Skeptic Ginger
Nasty Woman
- Joined
- Feb 14, 2005
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I had a reason to review the current state of the science of abiogenesis recently and it seemed worth sharing.
2009:The Origin of Life
A case is made for the descent of electrons
The science of our origins is moving right along. The Talk Origins page on abiogenesis was apparently last updated in 2001. The evolution deniers cite Talk Origins claiming there is no mechanism for 'selection' before the first complete organisms. But it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.
The authors of the above citation compare the problem to investigating the highway system. If you just took the current form, you might investigate asphalt, cars, oil and so on. Or you could instead start with mechanisms of movement and transportation. Then you might move on from walking to trails to horses and vehicles and roads and then to the highway system.
Instead of approaching the problem of abiogenesis by trying to find the mechanisms of replication, some scientists are looking at the chemical processes within the cell and looking for the pathway those process might have been involved in creating the first organic molecules. From there the line of inquiry is then to look at what might have happened next.
2009:The Origin of Life
A case is made for the descent of electrons
In this article we present a view gaining attention in the origin-of-life community that takes the question out of the hatchery and places it squarely in the realm of accessible, plausible chemistry. As we see it, the early steps on the way to life are an inevitable, incremental result of the operation of the laws of chemistry and physics operating under the conditions that existed on the early Earth, a result that can be understood in terms of known (or at least knowable) laws of nature. As such, the early stages in the emergence of life are no more surprising, no more accidental, than water flowing downhill….
…Since 1953, we have found many of the same simple organic molecules in meteorites, comets and even interstellar gas clouds. Far from being special, then, the simplest of the molecules we find in living systems—life’s building blocks—seem to be quite common in nature…
…The next major advance came in the early 1980s, when Thomas Cech and Sidney Altman showed that some RNA molecules can act as enzyme-like catalysts. The frozen-accident argument was then replaced by a suggestive scenario in which something like RNA was assembled by chance, and was then able to fill twin roles as both enzyme and hereditary molecule in the run up to life…..
…Networks of synthetic pathways that are recursive and self-catalyzing are widely known in organic chemistry, but they are notorious for generating a mass of side products, which may disrupt the reaction system or simply dilute the reactants, preventing them from accumulating within a pathway. The important feature necessary for chemical selection in such a network, which remains to be demonstrated, is feedback-driven self-pruning of side reactions, resulting in a limited suite of pathways capable of concentrating reagents as metabolism does. The search for such self-pruning is one of the most actively pursued research fronts in Metabolism First research.
…At the very core of metabolism—the starting point for the synthetic pathways of all biomolecules—is a relatively simple set of reactions known as the citric acid cycle (also called the tricarboxylic acid cycle or the Krebs cycle). The cycle involves eight molecules, each a carboxylic acid (a molecule containing —COO groups). In most present-day life forms on Earth, the citric acid cycle operates to break organic molecules down into carbon dioxide and water, using oxygen to produce energy for the cell—in effect, ”burning” those molecules as fuel….The cycle can also operate in the opposite direction, taking in energy (in the form of high-energy electrons) and building up larger molecules from smaller ones….
…The important pattern to appreciate is that the primordial cycle provides the stability and starting materials that make an age of selection possible. We think it was at the transition to this stage that geochemistry began to take on the features of replication and selection recognized by Darwin as distinctive of life. After such an age has begun, it can maintain the complexity and diversity needed to explore for refinements—in efficiency, in adaptation to the geological environment or in specialized division of labor within communal systems. The same pattern repeated itself when the environment was changed by the accumulation of a destructive toxin—oxygen—that was produced by primordial organisms as a waste product. As they adapted, organisms did not abandon the reductive citric acid cycle, which we believe was the unique foundation for biosynthesis. Instead they acquired the ability to run the cycle in reverse, extracting energy from the breakdown of molecules similar to those the cycle formerly produced.
The science of our origins is moving right along. The Talk Origins page on abiogenesis was apparently last updated in 2001. The evolution deniers cite Talk Origins claiming there is no mechanism for 'selection' before the first complete organisms. But it appears there is evidence for a purely non-organic chemical 'selection' process that preceded RNA molecules and replication.
The authors of the above citation compare the problem to investigating the highway system. If you just took the current form, you might investigate asphalt, cars, oil and so on. Or you could instead start with mechanisms of movement and transportation. Then you might move on from walking to trails to horses and vehicles and roads and then to the highway system.
Instead of approaching the problem of abiogenesis by trying to find the mechanisms of replication, some scientists are looking at the chemical processes within the cell and looking for the pathway those process might have been involved in creating the first organic molecules. From there the line of inquiry is then to look at what might have happened next.