Life is probably more than being in the right place at the right time.
Size May Really Be Everything
Among the more interesting and educational items that circulate among emails, the internet, and elsewhere, are the astronomy pieces that show and tell us about some of the more fascinating aspects regarding the Earth and its place within the cosmos.
One of the better of these kind of things recently made the rounds, so to speak, and while an exact description of what this mini-documentary contained is not important for this discussion, of particular interest is one of the more dramatic demonstrations the video presents.
Clearly illustrated was the disparity in sheer size among the objects in the universe. Amazing comparisons were shown between the size of the Earth and the sun, the other planets of the solar system, and most incredible of all, the differences in size among the stars themselves.
We see where the sun itself is not only a rather ordinary star, but within the entire family of detected stars, it is also one of the smallest members. For example, I'll use a common metaphor -- that of a beach full of sand -- and then offer a perspective, not one of quantity as is typically the case, but one which will illustrate an inequality of size and mass that staggers the imagination.
The various magnitudes involved are such that our abilities of comprehension are challenged to the point of incoherence and unintelligibility. To wit the placement of a single grain of sand in the palm of one's hand. Now imagine this tiniest of pebbles as representative of our sun. And then envisage that the Earth itself, upon which you're standing, is illustrative of the largest stars which populate the universe. It is clearly a difference in size that language cannot adequately describe.
Consider also, as part of this example, that the Earth is nearly microscopic by comparison to not only the sand grain, but practically sub-microscopic as relates to the Earth as a stand-in for the larger star.
Among the multitude of ramifications and conclusions that might be drawn from such a comparison, one in particular seems to stand out from the others. This is to say that given our observation of a cosmos which spans orders of magnitude -- in terms of size -- from the very small to the very large, we ourselves appear to exist at the very bottom of the chart, so to speak. While many things are considerably bigger than we, a relatively lesser number of significant objects are smaller. It would seem that we are indeed the pebbles (or grains of sand) within nature's otherwise immense garden of rocks and boulders.
This observation is interesting in many ways, none the least of which might be viewed as a tangible frame-of-reference. By this, I mean to say that based upon a perception of where the uppermost limits appear to exist, according to size, our occupation at the extreme lower end of the scale gives us an important clue as to "where" the actual party, in a manner of speaking, is really happening.
For example, even within our own solar system, among the so-named gas-giant planets, worlds like Jupiter, Saturn, and Neptune -- all of which are many times larger than our own planet -- the forces of gravity are such that human visitation and surface exploration will likely never be attempted. It is these tremendous core pressures which are found on extraterrestrial worlds, that is deserving of special attention, and upon which this essay is primarily focused.
Certainly noteworthy to yours truly is how we find no miniature solar systems surrounding us. Which is to say, small stars or suns around which a family of ultra-dwarf planets revolve, in some ways similar to own solar topography, but on a scale which is tiny when compared to ourselves. Such things do not appear to exist, and likely cannot exist. Not until we shrink our viewpoint to sub-atomic levels, which is a whole other article in this series.
Stars smaller than our sun are plentiful in the universe, but as opposed to "healthy" young stars, capable of supporting a large family of orbiting planets, such bodies are typically the residual remnants of their former glory as much larger stars, in many cases bigger than our sun at one time. When stars die, they tend to explode and shrink in size, thus the rather large population of these particular "dwarves".
Other small stars tend to be abnormal and exotic in nature, often paired with one or more other stars. Indeed, it is thought that a large number, if not most other stars, are so-called binary systems, where two stars revolve about a common center of gravity. But such a discussion digresses from our main center of attention -- that of gravity and the question of the implications and inferences that the forces of same might have on the existence of life.
Also not touched upon in this particular essay, is an in-depth discussion of the various aspects of luminance with respect to smaller versus larger stars. Thus if a star is a million times larger than our sun, it may well be a million times brighter. But other stars, perhaps several million times larger, might be a billion times brighter. As with the unimaginable forces of gravity exerted by larger bodies, the light produced by such stars is beyond comprehension, and deserving of its own examination.
