God is in the details. God is found in details that collude to create the bosom of reality each soul nestles into. Notice the bare sliver of chance by which nature succeeds, seemingly against the odds. Still, nature racks up win upon win, compounded until the Earth meets her destiny cradling the only known sentient life-form in the universe. The creationists are right. They are right but for one large supposition. The Earth, in all its sublime detail purportedly existing for man's delight alone, was not created for us. We were created for it. It is an ongoing process, stacking millennium upon millennia.
Terra appears more and more fragile as humanity learns where, when, and how it exists in the universe. Seemingly minor details, too numerous to completely detail here, become intrinsic to life's existence when properly understood. Limit the number of factors to just five and still science can paint a picture of the Earth happening at just the right place, at just the right time, and well, at just the right everything.
Humanity would have no solar system at all without it; the Sun displays special traits that cause it to be the perfect planetary-system incubator. A much larger star was first necessary to till the field, so to speak. It burned hot and it burned fast.(F) Our Sun's progenitor fused elements together, starting with the fusion of helium from hydrogen fuel, much as the Sun does today. But it also created most of the elements that make up our planet before reaching iron, and a critical juncture in its stellar life.* When the star exploded, the Sun and all of the planets eventually coalesced from the resulting debris. The smaller star that formed to be the center of our solar system inhabits a perfect Goldilocks balance, providing just the right amount of energy for billions of years. Considering that complex life evolved only recently in our planet's history**, one can surmise that complex life needs billions of years to develop.
Jupiter exists as the big brother in our system. As a very protective brother, Jupiter uses its massive gravity well to attract and repel large fast-moving bodies from the inner solar system. Our solar system has an asteroid belt kept strictly in line around the Sun in an orbit between Mars and Jupiter. Only occasionally does Earth see the epoch-changing impacts from large asteroids or comets. While Earth's formative years saw it pummeled with objects from space that contained among other things, water, today's Earth last saw a devastating impact around 65 million years ago.(B)
It may well have been Jupiter that sent a Mars-sized object on a collision course with the third rock from the Sun. After this violent event a moon approximately a quarter of Earth's size orbited the third planet.*** Such a large ratio between planet and moon is rare; the Earth and Moon can be regarded as a binary-planet, rotating around a barycenter three-quarters of the way out from Earth's center. In what is surely a team-effort, the Moon provides a stabilizing force on Earth in a number of different ways. Stability is good for life.
So what if a lifeless rock rotates around us, providing nocturnal illumination and tidal forces while still controlling the moods of half the human population every 29.5 days.(C) What could this seemingly useless sphere of green cheese offer life?
The Giant Impact Hypothesis is the theory du jour in moon-evolution circles.(G) To summarize, the theory supposes that a proto-planet the size of Mars collided with the Earth, forming a very unique planetary system. The Earth before the moon rotated much faster, and only slowed down because of the drag created by its new satellite. Picture an ice-skater, spinning rapidly, that slows down as she extends her arms out to her sides, and you can visualize how the Earth went from a 6-hr to 24-hr day.(I)
Bah! So the Earth would have shorter days, so what?
Without the moon, Earth's magnetic field would be four times stronger as its iron core's rotational speed would be four times faster. While this means that we would have that much more protection from the Sun's harmful radiation, evolution would be four times hindered by not being exposed to those energies that drive mutation, and thus evolution.(I) If 6-hr days**** don't bother you, and even regular 100 mph (161 kmh) winds fail to bring you down, then deadly hurricane force winds will have to do the trick.
Double bah! As I once said upon the island of Isla Nublar, 'Life finds a way', even without moderate winds. Or lysine. Or windy lysine.
Continuing on, then. The moon's stabilizing force provides a regular, if changing, axis around which our planet rotates. Chaotic climatic changes, resulting from wild shifts in the Earth's axis sans lunar gravity, prevent regular cycles and seasons from occurring. A climate defined by geographical boundaries would not exist, leaving evolution without the necessary time to drive life's development.
