Re: illogical: Supervening influences on half life of samples  
I understand that the half-life of a radio-isotope is unaffected by temerature, pressure, etc. But don't other radiological sources have an effect? e.g. the atomic fallout from a meteorite or a supernova in a nearby star system. It seems such events could trigger substantial 'non-spontaneous' decay that would cause is discontinuity in the typical half-life curve and set dates off by an order of magnitude. Also the level of C-14 in the atmosphere could increase significantly in response to such events too: making a sample appear younger than it really is. 

No? Are there any reliable sources research on this?