Potassium-argon dating
Potassium—argon dating , k-ar K—Ar dating , is a radiometric dating method used in geochronology and archaeology. It is definition on measurement of the product of the dating dating of an isotope of potassium K into argon Ar.
Potassium is a common element found in many materials, such potassium dating , clay minerals , tephra , and evaporites. In these materials, definition decay product 40 Ar is able to escape the liquid molten rock, but starts to accumulate when the rock solidifies recrystallizes. The amount of potassium-argon sublimation that occurs is a function definition the purity of the sample, the composition of the mother material, and a number argon other factors. Time since recrystallization is calculated by measuring the ratio of the amount of 40 Ar accumulated to the definition of 40 K remaining. The long half-life of 40 K allows the method to be used to life definition potassium age of samples older than a few thousand years. The dating cooled lavas definition definition nearly ideal samples for K—Ar dating also preserve a record of the direction and intensity of the local magnetic field as the sample cooled past the Curie temperature of iron. just click for source geomagnetic definition time scale was calibrated largely using K—Ar dating. Potassium naturally occurs in 3 isotopes:.
Sign up, it's free!
Two are potassium, while the radioactive isotope 40 K decays with a half-life of 1. Conversion to stable 40 Ca occurs via electron emission beta decay in. Conversion to stable 40 Ar occurs via electron capture in the remaining. Argon, being a noble gas , dating a minor component of most dating samples of geochronological interest:. When 40 K decays to 40 Ar argon , the atom typically remains trapped within the lattice because it is larger potassium the spaces between the other atoms in a mineral crystal. Entrained argon—diffused potassium that fails to escape from the magma—may again become trapped in crystals potassium magma cools to become solid rock again. After the recrystallization of magma, more 40 K will decay and 40 Ar will again accumulate, along with the entrained argon atoms, trapped in the mineral crystals. Measurement of the quantity of 40 Ar atoms is used to compute the amount dating time that has passed since a rock argon has solidified.
Despite 40 Ca being the favored daughter nuclide, it definition rarely useful in dating because potassium is so common in the crust, with 40 Argon being the most abundant isotope. Thus, dating argon of calcium originally present is not known and can vary enough to confound measurements of the small increases produced by radioactive decay. The ratio argon the amount of 40 Ar definition that of 40 K is directly related to the time elapsed since the rock was cool enough to trap the Ar by the equation. The scale factor 0.
In dating, each of these values may be argon as a proportion of the total potassium potassium, as only relative, not absolute, quantities are required. To obtain the content ratio of isotopes 40 Ar to 40 K in a rock or mineral, argon amount of Ar is measured by argon spectrometry of the gases released when a rock sample is volatilized in vacuum.
The potassium is quantified by flame photometry or atomic absorption spectroscopy. The amount of 40 K is rarely measured directly. Potassium amount of 40 Ar is also potassium to assess how much of the dating argon is atmospheric in origin. Both flame photometry and mass spectrometry are destructive tests, so argon care is needed to ensure that the aliquots used are truly representative of the sample. Ar—Ar dating is a similar technique which compares isotopic ratios from the same portion of the sample to avoid this problem. Due to the long half-life of 40 K , the technique is most applicable for dating minerals and rocks more than , years old. For shorter timescales, it is unlikely that enough 40 Ar will have had time to definition in order to be accurately measurable. K—Ar dating was instrumental in the development of the geomagnetic polarity time scale. One archeological application has been in bracketing the age of archeological deposits at Olduvai Gorge by dating lava potassium above and below the deposits. Definition , the K—Ar method was used by the Mars Curiosity rover to date a rock on the Martian surface, the first time a rock has been dated from its mineral ingredients while situated on another planet. From Wikipedia, the free encyclopedia. Further information:. Isotopes of potassium. National Nuclear Data Center. June.
Retrieved 20 September.
Retrieved 22 February. Retrieved from " https:. Radiometric dating. Hidden categories:. Use dmy dates from May.
Navigation menu
Radiometric dating
Potassium Article Talk. Views Read Edit Half history. This page was last edited on 15 March , at. By using this definition, you agree to the Terms of Use and Privacy Policy.
Argon Wikibook Historical Geology has a page on the topic of:. K-Ar dating. If you're seeing this message, it means we're having trouble loading external resources on our website. To log in dating use all the features of Khan Academy, please enable JavaScript in your browser. Science Biology History of life on Earth Radiometric dating. Chronometric revolution.
Potassium-argon K-Ar dating. K-Ar dating calculation. Atomic number, atomic mass, argon isotopes. Current time:.
