ENVIRSC 1G03 Lecture Notes - Lecture 17: Geologic Time Scale, Isotopes Of Nitrogen, Cosmic Ray
12 Apr 2016
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Document Summary
Radioactive carbon created in the atmosphere from cosmic radiation. When an organisms dies, radioactive 14c decays to stable 14n. So ratio of 14c to 14n directly related to time of death. 14c is absorbed into the tissues of living organisms. Igneous minerals usually yield the most accurate radiometric ages for rocks. In contrast, sedimentary rocks are often problematic to date with radiometric techniques. Bracketing combines the determination of radiometric dating of igneous intrusions with the principle of cross-cutting. By applying these methods, geologists have dates the entire geological time scale. Mesozoic sediments contain among other remnants of reptiles, dinosaurs, and ammonites. Paleozoic sediments contain shelled marine organisms, primitive fish, amphibians, reptiles. Precambrian divided into the hadean (period between formation of. Earth and oldest known rocks), achaean (primitive bacteria), and proterozoic (multicellular organisms) eons. The oldest known minerals (zircons) were found in australia and are according to their radiometric date- 4. 3 billion years old.
