By Matt Lefebvre

This post is a continuation of the teleological argument. Please see Part 1 if you have not read it yet.

To read along with audio for this article, click here Teleo-Part2

Life

What do I mean when I use the word “life”?  Certainly it is crucial in evaluating whether or not the universe is conducive to life to know what we are talking about when we say “life”.  Though there are varying requirements among those who have attempted to answer this question, a clearer point of agreement has to do with metabolism (Chemical reactions that break up molecules to release energy to be used and putting together molecules with the input of energy) (McGrath, A Fine-Tuned Universe, p.129).   So, the key to life has to do with some crucial chemical reactions.  With that in mind, it can be pointed out that all forms of life on Earth can be termed carbon-based life, because the chemical element carbon forms the foundation of many chemical reactions that life on this planet need.  Now, from this description of what life consists of on this planet, it certainly does not follow logically that life could not be based on some other element found in the universe.  In fact, silicon has been proposed by some as an alternative to carbon as a possible basis for life, being found just below carbon on the periodic table of elements and having the ability to support complex molecules.  However, there are solid reasons to position carbon as the best candidate for supporting life, such as its ability to form multiple bonds, its ability to form bonds with various other life-critical elements (hydrogen, nitrogen, oxygen, phosphorus), and its ability to form crucial gases, such as carbon dioxide, which plays a critical role in the above mentioned metabolism (A Fine-Tuned Universe, p.138-139; The Privileged Planet, p.32-33).  So, in order to have life in this universe, it would seem to require a foundational element such as carbon, of which it seems we only have one.  It would be fair to point out that we only have a limited view of the universe, and therefore, there could be other possibilities for life, but since Earth contains the only life that we know of so far, it is at least significant that the universe is hospitable to this kind of life.  Though it is not impossible that future developments will reveal other possibilities, our knowledge now is sufficient to elevate the status of carbon, while at the same time ruling out other elements as significant building blocks.  That being said, the question that might be arising in an inquisitive mind is how we got carbon in the first place, and the answer is coming in due time.  Before moving on to that question, though, I feel it is necessary to expand upon the requirements for life in the universe.

Water

Water has received attention from scientists of various disciplines, such as physics, chemistry, and biology (A Fine-Tuned Universe, p.143).  It has been proposed that the combination of water and carbon are uniquely suited to life (Lawrence Henderson, The Fitness of the Environment), but even on its own, water shows considerable life-favouring properties.  According to astronomer John Barrow and physicist Frank Tipler,

“Water is actually one of the strangest substances known to science.  This may seem a rather odd thing to say about a substance as familiar but it is surely true.” (The Anthropic Cosmological Principle, p.524).

In asserting this, it is not as if water has characteristics that no other chemical compound has, but rather that when the properties of water are taken together as an ensemble, water stands out as quite unique.  An important aspect of life is the presence of a solvent, a solution in which chemical reactions can take place.  It is best in the liquid state, for solids do not allow mobility and gases do not allow for frequent enough reactions.  Thus, the ideal solvent should be liquid over the same range of temperatures in which other basic molecules of life remain largely intact, and water meets this requirement (The Privileged Planet, p.33).  In addition to water being an adequate solvent, the density of water does not change rapidly with temperature, which is anomalous (unusual) but necessary, for if this were not the case, ice would not float on top of liquid water.  Ice insulates the water below and prevents it from losing further heat, but if water froze from the bottom up, the ice at the bottom would be separated from the Sun’s warmth and the whole body of water could eventually freeze, killing all aquatic life and being very difficult, if not impossible, to reverse.  Also, water has an unusually high latent heat, which means that it takes a lot of heat to turn liquid water into water vapor.  As a result, both Earth’s climate and larger organism’s body temperature can be regulated by water efficiently.  Another consideration is water’s surface tension, which contributes to a number of life essential processes, such as the erosion of rocks bringing vital minerals into cycles that life depends on, helping circulation in soil, plants, animals, and humans, and forming cells which are essential to all life-forms (A Fine-Tuned Universe, p.145-146; The Privileged Planet, p.33-35).  Planetary scientist John Lewis articulated the place of water (and carbon) in the chemistry of life well when he concluded,

“Despite our best efforts to step aside from terrestrial chauvinism and to seek out other solvents and structural chemistries for life, we are forced to conclude that water is the best of all possible solvents, and carbon compounds are apparently the best of all possible carriers of complex information.” (Worlds Without End, p.199).

