Discussion

In Boulder, CO, at noontime in the summer, there is 20 mW (milliWatts) of visible light hitting each 1 cm² of the surface. However, there is only about 0.022 mW of UV radiation between 290 nm and 320 nm (UV B) hitting each 1 cm² of the surface.

Why is there only that amount of UV radiation reaching the surface? Would this amount reach all parts of the earth's surface or would it vary by geographic location? State one other factor that would affect the amount of UV radiation reaching the Earth's surface and state how it changes the amount of UV radiation.

Returning to the amount of UV radiation reaching the surface in Boulder, CO, is this sufficient UV exposure to cause damage to our DNA and result in skin cancer? Does the exposure to 20 mW of visible radiation affect our DNA unharmed? Why doesn't exposure to so much more visible radiation harm our DNA?