Originally posted by aldo_14
What makes you think a lack of ozone would be bad for life? IIRC, radiation is good for stimulating mutation and thus evolution; even a nuclear war wouldn't destroy life.
Yes, a lack of ozone will be bad for life universally. You don't seem to realize what radiation does and why mutation is a side effect.
Radiation is harmful because it
destroys genetic material (DNA, RNA), breaking it apart. Low levels and short term exposure to radiation causes minor damage and the DNA can be reassembled with few errors. Moderate exposure causes more severe damage and usually a few dangerous errors occur such as certain tissue becoming cancerous. Prolonged and intense exposure to high intensity radiation will cause irrovocable destruction to the DNA and thus result in death. This is why the practice of irradiating materials to sterilize them is so effective.
Now any mutations that occur are due to moderate and relatively short exposure. Now this effect is usually highly different for each exposed area. It is impossible for all parts of a large, multicellular organism to experience the same level exposure to a single source of radiation (the skin will always get hit with more than internal organs), and the likelyhood that all cells' DNA will be subject to the same level of destruction and reassembled exactly the same way with exactly the same errors is next to zilch. And because germ cells (reproductive cells) are far more susceptible to radiation than normal body cells, high intensity radiation will cause sterility. So in summary, in a nuclear warzone, you're not gonna find a bunch of Godzillas running around, you'll just find a lot of dead bodies (which is the concept behind the neutron bomb, a nuclear weapon specifically designed to maximize the release of high intensity radiation to the surrounding environment).
Now today the ozone filters out the vast majority of ultraviolet radiation from the sun (think the figure was around to 97 or more %). This tiny level that eventually reaches the surface is enough to cause sunburns and skin cancer in humans after just a few hours of exposure. Now with the complete depletion of the ozone, we're talking 12 hours a day, every day for the next 5 billion years (or really 4 billion cause then the sun will swell up to a red giant and swallow the Earth) of exposure to virtually unmitigated solar radiation. All life on the surface will die, unless it happens to be hiding all the time under several meters of lead. As long as DNA is the genetic material of life, there's no two ways about it: life is dead on the surface. Under full exposure to the sun's radiation, even life in the ocean will eventually be dealt a lethal dose. Hell, even electronics would be eventually destroyed unless specially shielded (satellites and space probes have a limited life span, even with continuous power, because the radiation levels outside our atmosphere eventually cause damage in the electronic systems). The only survivors will be the bacteria that live deep underground, with hundreds and thousands of feet of rock to shield them, and these bacteria don't seem to be in a hurry to be moving anywhere or evolving (iirc, these underground bacteria are essentially the exact same as they were billions of years ago).
So, yeah, that's why I think a lack of ozone would be Bad(tm) for life. As for nuclear war, the primary theorized effect is the same as the asteroid scenario: so much debris and dust is thrown into the atmosphere that sunlight is considerably diminished, causing plant life to die and follows that all herbivores die and thus all carnivores die. The radiation contamination is just the finishing blow. Though in this case, only those at the very surface would die. Creatures living at the bottom of the ocean would escape relatively unscathed (unless everyone decided to drop tens of thousands of nuclear depth charges to the bottom of the ocean).
Anyway, that's all the most extreme case. I doubt even we would be that oblivious to let the ozone layer be completely destroyed or let Bush blow up the planet so there's nothing left. BUt it would still be Bad(tm).
