Fossil Data and the Origins of Life

Although the early efforts of chemists to envision how natural processes might have led to the formation of life are interesting, the engineer within me longs for real data to determine what actually happened. What does the fossil record and our geologic history in general have to say about the matter?  The early earth was a hostile and barren orb, hot with volcanic activity, oceanless, heavily bombarded with comets and meteors, and shrouded in a thick, opaque primordial atmosphere whipping around it at speeds up to 500 MPH. In short, not a place hospitable to even the survival, let alone the formation of life. About 4.5 billion years ago, a collision with a Mars-sized planetoid blew off the primordial atmosphere, saving earth from the runaway greenhouse effect that Venus is now subjected to. This collision also gave rise to the object we known as our moon.
Work by Miller and others shows that chemical evolution could not occur if water temperatures were greater than about 25C, as important intermediates would be too unstable, so the earliest earth could not have evolved life. By about 4.0 billion years ago, the meteoric bombardment  largely subsided and the earth had cooled and stabilized, which allowed  the formation of oceans and led eventually to a thick but transparent atmosphere. The gravitational pull of the moon slowed down the rotation of the earth, reducing the atmospheric wind speeds to more tolerable levels. By reason of this fortuitous but highly improbable series of events, the earth had become a place where the survival of life was possible, at least in its most simple forms. Recent chemical evidence now shows that life is likely to have been present 3.9 billion years ago. Basically, no rocks which are much older than this, but still of a type likely to show the influence of life during their formation, exist for scientists to analyze. For all intents and purposes, it seems that life appeared as soon as the earth reached a condition which could support its survival. No significant period of time between the formation of a stable earth and the appearance of life is available for the long "molecular" evolution envisioned by many biochemists where intermediate biochemical products such as RNA strands could replicate, change, adapt, improve and eventually "become" life. The fossil record and history of the earth simply do not allow for it.This has led at least one researcher to postulate that life might have evolved from simple amino acids to fully functional cells in periods as little as a few centuries to several thousand years - a theory utterly without supporting evidence.	Additionally, signs of the long hypothesized "primordial soup", an ocean heavy with organic materials which may have given rise to the first life have been repeatedly sought in the geologic column. However, no fossilized evidence that it ever existed, such as residual organic deposits of the correct age, have ever been found. Certainly liquid oceans existed, but no evidence of waters with high concentrations of of dissolved or suspended organics exists from this period. Most estimates which lead to conclusions that these concentrated organic waters were common, neglect the fact that the simple organics decompose over time. The reactions of Miller and others are reversible and organic materials can and do break down, especially on exposure to sunlight. Mechanisms to concentrate desirable organic materials and protect them from decomposition, such as concentration in warmed caves near volcanic sources, not only are somewhat far-fetched, but also neglect the fact that these same systems would also concentrate chemicals including sulfur oxides, which inhibit or are destructive to the desired reactions. Some researchers have also proposed mineral based mechanisms such as clay particle surfaces for the collection and concentration of organics, however, the work to date has yet to yield conclusive evidence that this mechanism would be capable of accomplishing the desired tasks.

Continue on to Part 4: The RNA World Theory
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