Transcript Slide 1
Paleoanthropology Professor Janaki Natalie Parikh [email protected] Paleoanthropology • • • • • Paleoanthropology: prefix paleo, meaning? Ancient, prehistoric…very, very old The study of human fossil remains What is a fossil? Natural record of an ancient life form Conditions conducive to fossilization • Do the majority of living things become fossils? • No. Fossils are RARE & replaced. Most organisms will decompose, leaving no record • What conditions facilitate fossilization? • Encased in lava, volcanic ash, tar, or sap • Freezing: being encased in ice • Dry, desert like conditions (natural mummification, a pause in disintegration) • Being quickly covered in sediment • http://vimeo.com/6581503 • http://www.sciencedaily.com/releases/2010/07/100727065647.htm Contextualizing fossil finds • Relative dating : nothing to do w/… A comparative method, doesn’t provide a specific date • Main technique: stratigraphy, utilizes process of superposition, complicated due to plate tectonics, useful for calibration Relative Dating cont’d • Calibration: comparing measurements obtained from 1 device by another measurement of estab. accuracy • Biostratigraphy: provides approx date by utilizing plant/animal remains from the site w/ well estab. Time frames • Paleomagnetic reversals: Earth’s magnetic field shifts @ irregular intervals, rocks contain evid. of the reversal Chronometric/Isotopic/Absolute Dating • 1) Carbon-14: living thing absorb carbon, isotope (14C, source: cosmic radiation) begins radioactive decay @ predictable rate • ½ life of 5730 yrs (+/-40 yrs): 14C → 14N • After ~5730yrs elapse, ½ of orig. amt. is left & aft. Another 5730 yrs, how much? • ½ of the ½, in other words: ¼, continuing until… • This method is useful through ~70,000 yrs ago Chronometric Dating cont’d 2) Argon-Argon & Potassium-Argon: based on decay of 40K → 40Ar (½ life ~1.25 billion yrs) or of 39Ar → 40Ar • Arg-Arg has mostly replaced Pot-Arg due to higher accuracy • Can only be used to date volcanic rock or ash • Such a long ½ life is an advantage, but also means that the sample must be @ least 500,000 yrs old to use either technique Arg-Arg or Pot-Arg 500,000 y.a. Beg. Of Earth ? Carbon-14 70,000 y.a. CurrentDay Chronometric Dating cont’d • • • • What species originates during this gap? Modern humans: us! Is there any way to get accurate dates for our origins? Yes, by using a combination of relative & chronometric techniques • 3) Dendrochronology: counting tree rings. Useful w/in last ~10,000 yrs. Chronometric Dating cont’d • 4) Thermoluminescence: measures trapped electrons by releasing their energy in the form of light (Useful to ~1 m.y.a.) • Used to date pottery, brick & possibly soil • 5) Electron spin resonance (ESR): detects magnetism of trapped electrons • Used to date: tooth enamel, shells, cave deposits & rocks • Can be used ~1 mya, most useful for dates less than 300,000 y.a. Debate regarding paleospecies • Review criteria for biological species • Can the same criteria be applied to paleospecies? • No. Thus, w/ extinct species, we have to go by similarities in physical characteristics • That’s difficult in a species w/ such variability in superficial physical features/traits Paleospecies Debate cont’d • For ex, say in a few million yrs, intelligent life comes to Earth to excavate • Will they find remains of millions of us? • No, let’s say that the most complete remains they find here are of Rosie O’Donnell & Yao Ming: can we be sure they’d consider these 2 the same species? • Yet, could they successfully mate? Yes. On that note…(if they mated) http://www.youtube.com/watch?v=1Qbt0pEgZOQ Lumpers vs. Splitters Debate • Splitters: require very few differences to draw a species designation • Lumpers: more conservative about species designations, require numerous differences • Vast majority of scientists fall into which category? • Splitters. Why? Due to what factors? • Due to notariety & financial considerations, there is pressure towards splitting