Bah upon your... Oh wait, that sounds pretty bad; worse than being accosted by a T-Rex while sitting atop the potty. Trust me, I'm in a unique position to judge these matters.
The Moon was once much closer to Earth.(C) The proximity created much larger tides that rushed inland and out, covering hundreds of miles twice each day. It is possible that a much greater amount of organic materials mixed and were concentrated by cyclic deluge and evaporation, allowing for a better chance for a greater diversity of life to form. Admittedly, this imagery brings to mind a vast planetary soup with life seething in the briny foam.
Space is dangerous, far from being the empty place we envision when we consider it a cold vacuum. In fact, space is filled with a veritable ether of energies and even gases. Most of the energy is quite caustic to life. We only benefit from a very limited exposure to a limited set of energy frequencies.
Thankfully the Earth has at its center a very hot, rotating iron-core. This core casts a protective magnetic blanket around earth, acting exactly like a force-field that blocks most of what the Sun and the rest of the universe throws at us.(D) Without the magnetic field, a day at the beach is more likely to resemble Sarah Connor's nuclear nightmare from Terminator. Like Sarah says, "There is no future except the... Oh noes.. My face is meltingggrwwhAAAHHH!!"
The blue in our marble points to the fact that Earth is a watery planet. The shared history of Earth-life and Earth-water is such that one history hinges entirely upon the other. No water, no life (as we know it). Our extraterrestrial searches illuminate just how rare and significant Earth's abundant water supply is. In fact, we have not yet found a planet with this selfsame feature. We also have not found complex life on any other planet. Coincidence? Maybe.
More than simply being life's creator, water exists as a very unique molecule. Water is polar; it has a different positive and negative charge at each pole. This quality translates to a greater solvency in the chemical world. Ions are attracted to these charges, which means that the small salty oceans humans carry inside themselves can transport things like oxygen and sugars throughout the body. Water's characteristic surface-tension is responsible for capillary action, which moves water and nutrients through the roots of plants and tiny human capillaries.(J)
Water is transparent, and solid water floats in liquid water. Transparency means that sunlight can propagate through water, allowing photosynthesis to occur at greater depths. The fact that ice floats means that we don't have sinking ice crushing water-borne life, instead it forms a barrier at the water's edge. Hydrogen-bonding and water's relatively light weight of 18 grams-per-mole both work to create water's high specific heat index.(J) Generally, this means that water exists as a liquid for a large range of temperatures. Liquid water is good for life.
It is obvious to most that four of the five factors discussed here are in fact contingent upon each other for their own place in and on planet Earth. The house of cards seems to pile higher and wobble precipitously. But it is our human senses, experience, and thus perspective that creates in us a trepidation at knowing just how special our Pale Blue Dot is. Whether your picture of the universe allows a place for an epic photo-bomb from god or not, rest assured that the laws of the universe are not easily muted. While one piece of the puzzle seems stacked upon the other in a Jenga tower, the resulting structure has stood the test of time and there is little reason to doubt that life will continue. Some form of the Earth will be around to be swallowed up by the Sun in its gasping death throes, some five billion years in the future.(E)
Still, the self-destructive tendencies of the human species have yet to be fully explored, so stay tuned.
* Our Sun is thought to be a third-generation star and our entire solar system is made of the recycled star stuff of previous star generations.(A)
** Simple animals have only been on this planet for the past 600 million years of a 4.5 billion year history, while single-celled organisms have been playing the evolution game for 3.8 billion years. Mammals have only been a part of the scene for 200 million years.(K)
*** A ring of debris orbits the planet, and in an amazingly short amount of time -- about one day -- it begins to coalesce into a satellite. It takes somewhere between 1 and 100 years for the Moon to gather most of the stuff into a ball.(C)
**** One estimate puts the day-length at 8-hrs, without the Moon, at our present point in the planet's timeline(I)
H. The Universe: Season 4, Episode 2: The Day the Moon Was Gone