1. EARTH’S HISTORY RADIOMETRIC DATING

2. TWO Ways to Date Fossils & Rocks
Relative Dating
Determines the sequence of events by comparing rock layers, but cannot tell how long go the events occurred.
Radiometric Dating
AKA – Absolute Dating
Precision of dating by measuring radioactive decay of elements in rock
****Used to measure igneous rock and sometimes metamorphic; NOT sedimentary
Radiometric Dating

3. Radiometric Dating (Absolute Dating)
Radioactive Elements (or Isotopes): unstable atoms giving off atomic particles as radiation to become stable – this is called radioactive decay
Ex: Uranium-238 & Carbon-14
Radioactive dating: Radioactive decay (going from unstable to stable) occurs at a constant rate called a half life. Each radioactive element has its own half life.

4. Half Life - Radioactive Decay
Half life: the amount of time it takes for half the radioactive atoms in a substance to become stable.
Example: Red Dots are radioactive elements
Green Dots are stable elements

5. Ex: of Radioactive Elements (Isotopes)
Uranium-238 has a half-life of 4.5 billion yrs (becomes Lead)
Potassium-40 has a half-life of 1.3 billion yrs (becomes Argon-40)
Carbon-14 has a half-life of 5730 yrs (becomes Nitrogen) – AKA – Radiocarbon Dating – used to date once living material
Which would you use to date a wooly mammoth bone?
Which would you use to date igneous rock that may be the oldest sample on North America?

6. Carbon 14- It’s in You!!!! Carbon atom is in every living thing
Some are radioactive Carbon-14
When an organism dies Carbon-14 begins to decay to stable Nitrogen

7. Carbon-14 Rate of Decay
Every 5,730 years is the half life of Carbon-14

8. Example of Radiocarbon Dating
Scientists were able to determine the age of the Iceman.
5,300 years old
Used the decay of radioactive carbon

10. Practice What percentage of a radioactive element will be left after:
1 half-life ______ half-lives _______ half-lives ______
A radioactive isotope has a half-life of 2,000 years. Using a 10 gram sample. How much will remain radioactive after 2,000 years, 4,000 years and 6,000 years?
2,000 yrs _________ 4,000 yrs ________ ,000 yrs __________