1. Fossils Remains of organisms (often partially or wholly replaced by “rock”) Bones, teeth, shells, hard exoskeletons Usually in sedimentary rocks (water carries and drops small particles that later formed layered rock) or in volcanic ash sediments

2. Fossil primates rare Habitat

3. Dating fossils Relative dating

4. Stratigraphic Correlation – matching strata from different locations based on chemical similarities between layers E.g., fluorine dating – vertebrate bones/teeth in fluorine containing soils accumulate fluorine over time. More fluorine = older.

5. Law of Superposition Fossils in a lower stratum (layer) of rock are older than those above it. RELATIVE AGE - older   younger

6. Relative Dating

7. Cosmic collisions Evidence of a significant impact, reported in early 1980s Chemical evidence: iridium Cretaceous / Tertiary boundary 95 localities Iridium: rare on earth common in asteroids & meteorites

8. Geological evidence: crater Asteroid 10-15 km dia 65 mya Shift from Cretaceous to Tertiary Epochs marked by dinosaur extinction Significance to us?

9. Absolute dating fossils Radiometric dating based on rates of radioactive decay Natural conversion of an element into a different form of that element (isotope) 1. Rates constant and independent of environmental factors 2. Rates of decay are known 3. Amount of decay from a parent element into a daughter isotope = a geologic clock.

10. 1. Determine ratio of parent isotope to daughter isotope. 2. Convert ratio to number of half- lives elapsed. 3. Multiply number of elapsed half- lives X number of years it takes for a half-life to elapse 4. This is the age estimate of that rock. Radiometric Dating

11. Potassium/Argon clock Decay of 40 K (potassium) produces 40 Ar (argon gas) Potassium bearing rocks. Igneous rock: heat drives off previously accumulated Argon gas Sets the “clock” to zero As rock cools and solidifies, 40 K continues to decay to 40 Ar which is trapped inside the rock.

12. To date the rock, it is reheated and the amount of 40 Ar given off is measured. The ratio of 40 K to 40 Ar permits dating the rock. 40 K has a half-life of 1.3 billion years. In 1.3 billion years, 1/2 of the original 40 K will have been converted to 40 Ar In 2.6 billion years, 1/4 of the original 40 K will remain.

13. Radiocarbon Dating: 14 C  14 N 14 C has a half life of 5,730 years Clock set to zero by death of the individual. Examining carbon-14 to nitrogen-14 ratio in organic remains. Only if organism-derived carbon is present and only back to 50,000 - 75,000 yBP)

14. Fossils found in sedimentary rocks, so fossils usually have relative dates

15. Absolute dating Dendrochronology – matching tree ring width variation Only where trees were present Seasonal climate Dates back to 8,000 - 12,000 yBP)

17. Dating estimates from genetic data Assumption: average mutation rate is constant.

18. pod dinosaurs

19. A bird and some dinosaur relatives