This is Scott. At our last meeting (yesterday, 7/7/07), I had a sudden thought, for which a perfectly good answer may be sitting in the origins-of-life literature, but I haven't looked. What do you all think of this?
Maybe the development of photosynthesis and oxygen respiration is another chicken-or-the-egg problem for the origins of life. Photosynthesis makes oxygen. Without it, the early earth had no free oxygen. Oxidative metabolism does no good w/o oxygen to breathe. But what good would it be to store energy in sugar, since an elaborate process is needed to liberate the energy out of sugar using oxygen? These are two very elaborate processes, each of which doesn’t seem to give any benefit without the other already existing.
I think the standard answer is that photosynthesis came first, and the local increase in oxygen (perhaps as bubbles trapped in algal mats, for example) gave oxygen metabolism the opportunity to arise. But, what good did photosynthesis do before oxydative metabolism was present? So what if a plant could make sugar out of sunlight? What good does that do by itself?
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Scott: Hugh Ross in his book Creation as Science has one answer to your chicken or the egg dilemma.
Page 127:
"Evidence now shows the simultaneous appearance of multiple, distinct, complex unicellular life-forms rather than just a single, ultra-simple organism. This ensemble includes, at minimum, both oxygenic and anoxygenic photosynthetic life, several species of sulfate-reducing bacteria, and a diversity of other chemoautotrophs (bacterial that exploit high-energy chemicals to sustain metabolic reactions). Each primordial life-form played a crucial role in preparing the way (with remarkable efficiency and speed) for the eventual appearance of more advanced animals, ultimately human beings, and finally for the rapid emergence of civilization."
Also, Ross discusses the oxygen question on pages 136 to 138 in the same book. He believes that the abundance of photosynthetic bacteria in the oceans could have transformed Earth's atmosphere from 1 or 2 percent oxygen to about 20 percent in only a few million years, perhaps less.
Scott,
As I think about the chicken or the egg, I think that photosynthesis gave a great advantage to early plants by permitting them to access abundant CO2. If there was anaerobic life competing at the same time, plants with photosynthesis would be able to dominate more niches. Then photsynthetic life would be able to actually poison anaerobic life with O2, over time.
None of this speaks to the central question we wrestle with:
Why should something as complex and context-dependent form and persist, much less evolve over huge time frames?
And another question comes to mind - why and how would the incredible leap from photosynthetic and anaerobic processes to animal life occur?
Time and randomness does not statisfy that very well at all.
Good point. I think Ed has the explanation. What Hugh Ross said could be true at the same time, of course!
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