Living on a Razor’s Edge (Part 3 of 3)

Last time, I wrote about various, highly unusual characteristics of the Milky Way Galaxy and of the Sun that allow for life to exist in this particular, small, local region of space. Before that, I posted about the many factors in the very structure of the universe that must be (and are, obviously) extremely fine-tuned to permit the existence of life. Now, I’d like to bring things a little closer to home and look at a few features of our solar system, the Earth, and the Moon that must be — indeed, are — optimized for life.

solar system (roughly to scale)

Glad To Be Here

In real estate, they say it’s all about “location, location, location.” In other words, your neighborhood can be very important for any number of reasons. We have already seen that the location of our star system within our galaxy is vital for life, as is the location of our galaxy within its “neighborhood” of galaxies. As it turns out, the Earth’s location within its “neighborhood” (i.e., our solar system) is significant, too. For example, French astrophysicist Jacques Laskar discovered that the stability of the inner planets’ (i.e., the “rocky” planets) orbits is dependent upon the regularity of the outer planets’ (i.e., the gas giants) orbits. If the other inner planets were more irregular, Earth’s orbit too would be affected and its climate subject to extremes unsuitable for life. Of the outer planets, Jupiter and Saturn are most important, and therefore have to be most finely tuned, since they are closer to Earth and so much more massive. Fortunately, the orbits of Jupiter and Saturn are unusually regular.

Speaking of Jupiter, did you know that it functions as Earth’s “guardian” against comets and cometary debris? Yep. Since Jupiter is so massive — 2.5x as massive as all the other planets in our system combined — its gravity either deflects comets out of our system altogether or, occasionally (as in July 1994), sucks them in to collide with itself. Without a planet of the particular mass and location of Jupiter, Earth would be hit by comets and debris about 1000 times more often. We’d be as extinct as the dinosaurs. (Or, more likely, we’d never have shown up to begin with.)

POW! Right In the Kisser!

Know what other heavenly body keeps us alive? (Other than the Sun, of course, which I discussed in the previous post. And, other than Kim Kardashian or Angelina Jolie.) Answer: the Moon. The Earth and the Moon have a very special relationship, and it starts with the origin of the Moon itself. It used to be assumed that the Moon formed about the same time as the Earth and from the same solar disk material, as seems to be the case for most moons, or it may have been a passing foreign body captured by the Earth’s gravity. But, the Moon is exceptionally large (relative to the Earth) and orbits a planet relatively close to its star. Furthermore, discoveries in recent decades show that the Moon is not only younger than the Earth (4.25 billion years vs. 4.57 billion years), but a) its composition is markedly different from the Earth’s and b) it has been spiraling away from the Earth, slowly but steadily, for over 4 billion years. There is related evidence that the Earth’s rotation has been slowing since about the same time. Add to all this the fact of the Earth’s unusually mild and “habitable” atmosphere. Normally, the greater a planet’s surface gravity and/or distance from its star, the thicker & heavier its atmosphere. Yet, instead of being more deadly than Venus, the Earth has an atmosphere about 40 times lighter & thinner.

What does all this mean? The theory that best fits all of the facts is that the Earth collided with another rocky body more than 4 billion years ago. But, not just any collision; this one was, of course, extremely… fine-tuned. The object (planet?) itself was at minimum the size & mass of Mars — probably closer to twice as big. The collision was certainly more than a glancing blow, but less than a head-on; the latest estimates put it at about a 45-degree angle. It must have been at a relatively low velocity — less than 4 kilometers per second. Most of the heavier elements would have been absorbed into the primordial Earth, with the lighter stuff — from the collider, but some from the Earth, too — forming a “cloud” of debris around it, most of which eventually consolidated to form the Moon. Meanwhile, Earth’s original, thick-n-heavy atmosphere would have been blown into space.

Earth's Moon as seen from Apollo 8

Earth's Moon as seen from Apollo 8

But, where’s the fine-tuning for life, you ask? I’m getting there. In fact, here are some of the beneficial conditions that resulted from the collision:

o  A replacement atmosphere formed that, as hinted at earlier, was both thin enough and made of the right stuff to allow for light to reach Earth’s surface — just right for efficient photosynthesis, in fact. It had the ideal air pressure for efficient lung performance, as well as optimal heat-trapping ability. It was also perfectly prepared for later transformation by simple lifeforms to sustain advanced life.

o  The mass & density of the Earth were now enough so that its gravity would hold large — but, not too large — amounts of water vapor (molecular weight 18) for billions of years, which is required for advanced life, yet allow potentially lethal amounts of ammonia (molecular weight 17) and methane (molecular weight 16) to escape.

o  Earth now had sufficient iron (a critical nutrient) in its crust to support a huge abundance of ocean life and, later, advanced land life. The amount of iron was now almost high enough (a later, smaller collision provided the rest) for a strong, stable magnetic field. This field shields life on Earth from lethal X-rays from the Sun and cosmic radiation.

