| Themes > Science > Paleontology / Paleozoology > About Paleontology / Paleozoology, Generalities > Geologic Time > Absolute Time |
In contrast to relative time, absolute time systems attempt to establish the age of an object or event in actual numbers of years. Theoretically, the principle behind absolute age determinations is simple. All one has to do, is to find some system which changes at a constant, known rate, determine how much change has taken place and, if one knows the rate of change, one can calculate how much time has elapsed. Over time, many people have taxed their ingenuity to find ways of determining the age of the earth. From the time when it became obvious that Bishop Ussher's 6000 year chronology of the earth simply ran counter to evidence, many calculations were attempted. They included attempts to calculate the age of the earth on the basis of the salinity of the oceans, as well as the rate at which the earth lost heat. None of these was entirely successful, not because they were conceptually flawed, but because they lacked sufficient information. Even so, they all clearly pointed to the fact that the earth is extremely old. Several techniques have been used with some success within the recent past. They include dendrochronology (aging based on tree rings), lichenology (based on the growth pattern of lichens), and the study of warves, annual layers deposited by the meltwaters of glaciers. All these methods leave something to be desired, being mostly limited to relatively recent materials, but they can nevertheless give reasonable ages. |
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