What will ET look like when we meet him/her/it?

Water


A quick google search on “Water as the Basis of Life” will come up with all sorts of unsubstantiated claims and calls to action to stop polluting.  I want to answer the question “WHY is water the basis of life as we know it?” (Please note: This is not a complete answer and I welcome additions in the comment section!)

The chemical structure of water is H2O meaning that for every Oxygen atom there are two Hydrogen atoms.  Because of the electron structure of these atoms, both hydrogen atoms sort of get pushed to one side of the molecule (see picture).  The angle between the two hydrogen atoms is 104.45 degrees.  Unlike many other compounds, this somewhat awkward angle means that water doesn’t stack neatly in solid form.  This is why water is less dense as a solid than it is as a liquid.  The great majority of people will say, “So?”  The real point to make here is that if ice sank, an entire body of water could freeze in the course of a winter and the lower layers of that body of water would never melt.  The great mixing pot of our planet (the ocean), which threw together self-replicating molecules and vesicles to create the first cells, would never have existed at all if ice sank.

Water is one of many compounds that form Van der Waals bonds.  Van der Waals bonds are weak electrostatic attractions between molecules.  It takes a relatively large amount of energy to heat water until the Van der Waals bonds break, so heat gain/loss happens relatively slowly.  This (and an atmosphere) is what keeps our planet at relatively stable temperatures, so that life has a relatively stable temperature platform to operate from.

The final point I’d like to make about water has to do with recent research into astrobiology.  Scientists have discovered that common (non-water) compounds in comet-ice, when subjected to high rates of radiation, form Polycyclic Aromatic Hydrocarbons.  These PAH’s are very similar to DNA/RNA and life on earth probably evolved because these compounds were present in the comets that bombarded earth early in her history.  This is a really cool discovery all by itself, but it also supports my idea that life is water oriented, even life on other planets.  Additionally, this means that life on other planets will have a genetic information storage mechanism similar (but probably not identical) to our DNA.

I have presented a couple of the many characteristics of water which make water a likely starting point for life on other planets. I welcome further additions/opposing hypotheses in the comment section so long as they are polite and relevant.  Tune in next time I post for an explanation of why I think the aliens will be multi-cellular with differentiated tissues!

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Comments on: "Water" (2)

  1. I found your entry to be interesting and thought provoking. There were a couple of observations and thoughts that I had that I would like to share. At one point, you said:

    “The great mixing pot of our planet (the ocean), which threw together self-replicating molecules and vesicles to create the first cells, would never have existed at all if ice sank.”

    Generally, I would agree with that except at no time in the history of the Earth has there been a point where all of the Earth’s oceans were frozen solid (or at least covered in surface ice). There was always a substantial amount of open ocean available. Therefore, if water ice did sink in water, the processes that threw together those early basic cells would have still occurred, but there would have had less room in which to do it (and that would also have reduced the likelihood of such an event happening in the first place).

    Even at the peak of the great ice ages (or approximately when I was born according to some of my coworkers), most of the actual ice that formed was on top of landmasses, which did lower ocean levels but still left plenty of open water. Besides, life was firmly established by then (see above comment about my age).

    A little later on in your post, you noted some of the advances in Astrobiology:

    “This is a really cool discovery all by itself, but it also supports my idea that life is water oriented, even life on other planets. Additionally, this means that life on other planets will have a genetic information storage mechanism similar (but probably not identical) to our DNA.”

    If you think about it, the mechanics of life require a medium in which nutrients and waste can be cycled through and between cells. Of course, a liquid fits the bill perfectly. But obviously not all liquids were created equal. I think that your idea about life being specifically water-oriented is probably dead on the mark.

    Certainly it makes sense that life on our planet would be heavily water-based since we have so much of the stuff. However, over the course of centuries of scientific study, it has become clear that the everyday and incredibly common substance that we call water is in fact a pretty remarkable and unique material. You have already pointed out that water expands when it freezes. That is just weird. Weird enough that Science teachers use the fact as a trick question for their students after they finally succeed in driving into their students’ collective heads the fact that cold materials generally contract.

    Water is also the “universal solvent”. Lots of stuff dissolves into water. There is a big distinction between being a solvent rather than a reactant or a catalyst. This makes it another “perfect” candidate for moving materials (nutrients and wastes) from one point to another within a biological system, whether we are talking about within a single cell or an entire ecosystem. it is also a key characteristic that makes Kool Aid possible.

    Water has an almost perfectly neutral pH value. This is another characteristic that helps make water such a good candidate for the transfer medium that facilitates life. Yes, water CAN have an alkali or acid mixed within it (and thus a higher or lower pH value), but that is a result of what is IN the water and not the water itself (see the note about Kool Aid above).

    Additionally, astronomers have found water to be fairly abundant in the greater universe, so the chances of life (specifically life dependent on water) is much more likely (which is probably a comforting thought for Kraft Foods, the company that makes Kool Aid).

    Then there is your idea that life on other planets would employ some sort of genetic storage mechanism similar to DNA (but probably not identical). I think that is absolutely true, but I also believe that their system of DNA will in fact be identical (or incredibly close to it). We still do not fully understand how the genetic code plays out to create the various life forms we see on Earth, but clearly it is all one basic system and the possible combinations are endless. While I do believe that DNA is a encoded data set, I don’t think there are multiple ways of reading DNA. After all, DNA is not decoded through some proprietary or arbitrary interface or driver (a la Microsoft or Apple). It is decoded through a process that has to obey the various scientific laws. If those scientific laws are indeed (literally) universal, then DNA on another planet would be subject to the same decoding processes (and rules) and therefore, the system would be pretty much identical.

    However, that is not to say that ecosystems or life forms using this DNA would be identical (though in many respects it would probably be fairly similar). The processes of natural selection and rate of mutation would be heavily influenced on the local environmental conditions and if those conditions are radically different from what we could find on Earth, then the lifeforms that evolve to live within those conditions will almost certainly be radically different as well… though I would shudder to think of what their version of inhabitants on “the Jersey Shore” would look and act like. Would they spike their Kool-Aid with Vodka as well?

    • My point about ice sinking was that if ice sank, the top melted layer of water would insulate the ice from warm summers. During the winter, more surface ice would form and sink and be insulated. If cold winters lasted long enough, eventually the oceans would become thin skins of water over ice and the thin skins would freeze every winter. I could be magnifying the insulating effect of water though. I want to design an expiriment to test it now! Freezing chunks of lead inside ice cubes to make them sink or maybe using strings to attach the ice cubes to the bottom of the “ocean”? You make some valid points! Thanks for the post!!

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