Speaking of having one's head in the ozone... not that anyone has ever accused this writer of that problem ;-)
In one of the great ironies of biology - the same deadly UV radiation from the sun, which causes cancer and/or creates an ozone layer and other toxicity - is also responsible for US (all humanity) in several different ways. Without the challenge of overcoming the grave threat of UV, back before an ozone layer even existed, life on earth might have have stagnated into a blob of underwater slime. And furthermore, without the slight genetic alteration provided by some smaller amount of UV getting through the ozone layer in more modern times, there would be less predictable and constant mutation in DNA, which can lead to beneficial changes over time. It is a huge balancing act, and UV is the fulcrum and hinge which makes it all oscillate in an anti-entropic way. The evolutionary significance of UV is not well-appreciated, but will be emphasized in the following version of time-compressed events (with help from Wiki). BTW to the extent that there is "ID" (intelligent design) and to the extent that "change" itself is stochastic (rather than truly random), that MO (modus operandi) IS itself evidence of one basic form of intelligence... ergo, such an intelligence seems to be strongly rooted in the UV spectrum. Life-and-death, dualities teetering on the knife's edge sharpened to 185 nm. Evolution of life depends first on reproduction, and second on stochastic change, and third on the occasional advancement (aka 'survival of the fittest') which depends on that small level of constant change being there (which 99% of the time is not advantageous). The early reproductive proteins of single cell life can be attributed - in modern models of evolutionary theory- to the necessity of having to deal with the intensity of ultraviolet light which was far greater than we experience it now - since we are protected by the ozone layer. For billions of years there was no ozone layer over earth. Ultraviolet light causes thymine base pairs next to each other in genetic sequences to bond together into thymine dimers, a disruption in the strand which reproductive enzymes cannot copy. This leads to huge problems during genetic replication, usually killing the organism. As early prokaryotes (billions of years ago) began to approach the surface of the ancient oceans, long before the protective ozone layer had formed, they would almost invariably have died out. The few that survived quickly developed enzymes which verified the genetic material and broke up thymine dimer bonds, known as excision repair enzymes. In terms of evolutionary advance- this was almost as large a step as the appearance of reproductive proteins. Many of the enzymes and proteins involved in modern mitosis, which is the kind of cell replication which is found in mammals, are extremely similar to these ancient excision repair enzymes yet there have long lost their original benefit ! IOW the most essential biological constituents and mechanisms which we have today are believed to be slight modifications of the enzymes originally used to overcome the deadly effects of UV light. This curious fact might lead to the conclusion that the appearance of advanced life (as we know it) is more unlikely and fragile than we think elsewhere in the universe ... in that any earth-like planet which was not bombarded, early-on, with unimpeded UV radiation, would not have presented the inherent challenges which were involved in creating those enzymes and proteins, which became involved in mitosis millions of years later. Of course there could be other routes to advanced life which might be available if life evolved elsewhere (a planet which always had an zone layer) - but all of which serves to reinforce the notion that if extraterrestrial life ever does reach us, it will probably look nothing like us, nor even like little green men (in the alien autopsy hoax) who are, after all fairly similar to us -- this is because the challenges faced would have been so different at a fundamental stage (with an early ozone layer, as compared to none). Confused ? I know I am ;-) ... but that is a characteristic of living in a constant ozone layer, as they say.
