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

Posts tagged ‘Abiogenesis’

Variability and evolution

Last post, I asked: would life in a stable environment evolve past the primordial ooze stage and what level of environmental variability is good for the evolution of intelligent life?

One of my college professors described evolution quite simply.  He wrote, “Evolution is change” and left it at that.  I’ve spent a long time trying to add qualifiers to that definition, because I, an individual, change and individuals cannot evolve.  I’ve always thought that as a model, the “evolution is change” definition is too simple to be really valuable.  Mathematically, though, that particular definition of evolution is useful.  If one defines evolution as change, finding the rate of evolution in a population becomes a calculus problem.

There are two competing theories about the rate of evolutionary change, punctuated equilibrium and gradual change.  The punctuated equilibrium theory argues that, because we see relatively few individuals in the fossil record in the process of speciation, speciation and evolutionary change happen quickly (thousands of years rather than millions).  Then species remain relatively unchanged for the remainder of their history.  The gradual change theory argues that the fossil record is not nearly complete so we should not expect to find examples of speciation, and that evolutionary change happens slowly but consistently.  I think these two theories are both present in the natural world, and the two theories can be combined.  Check out my super simplistic illustration of the concept below!

 

 

The chunks where rapid evolutionary change occurs would be caused by a big change in the organism’s environment.  Most of the time though, chunks of gradual evolutionary change would be caused by small changes in the environment and other processes on a small scale.  A stable environment could hold organisms that evolve intelligence, but I think evolution would be slow.  Instead of the 3.6 billion years it took to get us and our industrialized society, it would take what?  7 billion years?  14 billion years, the entire life of the universe?  Thankfully, our star is pretty young, so it might be possible for a species from a stable environment to evolve intelligence and then come find us as we evolved intelligence.  I don’t think it’s likely though.

What level of variability is good for intelligent life?  We can look at major sources of extinction and evolutionary change in the past to find about the stability of our environment.  Here’s a brief list of possible causes for major extinctions: Temperature shifts, atmospheric changes, shifts in our magnetic field (look at Mars!), food sources vanishing, competition.

Earth has a relatively narrow temperature band (compared to Mercury, or the prison planet in Chronicles of Riddick) from 57.8o C (136o F) to -89.2o C (-128.6o F).  Water doesn’t even get to boiling, here!  Our atmosphere has had some pretty extreme shifts in the past but it’s been pretty stable for a long time now, with a Nitrogen, Carbon Dioxide, Oxygen mix that suits us well.  The magnetic field has also been consistent for a long time, preventing solar winds from removing our ozone layer.  Our ozone layer is important in preventing radiation from frying us.  Life in general can deal with extremely variable environments but intelligent life needs a relatively stable abiotic environment in order to evolve I think.  However, I also think that the biotic environment (competing organisms, prey species, etc.) needs to be fairly complex in order for intelligent life to thrive.

Sorry, folks.  This post was not as exciting as the last one.  However, if someone knows of an equation that’s been used to express the concepts above, I would give you an honorable mention in the next post if you could bring it to my attention!

Dark Armies of Primordial Ooze

Once upon a time, two globs of primordial ooze met and fell in like. They then decided to form a Dark Army to compete with other globs of primordial ooze! Dark Armies of primordial ooze have evolved at least twice, once in plants and once in animals. What about multicellularity is so great?

Most modern life forms have cells contained by phospholipid barriers. There is probably a maximum size limit to the amount of space that can be contained inside the phospholipid barrier. Until the evolution of multicellular organisms, that meant that the size of the organism was limited by structural components of the cell. After this evolutionary leap forward, the size of the organism was no longer limited in this fashion. Multicellular organisms would therefore be able to out-compete other organisms where size confers an evolutionary advantage.

All life would begin as single celled organisms, but on most planets, I think this advent of multicellularity would occur. Your assignment, O (hypothetical) reader, is to comment on environmental conditions where large organism size would or wouldn’t impart an evolutionary advantage. Fred Meyer has a 1 hour internet time limit, so tissue differentiation will have to wait for next time!

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!