Fossilized remains of animals help scientists understand the ancient history of the Earth.
Radioactive dating uses the natural decay rate of radioisotopes to estimate the age of historic sites, landforms, fossils or other objects. One of the most common forms of radioactive dating is carbon dating, where the rate of decay of carbon radioisotopes is used to measure the age of organic materials, such as fossils.
Radioisotopes
Radioisotopes, or radioactive isotopes of materials such as carbon or rubidium, will decay into new isotopes at a consistent rate, regardless of other factors like temperature or physical state. The radioisotope is known as the "parent" radioisotope and the new isotopes are known as "daughters." The half-life of the radioisotope is the amount of time needed for half of a quantity of the radioisotope to decay into new isotopes.
Calculating Age
Calculating the age of an item is computed after using a mass spectrometer to analyze the make-up of the object -- looking for and determining the number of daughter isotopes in the object. Scientists then use the predictable rate of decay of that daughter's parent radioisotope to determine the length of time required to produce that many daughter isotopes. The known rates of decay can be found in the Geological Society of America's Geologic Time Scale. After analyzing the object, the researcher graphs the parent radioisotope's rate of decay to determine the time it took for the known number of daughter isotopes to be produced.
Applications
This method of determining age has applications in archeology, geophysics, geology, oceanography and paleoclimatology. Materials that can be dated this way include minerals, wood, shells, bones and organic sediments such as peat. Some historically significant uses of the method include the dating of late Pleistocene and Holocene era artifacts and determining when major geologic events occurred.
Uncertainty
Some radioactive dating, especially carbon dating, cannot be entirely exact in its age estimates. The level of carbon radioisotopes in the atmosphere in ancient times could have fluctuated, meaning that the radioisotope's decay rate is not always predictable. For example, during historic eras where there is a high level of carbon radioisotopes in the atmosphere, more radioisotopes would have been present in an object than in an object that originated during a period of low atmospheric carbon radioisotope levels.
History
This method of dating was discovered in the 1940s by a team of researchers lead by Willard F. Libby at the University of Chicago. The Nobel Prize in Chemistry was awarded to Libby in 1960 for his leadership in developing radioactive dating.
Tags: carbon radioisotopes, daughter isotopes, parent radioisotope, rate decay, carbon dating, carbon radioisotopes atmosphere, decay into
