Over half of all analyses implemented one or more fossil dates as constraints, followed by geological events and secondary calibrations (15% each).
Vertebrate taxa were subjects in nearly half of all studies, while invertebrates and plants together accounted for 43%, followed by viruses, protists and fungi (3% each). doi: 10.1016/20 Pubmed Abstract | Pubmed Full Text | Cross Ref Full Text Hamilton, P.
Molecular-based divergence dating methods, or molecular clocks, are the primary neontological tool for estimating the temporal origins of clades.
While the appropriate use of vertebrate fossils as external clock calibrations has stimulated heated discussions in the paleontological community, less attention has been given to the quality and implementation of other calibration types.
The calibration of a glacial varve record, series, or chronology is accomplished by applying numerical or calendar ages to existing varve numbers.
The true calendar age of a varve sequence can be obtained in areas where varves can be counted back from the present in modern lakes with varve deposition.
Our oldest living trees appear to be less than five thousand years old.
Radiocarbon corrections beyond that are often based on attempts to match the thickness variations of tree rings in old wood samples.
If a similar pattern of variation in tree-ring thickness is found in two pieces of wood, the two are assumed to have grown at the same time.
In order to determine what real-time age should be associated with a radiocarbon age, the radiocarbon data are often compared to historical and tree-ring data that are considered to be more reliable indicators of time.
Tree-ring data are especially important in the correction process for dates older than 1000 BC.
Cal Pal-Online is developed to give a quick reference.