Question: But don't trees sometimes produce more than one growth ring per year? Answer: If anything, the tree-ring sequence suffers far more from missing rings than from double rings.This means that the tree-ring dates would be slightly too young, not too old.Question: A sample that is more than fifty thousand years old shouldn't have any measurable C-14. Radiocarbon dating doesn't work well on objects much older than twenty thousand years, because such objects have so little C-14 left that their beta radiation is swamped out by the background radiation of cosmic rays and potassium-40 (K-40) decay. this isotope [K-40] accounts for a large part of the normal background radiation that can be detected on the earth's surface" (p. This radiation cannot be totally eliminated from the laboratory, so one could probably get a "radiocarbon" date of fifty thousand years from a pure carbon-free piece of tin.
Most of the tree-ring sequence is based on the bristlecone pine.
This tree rarely produces even a trace of an extra ring; on the contrary, a typical bristlecone pine has up to 5 percent of its rings missing.
Of course, species of tree tend to produce two or more growth rings per year.
But other species produce scarcely any extra rings.
Even so, the missing rings are a far more serious problem than any double rings.