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Re: When is a Year Not a Year?

HP Dann Pigdon stated:
<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.>
I'm willing to accept that a calendar year is a reasonable approximation of
the time required for one full rotation of the Earth around the sun, in the
same way that I can accept there is a working solution to equations
involving pi.  Age has granted me tolerance.  There is an inverse relation
between philosophical discussion and sleep attained.

He adds that:
<...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.>
and responds to HP Hecht's statement:
< Other radioisotope years are "real" years.>
<Not exactly. They are statistical likelyhoods, assuming a constant rate of
radioactive decay.>

So, if I'm following correctly, he means that:
- dates have a substantial range of error or
- dates are not expressed in calendar years or
- both.
I'm inclined to think that the correct answer is that when mya dates are
given for the Maastrichtian, for example, that these are referring to
calendar years, but that they could be off.
If so, is there a good rule of thumb possible error percentage to be
First it turns out that weight estimates for dinos are very tenuous...  Be
good to know that the years assigned to named periods are at least calendar
years, even if their number slides a bit.