>The evidence suggests that over the past 10,000 years there have
>been fairly rapid but small fluctuations in C-14 levels (on order
>of 1% of present level, taking a small number of decades), as well
>as larger longer-term fluctuations (on order of 10% of present
>level, taking thousands of years). The latter correlate well with
>changes to carbon-14 production rate that would be predicted from
>fluctuations in the Earth's magnetic field.
Since there are no trees that have 10,000 continuous rings, I would be
willing to bet that there is some tautological analysis involved in that
extrapolation. Although the picture of tree ring variation appears to be
pretty well closed for about 4000 years, I wouldn't stake my life on dates
older than that. Brown has done some interesting analysis on trends older
than 4000 years that is revealing.
BROWN, R. H. Implications of C-14 age vs depth profile characteristics.
Origins 15:19-29 --- 1988
Brown, R. H. C-14 age profiles for ancient sediments and peat bogs Origins
2:6-18 2:58. 1975
BROWN, R. H. The interpretation of C-14 dates. Origins 6:30-44 1979
BROWN, R. H. Correlation of C-14 age with the biblical time scale.
BROWN, R. H. The upper limit of C-14 age? Origins. 15:39-43 --- 1988