Test 3 Notes- Biological Anthro

Test 3 Notes- Biological Anthro - Test 3 Notes Chapter 12:...

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1Test 3 Notes Chapter 12: Primate Origins and Evolution The Study of the Fossil Record: Relative Dating: determines which fossils are older then others but not their exact date Chronometric Dating: determines the exact age of fossils or sites Relative Dating Methods: Stratigraphy- cumulative buildup over time of the earth’s surface; the older a site is, the deeper it is under the earth’s surface, lower layers are older; do not know how old the fossil is or the exact amount of time between two fossils, but you know which is older in geologic time Biostratigraphy- method in which sites can be assigned an approximate age based on the similarity of animal remains with those from other dated sites; measure of how old a site is using previously known knowledge about a similar site Paleomagnetic reversals- magnetic field of the earth runs between two poles and the polarity of this field changes at irregular intervals of long periods of time; sedimentary rocks preserve a record of these changes Chemical Methods: Fluorine Dating- looks at the accumulation of fluorine in the bones; allows us to see if two bones found at the same site are the same age Chronometric Dating: -radioactive decay is constant for a given radioactive atom no matter what chemical reaction it is involved in; if we know a certain element decays into another at a constant rate and if we can measure the relative proportions of the original and new elements in some object, then we can mathematically determine the age of the object Carbon-14 Dating- uses the constant rate of decay to determine the age of materials containing carbon; radioactive decay emits particles that can be measured; example: rate of emissions expected from a living organism (15 particles per minute per gram of carbon); if a sample is analyzed and emits 3.75 particles per minute then two half lives have elapsed (15/2 = 7.5, 7.5/2 = 3.75); 5,730 * 2= 11,460 years; if the sample was analyzed in 2005 then its date would be 11,405 because that is 55 years after B.P. (1950 is considered the “Present”); bone tends to not be reliable because there are chemical changes during fossilization; charcoal is the best material to use; this is useful only for sites over the past 50,000 years Half-Life- average length of time it takes for half of a radioactive substance to decay into another form; c14 has a half-life of 5,730 years Potassium-argon Dating- based on the half-life of radioactive potassium (1.31 billion years) decaying into argon; used to date volcanic rock that can be older than 100,000 years old; volcanic rock is best because the heat generated by volcanic eruptions removes any initial argon gas so any found is the result of radioactive decay Argon-argon Dating- decay of an argon isotope in to argon gas; used with very small samples, i.e. a single crystal Dendrochronology- trees accumulate new rings inside for every period of growth; by looking at the width of the rings, archaeologists created a master chart of tree ring changes; if there is a log
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Test 3 Notes- Biological Anthro - Test 3 Notes Chapter 12:...

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