o  It helped make sure Earth’s crust had the huge amounts of long-lasting radioisotopes it would need. (The heat from radioisotopes drives most of Earth’s unusually high rates of tectonics & vulcanism, which form land masses and recycle nutrients.)

o  The Moon’s relatively large size results in a tidal cycle that recycles nutrients in the oceans.

o  The Moon’s size & proximity also stabilize the Earth’s tilt on its axis, which keeps it from reaching temperatures too extreme at one end or the other for life — especially, advanced life — to survive. Yet, if the Moon’s mass was only 2% more, it would have unstabilized the Earth’s axial tilt.

o  The aforementioned slowed rotation rate ensured that a large assortment of primitive life survived long enough to sustain advanced life. If the Moon was a little less massive, it would have taken a lot longer to slow Earth’s rotation rate to the optimal 24 hours. By then, the Sun would be too bright and too unstable to support advanced life. On the other hand, a faster rotation rate would lead to destructive winds, greater temperature extremes, and less evenly distributed rainfall.

So, you see, the collision had to occur at just the right time, with just the right sort of object (i.e., made of just the right amounts of the right kinds of stuff), of the just right size, at just the right speed and angle. If any of these parameters were sufficiently off, some or all of the above characteristics would not be possible and we would likely not be here. Astronomer/author/apologist Hugh Ross sums it up this way:

“[The] degree of fine-tuning favorable to life manifested in this single event argues powerfully on its own for a divine Creator. Even if the universe contains as many as 10 billion trillion planets (10^22), we would not expect even one, by natural processes alone, to end up with the surface gravity, surface temperature, atmospheric composition, atmospheric pressure, crustal iron abundance, tectonics, vulcanism, rotation rate, rate of decline in rotation rate, and stable rotation axis tilt necessary for the support of life. To those who express the desire to see a miracle, we can assure them they are looking at one whenever they gaze up at the moon.”

What does the Moon get in exchange for all of this? Ummmm, it doesn’t get swallowed up by Jupiter or the Sun or bounced into outer space.

Spin Control

I’ve already mentioned the rotation rate of the Earth and how it is important that it remain just about where it is — within a few percent at most — if the planet is to remain life-sustaining. As bad as the hurricanes and tornadoes we experience are, a faster rotation rate would make them much worse and more frequent. (As it is, these “acts of God” are actually beneficial, including the dispersal of greenhouse gases. I may need to blog on this in more detail sometime….) I also mentioned that Earth’s rotation rate has been slowing for billions of years, which is also good for life. The gravitational effects of the Sun and Moon act to “brake” the Earth by a fraction of a second every year. Primitive life (which is much smaller) can survive the effects of much faster rotation, but advanced life (i.e., birds, mammals, reptiles & amphibians) wouldn’t last long.

satellite image of tornado

Satellite image of tornado

Another critical factor (included in the above quote) is the rate of change of the rotation period. Every species can tolerate a certain range of rotation rate, as well as a range of change in that rate. Most of those species throughout Earth’s history could not have survived had the decline in the rotation rate been much less or much more. The change rate must stay between about two and four hours per “day” per billion years.

Strange Brew

In order for life chemistry to work, biochemists tell us that water in all three physical states — solid, liquid, gas — must not only be available but stable & abundant. So, we are back to the matter of Earth’s (average) distance from the Sun. Just a 2% increase or decrease in that distance would make all life extinct.

Remember my earlier remarks about Earth’s gravity being just enough to hold huge amounts of water vapor while allowing methane & ammonia to dissipate? It is actually a combination of the surface gravity and temperature that determine these “escape velocities”. A change of just a few percent in either one would upset that delicate balance. But, methane and ammonia escape much faster than they should, if this was the only factor. As it turns out, more fine-tuning in the chemical conditions of the upper atmosphere serves to efficiently break down both molecules.

Speaking of atmospheric gases, here are a few things to consider. If the oxygen quantity in the atmosphere was a little greater, plants and hydrocarbons would burn up too easily. A little less, and advanced animals wouldn’t have enough to breathe. If the ozone level was a little greater, surface temperatures would be too low. A little less, and not only would surface temperatures be too high but there would also be too much ultraviolet radiation on the surface. Not only that, but the ozone quantity in each of the troposphere, stratosphere, and mesosphere need to be fine-tuned. If the oxygen to nitrogen ratio in the atmosphere was a bit larger, advanced life functions would proceed too quickly. A bit smaller, and those functions would be too slow.

