Lec 7 Bild 3 2011 for Ted

Lec 7 Bild 3 2011 for Ted - BILD3 Lecture 7 - History of...

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BILD3 Lecture 7 - History of Life on Earth I. Radiometric dating II. Changes in the fossil record
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fossil - any trace of organisms that lived in the past; often form in sedimentary rock permineralized fossils trace fossils resin fossils compression fossils cast fossils intact fossils
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“Living fossil”: no morphological change over very long time periods; no close living relatives Ginkgo tree 445 mya horseshoe crab 170 mya
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I. Radiometric dating isotopes - varieties of an element with different mass (different number of neutrons) e.g., 14 C, 13 C, & 12 C, 15 N & 14 N Radioactive isotopes - unstable and decay spontaneously into different element/isotope at a particular, constant rate NOT effected by temperature, moisture, pressure, etc.
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Half-life - amount of time for a parent isotope to decay into half of itself or to make a daughter isotope
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Every isotope has characteristic half-life Different isotopes are used to date different things: uranium-lead: dating age of earth 14 C used for more recent objects (e.g. human artifacts) When does life of an isotope begin? Living organisms have a stable ratio of 14 C / 12 C until they die, at which point 14 C decays into 14 N Fossils sandwiched in sedimentary rock (not in igneous rock) and thus record a longitudinal slice of time.
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14 C
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BILD3 Lecture 7: History of Life on Earth I. Radiometric dating II. Changes in the fossil record
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II. Changes in the fossil record Geological time scale: developed before Darwin based on distinctive fossil taxa originally based on relative ages of fossils (younger rocks lie on top of older ones) some boundaries - mass extinctions
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Background extinction - extinctions that occur at a normal rate (most extinctions) Background extinction rate (fossil record):10-100 spp / year Mass extinction - large percentage of species go extinct within short period of time (global event, broad range of organisms, rapid relative to expected lifespan of taxa)
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Are we on the verge of a 6 th mass extinction?
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This note was uploaded on 01/16/2012 for the course BILD 3 taught by Professor Wills during the Fall '07 term at UCSD.

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Lec 7 Bild 3 2011 for Ted - BILD3 Lecture 7 - History of...

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