HTML University

Science Dept.

Geology and Soils GEO 100 Notes
Geologic Time

1. Relative Vs Absolute Time

2. Relative Dating
   1. Uniformitarianism: "The Present is the Key to the Past"

   2. Law of Original Horizontality

   3. Law of Superposition

   4. Cross-cutting Relationships

   5. Correlation of Sedimentary Rocks
      1. By Simular Lithology

      2. By Structure and Sequence

      3. By Fossils
         1. Index Fossils

         2. Faunal Succession

         3. Fossil Assemblage

      4. By Walking Contacts Out

3. Absolute Dating
   1. Sedimentation and Absolute Time

   2. Radiometric Dating
      1. Radioactivity

      2. Half-Life

      3. Natural Long Term Radioactive Series
         1. ²³⁸₉₂U -----> ²⁰⁶₈₂Pb ... the Half-Life is About 4.5 Billion Years

         2. ²³⁵₉₂U -----> ²⁰⁷₈₂Pb ... the Half-Life is About 0.713 Billion Years

         3. ²³²Th -----> ²⁰⁸₈₂Pb ... the Half-Life is About 14.1 Billion Years

      4. Date Igneous Rocks and by Cross-cutting Relationships Therefore Date Sedimentary Rocks

      5. The Use of ¹⁴₆C
         1. ¹⁴₇N + n⁰ -----> ¹⁴₆C + p⁺

         2. and later ¹⁴₆C -----> ¹⁴₇N + b^-

         3. ¹⁴C/¹²C Ratio

         4. The Half-Life of ¹⁴C is 5,730 years (5,570 years Std) and is Usable to 50,000 Years BP

4. The Geologic Column and The Geologic Time Scale
   1. The Geologic Time Scale

   2. Geologic Time Scale Analogy