The Earth

The Earth is not the center of the universe, and in fact, is not even a particularly large planet.  We do not have to look too far to notice that even in our neighbourhood (solar system) we are far from the biggest, and are not in the center of the neighbourhood either.  However, could it be that Earth holds a position superior to more massive and/or centrally placed planets?  Well, to begin with, size matters in the planetary world, but in reference to life, not by way of being the biggest planet in town.  If a terrestrial (Earth-like) planet were to be smaller than Earth, its gravity would be weaker and its interior might cool too much to generate a strong magnetic field.  These are important for protecting a planet from harmful radiation and impact threats, while still allowing sufficient radiation for heat to come and sufficient meteorite impacts for life-essential elements to be brought.  Earth is just the right size to have these factors in adequate measure.  On the other side, a bigger planet would have its own problems.  Firstly, it could be pointed out that Earth may be as big as a terrestrial planet can get, so it might not even be possible to have a larger habitable planet.  A more massive planet would have a thicker atmosphere and might resemble Jupiter more than Earth.  However, even if there could be a giant Earth, this would not be a good idea for different reasons.  A bigger planet is a bigger target for asteroids and comets to hit.  In fact, this is another point for the Earth being a more ideal place for life, because Jupiter and Saturn, gas giants, shield the inner solar system from excessive bombardment by comets.   On that note, the fact that Earth occupies a position in the inner solar system is something to be considered as well.  Remember above how water plays a crucial role in life as we know it?  Well, the place in the solar system that Earth currently occupies has come to be called the Circumstellar Habitable Zone (CHZ) and what it is defined as is the temperate region around a star where liquid water can exist on the surface of a terrestrial planet for extended periods.  Think of it this way: the closer a planet is to a star, the hotter it is and thus the water could all evaporate and be water vapor on the surface of a planet.  However, too far away from the star and all the water on the surface of the planet would freeze.  Earth currently occupies a place in the Circumstellar Habitable Zone, which is not in the center of the solar system, but this is a good thing.  In fact, Earth can even be defined to lie within the Continuous Circumstellar Habitable Zone, because even though a star’s CHZ will move outward over time, Earth is in a place in which it will be continuously in the CHZ over an extended period of the Sun’s main sequence (which I will explain in the section on the Sun).  Earth is both as far away from and as close to the Sun as a habitable planet would want to be (keeping in mind that ice and water vapor are still important for other reasons, but not as the total expression of all the water on a planet).  Adding to this though, it is not enough to have a brief glimpse of the Circumstellar Habitable Zone, but to have an orbit that is at least close to circular, so that the right heat is distributed evenly.  If a planet had a highly eccentric (elongated or elliptical) orbit, then the temperature would vary too greatly in different seasons.

Different degrees of orbital eccentricity

Of the planets that have been discovered around other stars, their orbits are generally highly eccentric.  These planets are giant planets, so not only do they differ from most of the planets in our solar system (Pluto’s orbit is more eccentric than the other orbits), but the effect of having giant planets that do not have circular orbits would be to disturb the various orbits of any possible terrestrial planets that may orbit the same star, though the terrestrial planets are thus far undetected.  Giant planets affect other planets through their gravitational pull, being much more massive.  The fact that Jupiter is far enough away from Earth and the Sun to not disturb the inner solar system, but close enough to deal with many impact threats is comforting when considering that it did not have to be that way, as demonstrated by other systems with giant planets (The Privileged Planet, p.59, 97, 114, 129).  There is much more that could be shown in regard to the quality of Earth as a planet and of its place in orbit around the Sun, but it is sufficient to bring attention to the fact that the Earth did not have to be this way, though we should certainly be glad that it is.

 

The Moon

Of all the things that were thought in earlier times to revolve around the Earth, the Moon is one that actually does.  Though this celestial sphere shines in many a night sky and reveals wonders in the event of a solar eclipse, the effects of the Moon on the Earth go way beyond aesthetics.  The Moon actually keeps the Earth’s axial tilt, or angle relative to the Sun, from varying too much (only about 2 degrees).  If the Earth did not have a large moon as it does, the tilt of the Earth could vary more than 30 degrees.  That might not sound like much to inhibit life, but what it would mean is that Earth would not have night and day as it does now.  The summer months would consist of constant daylight for one hemisphere and constant night for the other hemisphere, causing the temperature differences to be severe, Earth’s wind patterns to be irregular, and many land areas to become dry for lack of adequate rain.  In addition, the Moon affects the ocean tides, which mix nutrients from the land into the oceans and contribute to the ocean currents regulating the climate through the circulation of enormous amounts of heat.  Without the Moon, tides would only be one-third as strong and many currently lush areas would be barren.  Another characteristic of a moon that suits life on the planet it orbits around is the size of the moon and the distance of the host planet.  Being the right distance and size comparable to Earth, the Moon is in the optimal position to generate tidal energy and stabilize the planet, but this situation is not as common as I would have thought.  The size of our Moon is anomalously large compared with the size of Earth, so a larger moon would thus be unlikely.  Most moons are relatively smaller compared with their planet.  A smaller moon could be more likely, but it would have to be closer to exert the necessary effects, and a smaller moon would likely have other problems associated with it (The Privileged Planet, p.4-6).  There is more that could be said concerning the benefits of the Moon for life on Earth, but the point is both that the Moon does more than just look pretty, lighting the night sky, and more importantly, that it did not have to do so.

Click here to see part 3 of the article

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