Radiometric Dating According to The American Heritage® Science Dictionary radiometric dating is: “A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotopes decay products (in this case strontium). The objects approximate age can then be figured out using the known rate of decay of the isotope. For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms. Radiocarbon dating is one such type of radiometric dating” (“radiometric dating”).
Carbon 14 Carbon 14 is the only radioactive isotope in organic matter. Half of the Carbon 14 will have changed to nitrogen 14 in 5,730 years (Mader 547). Carbon 14 dating is a technique to assign an actually date to a fossil. For example, let’s say that a fossil has one- fourth the amount of radioactive 14C as a modern sample, then the fossil is approximately 11,460 years old (Mader 547). This is because it is about 2 half-lives of 14C.
Radiometric Dating with Fossils Because Carbon 14 has such a short half- life, it is useful in archaeology for dating artifacts (man-made objects) and the bones of animals up to 50,000 to 60,000 years old (Eschberger). However, it cannot be used on anything older than 50,000 to 60,000 years old.
Radiometric Dating with Fossils In order to date older fossils, scientists use Potassium-Argon dating. The element potassium is found in most rock-forming minerals, and the half-life of the radioactive isotope Potassium 40 is 1.25 billion years, allowing measurable quantities of Argon 40 to accumulate in potassium-bearing minerals of almost all ages (Eschberger). The amounts of potassium and argon isotopes can be measured accurately, making Potassium- Argon dating useful for very old rocks.
Works Cited Eschberger, B. "suite101.com ." Dating fossils II: Radiometric dating. suite101.com, 2000. Web. 2 Apr 2012. <http://archive.suite101.com/article.cfm/ paleontology/38275>. Mader, Sylvia S. Inquiry into Life. Thirteenth. New York: McGraw-Hill, 2011. 547. Print. "radiometric dating." The American Heritage® Science Dictionary. 2005. Houghton Mifflin Company 1 Apr. 2012 http:// www.thefreedictionary.com/radiometric+dating