1. Geochronology is the study of time in relation to earth’s existence  Relative Dating  Determines how old a rock is in relation to its surrounding  Numerical Dating  Determines actual age in years Chapter 8: Geological Times

2. Geologic Time - Perspective Differing Views of the Earth’s Age James Ussher (1664): 5,668 years old Biblical Perspective Modern Scientific View

3. Relative Dating Relies on Key Principles such as Uniformitarianism - the present is key to the past Original horizontality  Sediments deposited in horizontal layers Superposition  Youngest rocks are on top (assuming no tectonic activity) Cross-cutting relationships  Cut layer is older than ‘cutting’ rock Faunal succession  Organisms succeed one another in recognizable reproducible pattern Unconformity  Represents a break (gap) in the rock record

4. Earth History

5. Sedimentary Structures

6. An organism buried in sediment

7. 3 Types of unconformities

8. 3 Types of unconformities-contd

9. 3 Types of unconformities-contd.

10. Hypothetical view of early earth

11. Grand Canyon

12. Sedimentary Rock Sequence

13. Hypothetical Landscape

14. Relative Dating-contd. INDEX FOSSILS: Species that had wide geographical distribution, but lived for only a brief period of time Unconformmities: Boundary between 2 layers that are of different age Reasons: – Rock layers removed by erosion – No rock Layers deposited CORRELATION METHODS METHODS OF CORRELATION: Paleontological Similarities Mineralogical Similarities

15. Numerical Dating Method Isotope Dating relies on the rate of decay of radioactive isotopes within a rock Radioactive isotopes have nuclei that spontaneously decay emitting or capturing a variety of subatomic particles Decaying radioactive isotope- parent isotopes decay to form daughter isotopes Half-life- is the time it takes for half the atoms of parent isotope to decay Some radioactive isotopes with daughter products  U-238 => Pb-206; K-40 => Ar-40; C-14 => N-14

16. Unstable atomic nuclei decay

17. Beta Decay – unstable atomic nuclei

18. Electron Capture – unstable nuclei

19. Radioactive Decay

20. Bracketing Ages

21. Factors affecting Isotope Dating Results Isotope dating is more useful for igneous rocks  Clock is set when igneous rock crystallizes locking the radioactive isotopes within its crystal lattice Rock/Mineral must be a closed system  Atoms of parent and daughter are still present in rock/mineral being dated Condition of parent Material  Fracture, weathering and migrating ground water Age of Substance  Enough measurable daughter isotope, use appropriate radioactive isotope

22. Enough Number of Atoms?? Case Study: Half-life = 10 days Time (d)Number of atoms: 0102480 d4 1051290 d2 20256100 d1 301281000 atoms----- 1 atom 4064in 10 half-life 5032 6016 708

23. Loss of daughter isotopes

24. Loss of daughter isotopes-contd.

27. Carbon-14 Method

28. Other Numerical dating method Fission Track  High speed particles emitted during radiation may pass through crystal leaving ‘tears’ within the crystal- the older the rock, the more fission tracks Dendrochronology (Tree-Ring dating)  Annual growth rings Varve- deposited layers of lake-bottom  Paired layers of sediments Lichenometry  Lichens grow at a fairly constant rate Cosmogenic isotopes  Used in dating land features

29. Fission-Track Dating method

30. Correlation of tree ring section

31. Origin of Lake Varves

32. Origin of Lake varves-contd.

33. Age of Lichen

34. Cosmogenic Isotopes-surface exposure dating

35. Geology at a Glance

36. Geological Time Scale Contrasting several dating techniques chronicling Earth’s history to produce a geologic Time Scale Geologic Time Scale- divided into Eons, Eras, Periods, and Epoches Phanerozoic Eon (evidence of life began) divided into three eras  Paleozoic (ancient life) dominated by marine invertebrates  Mesozoic (middle life) dominated by reptiles  Cenozoic (recent life) dominated by mammals

37. Geological Time Scale

38. Sequence of Time scale Eons--- Eras---Periods---Epochs Life on earth ~4.6 byr old Lack of 4.6 byr old on earth – however, moon rocks and meteorite provide a handle on this

39. Extinction Graph

40. METAMORPHISM & METAMORPHIC ROCKS `