|Jul/Aug 2004 Book Reviews|
The Emergence of Life on Earth: A Historical and Scientific Overview
Rare Earth: Why Complex Life is Uncommon in the Universe
Peter D. Ward & Donald Brownlee
Paleontologist Peter D. Ward and astronomer Donald Brownlee's Rare Earth: Why Complex Life is Uncommon in the Universe brings to the fore the very precept, and percept, of "What Is Life?" including the astronomical and geological forces that helped, fostered, elevated, or hampered, life's origins. For one simple reason: life's origin is not a mumbo-jumbo accord. Rather, it is a complex idea, which requires not only equanimity, but also an innate grasp of things—great and petite. In so doing, it delves into the raison d'etre of Charles Darwin's ingenuity, a pioneer who never really construed the actual origin of life in his noteworthy book, On the Origin of Species...
In factual terms, Darwin was more concerned with the mechanism of evolutionary change as maybe seen in the anthology of life today, including a host of "medals" of nature that "originate" in fossils. Not only that. His other equally popular writings did not also swat the question—no more, no less. Yet, they all delivered a sledgehammer-like effect on the "character" of humanity. How? By putting us under the analysis of evolutionary happenstance, albeit modern thinkers, thanks to new information and separated from religious conviction, are better perched to answering, or at least understanding more fully, how exactly life evolved.
Rare Earth... provides "a long grocery list of ingredients seemingly necessary to make a planet teeming with life," all right. In so doing, it elaborates a medley of fascinating parameters: from the formation of our planet itself, its position in a solar system, its own potential habitable zone to its rubble-catching "compatriot," Jupiter, besides its location in the galaxy, where "celestial catastrophes" like supernovae, impacting bodies, intense radiation and heat, abound. The best part of it all, of course, would prove relatively dangerous for any life form to begin its journey through time, just as much as its enormous capacity to "uphold" life per se. All the same, the duo's new science, astrobiology, is a field that not only encompasses life on Earth but also life beyond it—a re-evaluation of life of our planet as a single example of how life might just work.
Ward and Brownlee also expand on the revolution in astrobiology during the 1990s—a two-fold pattern. First, when scientists began to value how incredibly cogent microbial life can be found in the superheated water of deep-sea vents, pools of acid, or even within the crust of the Earth itself, they thought why the chances of finding such simple life on other bodies, in our solar system, never seemed more practical. Second, scientists have also now begun to understand how a host of unusual factors seem to have co-operated to make Earth a hospitable home for animal life: Jupiter's constant orbit, the existence of the Moon, plate tectonics, the right amount of water, and our precise position in the correct sort of galaxy. In short, a persuasive defense that chips away at the principle of mediocrity—that the "Earth isn't all that special"—a "standard" that has ruled astronomy since Copernican times.
It, therefore, comes as no surprise that Ward and Brownlee support the first-RNA-catalyst doctrine, though it maybe surmised that an exclusive RNA preserve would, obviously, limit the choice/s of origination. Why? Because, RNA is more temperature-sensitive than DNA, aside from the premise that the RNA-first idea would probably rule out such suspects for the origination of life—as thermophilic microbes—even though mesophiles—organisms that accept warm but not hot temperatures—would be more appropriate.
As complex genes developed, Ward and Brownlee summarize how all three taxonomic domains—Archaea, Bacteria and Eucarya—emerged. And, as eukaryotic-cell development took time, over a billion years, they also add, that, "the jump from single-celled organisms to organisms of multiple cells [which] requires numerous evolutionary steps," took place, more so for animals, what with alterations in atmospheric conditions—the modern shift towards a higher quotient of oxygen.
Ward and Brownlee synthesize several interpretations of early biotic research, especially the consequences of the near-fatal global glaciations of billions, and millions, of years ago, "when Earth teetered dangerously close to becoming too cold for any life." They add, that, the challenges our planet has faced throughout its history should also provide exemplary "challenge/s to astrobiology." For instance, was the Cambrian Explosion, a biological event of 600 million years ago, that saw the rapid emergence of all the phyla, we see today, "inevitable once a certain level of biological organization had evolved"? The fact that it took 3 billion years from the emergence of life to reach this level of multi-cellular organization, they say, suggests "that forming animal life is much more difficult than the initial formation of non-animal life."
Examples of lifeless planets in our solar system are legion. This also explains why our proximity to the Sun, including broad-spectrum predilections such as rotational axis, orbital motion, and large-scale impacts, could all prove damaging. Here's why. Impacts, as maybe surmised, were rather common in the early solar system. So much so, it's only when the effect of impacting agents dropped down that life got a chance to really blossom. A case in point: how well do we all know that many other planets, understandably so, had the right chemistry early on in their formation, but were comprehensively "wiped" out. However this maybe, it's obvious that such early colliding agents may have, in fact, conferred some of the essential biochemical units of life. Their identity: amino acids from which proteins evolved. This was followed by complexity—of proteins that had to be in attendance to "pull together" molecules.
The thought of diversity is still a very thorny question, so also mass extinction. Mass extinction, Ward and Brownlee imply, could have provided pathways for previously submissive taxa to radiate "near-global calamities." You know them, don't you: the famed asteroid/comet impacts, alterations in the axial spin of the planets, energy harvest of the Sun, radiation emissions, including the ice and runaway greenhouse gases. Which only means that events—astronomical, or geological, which is quite novel to our planet, and biological—charted require sublime, well-reasoned, comprehension; and, that higher forms of animal life are uncommon.
