地质中的时间尺度.ppt

Cross-cutting relationships in sedimentary rocks allow is to date the relative timing of events such as faulting and igneous intrusion The Geologic Time Scale …..is still under construction Life began only 2500 Ma Radioactive Dating Methods Mining Uranium Oxide U3O8 U-238 99.3%, U-235 0.7% Milling crushed soaked in sulfuric acid Yellow Cake U3O8 CONVERSION: yellowcake is heated to about 147 F, converted into uranium hexafluoride gas (UF6). ENRICHMENT:The UF6 gas centrifuged heavier U-238 moves outside U-235 concentrates inward Convert to UO2 powder Nuclear Reactors: enriched 3-5% U-235 Nuclear Weapons: enriched 90% U-235 Rubidium exist Rb87 is unstable Rb has an average atomic weight of ~85.5 Rb87 has an atomic mass ~87 Rb87 has 37 protons and 50 neutrons in its nucleus Sr87 is stable Sr has an average atomic weight of ~87.62 Sr87 has an atomic mass ~87 Sr87 has 38 protons and 49 neutrons in its nucleus Source: wikipedia 11-5-2012 Rb37p+50n Sr38p+49n + electron Neutron -------? proton + electron All lead, except 204Pb (1.4%), is the end product of a complex radioactive decay. The most common isotope of Lead is: 208Pb 52.4% (stable) The END ….. For now Understanding Earth Chapter 8: The Rock Record and the Geologic Time Scale Copyright ? 2007 by W. H. Freeman Company John Grotzinger, Thomas H. Jordan Frank Press and Raymond Siever Fifth Edition Concepts you will need to know for the exams CHAPTER 8 Geologic Time Scale Relative age Absolute age Principle of original horizontality Principle of superposition Principle of cross-cutting relationahips Unconformity Angular unconformity Disconformity Half-life Geologic Time Scale Geologists differ from other professional scientists in their view of time. Geologists deal with periods of time that go as far back as the origin of the universe. Before we had the ability to read the “atomic clocks” of nature, geologists used the concept of relative ages. We can see changes in the landscape over time. We can