Chapter 6.3 Absolute Dating

Radioactive Decay Everything around us is made of matter. Matter is made of tiny particles called atoms. Draw an atom When atoms in matter are the same, the matter is an element. There are currently 115 known elements. Pg. 794 is the Periodic Table E P & N nucleus

Most elements are stable, but some exist in forms that are unstable elements. Over time, unstable elements become radioactive isotopes (atoms of the same element that have the same number of protons but different numbers of neutrons) Radioactive isotopes break down or decay into stable isotopes by releasing particles & energy in a process called radioactive decay.

Radiometric Dating of Rocks An unstable radioactive isotope is called the parent isotope. Radioactive decay of the parent isotope breaks it down into a stable isotope called the daughter isotope. To get absolute age of rocks, compare ratio of parent isotope to daughter isotope thru process called radiometric dating.

Radioactive elements occur naturally in igneous rocks. Time it takes for atoms in a radioactive element to decay is used to calculate a rock’s age. A half-life of a radioactive element is: amount of time it takes for ½ of radioactive atoms to decay.

After each half-life, ½ the amount of the parent isotope decays. Radioactive Decay After each half-life, ½ the amount of the parent isotope decays. 50% 75% 87.5% 93.75% 100% parent isotope 100% daughter isotope 50% 25% 12. 5 % 6.25% 1 half-life 2 half-lives 3 half-lives 4 half-lives After many half-lives Any living thing has the radioactive isotope C-14 in it. The half-life of C-14 = 5,730 yrs. C-14 radiometric dating can determine how old a bone is by comparing the ratio of parent to daughter isotope.

Determining the Absolute Age of a Rock Each radioactive element has a particular half- life. To date bones and other objects: 1. look for a radioactive isotope in the sample 2. use radiometric dating by comparing the amount of the UNSTABLE parent isotope to the amount of STABLE daughter isotope that is in the sample. 3. determine how much of the stable isotope the sample contains.

Determining Absolute Age After 3 half-lives, how much (%) of the parent isotope & daughter isotope remains? The half-life of the radioactive element Carbon-14 is 5,730 years. If we test for C-14 & find a sample that has been through 3 half-lives, how old is it?

Dating Moon Rocks Does the moon have an atmosphere? Does it have water? How much weathering & erosion takes place on the moon? What type of rock can be found on the moon? Can we use radiometric dating on moon rocks? *Radiometric dating would indicate steady decay since the moon’s formation. The oldest moon rocks date to 4.6 billion years.