Dating Fossils.ppt
- 3. I. Relative Dating • Relative Dating is when you give the age of a rock or fossil compared to another rock or fossil. – Example: Rock A is OLDER than Rock B. – An actual age in years is not determined.
- 4. II. Rules of Relative Dating 1. Law of Superposition: When sedimentary rock layers are deposited, younger layers are on top of older deposits.
- 5. Rules of Relative Dating 2. Law of Original Horizontality: Sedimentary rock layers are deposited horizontally. If they are tilted, folded, or broken, it happened later.
- 6. Rules of Relative Dating 3. Law of Cross-Cutting Relationships: If an igneous intrusion or a fault cuts through existing rocks, the intrusion/fault is YOUNGER than the rock it cuts through
- 7. Rules of Relative Dating 4. Law of Lateral Continuity: states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
- 8. 4. Law of Lateral Continuity
- 9. • Nicolas Steno (Danish scientist), in his Dissertationis prodromus of 1669 is credited with four of the defining principles of the science of stratigraphy.
- 10. Index Fossils • Some species of organisms only lived for a short period of time before they became extinct. If you use radiometric dating to get an age for the fossil, then you know that the rock the fossil is found in is also that age. Trilobite: Index fossil for the Paleozoic Era Age: 590-250 mya
- 11. Absolute Dating • Determines the actual age of the fossil • Radioactive isotopes carbon-14 (The half- life of C-14 is only 5,700 years), potassium-40 (1.3 billion years), and U- 235 (U-235 decays to Pb-207 with a half- life of 704 million years.) • Considers the half-life or the time it takes for half of the atoms of the radioactive element to decay
- 12. • The decay products of radioactive isotopes are stable atoms.
- 14. • What is the limit in using carbon-14 as a measure to determine a fossil’s age?