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historical geol 2
Dating
| Question | Answer |
|---|---|
| measured by man directly | Time |
| heart beats | Time |
| pendulum swings | Time |
| atomic cyclic vibrations | Time |
| redefined in 1967 | Time |
| 9,192,631,770 vibration cycles of a cesium atom | second |
| rotation of the Earth | day |
| lengthening 1 sec/year | variable |
| 1.5 Ga day | 11 hours |
| 20 hours - based on daily growth rings | 400 Ma day |
| moon around the Earth | month |
| Earth around the Sun | year |
| changes in growth cycles | seasons |
| because the Earth is inclined on its axis | seasons |
| produces growth rings in plants | seasons |
| bristle cone pines in the southwest U.S. | example of growth rings |
| oldest known trees | >5000 yrs. |
| used to calibrate 14C dates | trees |
| produces growth rings in animals | seasons |
| tidal control | claims |
| fish scales | growth rings |
| scallop growth bump | growth rings |
| high erosion, low erosion cycles | varves |
| back to ~15,000 years b.p. | glacial |
| more cycles in the past indicates shorter days in the past | growth rings |
| salt in the ocean | major argument on Earth age |
| 1899,Irish physicist estimated - Earth age ~99.4 million years old | Joly |
| ocean thought initially salty | refuted |
| cooling rate of the Earth | major argument on Earth age |
| middle 1860s -a physicist | Lord Kelvin |
| time necessary to cool from a liquid | Lord Kelvin |
| Earth age 10-20 million | Lord Kelvin |
| radioactive heating discovered 1896 | Becquerel |
| sediment deposition rate since fossils appeared | major argument on Earth age |
| total thickness versus rate of accumulation137,195 0.305m/1000 years | sediment deposition rate |
| >450 million years old | fossil bearing rocks |
| age estimates based on radioactive decay estimates | major argument on Earth age |
| spontaneous breakup of the atomic nuclei of certain unstable substances | radioactivity |
| discovered in 1896 by Becquerel - French physicist | radioactivity |
| isolated energy producers from Uranium | Curies |
| 1898 - Curies discovered Radium, atomic number 88 | Radium |
| radioactive disintegration | decay |
| nuclei of helium atoms | alpha particles |
| 2 protons | helium |
| 2 neutrons | helium |
| electrons | beta particles |
| electromagnetic radiation | (gamma) rays |
| - like light but with a very short wavelength | gamma rays |
| unstable elements | radioactive isotopes |
| spontaneous decay of individual particles is unpredictable | radioactive isotopes |
| decay of half of the atoms is statistically predictable | radioactive isotopes |
| (t1/2) - time it takes for half of the atoms of an isotope to disintegrate | half-life |
| (ln 2)/l; where l = decay constant | t1/2 |
| varies from fractions of a second to billions of years | t1/2 |
| a constant relating the instant rate of radioactive decay of a radioactive species to the | decay constant |
| naturally -in our atmosphere (14C) | cosmic radiation |
| in the laboratory | cosmic radiation |
| absolute dates | Isotopic Dating |
| based on Parent/Daughter ratio when the decay is known | Isotopic Dating |
| requires a closed system | Isotopic Dating |
| no parent or daughter product can leave the system | closed system |
| changes based on particle emissions/capture | Isotopic Dating |
| parent nucleus loses an alpha particle | alpha particle emission (nucleus of helium atom) |
| daughter atomic number is 2 lower | alpha particle emission (nucleus of helium atom) |
| daughter atomic weight is 4 lower | alpha particle emission (nucleus of helium atom) |
| parent nucleus loses a beta particle | beta particle emission (electron) |
| neutron changes to a proton in the nucleus | beta particle emission (electron) |
| daughter atomic number is 1 higher | beta particle emission (electron) |
