GEOL 1101 Lecture Notes - Lecture 10: Zircon, Hornblende, Absolute Dating
3 Nov 2016
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Relative: putting things in order from oldest to youngest. Uniformitarianism - the present is key to the past. Marker beds a geological deposit that is (cid:498)dateable(cid:499) and can be traced over large areas. A volcanic ash bed is from large eruptions like mt. St. helens, where the ash settles among a large area. Based on radioactive decay products (mainly found in igneous and metamorphic rocks) Radioactive isotopes: occur in garnets, micas, feldspars, hornblende, uranium bearing minerals like zircon and uraninite. The temperature at which the radioactive decay process starts in certain minerals (magma cooled enough for the minerals to start the decay process into other minerals) Based on igneous and metamorphic minerals after they have reached (cid:498)blocking(cid:499) temperatures. Parent uranium : daughter lead (u to pb) C14 mostly works for organic material no older than 75000 years because this isotope has a short half life of about 5700 years. C14 is produced in the upper atmosphere.
