(1) The chemistry of "formations" growing under concrete structures is not the same as speleothem growth in caves. But this doesn't really have any implications for comparing their rates of growth. (2) Carbon dating is not the usual way of dating formations (partly because they are usually too old, as has been pointed out). Various other means of dating based on radioactive decay are used (uranium/thorium, etc.). These work back hundreds of thousands of years, at least. (3) Dating of a non-speleothem mineral in the caves of the Quadalupe Mountains has indicated that they are at least some millions of years old. The higher-elevation ones are older, c. 6 MY, if memory serves, and the lower ones around 2 MY. (4) When carbon-14 dating is used (generally for archaeological purposes) one sees either a calibrated or an uncalibrated date. The latter is adjusted for known variations in original C-14 content. I think (without looking it up) that "years before present" when stated as a C-14 date means uncalibrated years before 1950. The uncertainty in uncalibrated dates pretty much reflects radioactive counting statistics and other experimental errors, but uncertainties in calibrated dates depend also on the local slope of the calibration curve. (5) One _cubic_ inch per anything is an nonsense way to state speleothem growth. Obviously a ten-foot-wide flowstone thickening at such and such a rate will gain a lot more cubic inches per hundred years than a tiny stalactite thickening at the same rate. (6) An interesting illustration of how tiny molecules are: If a 1 kilogram stalactite grew from one drop per second over a million years, each drop will have deposited about 200 billion molecules of calcite. -- Mixon ----------------------- You may "Reply" to the address from which this message was sent, but note the following permanent addresses for long-term use: Personal: [email protected] AMCS: [email protected], [email protected]
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