W. Kevin Vicklund
Posts: 68 Joined: Oct. 2005
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Due to the fact that I'm on a DHCP server, I'm currently blocked from posting to Panda's Thumb (the IP address assigned to me today was apparently blacklisted at some point in the past). So if someone could please post this to the original thread over at PT, I would be grateful.
<quote author="Heddle">Evolution can explain how either (a) our eyes are most sensitive to the peak of our sun’s spectrum or (b) how our eyes are sensitive to a narrow range of radiation to which the atmosphere is transparent. But evolution cannot explain the happy fact that we don’t have to choose (a) OR (b), the two parts of the spectrum being one and the same. Design, of course, explains it trivially.</quote>
The problem here is that Heddle posits the wrong question for point a). Point b) is trivial for evolution of the eye - the eye has evolved to view radiation that is abundant and has wavelengths amenable to cellular construction (the second part explains in part why we see in the 100's of nanometers {visible light} as opposed to radio frequencies, which require a longer "antenna length", or x-rays, which damage cell structures). Evolution would favor the peak energy frequencies permitted by the atmosphere, even if those frequencies were not the peak range output by the sun.
However, evolution also can account for (the proper phrasing of) point a), which is "Why is the atmosphere transparent at the peak frequency output of the sun?" Sound-byte answer: It's the energy, stupid. Life that relies primarily on energy delivered by the sun will prefer atmospheric conditions that maximize the usable energy (see wavelength amenable to cellular life argument above) delivered by the sun. And since life affects the composition of the atmosphere, differential reproduction favors a balance that keeps the atmosphere transparent to the peak radiation band. It also explains in part why the atmosphere is opaque to harmful radiation.
Note: this doesn't prevent life from living (sorry, poor choice of words there, but I'm hitting writer's block) in opaque atmospheres, provided sufficient energy does make it to the surface to support minimal life. It does mean that we should expect to see transparent atmospheres on planets where evolution has had time to significantly alter the atmosphere.
Disclaimer: This is written from an educated layman's perspective. It is not intended to be a rigorous discussion of evolutionary or electromagnetic theory, and there are many places where I likely could have used better phrasing. This is, at it's heart, speculative, based on my understanding of evolutionary and elctromagnatic theory.
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