Ch 12outline


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Ch 12outline

  1. 1. Historical Geology Chapter 12 Geologic Time
  2. 2. Determining the Age of the Earth <ul><li>_____________ – Greek (570-470B.C.) realized the fossils were the ancient remains of life on Earth.  </li></ul><ul><li>_____________ – Greek, (450 B.C.) dug into the Nile River bank and counted the layers. He determined the Earth to be may thousands of years old. </li></ul><ul><li>_____________– 1779, compared the Earth to a ball of cooling iron. He determined the Earth’s age to be 75,000 years. </li></ul>
  3. 3. <ul><li>Several scientists tried to use the saltiness of the ocean. </li></ul><ul><li>They measured how much salt was being added by rivers and concluded the age to be 90 million years. </li></ul><ul><li>(Salt precipitates out of ocean water when it becomes supersaturated.) </li></ul>
  4. 4. <ul><li>_____________(Lord Kelvin) 1897, used heat conduction combined with actual measurements of the rate of heat flow out of the Earth’s surface. </li></ul><ul><li>He concluded the Earth to be no more than 20-40 million years old. </li></ul><ul><li>His calculations upset the biological science community of the time. </li></ul><ul><li>Most thought the Earth to be much older. </li></ul>
  5. 5. <ul><li>_____________ wrote that he would die unhappy if Thompson’s calculation were correct. </li></ul><ul><li>Radioactivity proved that Darwin was correct. </li></ul>
  6. 6. Discovering Earth’s History <ul><li>_____________, 1869, led an expedition down the Colorado River through the Grand Canyon. </li></ul><ul><li>Rocks record geological events and changing life forms of the past.   </li></ul><ul><li>How is this history revealed? </li></ul><ul><li>_____________ </li></ul>
  7. 7. <ul><li>Geological events are almost meaningless unless they are put into a time perspective.   </li></ul><ul><li>The Earth is much older than anyone had previously thought and that its surface and interior have been changed. </li></ul>
  8. 8. A Brief History of Geology <ul><li>The primary goal of geologists is to interpret Earth’s history . </li></ul><ul><li>In the mid-1600s, _____________ constructed a chronology or time line of both human and Earth history. </li></ul><ul><li>He determined the Earth to be 5,000 years old. </li></ul><ul><li>He believed the Earth to be created in 4004 B.C. </li></ul>
  9. 9. <ul><li>In the 1700s, _____________, published his Theory of the Earth. </li></ul><ul><li>He set forth the _____________. </li></ul><ul><li>Uniformitarianism means that the forces and processes that we observe today have been at work for a very long time. </li></ul>
  10. 10. <ul><li>Scientists know that these processes have not always as observable as they were in the past. </li></ul><ul><li>EX: large meteorites have hit the Earth even though no one saw them happen. </li></ul><ul><li>This leads to the belief that the Earth is very old. </li></ul>
  11. 11. Relative Dating: Key Principles <ul><li>Relative dating tells us the sequence in which events occurred, not how long ago they occurred. </li></ul><ul><li>Nicolaus Steno…… _____________ : states that in un-deformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it. </li></ul>
  12. 12. <ul><li>Principle of _____________ - means that layers of sediment are generally deposited in horizontal position. </li></ul><ul><li>EX: _____________ </li></ul>
  13. 14. <ul><li>Principle of _____________– when a fault cuts through or when magma intrudes other rocks and crystallizes, we can assume the fault and the intrusion are both younger than the rocks affected. </li></ul>
  14. 16. <ul><li>Law of _____________ : </li></ul><ul><li>_____________ – pieces of one rock contained in another. </li></ul><ul><li>Ex: _____________ rocks are formed in streambeds. </li></ul>
  15. 18. <ul><li>_____________ – represents a long period during which deposition stopped, and erosion removed previously formed rocks, and then deposition resumed. </li></ul>
  16. 19. <ul><li>_____________– indicates that during the pause in deposition, a period of deformation (folding and/or tilting) and erosion occurred. </li></ul>
