1. Geology Notes Part 12

2. What is absolute dating? any method of measuring the age of an event or object in years radiometric dating radioactive decay.

3. Radioactive Decay and Half-Life

5. What is absolute dating?

6. What is a half-life? It is the time for half the radioactive nuclei in any sample to undergo radioactive decay. After two half-lives, there will be one fourth the original sample, after three half-lives one eight the original sample, and so forth.

7. How are radioactive elements used to date the rocks that contain them? All rocks and minerals contain tiny amounts of radioactive elements. Radioactive elements are unstable; they breakdown spontaneously into more stable atoms over time, a process known as radioactive decay. Each radioactive element decays at its own nearly constant rate. Using a method called RADIOMETRIC DATING geologists can estimate the length of time over which decay has been occurring by measuring the amount of radioactive parent element and the amount of stable daughter elements.

8. Why can C-14 be used to date a 40,000 year old tree, but U-Pb cannot. The half-life of C-14 is 5730 years, so the tree specimen would have undergone 7 half- lifes Uranium to Lead has a half- life of 4 billion years. It would only have experienced a small amount of decay and it would be extremely inaccurate to measure the amount of decay in the material.

9. Geology Notes Part 13

10. What is a geologic time scale? The division of Earth’s history into time units based largely on the types of life-forms that lived only during that period

11. How is the geologic time scale divided? Eons are the largest division Era’s are divided based on the types of life- forms that were present Periods are subdivisions of Era’s Epochs are subdivisions of periods the divisions are based on changes in the fossil record

12. BIG EVENTS IN GEOLOGIC TIME TODAY 100 MYA 600 MYA 1100 MYA 1600 MYA 2100 MYA 2600 MYA 3100 MYA 3600 MYA 4100 MYA 4600 MYA PRECAMBRIAN ERA Lasted 4 billion years 88% of Earth’s History Formation of Earth Formation of Life Oxygen rich Atmosphere

13. Describe the Paleozoic Era. The “Age of Fish” marine life flourished very few land animals until the end largest mass extinction on record ended this period wiping out most invertebrates

14. Describe the Mesozoic Era. The “Age of Reptiles” Pangea splits Dinosaurs flourish first mammals appear mass extinction at the end causes extinction of dinosaurs and other land and sea life

15. Describe the Cenozoic Era. The “Age of Mammals” first sea mammals appear humans appear