I'm quoting from the most up-to-date book on the Geophysical History of the Earth available, by a NASA scientist (and colleague) well known and respected for his own contributions to the Origin of Life question:
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"No one yet knows how (or when) the ancient transition from a lifeless to a living world took place, but basic principles are emerging from focused research at dozens of labs around the world. (p.131) ... The first and best understood step in biogenesis was the rampant production of life's molecular building blocks: sugars, amino acids, lipids,and more. ... Modern Origins-of-life research began in 1953, with what remains to this day the most famous experiment in biogenesis. Chemist Harold Urey, ..and his resolute grad student Stanley Miller designed a simple and elegant tabletop glass apparatus to simulate early Earth. ...After a few days, the water turned brown with a complex mix of organic chemicals. Miller's 1953 paper in Science ..generated sensationalistic headlines around the world.... This initial enthusiasm and subsequent focus may have come at a price. Miller's experiment placed origins-of-life squarely in the camp of organic chemists and established the paradigm of life emerging from a prebiotic soup - perhaps from a "warm little pond" (echoing Darwin's speculations). Few experimentalists of the 1950s considered the staggering complexities of natural geochemical environments, altered as they are by daily cycles of night/day, hot/cold, wet/dry, and more. Nor did they consider the range of natural gradients - in temperature, for example, as volcanic magma contaacts cold ocean water,; or in salinity, as a fresh stream enters the salty ocean. And none of Miller's experiments incorporated rocks and minerals, chemically diverse with dozens of major and minor elements, and their reactive energetic crystalline faces. Earth's sunlit surface, they assumed, was where all the action must have occurred. Miller's influence was strong, and he and his followers dominated the origins-of-life community for more than three decades. A flood of publications ensued, new journals arose, and honors and awards were bestowed, while government funding flowed to the "Millerites". Then in the late 1980s, the discovery of deep-sea black smoker ecosystems gave rise to a viable alternative to "primordial soup". In those deep dark zones, far from the sunlit ocean surface, mineral-rich fluids interact with hot volcanic crust to generate ocean-floar geyser-like vents. Jets of scalding water contact the frigid deep ocean to create a constant precipitation of minerals (the microscopic particles that produce the black "smoke"). Life abounds in those astounding hidden places, fueled by the chemical energy at the interface between crust and ocean. The battle over origins paradigms reveals a lot about the sociology of science. On the one hand, the Miller-Urey process produced a suite of biomolecules stunningly similar to what life actually uses. The mix of amino acids, carbohydrates, lipids, and bases almost looks like a well-balanced diet. As Harold Urey quipped, "If God did not do it this way, then He missed a good bet." But the true believers of the Miller camp did more than just support the lightning-seeded primordial soup idea; with a vengeance they rejected any and all competing ideas. The effectiveness of the La Jolla cabal's obstructionism began to decline with the startling discovery of those living black smokers described above, coupled with the powerful and far-reaching ambitions of NASA. ... NASA Steps in... NASA, whose science funding is tied closely to the prospect of great discoveries, jumbe at this possibility. If life is constrained to arise in Miller-Urey scenario, at the sun-drenched surface of a watery world, then Earth and possibly Mars (in its earliest stages, its first 500 Myrs) are the only plausible living worlds within our reach. But if life can emerge from the black, hot depths of a sub-surface volcanic zone, then many additional celestial bodies become tempting targets for exploration. Mars today must have deep hydro-thermal zones; perhaps life endures there even now. ... My Carnegie Inst. colleagues and I are relative latecomers to the origins game. Our lab's first NASA-sponsored experiments in 1996 were specifically designed to test organic synthesis in black smoker regimes, where high temperatures prevail. Like Miller, we subjected mixtures of simple gases to energetic conditions - in our case, heat and chemically reactive mineral surfaces, just as you'd find in a deep volcanic zone. Like Miller, we produced amino acids, lipids, and other bio-building blocks. Our results, now duplicated and expanded in numerous labs, show beyond doubt that a suite of life's molecules can be synthesized easily in the pressure-cooker conditions of the shallow crust. Volcanic gases containing carbon and nitrogen readily react with common rocks and seawater to make virtually all of life's basic building blocks. What's more, these synthesis processes are governed by relatively gentle chemical reactions called reduction and oxidation reactions, or redox reactions, such as the familiar rusting of iron or caramelizing of sugar. These are the same kinds of chemical reactions that life uses in metabolism, in sharp contrast to the violent ionizing effects of lightning or ultraviolet radiation. Indeed, while harsh lightning bolts may faciilitate the production of small biomolecules, they just as easily rip those building blocks to molecular shreds. To many of us in the origins game, it makes a lot more sense for Earth to have made its prebiotic molecules with less energetic chemical reactions, in more or less the same way that cells do today. Miller's Continued Obstructionism... Stanley Miller and his followers did what they could to squelch our conclusions and abort our research program. In a flurry of critical publications, they argued that the high temperatures of the volcanic vents would quickly destroy any useful biomolecules. "the Vent hypothesis is a real loser," Miller complained in a 1998 interview. "I don't understand why we even have to discuss it." They based their arguments on meticulous experiments in which biomolecules degrade in boiling water. But these simplistic studies failed to mimic the complexity of the primordial Earth; missing were the deep ocean's extreme gradients of temperature and composition, the turbulent flow and cycling of volcanic vents, the chemical complexity of mineral-rich seawater, or the protective surfaces of rocks on which biomolecules are now known to bind. Nonetheless, the origins field has now moved beyond the Miller-Urey scenario, and for many experts, Earth's deep dark zones are today the primary focus in the biogenesis game. As I mentioned earlier, every ancient environment with sources of energy and small carbon-bearing molecules probably produced its share of amino acids, sugars, lipids, and other molecular building blocks of life. ... Every year tons of organic-rich dust rain down on Earth's surface from outer space, as it has for more than 4.5 billion years. We now know that life's building blocks litter the cosmos. " - The Story of Earth, Robert M. Hazen, (2012, Viking Pub.), pp. 133-136. Exerpted for Review purposes |
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