1. CHAPTER THREE Time and Geology

2. Agenda Scale of Geologic Time Organization of Geologic Time Development of Time Scale Principles of Relative Dating Origin of the Phanerozoic Eon Periods Absolute Dating –Early Attempts –Radiometric Dating –Fission Tracking Application of Absolute Dating

3. SCALE OF GEOLOGIC TIME

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5. Geologic Time Scale International Commission on Stratigraphy (ICS) is the official organization that formally defines the Geologic Time Units. International Commission on Stratigraphy On the Geologic Time Scale, boundaries between time units are placed where the Fossil Record reveals important changes in plants and animals. http://palaeos.com – Good Referencehttp://palaeos.com

6. The Geologic Time Scale is generally divided on the basis of the earth's biotic composition, with the Phanerozoic Eon representing the period of Earth's history with advanced life forms, and the Pre Cambrian (Proterozoic, Archean and Hadean Eons) representing the period before advanced life.

7. Organization of Geologic Time

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9. Eons Phanerozoic – Modern Life The following 3 eons were originally classified as eras but have recently been promoted to eons: Proterozoic – Ancient Life Archean – First Life Form Hadian – No Life

10. Eons Originally the Precambrian was divided into a more recent Proterozoic ("age of first life") a preceding Archeozoic ("first life") and an even earlier Azoic (lifeless) era. Currently, Archeozoic and Azoic have been replaced by Archean ("first", "primary") and Hadean the latter term referring to the hellish conditions of the very early Earth.

11. Eras Eras are geological time divisions based on the resemblance of living things to modern living things (Paleozoic Era = Old Life; Mesozoic Era = Middle Life, and so forth).

12. Periods Periods are subdivisions of Eras, based on many things, such as appearance of certain life forms, mountain building or orogenic episodes, volcanism, and so on, and are shorter than Eras.

13. Epochs Subdivisions of Periods are called Epochs, and are based on similar but "smaller" episodes of mountain building or changes in forms of life present.

14. Development of Time Scale

15. f03_03_pg31 Famous Geologists Adam Sedgwick(1785-1873) –Protégé: Sir Roderick Murchison

16. Development of Time Scale The Geologic Time Scale was developed through the independent work of several scientists using relative dating methods. These scientists cross-correlated geologic time units based on fossil evidence. This Time Scale continues to evolve as more information is collected.

17. Principles of Relative Dating Principle of superposition Principle of lateral continuity Principle of original horizontality Principle of cross-cutting relationships Principle of faunal succession

18. f03_02_pg30 Principles of Relative Dating

19. f_pg26 Principles of Relative Dating

20. Time Scale Development Much of the geologic time scale had been constructed prior to the 20th century. The modern Geologic Time Scale is a compendium of both relative and absolute age dating and is used to study the rates of environmental and biologic change occurring on Earth.

21. Time Scale Development Geologists began in the late 1700's to examine fossils from the Phanerozoic Eon. They recognized that the fossils appeared in an orderly fashion in stratigraphic units. The fossilized biota was found to demonstrate rather large changes in overall composition and showed both similarities with, and differences from living taxonomic groups.

22. Time Scale Development The majority of fossil organisms did not match with modern groups, which led to the classification of three major eras within the period of time when the Earth's surface was populated with advanced life forms of the Phanerozoic Eon: –Paleozoic (meaning ancient life), –Mesozoic (meaning middle life), and –Cenozoic (meaning recent life).

23. Origin of the Periods of the Phanerozoic Eon

24. Units of the Paleozoic Era 1830’s: Cambrian – Cambria, Roman name for Wales (Adam Sedgwick) 1835: Silurian – Silures, Celtic Tribes (Sir Roderick Murchison) 1830’s: Ordovician, Taken from upper Cambrian and Low Silurian landforms. 1839: Devonian, Fossil Evidence, Sedgewick & Murchison. 1822: Carboniferous, Coal Beds in Europe and U.S. 1840’s: Permian, Permia – an ancient Russian Kingdom

25. Units of the Mesozoic Era 1834: Cretacious, Rock Outcrops in France, Belgium, and Holland (Chalk), White Cliffs of Dover 1859: Jurassic, Strata of the Jura Mountains of France and Switzerland 1834: Triassic, For trifold division of rocks of this age

26. Units of the Cenozoic Era 1760s/1770s: Tertiary - Giovanni Arduino coined the term based on rocks found in Tuscany, Italy. Early 19 th Century: Quaternary – From deposits in the Paris Basin by Jules Desnoyers. 2008: The International Commission on Stratigraphy (ICS) replaced the Tertiary Period with the following 2 periods: –Neogene –Paleogene

27. Absolute Dating “Radioactive Dating”

28. Early Attempts to Determine Earths Age Biblical Calculation - 6,000 Evolution of Fossils – 80 Million Sediment Deposition Rate:1 Million to1Billion Ocean Salinity – 90 Million Cooling Rate – 24 to 40 Million Radioactive – 4.6 Billion

29. Radoactive Dating –The Alpha, Beta, and Gamma of Decay –Radioactivity Lets Us Date Ancient Rocks with Confidence

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32. The Principal Radioactive Timekeepers –Uranium-Lead Methods –The Potassium-Argon Method –The Rubidium-Strontium Method –Carbon-14 –Fission Track Dating Method

33. Rocks Used in Radioactive Dating

34. Why Igneous Rocks Are Best 1.Igneous rocks crystallize from magma, locking in the atoms of radioactive elements. 2.Igneous rocks minimize the loss of daughter atoms that are a result of the break-down of parent elements

35. Problems With Sedimentary Rocks Mineral Grains become weathered affecting the concentration of daughter elements. Problems With Metamorphic Rocks Changes in heat and pressure affects the concentration of daughter elements.

36. Carbon 14 Dating

37. f03_14_pg41 How Carbon-14 Enters the Environment

38. Carbon-14 Dating Compares the original C-12 concentration to the C-14 Concentration. Fission Track Dating Method Analyzes the number of tracks that are produced from the break-down of uranium- bearing minerals.

39. Fission Track Dating Method

40. Analyzes the number of tracks that are produced from the break-down of uranium- bearing minerals.

41. f03_15_pg42 Fission Track Dating Method

42. Application of Absolute Dating

43. f03_09_pg37 INDEX FOSSILS

44. f03_08_pg37 CROSS-CUTTING RELATIONSHIPS

45. THE END