| daughter atomic weight is the same | beta particle emission (electron) |
| parent nucleus gains a beta particle | electron capture |
| proton changes to a neutron in the nucleus | electron capture |
| daughter atomic number is 1 lower | electron capture |
| daughter atomic weight is the same | electron capture |
| 14C dating - Carbon - Nitrogen - 1/2 life 5,730 years | Carbon dating |
| in atmosphere 14N + e --> 14C + H | Carbon dating |
| 14C + O2 --> 14CO2 into plants and animals | Carbon dating |
| dates 14C/12C after death | Carbon dating |
| normal methods good to ~40,000 years | Carbon dating |
| accelerator dates to ~100,000 years | Carbon dating |
| tree rings used to calibrate dates | Carbon dating |
| 14C production assumed constant through time | Carbon dating |
| 14C disappears at the 1/2 life rate- 14 14 6 C --> 7 N - " decay | Carbon dating |
| Earth age = 4.6 billion | Uranium-Lead dating |
| 1/2 life = 713 million to 4.5 billion years | Uranium-Lead dating |
| dated oldest rocks on Earth | Uranium-Lead dating |
| Zircon U/Pb age - 4.06 Ga | oldest rocks |
| Northwest Territories of Canada | oldest rocks |
| gneissic rock type (Acasta Gneiss) | oldest rocks |
| 1/2 life 48.8 b.y. | Rubidium-Strontium dating |
| discovered 1948 | Potassium-Argon dating |
| 1/2 life = 1.3 b.y. | Potassium-Argon dating |
| 40Ar/39Ar method | Potassium-Argon dating |
| argon loss at 50-200o C | Potassium-Argon dating |
| metamorphism resets the atomic clock | Potassium-Argon dating |
| usually igneous rocks dated- biotite, others | Potassium-Argon dating |
| 1/2 life 106 b.y. | Samarium-Neodymium dating |
| 1/2 life = 13.9 b.y. | Thorium-Lead dating |
| global | MAGNITUDE |
| Cenozoic; specific events in time | TIME |
| CaCO3; water in ice cores; mineral specific | MINERALOGY |
| ice volume and climate | CAUSE |
| evaporation and precipitation fractionation | INTERPRETATION |
| diagenetic problems; organism specific, | ANALYTICAL |
| good | PRECISION |
| cycles - Cenozoic; event specific | UTILITY |
| measured using mass spectrometers | oxygen isotopes |
| rare isotopes | 180 |
| common isotope | 160 |
| lighter 16O more readily | during evaporation |
| heavier 18O is left behind and concentrated | during evaporation |
| ice is light-isotope enriched | during glaciation |
| oceans become heavier | during glaciation |
| in general, marine organisms concentrate 18O | during glaciation |
| some organisms fractionate isotopes | problems with fractionating |
| salinity causes local isotope anomalies | problems with fractionating |
| temperature decreases and organisms concentrate 18O | problems with fractionating |
| first identified by Urey in 1947 | fractionation |
| method established by Emiliani beginning in 1954 | fractionation |
| (1967) estimated paleotemperatures | Shackleton |
| (1973) established $18O to 120 Ka | Shackleton and Opdyke |
| record pushed back beyond 2 Ma | Shackelton |
| (1984) | Imbrie and others |
| established a well dated $18O composite to 780 Ka | Imbrie and others |
| back to 500 k still used today as established in 1984 | Imbrie and others |
| based on 5 marine cores | Imbrie and others |
| showed Milankovitch periods | Imbrie and others |
| precession at ~20 kyr | orbital |
| obliquity at ~40 kyr | orbital |
| at ~100 kyr | eccentricity |
| the state of the atmosphere at a place and time as regards heat, cloudiness, dryness, sunshine wind, rain, etc., | weather |
| the weather conditions prevailing in an area in general over a long period - classically defined as 30 yrs | climate |
| of/or relating to the entire Earth as a planet | global |
| as used by geologists represents the temperature, rainfall and wind over thousands of years | Global Climate |
Created by:
lmulke1
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