A Better Test.

In the 1950s important advances were made in scientists' ability to date fossils accurately. While radioactive dating techniques had been developed before 1950, the new radioactive-potassium dating system devised during the decade was much more reliable.

Decaying Isotopes.

Radioactive dating is possible because all naturally occurring material contains small amounts of radioactive isotopes, which are maintained at a predictable ratio to nonradioactive elements in the same material. When an animal dies, the nonradioactive traces remain stable during decay, but the radioactive traces diminish at a steady rate over a very long period of time. Long after an organism's death, the amount of radioactive element remaining in dead tissue can be carefully measured and compared to nonradioactive material to determine how long it has been since the organism's death.

Carbon Dating.

Standard radioactive dating processes such as carbon dating, discovered in 1948, will not...