evolution?

David J. Thomas thoma457 at uidaho.edu
Fri Sep 20 04:33:02 EST 1996


V. wrote:
> 
> If the hole in the ozone grows would plant life on earth benefit from
> the increase in solar radiation?

Probably not.  Ozone primarily absorbs UV radiation, which is not 
beneficial to plant or any other life.  A decrease in ozone probably 
would allow more UV-B to reach the earth's surface.

> Is there any way of determining the amount of solar radiation that
> reached the earth when life fist evolved?To some extent it can be done experimentally with artificial atmospheres. 

There have also been some models of the early atmosphere, but I can't 
provide any references off the top of my head.

> I read my text, it gave me N2 as 78% of the atmosphere.
> From Enviromental Chemistry by Colin Baird "Uv light having wavelengths
> shorter than 120 nm is filtered in andabove the stratosphere by O2 and
> other constituents of the air such asN2."
> I want to know what excatly N2 does to all solar radiation that reaches
> our planet.

Actually, I believe that ozone and oxygen are the primary absorbers of 
short wave radiation.  I'm not sure about the role of nitrogen, although 
nitrogen oxides abosorb shortwave radiation.

> What if N2 was the sole gas in the atmosphere how much UV would the
> surface of the earth get?
> I read somewhere that in the overall age of the planet free oxygen was
> small or nonexistant when life first evolved.

That is what current theories suggest.  The evolution of oxygenic 
photosynthesis in cyanobacteria, and later algae and plants produced the 
oxygen in the atmosphere.
 
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