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Evolvovision by Ray Troll

Evolvovision by Ray Troll. We will finish Geologic Time on Monday. The window for Test #2 starts Monday afternoon, And closes Sunday evening, February 26. Chapters 5, 6, 7 & 8: Sedimentary Rocks Metamorphic Rocks Structure of Rock Bodies Geologic Time. Succession in Landscape Development.

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Evolvovision by Ray Troll

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  1. Evolvovision by Ray Troll We will finish Geologic Time on Monday. The window for Test #2 starts Monday afternoon, And closes Sunday evening, February 26. Chapters 5, 6, 7 & 8: Sedimentary Rocks Metamorphic Rocks Structure of Rock Bodies Geologic Time

  2. Succession in Landscape Development St. George, UT We won’t finish Chapter 8 until Monday. Test 2 window starts Monday morning and goes to Sunday, February 26. 2 Inversion of topography-- what was low becomes high

  3. Succession in Landscape Development St. George, UT 3 Inversion of topography-- what was low becomes high

  4. Which is older? A. The higher surface B. The lower surface B A

  5. Succession in Landscape Development Younger valley fill Present course of Virgin River Older valley fill 5

  6. Skeptical about the river-to-ridge topographic inversion? Skeptical scientists think of ways to test hypotheses. In Science, it’s hard to “prove” something. Conclusions are almost always tentative. The best ideas survive many tests; ideas that fail a good test are replaced with better ideas. To test the inversion of topography hypothesis, think about this: What should lie directly under the basalt?

  7. To test the inversion of topography (river valley-to-ridge) hypothesis: What should lie directly under the basalt? Granite Limestone Wind-blown sand dunes Rounded cobbles Tilted strata

  8. basalt Stream cobbles 8

  9. Enough of relative dating. Next subject: absolute dating (putting numerical dates on geologic events) Varves-pairs of thin sedimentary layers deposited on the floor of a lake in a single year. Coarse material records spring runoff; fine material accumulates in winter when lake surface is frozen and lake water is very still. Counting the varves gives you the number of years of accumulation (about 25 years for the layers shown).

  10. Studying annual layering in snow on Greenland Ice Cap helps in the interpretation of ice cores.

  11. Bristlecone Pines

  12. Snake Range, NV White Mountains, CA

  13. Radiolab (bristlecone story starts at 15:00 min.) The stump of what was once the world’s oldest living tree. http://en.wikipedia.org/wiki/Prometheus_(tree)

  14. Growth rings in trunk of bristlecone pine

  15. How does the age of the tree compare to the age of the mountain, or to the age of the rocks that make the mountain? 10 million year-old mountain ~2000 X 5,000 year-old tree = X 1 billion year-old granite ~200,000 X Age of Earth ~1,000,000 X (= 1 mm/yr

  16. All carbon atoms have 6 protons. The most common isotope of carbon has 6 neutrons; 14C has 8 neutrons. 14C is radioactive, with a half-life of 5730 years.

  17. yBP=“years before present”

  18. BP = years before present Pretty good until about 3000 years ago Match of calender ages of tree rings (horizontal axis) against carbon dates from wood within the rings (vertical).

  19. If technique were perfect, data would plot along this line Match of calendar ages of tree rings (horizontal axis) against carbon dates from wood within the rings (vertical). Radiocarbon dates are too young; can be 1000 years off; a calibration is now applied to all radiocarbon dates.

  20. If technique were perfect, data would plot along this line Error probably due to changes in Earth’s magnetic field, which change rate of C-14 generation in upper atmosphere. Sunspot cycles make the wiggles. Match of calender ages of tree rings (horizontal axis) against carbon dates from wood within the rings (vertical). The Trees that Rewrote History

  21. Production rate of 14C depends on flux of cosmic rays (which changes slightly with changes of Earth’s magnetic field (which partially shields Earth from the rays) and with solar changes (sun spot cycle). All carbon atoms have 6 protons. The most common form of carbon has 6 neutrons; 14C has 8 neutrons. 14C is radioactive, with a half-life of 5730 years.

  22. from Diamond (1992) The Third Chimpanzee, p. 49 14C is useful for dating events as old as 40,000 years ago.

  23. The Nuclear Arms Race and 14C Test ban treaty Atmospheric testing of H-bombs begins (Nov. 1, 1952) ?

  24. What about geologic events older than 40,000 years?

  25. Chart of the nuclides How many isotopes of potassium?

  26. How many isotopes of potassium? 1 2 3 12

  27. Chart of the nuclides These are useful for absolute dating Potassium has 12 different isotopes; only 3 are found in Earth’s rocks today Potassium-40 is a major contributor to Earth’s geothermal heat -when it captures an electron, it changes to Argon and releases energy

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