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Re: When is a Year Not a Year?



 philidor11 wrote:
> 
> (Radiocarbon years do not equal calendar years because...
> 
> And I wonder if the same ratio of difference (11,300/13,250) applies
> to all dates used.  Clarifies my mind.
> Anyway, when we get substance-based dates for dinos, can I assume they
> are calendar years, or should I do an equivalent to my meters-to-feet
> conversion calculation?
> 

No radiometric dates are calendar years (and even calendar years aren't
"real" years, hence the constant recalibration with leap years, etc).
However some are closer than others.

C-14 depends on solar radiation to be created, which means the amount of
C-14 in the atmosphere relative to C-12 (or C-13 for that matter) will
vary. Then there is the question of whether living creatures accumulate
C-14 differentially than C-12. Plus, the radiocarbon technique assumes
that the sample was 100% carbon to begin with, and the decay rate of
C-14 is quite rapid compared to other radio-isotopes. Put all those
factors together, and you get quite a deviation from "calendar" years
(assuming even those are useful).

I suspect other radio-isotopes have more predictable original ratios.
Just be thankful palaeontologists don't use thermo-luminescence dating.
Just having a piece of quartz sitting in strong sunlight for long enough
is enough to reset the "clock".

-- 
________________________________________________________________

Dann Pigdon                   Australian Dinosaurs:
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://www.alphalink.com.au/~dannj/
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