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Geosciences LibreTexts

1: Introduction to Physical Geology

  • Page ID
    5433
  • Learning Objectives

    After completing this chapter, you should be able to:

    • Discuss the importance of time in the study of Geology
    • Discuss the difference between Relative Time and Absolute Time
    • Apply Geologic Laws in the relative dating of geologic events
    • Use fossils to date a rock unit
    • Use ideas behind radiometric dating to date rock units

    • 1.1: Introduction
      The average introductory geology student’s perception of geology normally involves the memorization of rocks and discussions of natural disasters, but Geology contains so much more. Geology is the study of our planet, which is vital to our everyday lives from the energy we use, to the growing of the food we eat, to the foundations of the buildings we live in, and to the materials that are used to make everyday objects (metals and plastics).
    • 1.2: Geologic Time
      The amount of time that is involved in the carving of the landscape, the formation of rocks, or the movement of the continents is an important scientific question. Different hypotheses about the age of the earth can essentially change our perspective of the workings of geologic events that molded the Earth. If the geologic time is relatively short, then, catastrophic events would be required to form the features we see on the surface of the earth.
    • 1.3: Lab Exercise (Part A)
      Relative time is an important tool for geologists to quickly construct a series of events, especially in the field. In the following section, apply what you have learned regarding relative time to the questions below.
    • 1.4: Faunal Succession and Index Fossils
      Another useful tool in relative dating is fossils which are the preserved remains of ancient organisms found within sedimentary rocks. Organisms appear at varying times in geologic history and go extinct at different times. These organisms also change in appearance through time. This pattern of the appearance, change, and extinction of thousands of fossil organisms creates a recognizable pattern of organisms preserved through geologic time. This concept is called the Law of Faunal Succession.
    • 1.5: Lab Exercise (Part B)
      The use of animals and their preserved remains (fossils) can help build a highly precise time sequence, often with a higher resolution than absolute dating. In the following section, use this principle to answer the following questions.
    • 1.6: Absolute Time and Radiometric Dating
      Absolute time is a method for determining the age of a rock or object most often using radiometric isotopes. Atoms are made of three particles, protons, electrons, and neutrons. All three of these particles are important to the study of geology: the number of protons defines a particular element, the number of electrons control how that element bonds to make compounds, and the number of neutrons changes the atomic weight of an element.
    • 1.7: Lab Exercise (Part C)
      Complete the following chart by calculating the amount of parent isotope remaining for all of the given half-lives, then plot your findings on the graph. Make sure you connect the data points on the graph by drawing in the decay curve.
    • 1.8: Dating Systems
      There are several different radiometric isotopes that are commonly used in absolute dating. Each of these systems has different uses within geology in that they require different materials and can date objects within specific time frames. These systems include carbon-14 dating, uranium dating, and potassium-argon dating.
    • 1.9: Lab Exercise (Part D)
      Using what you learned in the previous section regarding absolute dating, determine the most appropriate methods and the ages of the materials in the following questions.
    • 1.10: Student Responses
      The following is a summary of the questions in this lab for ease in submitting answers online.