As we all know, if either the level of water vapor or that of carbon dioxide in the atmosphere were a little more, we would get a runaway greenhouse effect. But, less water vapor could not provide sufficient rainfall for advanced life on land. Or, less carbon dioxide would prevent plants from maintaining efficient photosynthesis. Even the quantity of chlorine in the atmosphere must be just right to make sure that erosion rates, acidity levels (i.e., of rivers, lakes, & soils), and certain metabolic rates are not disrupted.

The Earth’s crust contains an abnormal amount of several different substances — very different from any other planet in the system. Oddly, it contains “the precise quantities of all the life-essential elements necessary to permit the existence of advanced land life.” (Hugh Ross) Those substances include water, carbon, sulfur, gold, phosphorus, uranium, and thorium, among others.

Believe it or not, MIT scientists’ best models indicate that, under normal conditions, Earth would have had much more water (i.e., deeper oceans) and a thicker, carbon-rich atmosphere. When it was only 30-50 million years old, this did describe the Earth. Fortunately, there was that big ol’ collision we talked about. If not,…

“The problem posed by deep oceans is that no conceivable amount of plate tectonic activity would ever produce continents. Without continents there would be no possibility for land life, and many important nutrient-recycling mechanisms would be absent. The problem posed by thick atmospheres loaded with carbon compounds is that such atmospheres would trap tremendous amounts of heat, would result in such high atmospheric pressures as to make lungs inoperable, and would block out so much stellar light as to impede photosynthesis.

While water and carbon are essential for life, too little or too much proves deadly, especially in the case of advanced life. Earth possesses the just-right amount of each. The MIT team’s study underscored Earth’s uniqueness. For a planet as large as it is and as far away as it is from its star, Earth is miraculously water- and carbon-poor. Water makes up just 0.02 percent of Earth’s mass; carbon just 0.003 percent.”

Blue_Earth_and_MoonNow, let’s look at sulfur a little more closely. (Yeah, that stuff that smells like rotten eggs.) There should be a lot more of it in the Earth, too — and a lot closer to the surface. It’s the 10th most abundant element in the universe, but only the seventeenth most abundant in the Earth’s crust. Mars has 3 to 4 times as much sulfur in its mantle as Earth does in its, even though its a lot smaller. Not long ago, the sulfuric volcanic gases that Mars retained were dominated by sulfur dioxide (SO2), which would have permeated any water that might have been there and made it much too acidic for the origin of life or for the maintenance of anything other than the most extreme acidophilic bacteria. Why didn’t this happen on Earth? First, that Moon-forming collision caused a good deal of the sulfur in Earth’s crust and mantle to either sink into Earth’s core or be ejected into the interplanetary medium. Second, countless smaller — but still devastating — collisions during the Late Heavy Bombardment period (approx. 3.9 billion years ago) forced additional sulfur in the Earth’s crust and mantle further down into the core. Whew!

Earlier in this post, I mentioned that heavy elements were formed in stars and spit out into space by supernovae. Well, there is one life-essential heavy element that does not come out of supernovae. Fluorine is made (in the necessary quantities) on the surfaces of white dwarf stars bound into binary systems with larger companion stars. A rare thing. The stars need to orbit closely enough that the white dwarf is able to siphon a lot of material from the larger star. Some of this material gets converted into fluorine before being released into space, where it gets incorporated into future solar systems. In order for Earth to get the crucial-for-life amount of fluorine, everything has to work together “just so” in the timing & positioning of our galaxy, at least one white dwarf stuck in a binary, our Sun, etc.

Several other elements exist in just-right amounts in/on the Earth, where a little more or less would be lethal to life (or, at least, advanced life). These “vital poisons” include arsenic, boron, chlorine, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, nickel, phosphorus, potassium, selenium, tin, vanadium, and zinc — many (all?) of which can probably be found in your multi-vitamin supplement. You need a little, but not too little or too much, of each. (Yes, even iron can be deadly.)

A Few More for the Road

Here are a few more conditions that have to be tuned juuuuuuust right to allow for life:

— thickness of Earth’s crust
— albedo (ratio of reflected light to total amount falling on surface)
— asteroidal and cometary collision rates
— seismic activity
— volcanic activity
— frequency & extent of ice ages
— oceans-to-continents ratio
— biomass to comet infall ratio

There are many more of these “life parameters” and they all have to be just right at the right time — often the same time — for conditions to be feasible for life to exist at all, let alone to persist for any appreciable length of time. Yet, some people will insist that this can all be explained away by chance, especially if we inhabit just one of an infinite number of universes within a “multiverse”. Trouble is, there is no evidence whatsoever for there being a “multiverse”. (And, by definition, another universe could never actually be detected from within our universe.) We have to go with the evidence we have, and it gets stronger every year. That evidence points to a universe (as Penzias said), galaxy, and sun/planet/moon system of incredible design that has been exquisitely fine-tuned for life. Not just simple life, either — advanced life.

In fact, it’s as if Someone knew we were coming!

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