5. 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 isotope's decay products (in this case
strontium). The object's 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”).
6. 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.
7. 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.
8. 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.
9. 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
