolutionary biologist and writer Richard Dawkins discussed the crystals-as-genes hypothesis in his 1986 book The Blind Watchmaker.
[...]
> His aim was to find a system much simpler than modern life, but which had some of the crucial properties of a living system. He found an answer in an unlikely place: clays.
Life is a phase of matter in which the dynamics of information and Turing-complete computation overcome the ordinary dynamics of matter and energy. I am not aware of who originated this idea, but I heard it from Christoph Adami (a researcher in evolutionary information theory). I also recall someone at a conference proposing the term "Turium," for "Turing-complete phase of matter."
Earth just happens to have an environment that contains a large abundance of this phase of matter, much like how stars are full of plasma etc.
Side note: computation seems like a wrong term, because it's not about counting/calculating/determining any abstract value, is it? A Turing-complete mechanism maybe?
Of course I have yet to see an attempted definition of life that isn’t a little squirrely or that isn’t just a list of criteria taken from the one example we have.
So any biosphere that fails to escape its looming red giant was never alive?
I'm not a "all abstractions leak" type of person, so I will choose my definitions very carefully, with funny choices about clays, crystals, virus, etc. as an acceptable causality.
People commonly theorize that virus came from rump parasitic cells. I wouldn't be surprised if at some point a huge virus with a membrane accidentally picked up enough stuff to become a cell again. To go back to chloroplasts again, it would be like how brown algae is an ex-heterotroph.
On the other hand, other forms of anabolism require crossing an energy barrier (and consumes energy) ?
While catabolysm is the inverse operation : crosses a barrier, but releases energy?
The formation/destruction of "exothermic" crystals like dissolution of Sodium Hydroxide if put in contact with water is I guess similar to above two reactions ? (Or better example: explosives)
That simply means "metabolism" isn't the concept to generalize further, and I'm OK with that.
I have an alternate theory, that I've never seen articulated elsewhere: Viruses might be inter-microbial biochemical warfare gone wild; Among primitive and not-particularly robust cells, one competitive strategy might be to package toxins or other disruptive molecules into capsids that cleverly get past the 'enemy' cell membrane, perhaps aimed simply at disrupting the initially brittle reproductive process. Packaging random genes in with these capsids would be the beginning of the Horizontal Gene Transfer function that viruses perform in the ecosystem. A refinement would be to add in the specific genes for producing capsids as a deliverable so a subverted 'enemy' then takes out several neighbors (but 2nd gen capsids don't have to necessarily contain the same genes in order to accomplish their 'mission', or even be entirely identical to the 1st gen, as long as they work). A further refinement would be increasing fidelity, and packaging the responsible genes into the 2nd gen capsids produced by subverted cells so the 'weapon' can spread exponentially.
And voila, the 'weapon' has now escaped the originating organism and can evolve independently parasitizing the target. Each incremental step can at least hypothetically provide an evolutionary advantage so the whole thing doesn't have to spring forth fully formed.
Depending on how widespread variants of the original strategy were, viruses might have independently emerged more than once.
If I'm right, we ought to still be able to find cells that attack or suppress competitors with capsid-like molecules that don't particularly resemble existing virus lineages, possibly containing non-genetic payloads of various sorts.
We might also find bacteriophage endoviruses that as their 2nd stage only produce capsids sans-genes or that otherwise aren't identical to the endovirus, or ones that aren't very good at packaging up the correct genes, or that are much better at disrupting cell reproduction than hijacking it, or that the subsequent copies are only low-fidelity ones that can similarly penetrate the host but not spread any further; basically any indicators that the mechanisms for penetration of the membrane, attacking the cell, and even for making poor 2nd gen copies, have been evolving longer than capabilities only needed for indefinitely repeated copying, retransmission, and reinfection.
I suspect though that the oldest reconstructible endoviruses will no longer be capable of penetrating current members of their host cohort, which tells us little about the virus itself, but may offer clues about whatever ancestral cells were still prone to infection were like.
Nowadays however it is more widely believed that eukaryota descend from archea, but anyway it's pretty much a given that viruses are not and have never been alive. And while the opposite has happened, gene transfer usually goes from viruses to cells, endowing them with new abilities, more than the opposite direction.
Hosts do the replication for the viruses.
Environments do NOT do the replication for the fish.
Mammals are the exception here, there the environment for replication is an integral part of the body of the parent. But in all those other cases, including, technically, marsupials it isn't.
An egg is a complex life that can reproduce the whole organism (and actually with energy stored INSIDE, that’s why they are great nutritios value for others)
Single cells of multi-cellular organisms replicate.
Shoot me in the head and all my cells will eventually stop replicating.
To a cell in my body, is the body a host or an environment? Is the distinction useful?
As for shooting into the head, some multicellular life forms can actually heal from that. From planaria you can remove any part of their bodies, it will grow back. Shooting into an ant colony won't do much harm to them either, nor is removing the branch of a tree. It's only a property of animals I'd say who have given up this property (for the most part) in exchange for more complex metabolic systems. (heart, nervous system, etc)
Very few things are obvious. Is this?
In contrast, if you put a plant and its media (soil, air, water) into constant temp and pressure, the plant will continue to grow and change until it exhausts the media. (assuming the temp and pressure are conducive to life) Ultimately plants become their own media by decomposing into soil.
Planet Earth would/should definitely count as alive, especially if it "reproduces" via us terraforming other planets to become like Earth.
Life permeates deep into Earth and even influences its geology:
https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole#Resear...
Parts of yogurt are alive. Yogurt is not alive. I have no problem with this.
(When you feel compelled to “air quote” a key term in your argument, that’s a clue you probably don’t have a good argument.)
Earth+Life is a different entity than Earth on its own, or any other planet.
Earth allows and protects life, and life in turn influences Earth. That kind of symbiosis on such a scale is in a class of its own, with no other equivalent or analogy that we know of. It deserves a special classification.