By Sam Ejike Okoye
DESPITE unparalleled advances of scientists in their quest for knowledge about the natural world, life itself still remains one area that has proven intractable and elusive to fully understand. For the average individual, the perennial questions have always revolved around "Who am I?"; "Why am I here on this planet - and at this time?"; "What is my mission on planet Earth?" Indeed, could humans be the only intelligent beings in all the vastness of the universe? Or are we just one humble race, a member of a vast intergalactic fraternity of advanced civilizations?
As of now, all we have are questions, but we know the answers, whenever they come, could transform our world. Perhaps that is one of the major motivations for astronomers in their search for extraterrestrial life in the cosmos.
Nonetheless many people after watching recent movies about aliens in outer space would naturally have wondered about the possibility of life existing elsewhere. What would it be like? Of what would it be made?
All living things on our planet are after all, constructed of organic molecules - complex microscopic architectures in which the carbon atom plays a central role. Indeed there was once a time before life as we know it existed, when the earth was barren and utterly desolate.
But our world is now overflowing with life of multifarious forms. How did it all come about? How, in the absence of life, were carbon-based organic molecules made? How did the first living things arise? How did life evolve to produce beings as elaborate and complex as we are, able to explore even the mystery of our own origins?
Indeed, is there life also on the countless other planets that may circle other suns? Is extraterrestrial life, if it exists, based on the same organic molecules as life on Earth? Do the beings of other worlds look much like life on Earth? Or are they stunningly different - or are they other adaptations specific to other environments?
In the great dark spaces between the stars there are clouds of gas and dust and organic matter. Dozens of different kinds of organic molecules have been found by astronomers, using radio telescopes. The abundance of these molecules suggests that the stuff of life is everywhere. Perhaps the origin and evolution of life is, given enough time, a cosmic inevitability.
On some of the thousands of millions of plants in our galaxy, the so-called Milky Way Galaxy, life may never arise. On others it may arise and die out, or never evolve beyond its simplest forms. And on some small fraction of worlds there may develop intelligences and civilizations more advanced than our own.
The effort by scientists to seriously address the ancient question, "Are we alone?" is surprisingly recent, dating from just the late 1950s. Indeed, the discovery of what is now more than seventy planets around stars other than the Sun continue to stimulate tremendous public and media interest. In this case, attention was driven not so much by the discovery of the extra-solar planets themselves, but by the prospect of them hosting intelligent life that may be able to threaten us.
Nearly every space movie to come from Hollywood includes some encounter between humans and alien life forms. Most recently we have had the high-budget Mars-based films Mission to Mars, and The Red Planet. Astrophysicists appear to be the ladder to what people really care about: whether or not we are alone in the universe
Leaving the make-believe world of movies aside, astronomers have often wondered what a lucky coincidence it is that the Earth is perfectly suitable for life - availability of moderate temperatures, liquid water, oxygen atmosphere, and so on. But this is, at least in part, a confusion of cause and effect.
Earthlings are supremely well adapted to the environment of the Earth because we grew up here. Those earlier forms of life that were not well adapted obviously died out. We are descended from the organisms that did well and made it in the survival struggle. Organisms that evolve on a quite different world will doubtless sing its praises too.
All life on Earth is closely related. We have a common organic chemistry and a common evolutionary heritage. As result, our biologists are profoundly limited. They study only a single kind of biology, one lonely theme in the music of life.
Is this faint and reedy tune the only voice for thousands of light-years? Or is there a kind of cosmic musical composition, with themes and counterpoints, dissonances and harmonies, a thousand million different voices playing the life music of the Galaxy? What happened here on Earth may be more or less typical of the evolution of life on many worlds; but in such details as the chemistry of proteins or the neurology of brains, the story of life on Earth may be unique in our own Galaxy.
The Earth condensed out of interstellar gas and dust some 4.6 thousand million (billion) years ago. We know from the fossil record that the origin of life happened soon after, perhaps around four thousand million years ago, in the ponds and oceans of the primitive Earth. The first living things were not anything so complicated as a one-celled organism, already a highly sophisticated form of life.
The first life stirrings were much more humble. In those early days, lightning and ultraviolet light from the Sun were breaking apart the simple hydrogen-rich molecules of the primitive atmosphere, the fragments spontaneously recombining into more and more complex molecules.
The products of this early chemistry were dissolved in the world's oceans, forming a kind of organic soup of gradually increasing complexity, until one day, quite by accident, a molecule arose that was able to make crude copies of itself, using as building blocks other molecules in the soup.
This was the earliest ancestor of deoxyribonucleic acid (DNA), the master molecule of life on Earth. It is shaped like a ladder twisted into a helix or spiral, the rungs available in four different molecular "colours" or parts, which constitute the four letters of the so-called genetic code. These rungs, called nucleotides, spell out the hereditary instructions for making a given organism
By three thousand million years ago, a number of one-celled plants had joined together, perhaps because a mutation prevented a single cell from separating after splitting in two. The first multi-cellular organisms had evolved. Every cell of your body is a kind of commune, with once free-living parts all banded together for the common good. And each one of us is made of a hundred million cells or so. We are therefore, each of us, a multitude.
Sex seems to have spontaneously emerged around two thousand million years ago. Before then, new varieties of organisms could arise only from the accumulation of random mutations - the selection of changes, letter by letter, in the genetic instruction. Evolution must have been agonizingly slow.
With the emergence of sex, however, two organisms could exchange whole paragraphs, pages and even books of their genetic code, producing new varieties ready for the evolutionary sieve of so-called "natural selection".
To be Continued.
Sam Okoye is black Africa's first radio astronomer and a Fellow of the Nigerian Academy of Science.
http://www.ngrguardiannews.com/science/article02
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