Fossils and rocks can be dated using radioisotopes (radioactive isotopes of chemical elements).
When an atom of a radioisotope decays, it changes to another isotope and gives off radiation.
Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed.
The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
The half-life is 5730 years so it can be used to date samples between 1000 and 50,000-60,000 years old.
Paleoanthropology is an example of the diverse aspects of science, in that it is a data-poor science with largely uncontrollable subject matter.
Paradigm shifts are more common in a data-poor science.
In K-40 dating the proportions of K-40 atoms to Ar-40 atoms is measured.
The half-life of K-40 is 1.26 billion years so it is useful for dating samples over 100,000- 1 million years old. The time it takes for the radioactivity to fall to half of its original level D.3.3 Deduce the approximate age of materials based on a simple decay curve for a radioisotope.