[Right Wing Professor]

You're confusing reflection with absorption.

When light hits something, it can be transmitted, absorbed or reflected. Whatever fraction UV is reflected, a similar fraction of visible light would be reflected. So, sure, a shiny surface above the earth could reflect 80% of the UV, but only if it reflects about 80% of the visible light. Without visible light, plants don't grow. What you want is to absorb the UV and transmit the light. That's what sunscreens do.

Ozone actually absorbs UV; if you could see UV, the sky would have a color (just as, say, wine has a color) because the UV light is missing from the region of the ozone absorbtion band. The atmosphere actually scatters red light differentially, as a result of a weird effect called Rayleigh scattering, so the sky looks slightly blue.

[Terriergal]

You're confusing reflection with absorption....What you want is to absorb the UV and transmit the light. That's what sunscreens do. Ozone actually absorbs UV

Plants don't grow? What kind of plants? Plants we have today that have adapted, or plants we had back then? I find it more plausible to believe that the kind of light spectrum they were able to utilize back then was different than today, rather than believe a cat evolved from a rock.

I did actually think of ozone. Would an ozone layer combined with a translucent ice canopy give you that effect?

[BiffWondercat]

Perhaps telomerase simply worked better back then?