The duo also likens the famous Drake equation, which measures the mathematical potential of intelligent life in the Universe. They place their own "Rare Earth Equation," with the more qualified dynamics vis-à-vis the existence possibility of higher animals in other worlds. They recommend that each component in the equation maybe multiplied after the other, so that if each component nears zero, the entire equation will have a lower "worth." It is, thus, through galactic, planetary, geological and biological history, they observe, we may have emerged. Call it the only cadence in our own self-propelled symphony, or what you may, one fact remains: we may not be alone.
Interestingly, however, another book that "demystifies"—and, adds to—Rare Earth..., besides looking at the subject pretty perceptively, including the search for extraterrestrial intelligence, within the realms of mainstream science, is David Darling's steady book, Life Everywhere. It explains what we know and what's actually doable. It also explores the history and current state of astrobiology, a name for a fascinating subject, which some minds don't like. All the same, astrobiology, says Darling, is devoted neither to organisms floating away from the Sun's surface nor to possible signs of ET intelligence. It questions whether it is worthwhile trying to communicate across light years. It is, in so relating, that Darling scores a wonderful point.
He writes: "Their [scientists'] efforts will revolutionize astrobiology, more so, perhaps, than spacecraft parachuting down out of the orange sky of Titan or roving the rock-strewn deserts of Mars. The world-shaking headlines of the next twenty years will likely come from giant instruments, on the ground and in Earth orbit, gazing with far sight at the planetary systems of other stars."
Besides, Darling's work "walks" us around very sizzling topics as heat vents and other geothermal mini-biomes, meteoritic dissection, and, most importantly, SETI's radio telescope assays. Mars, Venus, and the moons of the outer planets are all his foremost typescripts, as much as their stories. Result: Life Everywhere is a thought-provoking exposition at what could eventually be the most world-shaking research ever performed. It also asks pertinent questions: what defines life at its root?; how does evolution work, and where does it tend to occur?; and, how different could life be across the cosmos?
Iris Fry's The Emergence of Life on Earth is yet another impressively written book on the captivating subject. It focuses on the biological aspects, not so much on the astronomical and geological parameters—in question. Its contention is also more than factual: "Life based on carbon and water is anything but a rare phenomenon." Hence, it prefers to place its perimeter of thought afar from the question of higher or lower life forms, while taking a broad scientific dekko at the origins of Earth... with a view of possible life on Mars.
The inference is quite simple, lucid, and weighty. The emergence of species has always been a non-issue, no matter the flow of sublime philosophical thought throughout the ages. Conventional wisdom has been, or will always be, of an "intelligent designer," although Darwin implied profoundly to a method of species transmutation. Yet, the idea of spontaneous generation did not see its hold wane until the latter part of the 19th century, thanks to the genius of Louis Pasteur. Thereafter, it was nothing short of an "expanding" stillness.
However, the idea got a shot in the arm, in the 1920s, with the exemplary work of Alexander Oparin and J.B.S. Haldane, who "proposed for the first time," as Fry notes, "specific hypotheses about the geographical conditions on an ancient Earth and the constituents of the early atmosphere that made this synthesis possible." Oparin, by understanding colloid chemistry, not only found that when certain polymers reach a critical level, but also two distinct reactions. When micro-droplets form, he explained, they gather more substances and a kind of primeval metabolism. He concluded: "The droplets grow and eventually divide."
To cull an evolutionary presage, "While the first creatures exploited the chemical energy stored in organic substances in the environment, those that followed were forced to rely on alternative means to produce energy"—a form of natural selection. This prompted Haldane to suggest the proposition that prebiotic chemical "potage," or soup, was stimulated and changed through ultraviolet radiation.
However, it wasn't, again, until the 1950s that the origin-of-lifers got a boost, thanks to the work of Stanley Miller who was able to "fuse" organic molecules in a laboratory "edition" of the ancient world. It's at this point that, Fry, in much more extensive detail, describes whether the chicken came first or the egg, along with the evolution of possible solutions and the coming of age of the so-called RNA global hypothesis. In addition, she also hints at matters seemingly external to the issue of scientific temper in the origin-of-life question.
Not only that. Fry, a teacher of history and philosophy of biology at Tel-Aviv University and the Technion-Israel Institute of Technology, contends that as the issue of the origin of life became more possible to discover, and more widely recognized, the social implications, primarily the religious connotations, emerged as germane. She observes that the chicken-and-egg dilemma has goaded many creationists to mark it as a predicament in science, whereas scientists "consider it a challenge that calls for new ideas about the mechanisms responsible for the emergence of life under prebiotic conditions."
All the same, Fry's good read delineates a number of advances, including the inorganic "scaffolding," or exemplar, from which organic molecules could have, perforce, occurred, not to mention the newly discovered ribosymes that "catalyze the cutting and joining of segments of RNA." This landmark discovery, Fry believes, could just as well represent the basic, or fundamental, core of the RNA-first credo. Finally, Fry also examines sociological and religious implications, and why the idea may hold palpable zest to every creationist who believes the "intelligent design" canon, besides the search as to how life emerged on a scientific methodology, replete with the empirical evidence that would, doubtless, promote our continued quest for knowledge.
All meaningful studies, in their own diverse ways—on what the beginning of life was, and how it would be construed in the future—the three books, in review, it maybe conveyed, with conviction, have the wherewithal to hold a special place—for a newly emerging stream—in every science, or general, reader's bookshelf.