JUST SO IT GOES:

Where Does Intelligent Life Come From? (Universe Today, Mar 8, 2005)

A lot of things had to go well for life to come about. If you go way back, it all begins with a Big Bang universe giving birth to space and time. In that early universe light echoed about, slowed in vibrancy, the primordial elements coalesced then condensed into a first generation of massive breeder stars. After warming to the notion (by gravitational compression), primordial matter began fusing in stellar cores and a lesser form of light moved outward to warm and illuminate a young and potentially ever-expanding Universe.

More time and more space saw many of those early blue stars implode (after living very short lives). Subsequent explosions spewed vast quantities of heavier - non-primordial - atoms into space. Out of this rich cosmic endowment new stars formed - many with planetary attendants. Because such second and third generation suns are less massive than their progenitors, they burn slower, cooler, and much, much longer - something essential to the kind of benignly consistent energy levels needed to make organic life possible.

Although breeder stars formed within a few hundred million years of the Big Bang, life here on Earth took its time. Our Sun - a third generation star of modest mass - formed some nine-billion years later. Life-forms developed a little more than one billion years after that. As this occurred, molecules combined to form organic compounds which - under suitable conditions - joined together as amino acids, proteins, and cells. During all this one layer of complexity was added to another and creatures became ever more perceptive of the world around them. Eventually - after more billions of years - vision developed. And vision - added to an subjective sense of awareness - made it possible for the Universe to look back at itself.

Empirical research into the fundamentals of life shows that a concoction of well-chosen elements (hydrogen, carbon, oxygen, & nitrogen) exposed to non-ionizing ultraviolet radiation forms amino acids. Amino acids themselves have a remarkable capacity to chain together into proteins. And proteins have a rather "protean" ability to give shape and behavior to cells. It is now considered entirely possible that the very first amino acids took form in space1 - shielded from harder forms of radiation within vast clouds comprised of primordial and star-stuff material. For this reason, life may be an ubiquitous phenomenon simply awaiting only certain favorable conditions to take root and grow into a wide variety of forms.

Currently, exobiologists believe that liquid water is essential to the formation and multiplication of organic life. Water is an extraordinary substance. As a mild solvent, water enables other molecules to dissociate and mix. Meanwhile it is very stable and is transparent to visible light - something useful if biotics are to derive energy directly from sunlight. Finally water holds temperature well, carries off excess heat through vaporization, and floats when cooled to solidify as ice.

According to NASA exobiologist Andrew Pohorille, "Water brings organic molecules together and permits organization into structures that ultimately became cells." In so doing, water acts in an unparalleled matrix enabling organic molecules to form self-organizing structures. Andrew cites one property uniquely associated with water that makes self-organization and growth possible: "The hydrophobic effect is responsible for the fact that water and oil don't mix, soaps and detergents 'capture' oily dirt during washing in water and for a vast number of other phenomena. More generally, hydrophobic effect is responsible for segregating nonpolar (oily) molecules or parts of molecules from water, so they can stick together even though they are not bonded. In biology these are precisely the interactions responsible for the formation of membranous cell walls and for folding proteins into functional structures."

For water to take the liquid state, it must remain in a relatively narrow range of temperatures and pressures. Because of this only a certain few well-placed planets - and possibly a handful of large moons are favored with the conditions needed to let life live. In many cases it all comes down to a form of celestial real estate - location, location, location...

Indeed, centrally located.

Posted by Orrin Judd at March 9, 2005 12:00 AM