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origins of humanity - midterm 2 study guide

origins of humanity - midterm 2 study guide - Origins of...

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Origins of Humanity: Midterm #2 This is NOT everything!! Note cards are made for bold-face words and other facts Chapter 9 Geologic time scale : divided into nested sets of time; eons, eras, periods, epochs -eons: Precambrian and Phaneorozoic -eras of Precambrian: Hadean, Archaen, Proterozoic -eras of Phaneorozoic: Paleozoic, Mesozoic (mammals arose), Cenozoic -periods of Mesozoic: Triassic, Jurassic, Cretaceous -periods of Cenozoic: Tertiary, Quaternary -epochs of Tertiary: Paleocene, Eocene, Oligocene, Miocene, Pliocene -epochs of Quaternary: Pleistocene, Holocene we live Relative dating techniques : tell us how old something is in relation to something else w/ out applying an actual chronological age - lithiostratigraphy - using the characteristics of the rock layers themselves to correlate across regions - tephrostratigraphy - the identification of a volcanic ash by its chemical fingerprint or major, minor, and trace elements -ashes = tephra - biostratigraphy - making correlations based on biological organisms; we can use biological organisms found in rocks to correlate age between sites and across regions and thus to provide age estimates for fossils found at those sites -rodents- good biostratigraphic indicators of age -chemical techniques w/in sites- include analysis of the fluorine, uranium, and nitrogen content of the fossils -bones and teeth take up elements as they lie buried -techniques not useful between sites (only w/in sites) Calibrated relative dating techniques : include regular or somewhat regular processes that can be calibrated to a chronological age if certain conditions are known -obsidian hydration -amino acid racemization - paleomagnetism - sequence of changes in the magnetism of ancient layers - geomagnetic polarity time scale (GPTS) - records the orientation of sediments from different intervals -based on paleomagnetism that has been pieced together -divided into 2 long intervals of similar polarity = chrons Chronometric dating techniques : provide a chronological age estimate of the antiquity of an object in years before the present; rely on clocks to measure time annual growth rings, recording of annual glacial retreat, radioactive clocks for distant events
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- radiometric dating - relies on natural, clocklike decay of unstable isotopes of an element to more stable forms -Carbon-14 (^14C, or radiocarbon)- most famous radioactive clock - potassium-argon (K-Ar) - measures the decay of the isotope ^40K (potassium) to ^40Ar (argon) and requires potassium-bearing minerals, such as feldspars, to work -useful in dating the timing of the eruption of volcanic sediments because heating during the eruption drives all argon gases, and at the time the volcanic material cools, the clock is effectively set to 0 -entails 2 samples of the same rock (potassium exits as a solid, argon is a noble gas) - argon-argon (^40Ar/^39Ar)- a refinement of the K-Ar method tat allows the use of smaller samples, sometimes even a single crystal, and a greater control over the measurements and possible sources of sample error -both isotopes of argon are measured as gases -
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