It has now been established, with the dendrochronological sequence for the , that the C14 concentration has fluctuated.
The reasons for the fluctuation are not yet fully understood.
The method drastically reduces the quantity of datable material required.
A previous limit of 50,000 years on the age of material which could be dated, set by the limits on the ability of the proportional counter used to record beta particle emissions, has been extended to 70,000 years by the use of isotopic enrichment, the artificial enrichment of the C14 to C12 ratio.
CATEGORY: technique DEFINITION: Absolute pollen counting is the determination of the number of grains of each pollen type per unit weight (grains/gram) or unit volume (grains/cm3) of sample.
It is native to the Rocky Mountains of the United States, at elevations above 7,500 feet (2,300 m), and they have the longest life-span of any conifer.
A stand of this tree in eastern Nevada is known to have several trees over 3,000 years old, and one of them is thought to be about 4,900 years old.