Meanwhile, back to our original topic, were astronauts to visit an earthlike planet several times larger than our own world, the surface gravity would also be several times greater. The exact opposite of what we saw on the moon, these explorers would be weighted down -- literally -- by either atmospheric pressures, the pull of the planet itself, or both. In either case, the limitations and restrictions on both men and equipment would not only be significant, but in all likelihood, prohibitively cumbersome and complex.
On the truly larger worlds, proximity positions -- elevated stations well above the surface -- should be the norm. In a more abstract view of such situations, however, the question arises as to what impact these large forces of gravity would have on the forces and conditions necessary to the spawning of life (as we know it). Scientists have recently turned their attention to whether or not life may evolve in these upper regions -- cloudy, gaseous areas far from a planet's surface, where any manner of more interesting conditions might well exist. Conditions not unlike the primordial "soup" of Earth where life, at some point, brewed into being.
Furthermore, just as the distance between Earth and the sun represents a so-called "Goldilocks" zone whereby ambient temperatures allow for water to exist in its three separate states of gas, liquid, and solid -- is there an equivalent zone with respect to gravity? Does Earth not only reside at just the right distance from its sun, but does so at just the right size -- meaning mass -- as well?
Such a notion would suggest that a planet like Mercury, for instance, would lack sufficient mass, in any event, to provide the conditions necessary for life to evolve. By the same token, the earthlike planets which are now known to orbit any number of friendly stars, but are significantly larger than Earth, may possess gravitational forces and atmospheric pressures which are equally deleterious to the life-forming process.
One interesting argument begs us to recognize that life on Earth exists in a wide variety of hostile environments. At the bottom of the deepest ocean trenches, pressures certainly approach, equal, or exceed what we might expect to find at the surface of atmosphere-bearing rocky planets (or cloudless others) which are several time larger than Earth. Yet life abounds in such places. Might they do so also, then, on other planets regardless of size or air pressure?
When advancing such arguments, it must be remembered and acknowledged that life on Earth did not originate in what we refer to as inhospitable environments. Called "extremophiles", organisms which thrive in near-boiling temperatures and under tremendous per-square-inch pressures transitioned to such localities. They gradually, over thousands and millions of years, moved from hospitable regions into areas that only by comparison, appear to be less welcoming.
It is somewhat the reverse of the frog-in-the-pan-of-water scenario. In that example, a frog is placed in a pan of cold water and ever-so-slowly, the temperature is raised to the boiling point. The doomed frog doesn't notice until it is too late because the change was gradual. Do the same experiment over a period of a million years, however, where numberless generations of frogs and tadpoles are allowed to spawn over and over again, and the chances are good that we will evolve a frog which can tolerate very hot temperatures indeed.
The catch, of course, is that we necessarily began with an organism already existing in an environment less extreme, and probably one far more conducive to life evolving than boiling water and crushing temperatures. One of the things we see in the microscopic fossil record are fragile, delicate life forms. It is highly doubtful that such creatures, likely the progenitors of all life, would have spawned successfully under any but the most favorable -- and relatively mild -- of conditions. Which is to suggest that these same conditions are prerequisites throughout the universe, with respect to the evolution of life "as we know it".
This latter proviso leads us into the very tenuous territory of life forms based on other than the carbon atom, upon which we ourselves are derived. One of the favorites of those who like to think outside the carbon box, so to say, is silicon, equating to a silica-based, i.e., crystal-quartz life form. And there are others. Lots of others, with almost no limit. Since the very definition of life is undergoing constant change, the possibility grows increasingly that even on Earth, what we now call life may be expanded to include hitherto unknown or unnamed entities.
In summation, it is certainly no surprise to me that the listening machines of SETI (Search for Extraterrestrial Intelligence) have remained silent all these years. It seems as though under precisely the right conditions, life simply bursts into existence and can hardly be restrained. Simultaneously, the recipe of ingredients, the directions for cooking, if you will, become at one and the same time, more complicated and increasingly limited.
Not only must the right temperatures be available, but gravitational pressures as well. The planet must be rocky and not gaseous, with a molten, magnetic core that both blocks and deflects the harmful radiation that bathes all cosmological bodies. The parent star must be stable and not given to sudden and dangerous outbursts.
