Absolute chronometric dating
Absolute dating is a method of determining the specific date of a paleontological or archaeological artifact or location based on a specific time scale or calendar.Scientists base absolute dating on measurable physical or chemical changes or on written records of events.The L-amino acids change to D-amino acids more or less steadily following death. As a result, remains of organisms that died long ago will have more D-amino acids than ones that died recently.Aspartic acid (one of the 20 amino acids) is usually extracted from samples for this dating technique.Using these methods, the scientist determines a date range for when an event took place rather than where it fits in the overall record. The techniques scientist need for absolute dating did not become available until the later half of the 20th century.
Chronometric or calendar dating is a better choice. The earliest evidence of writing anywhere in the world only goes back about 5000 years.Paleoanthropologists frequently need chronometric dating systems that can date things that are many thousands or even millions of years older.Subsequently, a diminishing field is likely to result in a significant rise in the frequency of radiation induced cancers in the future.Despite this limitation, paleoanthropologists have found dating by association with polar reversals to be a helpful additional method of tracking the evolution of our fossil ancestors in regions such as East Africa where there has been frequent volcanic activity leaving clear thermoremnant magnetic evidence.