1 / 40

Chapter 8: Geological Times

Chapter 8: Geological Times. 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. Geologic Time - Perspective. Differing Views of the Earth’s Age

susananderson
Télécharger la présentation

Chapter 8: Geological Times

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 8: Geological Times 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

  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- thepresent 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: • 0 1024 80 d 4 • 10 512 90 d 2 • 20 256 100 d 1 • 30 128 1000 atoms----- 1 atom • 40 64 in 10 half-life • 50 32 • 60 16 • 70 8

  23. Loss of daughter isotopes

  24. Loss of daughter isotopes-contd.

  25. Loss of daughter isotopes-contd.

  26. 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 `

More Related