Dating fossils
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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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Dating fossils

Dating Fossils

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


How old are fossils

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.


What are fossils

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.


Other fossil formation methods

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


How do we know how old fossils are

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


What is an isotope

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


How does dating work con t

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.


What about old fossils

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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