Last but not least, the planet's orbit must be mostly circular in configuration and lie along the star's plane-of-the-ecliptic -- it's equatorial zone. Elliptical orbits that first swing blazingly close to a star, then move far away and freeze before returning, likely doom all life before it chances to begin. Life appears to like things to remain the same for long periods of time, and freezing, thawing, burning, melting, then freezing again, are not exactly optimal conditions. Some scientists hold out for life surviving in those moderate areas located between a planet's cold and hot zones or longitudes -- so called terminator zones -- but it sounds like wishful thinking more than hard science.
One final note of worth, for what it's worth, is in regard to Earth's tagalong companion, the moon. Of all the inner planets, only Earth possesses a moon. Mercury doesn't. Venus, the same size as Earth, has no moon. Nor does Mars, last of the rocky planets between ourselves, the great asteroid belt, and outer gas giants. And no, Mars does not have any true-blue moons. Two small asteroids, Demos and Phobos, were captured by the planet at some point in its distant past.
So why does only Earth have its one moon? And what bearing might that have on the evolution of life? It is now widely believed and accepted that our moon is the result of a catastrophic collision between ourselves and another planet, roughly the size of Mars. All of which took place not long after the Earth had already settled somewhat, but prior to the arrival of the great seas. When the collision finally occurred, the entire surface of the Earth was re-vulcanized and once again turned into a single ocean of liquid magma.
After the many leftover, orbital fragments had accreted into their current spherical shape, and began a slow progression away from the Earth -- which continues to this very day -- nothing on our planet would ever again be the same. The entire destiny of Earth, as a geological entity, was forever altered by the presence of this new and relatively massive body.
The errant wobbling of the Earth on its axis -- common to such planets -- was stabilized by the moon's presence. The result of this stabilization was a world with four distinct seasons, and polar icecaps which remained perpetually frozen for the most part. Most striking of all would have been the newly arrived oceans of Earth which, instead of puddling like immense lakes, rose and fell as great tides, a mile or more high in some cases, and washing inland hundreds of miles.
Because much of this water, delivered by comets and other icy objects, was held in the polar caps, large land masses that would otherwise have been sunk beneath hundreds of feet of ocean, were exposed to direct sunlight. And to the daily tsunamis -- of Biblical proportions -- that year in and year out, for countless millennia, washed into the waters a trillion tons (or more) of minerals and chemicals.
On other planets, moonless worlds more like Earth than not, their eccentric orbits and ever-shifting tilts of their axes bathe the surface in deep, endless expanses of water. Life may still evolve in such places, but it's doubtful that a planet of swimmers and flyers -- sans any land masses to speak of -- would produce technologically advanced civilizations. Far more likely, the ruling masters of such worlds are akin to whales and flying fish. No doubt beautiful and sophisticated in their own right, but not a radio in sight.
On Earth, these early millennia had been a tumultuous time of great stirring and churning, of endless lightning strikes, and the constant mixing of exotic compounds -- over and over again -- for billions of years or more. The question is not so much one of why life began on Earth, and how we ourselves evolved. But rather, given the presence of a fairly large moon, most of everything that exists seems, in hindsight, practically inevitable.
No, I believe the real conundrum is why life isn't more abundant than it appears to be. Which is utterly nonexistent -- at least in our neck-of-the-woods, so to speak. Where is everybody? We're still holding onto the idea that hidden deep within the sub-surface oceans of the various moons that encircle the major planets, all manner of life forms swim through seas warmed by subterranean volcanism, especially thermal vents similar to Earth's own. Maybe. Maybe not.
My fear is that life is far more rare than we might otherwise choose to think. Or hope. The highly conditional forces poised against it are formidable indeed. The real miracle may be that life ever happened in the first place. That it came into existence at all.
And the place of that amazing event was on a small world whose temporary inhabitants gave it the name of Earth. And who once lived in a relatively ordinary galaxy they called the Milky Way.
Thus the ultimate query, I suppose, is whether these human beings, as they were known, would have taken to ensuring their survival more, had they known or suspected even, that they were indeed the only game in town.
So to speak.