Tips on Dating

Why Date? Different methods of dating will help determine the actual age of a layer of rock or a fossil Scientists look at how much radioactive isotopes are left after years of decay Radioactive isotopes are isotopes that have have a different number of neutrons compared to the original element and give off radiation Eventually, they break down into more stable isotopes through radioactive decayradioactive decay

Parents vs. Daughters The radioactive isotope is also called the parent and is unstable, giving off radiation The parent decays and changes into a more stable isotope called the daughter To figure out the age of a rock or fossil, scientists compare the amount of parent and daughter The more daughter there is, the older the rock or fossil is!

Half-Life By knowing the rate of decay of a radioactive isotope, the age can be determined. This is called its half-life, which is the time it takes for half of the radioactive isotope to decay into the daughter With each half-life, the amount of parent remaining is cut in half The three most common radioactive isotopes are uranium-238, potassium-40, and carbon-14

Common Radioactive Isotopes & Their Daughters Uranium-238 decays into Lead-206. Uranium’s half-life is 4.5 billion years, which means it takes 4.5 billion years for half of the uranium to decay!Uranium-238 Potassium-40 decays into Argon-40. Potassium’s half-life is 1.3 billion years. Carbon-14 decays into Nitrogen-14. Carbon’s half-life is 5,730 years. Since all living things contain carbon, this method is used most often for organisms that lived within the last 50,000 years.

More About Half-Lives After 1 half-life, there is 50% (1/2) parent, 50% daughter After 2 half-lives, there is 25% (1/4) parent, 75% daughter After 3 half-lives, there is 12.5% (1/8) parent, 87.5% daughter After 4 half-lives, there is 6.25% (1/16) parent, 93.75% daughter