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Dating Fossils

Dating Fossils. http://www.uwo.ca/biology/images/undergraduate/trilobite.jpg. How old are fossils?. Oldest fossils – 3.5 byo prokaryotes 1 st life forms are probably older What is evolution? The scientific theory that explains how species change over time

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Dating Fossils

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  1. Dating Fossils http://www.uwo.ca/biology/images/undergraduate/trilobite.jpg

  2. How old are fossils? • Oldest fossils – 3.5 byo prokaryotes • 1st life forms are probably older • What is evolution? The scientific theory that explains how species change over time • Today, species have changed both structurally & physiologically from what they were.

  3. What are fossils? • Remains/traces of once living organisms that no longer exist. • Usually found in sedimentary rock – the formation process is quick, preventing bacteria from decaying the organism. • Usually consists of ‘hard’ parts of the organism. • Minerals may replace remains, preserving microscopic structures.

  4. Other fossil formation methods • Freezing – i.e. Mammoths • Imprints – film of carbon left after decay • Casts – sediments fill mold of organism • Kinds of fossils =- • Whole organisms, bones, plants; feathers; pollen grains • http://images.google.com/imgres?imgurl=http://notexactlyrocketscience.files.wordpress.com/2007/01/800px-microraptor_fossil1.jpg&imgrefurl=http

  5. How do we know how old fossils are? • Relative age – position in layers of sedimentary rocks. • Absolute age – radioisotopes w/unstable nucleii & a constant (known) rate of decay • Half-life – length of time it takes ½ of radioactive material to decay • http://razd.evcforum.net/Pictures/CvE/carbon14decay.jpg

  6. What is an isotope? • Atom with a different # of neutrons • 12C and 13C= 6P, 6N (7N) and are stable • 14C = 6P & 8N, unstable, ½ life = 5730 yrs • How does dating work? • 1) ratio of 14C production/decay in atmosphere is constant • 2) organisms take in 12C & 14C at a constant rate

  7. How does dating work? (con’t) • 3) organism dies – 12C & 14C in atmosphere remain constant • 14C in organism decays • 12C : 14C ratio in organism changes • 4) compare 12C : 14C ratio in organism to atmospheric ratio • 5) scientists can date organisms up to 50K years using carbon dating.

  8. What about old fossils? • Use different isotopes – • i.e. 40K (potassium 40), ½ life = 1.28 billion years • So……. • How is all of this information applied to fossils we find in the dirt? http://images.usatoday.com/tech/_photos/2006/11/07/fossil472.jpg

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