  17. 21. <ul><li>Two sedimentary rock layers that are separated by an erosion surface are called a _____________. </li></ul>
  18. 22. <ul><li>_____________ – means the erosion surface separates older metamorphic or igneous intrusions from younger sedimentary rocks </li></ul>
  19. 23. <ul><li>_____________ of Rock Layers – matching rocks of a similar age in different regions. </li></ul><ul><li>_____________ help with correlation. </li></ul>
  20. 24. Distance is 12 miles between these two rock units
  21. 25. Distance is 17 miles between these two rock units
  22. 26. Fossils: Evidence of Past Life <ul><li>Fossils contain traces of prehistoric life. </li></ul><ul><li>They are important components of sediment and _____________ rocks </li></ul>
  23. 27. Fossil Formation <ul><li>The type of fossil that is formed is determined by the condition under which an organism died and how it was buried. </li></ul><ul><li>1. _____________– fully preserved mammoth, insects preserved in amber. </li></ul>
  24. 29. <ul><li>2. _____________– _____________wood and bones. </li></ul><ul><li>Mineral rich water soaks into the small pores and cavities of the original organism. </li></ul><ul><li>The minerals later crystallize. </li></ul>
  25. 31. <ul><li>3. _____________– common in shelled organisms. </li></ul><ul><li>Similarly carbonation occurs when pressure squeezes out liquids and gaseous components of an organism leaving behind a thin residue of carbon </li></ul>
  26. 32. Fossil Types
  27. 33. Indirect Evidence <ul><li>4. _____________– animal tracks, foot prints, burrows or holes, worm tubs, coprolites or petrified animal dung, gastroliths or gizzard stones </li></ul>
  28. 35. <ul><li>Conditions Favoring Preservation : </li></ul><ul><li>1. _____________– slows decay </li></ul><ul><li>2. _____________– </li></ul>
  29. 36. Fossils and Correlation <ul><li>William Smith in the 18 th century determined that fossils weren’t randomly distributed. </li></ul><ul><li>Each layer contained distinct fossils that may not occur in the layers above and below it. </li></ul>
  30. 37. <ul><li>The Principle of _____________– states that fossil organisms succeeded one another in a definite and determined order. </li></ul><ul><li>Therefore, any time period can be recognized by its fossil content can recognize any time period. </li></ul>
  31. 38. <ul><li>Geologists have identified an order of fossils; an Age of Trilobites, an Age of Fishers, an Age of Coal Swamps, an Age of Reptiles, an Age of Mammals. </li></ul><ul><li>Once fossils were recognized as tie indicators, they became more useful in correlating rocks of similar age. </li></ul>
  32. 39. <ul><li>Index fossils – are….. </li></ul><ul><li>1. _____________ </li></ul><ul><li>2. _____________ </li></ul><ul><li>3. _____________ </li></ul><ul><li>Ex. _____________ </li></ul>
  33. 41. Interpreting Environments <ul><li>Fossils can also be used to interpret and describe ancient environments. </li></ul><ul><li>Ex: Determining where ocean water and shorelines once were, climate, water temperature, corals indicate warm shallow oceans </li></ul>
  34. 42. Dating with Radioactivity <ul><li>Earth is about _____________ billion years old. </li></ul><ul><li>Basic atomic structure </li></ul>
  35. 43. <ul><li>An atom’s _____________ is the number of protons and neutrons in an atom’s nucleus. </li></ul><ul><li>The number of neutrons can vary, and these variants, or _____________, have different mass numbers. </li></ul>
  36. 44. Radioactivity <ul><li>Radioactivity is when atomic nuclei are unstable and spontaneously break apart, or _____________. </li></ul><ul><li>What is an isotope? </li></ul><ul><li>_____________ </li></ul><ul><li>An unstable or radioactive isotope of an element is called the _____________. </li></ul><ul><li>The isotopes that result from the decay of the parent are called the _____________ products . </li></ul>
  37. 45. <ul><li>When the unstable nuclei begin to break down, radioactive decay begins and continues until a stable or non-radioactive isotope is formed. </li></ul><ul><li>Example – _____________ decays until lead 206 (Pb-206) is formed. </li></ul><ul><li>This process has 13 intermediate steps before the stable Pb-206 is reached in the 14 th </li></ul>
