1. Absolute Dating

2. Relative Time vs. Absolute Time Relative: based on a sequence of geological events, does not provide a specific age in years, general dating technique, easier to conduct then absolute age dating. Absolute dating: based on the decay rate of specific elements found in rocks, provides an age in years, more expensive and more time to calculate.

3. Review of Chemistry You need to understand this to “get” absolute dating.

4. Elements An element is a substance that can not be broken down into other substances. 113 known elements (92 occur naturally) All are found on the periodic table of elements.

5. Atom An atom is the smallest possible particle of an element (and still has all the element’s characteristics!)

6. Parts of an atom Electrons: (negative charge) they orbit around the nucleus in energy shells. Protons: (positive charge) located in the nucleus Neutrons: (neutral charge) located in the nucleus.

7. Unstable atoms : Isotopes An atom needs energy to hold together. If there is not enough energy to hold all components together then it can become unstable and neutrons will leave the nucleus. Isotope – an unstable atom with differing amounts of protons and neutrons in the nucleus. When this happens, radioactive energy is released. This energy can kill you if you receive a high enough dose. They eventually will become stable again.

8. Radioactivity Geologists will focus in on these unstable atoms (isotopes) to determine the age of rock. WHY? –These radioactive elements decay/break down into a “daughter product.” –This decay takes place at a known rate called the “Half-life”.

9. Half-life is the time required for one-half of the original number of radioactive atoms to convert to a stable daughter product. The remaining number of radioactive atoms is halved every half-life. ParentProductHalf-Life in Years Uranium-238Lead-2064.5 billion Potassium-40Argon-401.26 billion Uranium-235Lead-2070.7 billion Beryllium-10Boron-101.52 million Chlorine-36Argon-36300,000 Carbon-14Nitrogen-145,715

10. What else should you know… The original radioactive element is called the Parent material. The new stable element it forms is called the daughter product. ParentProductHalf-Life in Years Uranium-238Lead-2064.5 billion Potassium-40Argon-401.26 billion Uranium-235Lead-2070.7 billion Beryllium-10Boron-101.52 million Chlorine-36Argon-36300,000 Carbon-14Nitrogen-145,715

11. ParentDaughter Product Half-Life in Years Rubidium-87Strontium-8749 billion Uranium-238Lead-2064.5 billion Potassium-40Argon-401.26 billion Uranium-235Lead-2070.7 billion Beryllium-10Boron-101.52 million Chlorine-36Argon-36300,000 Carbon-14Nitrogen-145,715 Radioactive Decay Rates

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

13. 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% parent 0% daughter 0 half lives

14. One half-life 50% parent 50% daughter 1 half-life

15. Two half-lives. 25% parent 75% daughter 2 half-lives

16. Three half-lives. 12.5% parent 87.5% daughter 3 half-lives

17. Four half-lives. 6.25% parent 93.75% daughter 4 half-lives

18. 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.)

19. Shape of curve similar for each radioactive isotope

20. Remember…Half Life Continues indefinitely Random and spontaneous Not affected by temperature or pressure Not affected by mass or volume of parent