Radioactive dating

III. Radioactive Dating

• A. Used to find ABSOLUTE age in years.

• B. Radioactive ISOTOPES in rocks DECAY away at a predictable rate.

III. Radioactive Dating

• 1. Carbon-14 – Used to date RECENT, ONCE LIVING things.

• Decays into Nitrogen-14

III. Radioactive Dating

• 2. Uranium-238 – Used to date very old rocks. Decays into Lead-206.

Half Life

• C. The amount of time it takes for HALF of the radioactive isotope to DECAY is called its HALF LIFE.

• 1. Half life DOES NOT CHANGE. (That’s why it’s on the ESRT!)

Radioactive isotopes decay from the “Parent” material into the “Daughter Product”.

Original“Parent” Material

Daughter Product

Each half-life, the amount of atoms gets cut in half.

One half-life.

Two half-lives.

Three half-lives.

Four half-lives.

Don’t worry about the last atom. You start with so many trillions that you never really get there.

(It will just decay and then

they’re all gone.)

Since you don’t know how many atoms you started with, a ratio between parent to daughter will tell you how many half-

lives have gone by.

100% parent0% daughter0 half lives

One half-life.

50% parent50% daughter1 half-life

Two half-lives.

25% parent75% daughter2 half-lives

Three half-lives.

12.5% parent87.5% daughter3 half-lives

Four half-lives.

6.25% parent93.75% daughter4 half-lives