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!
As a life-long science fiction fan and an aspiring evolutionary biologist, I have given a great deal of thought to the presence of extra-terrestrial life. For the purposes of this blog, I am going to assume that extra-terrestrial life exists somewhere in the universe. To all the party-poopers who would argue with me I have several points to make: 1) The universe is vast and among all the uncountable combinations of stars and planets and moons, it is likely that there is a planet similar to Earth orbiting a star similar to our Sun somewhere out there. 2) Life evolved on this planet relatively quickly considering how complex and strange our basic chemical makeup is (DNA is nothing short of astounding when you examine it closely!). Meaning that life may take a while to happen but it could happen on any Earth-like planet. 3) It’s just more fun this way! Also I really don’t want to argue creationism with anyone, so if you try to make this post about your religious beliefs rather than a science-fiction-y exploration of complex life, I will ignore you.
Given this assumption that extra-terrestrial life exists, the next question is what would it look like? What kind of adaptations would an alien species exhibit? By looking at our own evolutionary history we can throw out some ideas about what we might see upon encountering this alien race. Unfortunately, I speak Bio-Geek almost exclusively so I need to define some terms so people will understand me. First, evolution is the total processes resulting in species differentiation, including natural selection (survival of the fittest), mutation (survival of the freakazoids), genetic drift and bottlenecks (survival of the lucky). Second, convergent evolution is when two species in different groups evolve some characteristic for generally the same purpose but from different starting points. The classic example is flight. Flight has evolved in at least three different groups on Earth (birds, bat and insects) for the purposes of escape from predators and pursuit of prey. Convergent evolution is important because it means that the evolutionary pressures driving a species, towards flight for example, are fairly consistent and we can generally assume they would be consistent on another planet. Third, stochasticity is randomness or unpredicatability in processes. The prevalence of stochasticity basically means that if we should meet aliens tomorrow, I cannot be held accountable for the differences between my predictions and reality.
In this blog I intend to point out some chemical and biological factors which are assumed to be present in any ecosystem based on logic and a basic knowledge of science. As you can probably guess, I also intend to make some loose predictions about alien life by examining convergent evolution in our own evolutionary history. (I’m already giddy about it!) We are only likely to meet intelligent races (at least until we figure out that pesky FTL drive) so I’ll give some thought to the origins of intelligence. Finally, I’ll take some of my favorite examples of aliens from sci-fi and explain why I think they would or wouldn’t exist on a “real alien planet”. I would welcome discussion about the topics I propose (if anyone actually reads this blog) but please keep it civil and off the topic of evolution vs. creationism. I am sure there are other bloggers that would love to argue that particular point with you.