Re: Does Ultra Violet (UV) radiation penatrate the surface of the Earth?

Question: Does Ultra Violet (UV) radiation penetrate the surface of the 
Earth?

...Even if by less than 12 inches? Can one assume that disturbed soil, 
because through the act of digging or disturbing, is less dense and UV 
may penetrate more so that soil that has not been disturbed? 



Hello James,

As you probably know, UV radiation is a small band of radiation on the 
very large electro-magnetic spectrum.  The wavelength range for UV is 
approximately 400 to 200 nanometers (see link below for definition), and 
falls between visible light and x-rays. The smaller the wavelength, the 
higher the energy is of the radiation.  

There is often a misconception that the smaller the wavelength is (and 
the higher the energy), the better the penetrating power of the radiation 
will be. This is actually not true, except in the very high energy ranges 
of x-rays and above.  An example of this is the penetrating power through 
air:  Visible light, with lower energy than UV, is not absorbed when 
passing through the atmosphere.  However, UV is partially absorbed by the 
atmosphere.  The highest energy range of UV (called UVC) is completely 
absorbed by the atmosphere, and does not reach the surface of the earth. 
(This is a good thing, because UVC would kill us!)


The short answer to your question “Does UV penetrate the surface of the 
earth” is NO.  Soil absorbs all of the UV radiation within a fraction of 
an inch.  The best example that demonstrates this is the fact that some 
animals, such as elephants will cover themselves with mud (wet soil) to 
protect themselves from the burning effects of UV. Mud can be an 
effective ‘sunscreen’ for people as well! This thin layer of “earth” 
covering the skin effectively blocks the UV radiation. 

The physics of exactly ‘how’ electro-magnetic radiation penetrates a 
material is very complicated, and relates to how the photons of the 
radiation interact with the atoms within a particular material.  It turns 
out that UV radiation has the least penetrating power of all ranges of 
the electro-magnetic spectrum.

I hope that this answers your questions.

Best Regards,

Jay Shapiro
 http://www.nanooze.org/english/articles/article4_howbigisananometer.
html