Gene-based trees drawn for living animals can usually be dated by estimating the rate of DNA change and anchoring at least one branch of the tree to a fossil of known age.
This is because the rocks have been dated using only biostratigraphy, a process in which paleontologists compare the fossils preserved in a rock unit of uncertain age with rock units of known age that preserve similar fossils.
The problems stemming from temporal variations can be overcome to a large degree by the use of calibration curves in which the carbon-14 content of the sample being dated is plotted against that of objects of known age.
This "bomb curve", as it is known, changes so fast that year-by-year differences in the 14C levels of recent specimens should be detectable.To test this hypothesis, Dr Uno and his colleagues looked at 29 specimens of known age, from 1905 to 2008.
The single-grain data from 12 samples of known age (reported by Olley et al. [2004b.
We correlated our results with structures of known age from adjacent areas.
This model used time-series data of the diameter of root systems and canopies (crown) of P. radiata of known age projected onto the ground as circles for different planting density and silviculture scenarios.
By conducting comparative studies on moraines of known age in Alaska, we are able to estimate the ages of moraines in Russia and develop a framework for the correlation of glacial history across Bering Strait.
The length of the abdominal aorta before, l, and after excision from the body, L, the diameter, heart weight, thickness of left ventricle and degree of atherosclerosis were collected in autopsies of 156 male cadavers of known age.
Growth data and ageing criteria of 177 individuals of known age, obtained from a captive population, kept under uniform conditions at King Khalid Wildlife Research Centre in Saudi Arabia, were examined.
Researchers can guess the length of this phase, but not an individual star's age, by comparing the number of young stars in a region to the number of older stars of known age.
