H ph is important best adhesion at mildly acidic to

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H - ) pH is important: best adhesion at mildly acidic to neutral pH o Some thing to think about: In solution, cleavage reactions are thermodynamically favored. Synthesis reactions require highly reactive groups to drive the reaction and freedom of rotation is high (lowers probability of a reaction). But on charged surfaces, the formation of large molecules is thermodynamically favored; freedom of rotation is absent and there is a narrow range of
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orientation through which molecules may interact. However, high temperature is required to force some reactions (recall periodic heating/cooling). o Evolution Reactions on surfaces favor Binding by strongly anionic molecules with relatively low chemical reactivity Highly reactive molecules participate only when their bonds form more stable complexes Stable reaction tend to persist with novel reactions forming branches to the ‘main’ metabolism Environment changes could cause novel reaction events (change in pH, rapid change in temperature, invasion of novel organic molecules) A major outcome is a change from aqueous to non-aqueous environment brought about by lipid synthesis and exclusion of water from lipid blebs. Detachment possible. No matter the path, lets say that some com bination of a ‘warm little surface’, organic slop, and perhaps a meteor originating from Mars….life began. But when?
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The Fossil Record The fascination with fossils and previous forms of life is understandable…you can see them. A very difficult task for microscopic things with no bony material that nevertheless is converted to rock-like objects imbedded in rock itself. The first examples of a fossil record for microbes comes from stromatolites Review stromatolites (Source of Figure 11.2: Madigan et al. 2003, Figure 24.3: Campbell, 1996)
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These structures could be harvest, thin sectioned, examined and dated. From these, the oldest evidence suggests ’cellular’ life existed about 3.6 billion years ago.
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