-=> Quoting Ron Taylor to George Jiri Opletal <=-
 RT> A couple of years ago, someone on this echo explained how isotope
 RT> ratios would conclude the origin of any material.  That person was
 RT> possibly Michael Tauson who has just recently resurfaced....  if so,
 RT> maybe he will address the question again.
     Wasn't me, but I do remember the conversation.  Sort of.
     The gist of it was that on Earth, isotopes of the elements 
occur in known ranges - for example, for each iron atom (Fe56? - 
I *knew* I should have memorized the periodic table ), there 
is a known (and reasonably consistant) range of isotope 
occurances of iron as well.  This is due to how the planet was 
formed and it's geological history.  
     A planet in a different star system, while it may have had a 
similar history, was formed from a different cloud so the 
elements will be in different ratios *plus* the isotope 
occurances will be different.  
     Any sample of a material will contain not only the base 
atoms but isotopes of the elements as well.  So, if you take your 
basic stainless steel ashtray and analyze it, you'll find iron 
(carbon, chromium, et al) and isotopes of iron (and the others, 
of course) consistant with their occurance in nature on the world 
on which that ashtray was made. 
     There is another point about materials from alien craft as 
well that maybe should go here.  The elements occur in nature 
according to how they appeared in the dust cloud from which a 
stellar system was formed.  As a result, we have a relative 
abundance of iron on Earth but things like Yttrium (I know that's 
not the right spelling *sigh*) occur rarely - hence the term 
"rare earths".  
     This will not necessarily be true on a planet formed from a 
dust cloud that had a different composition initially.  While 
iron would likely still be a high abundance element (as would 
others), the relative mixtures of the other elements would be 
slightly different and a would could wind up with a more abundant 
supply of what is rare on earth.  
     As a rule, you use the tools and toys you have.  We don't 
use much Yttrium (for example) simply 'cuz there isn't much to 
use.  That would not necessarily be true on another world, which 
would give another clue to alien origin.
     Take the above as hypothesis ... simply 'cuz there is no way 
at present to test any of it.
Michael
... Analysis of space signals shows aliens are the source of infomercials.
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