  38. 46. Half - life <ul><li>_____________ is the common way of expressing the rate of radioactive decay. </li></ul><ul><li>_____________ is the amount of time necessary for ½ of the nuclei in a sample to decay to its stable isotope.   </li></ul><ul><li>The half - life of U-238 is _____________ billion years . </li></ul>
  39. 48. Radiometric Dating <ul><li>is the process by which the age of rocks and minerals can be determined by using certain isotopes. </li></ul><ul><li>The rates of decay have been precisely measured and _____________ under the physical conditions that exist in the Earth’s outer layers. </li></ul>
  40. 49. <ul><li>Each radioactive isotope has been decaying at a constant rate since the formation of the rocks in which it occurs. </li></ul><ul><li>Example – When uranium is incorporated into a mineral that crystallizes from magma, lead isn’t present from previous decay. The radiometric “clock” starts at this point. </li></ul>
  41. 50. <ul><li>As the uranium decays, atoms of the daughter product are formed, and measurable amounts of lead eventually accumulate. </li></ul><ul><li>The five radioactive isotopes in this table exist in nature and have been useful in determining ages of ancient rocks. </li></ul>
  42. 52. <ul><li>An accurate radiometric date can be obtained only if the mineral remained in a closed system during the entire period since its formation. </li></ul><ul><li>Example: potassium – argon method stems from the fact that argon is a gas and may lead from the sample making the measurement inaccurate. </li></ul>
  43. 53. <ul><li>Cross checking or using more than one radiometric method is used to insure accuracy. </li></ul>
  44. 54. Dating with Carbon – 14 <ul><li>To date recent events, _____________ is used in a method called radiocarbon dating. </li></ul><ul><li>_____________ is continuously produced in the upper atmosphere and is quickly incorporated in carbon dioxide. As a result, all organisms contain a small amount of carbon – 14. </li></ul>
  45. 55. <ul><li>While the organism lives, carbon – 14 is continually replaced. </li></ul><ul><li>The ratio of carbon – 14 to carbon – 12 remains constant.  </li></ul><ul><li>When an organism dies, the amount of carbon – 14 gradually decreases as it decays. </li></ul><ul><li>By comparing the ratio of carbon – 14 to carbon – 12 in a sample, radiocarbon dates can be determined. </li></ul>
  46. 56. <ul><li>Because the half-life of carbon – 14 is only _____________ years, it can be used to date recent geologic events up to about _____________ years ago. </li></ul>
  47. 57. Importance of Radiometric Dating <ul><li>Radiometric dating has supported the ideas of James Hutton and Charles Darwin. </li></ul><ul><li>These dating methods have proved that there has been enough time for the processes we observe to have accomplished tremendous tasks. </li></ul>
  48. 58. Other Dating Methods Used <ul><li>1. _____________ from _____________ trees (3,000 years) </li></ul><ul><li>2. _____________ – which are sediment layers found in glacial lakes (15,000 years) </li></ul>
  49. 59. Bristlecone Pine
  50. 60. Varve
  51. 61. The Geologic Time Scale <ul><li>The geologic time scale divides Earth’s 4.56 billion year history into specific units of time. </li></ul>
  52. 62. Structure of the Time Scale <ul><li>Time is divided into units, which include: </li></ul><ul><li>_____________ – longest unit of time </li></ul><ul><li>_____________ </li></ul><ul><li>_____________ </li></ul><ul><li>_____________ – shortest unit of time. </li></ul>
  53. 63. <ul><li>Phanerozoic eon began 450 million years ago. It means “visible life.” </li></ul><ul><li>There are three eras with in the Phanerozoic. </li></ul><ul><li>1 – _____________ – meaning ancient life </li></ul><ul><li>2 – _____________ – middle life </li></ul><ul><li>3 – _____________ – recent life </li></ul>
  54. 64. <ul><li>Any unit of time is separated by a major change in life forms . </li></ul><ul><li>Each era is subdivided into periods, which are separated by somewhat less significant changes in life forms. </li></ul><ul><li>The Cenozoic is further divided into epochs. </li></ul>