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RADIOISOTOPE DATING

RADIOISOTOPE DATING . How to determine a fossil’s age. The oldest fossils. Approximately 3.5 billion years old First life forms are probably much older Biologists accept evidence that all organisms that exist today are descended from those first cells nowpublic.comnowpublic.com.

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RADIOISOTOPE DATING

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  1. RADIOISOTOPE DATING How to determine a fossil’s age

  2. The oldest fossils • Approximately 3.5 billion years old • First life forms are probably much older • Biologists accept evidence that all organisms that exist today are descended from those first cellsnowpublic.comnowpublic.com guardian.co.uk

  3. What are fossils? • Remains or traces of once-living organisms • Usually found in SEDIMENTARY ROCK • wind/water form layers of sand and/or silt • It is a quick process – prevents bacteria from decomposing the organism • Usually formed from organism’s hard parts (shells/bones) • Sometimes minerals replace remains – preserves microscopic structure

  4. Other methods • Frozen mammoths • poespirits.com • Insects in amber • don-lindsay-archive.org

  5. Fossils may be: • Imprints – film of carbon left after decay • Molds – impressions have survived (tracks) • Cast – sediments fill mold of decayed organsism • Whole organisms or parts – • bones, plants, feathers • tywkiwdbi.blogspot.com

  6. How do we know how old a fossil is? • Relative age – position in layers of sedimentary rock: bottom – oldest; top – youngest • Absolute age – radioactive isotopes, which have unstable nuclei and a constant decay rate • Half life – length of time it takes ½ of radioactive material to decay • Isotopes – different # of neutrons • 12C = 6p, 6n and stable • 14C = 6p, 8n unstable decay rate of 5730 years

  7. How does radioisotope dating work? • 1) ratio of 14C production in atmosphere assumed constant • 2) organisms take up 14C and 12C at a constant rate • 3) organism dies: 14C & 12C in atmosphere stays constant; 14C in organism decays; 14C & 12C ratio in organism changes • 4) compare 14C /12C ratio in organism to atmospheric ratio • 5) scientists can date organisms up to 50K yrs using 14C • 6) to date older fossils: use 40K, half-life 1.28 billion yrs

  8. Radioisotope dating problem:an organism is found with 2.5g 14C and 40g 12Cstandard atmospheric ratio, 14C/12C is 1:2How old is the specimen?

  9. How does one interpolate?

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