From: allenroy (allenroy@peoplepc.com)
Date: Fri Oct 03 2003 - 15:33:05 EDT
Dawsonzhu@aol.com wrote:
> The first question I would ask is what kind of error bars should I expect
> from Rb/Sr measurements. Is 50% error sometimes to be expected in
> very old rocks? I'm not saying that's great if we can only expect this
> kind of broad-side-of-a-barn estimate, but it would still provide at least
> that level of objectivity to the issue.
Rb-Sr dates for the Cardenas basalts (McKee and Noble, 1976, p. 1189) run like
this.
1.06 +/- 0.07 billion years. (or +/- 70 million years) or 6.6% error
0.98 +/- 0.06 b.y. (6.7 % error)
1.09 +/- 0.08 b.y. (7.3 % error)
1.09 +/- 0.10 b.y. (9.2 % error)
1.07 +/- 0.04 b.y. (3.7 % error)
1.10 +/- 0.05 b.y. (4.5 % error)
This is typical of the other Rb-Sr dates at Grand Canyon. It is far better than
the 50% error you suppose.
* McKee and Noble, "Age of the Cardenas Lavas, Grand Canyon, Arizona,"
Geological Society of America Bulletin, 87 (Aug. 1976):1188-1190.
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