Expain the assumption that C14/C12 ratio is the same now as it has been "milliions of years ago".?

Question

In order for C-14 to be accurate at all( I understand its only good up to 60,000), this ratio must be that same now as it was yesterday. But test show that just in the past 100 years that it varies considerably. And Calibration methods seem to only narrow the error down to 200%. Isn't it time to through this dating method out yet?

Answer 1

Bottom line: if the technique were not useful to archaeologists, climatologists, and earth scientists studying the last 50,000 years of the earth's history, they wouldn't waste their time.

It is NOT the assumption of modern specialists in the field of carbon-14 dating that the C14/C12 ratio has never varied. You must have gotten that information from a very outdated source. Over the past 15-20 years, radiometric carbon specialists have developed ever-improving standard calibration tables and curves to take into account recognized temporal variability in carbon ratios. And, given that Carbon 14 dating is only useful for the interval from pre-Industrial Age to about 50,000+ years ago, the specialists don't have to worry about the C14/C12 ratios for strata that are millions of years old. In other words, archaeologists use it to study human history (not very old in the geologic sense) but paleontologists can't use it to date dinosaur sites, which are way too old (they use other methods).

The radiometric carbon standardized calibration tables have been created with lots of cross-dating techniques and with a range of available data from tree growth rings, ice cores, deep ocean sediment cores, lake sediment varves, coral samples, and cave deposits. Within the range of the upper and lower limits of time where scientists consider carbon-dating to be useful, the error rate is NOT the 200% rate that you suggest--it is much more precise. To increase precision for individual sites, however, archaeologists try to date multiple samples from a site, and samples from higher and lower intervals. And where/when possible, they try to bring in other methods for dating sites (cross-dating)--such as dendrochronology (tree ring dating), obsidian hydration, luminescence, archaeomagnetic and paleomagnetic dating, etc.

Answer 2

Actually, calibration has been done with Carbon 14 dating. A core was taken from a tree and the tree rings were counted. The tree had been alive for over 2000 years. Carbon 14 dating undercalculated it by about 5%, not bad by scientific standards. I don't know where you came up with an error of 200%, maybe you pulled that number out of your head. In any case, it is wrong.

Answer 3

Actually C-14 dating is pretty accurate... within set parameters. Because C-14 has a half-life of 5 730 years it isn't all that reliable in dating specimens from recent sites. And you already know that it is unreliable on specimens over 60 000 years old. However, on a specimen between +- 6 000 and +- 40 000 years old it has a margin of error of only plus or minus 50 years.

C-14 dating is not used on older specimens, K-Ar dating is and it's very reliable. And, the older the specimen, the more accurate it is. K-Ar dating cannot be used on organic specimens though.