TC> GJO> The isotope method you are thinking of work by comparing a
 TC> constantly
 TC> GJO> decaying ratio of a stable element to its unstable isotope (like
 TC> GJO> radiocarbon)...
 TC> The one I'm thinking of works by comparing the more-or-less constant
 TC> ratio of two or more stable isotopes of the same element. And my
 TC> problem with this is that if we can detect the difference between
 TC> the (to manufacture an example) isotope with 16 neutrons that's
 TC> found in 98% of the sample and the isotope with 18 neutrons that's
 TC> found in 2%, then we can also extract enough of the second isotope
 TC> to dope another specimen with so that it's 90%/10%.
 Ok...like enriching uranium to weapon grade material.....Indeed this would 
tell you the difference between natural and constructed materials, but 
between human and Extraterrestrial?  I am not sure...you really need a great 
deal of material understanding....the are experts on this however.  You 
probably knew the answer anyhow. 
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