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Optional Field Trip Exercise Changed from March 18 to March 4 Due March 9 at 1:10 pm

Optional Field Trip Exercise Changed from March 18 to March 4 Due March 9 at 1:10 pm. Zuhl Museum Alumni Center, 775 College Av. Geologic Time Scale. Precambrian (4.6 Ga to 540 Ma) Paleozoic (540 Ma to 250 Ma) Mesozoic (250-65 Ma) Triassic Jurassic Cretaceous

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Optional Field Trip Exercise Changed from March 18 to March 4 Due March 9 at 1:10 pm

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  1. Optional Field Trip ExerciseChanged from March 18 to March 4Due March 9 at 1:10 pm Zuhl Museum Alumni Center, 775 College Av.

  2. Geologic Time Scale • Precambrian (4.6 Ga to 540 Ma) • Paleozoic (540 Ma to 250 Ma) • Mesozoic (250-65 Ma) • Triassic • Jurassic • Cretaceous • Cenozoic (65 Ma to the present)

  3. LIFE ON EARTH 3.5 billion year old bacteria and algae

  4. Cambrian explosion of life: 540 million years ago

  5. Trilobites-Paleozoic arthropods Today: 80% of species are arthropods

  6. another Trilobite

  7. Crinoids

  8. First land animals: 365 Ma

  9. Dimetrodon-Permian reptile

  10. End of the Paleozoic Major extinction event:96% of marine life was killed70% land vertebrates killed

  11. End of the Paleozoic

  12. Mesozoic-Ammonites

  13. Mesozoic-Ammonites

  14. Mesozoic-Triceratops

  15. Cretaceous-Tyrannosaurus Rex

  16. End of the Mesozoic Major extinction event:85% of all species died.

  17. Cenozoic-Mammoth

  18. Cenozoic-Sabre tooth tiger

  19. Summary Principle of superpositionPrinciple of original horizontalityPrinciple of faunal successionUnconformitiesTime scaleEvolution of life

  20. Elements with SAME number of protons and different number of neutrons ISOTOPES

  21. SOME isotopes are radioactive... Example: 12C is stable 14C is radioactive, and decays into 14N ISOTOPES

  22. Radioactive decay--constant rate Gives off energy Constant rate of decay gives us a geologic clock Radioactivity

  23. Different elements decay at different rates. The time it takes for HALF of the atoms to decay is the “half-life” Parents decay into daughters… Need both parents and daughters Half-lives

  24. 0 half lives: 100 parents 0 daugh- ters Ratio: 100:0

  25. 1 half lives: 50 parents 50 daugh- ters Ratio: 1:1

  26. 1 half lives: 50 parents 50 daugh- ters Ratio: 1:1

  27. 2 half lives: 25 parents 75 daugh- ters Ratio: 1:3

  28. 3 half lives: 13 parents 87 daugh- ters Ratio: 1:7

  29. Parent Daughter Half Life 14C 14N 5730 yrs 40K 40Ar 1.3 Ga 238U 206Pb 4.4 Ga Half-lives of elements

  30. Pick the best isotope for the job • C: Young, organic material • Ex.: Charcoal, peat • K: Young or old minerals with K • Ex.: Feldspar, biotite • U: Old minerals containing U • Ex.: Zircon

  31. Need to know: Ratio of parent to daughter atoms (measured with Mass-Spectrometer) 2) Half-life of the element (known by experiment or estimated) To get the age of a mineral...

  32. You have 1000 parent atoms to start. After one 1/2 life, you have how many left? If the half life is 700 million years, the rock is 700 Ma. If you have 250 parent atoms left, how old is the rock? Example

  33. ZIRCONS ARE FOREVERZircons have Uranium and makeexcellent geologic clocks 4.364 Ga zircon: Jack Hills Quartzite, Australia

  34. This zircon is about 0.1 mm long

  35. Igneous Zircons

  36. Metamorphic zircons

  37. Zircons in sedimentary rock

  38. Zircons • Igneous: age of cooling of magma • Metamorphic: age of heating • Sedimentary: age of source rocks

  39. Short half life: 5730 yrs. Why is it still here? Cosmic rays convert N to C Photosynthesis and animal food: C exchange with environment After death, C exchange stops, “clock starts” 14C decays and forms 14N Carbon dating

  40. Useful for archeology Shroud of Turin: 3 labs determined an age of 1260-1390 A.D. Applications

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