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GLG105 Lecture 7-13 Study Notes

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University of Toronto St. George
Earth Sciences

GLG Study Notes Lecture 7: Empirical Measurements Charles Darwin the evolutionist observation (common sense) Lord Kelvin the physicist theory (precise calculation) (the 2 different ways of doing science) Sea-level Fall Benoit de Maillet Book Telliamed 1748 supported evolutionary sequence for plants and animals (both originated from the ocean) said earth is drying over time (water lost into space) Sea-level drops 3 inches per century Estimated age of the earth: 2 billion yrs Glacial Boulders Edward Lhwyd catalogued fossils estimated that one rock fell every 20 yrs Estimated age of the Earth: more than 200,000 (but boulders could have been thrown down the slopes by the flood) so inaccurate. Saltiness of the ocean Edmund Halley 1715 said salt content of the oceans can determine age No estimate age of the earth John Joly irish 1900s - developed radiotherapy calculated age of earth from sodium content in oceans 3 assumptions: 1. Oceans were freshwater originally 2. Sodium supplied at constant rate from dissolution of rocks 3. No process has removed salt from oceans Estimated age of the Earth: 95 +/- 5 million years Accumulation/erosion of sediments Herodotus 450BC studied Nile and Red sea Red sea would fill up with silt in 5,000 yrs John Phillips mid 1800s calculated how long it took sedimentary rocks to accumulate in Ganges basin Estimate age of the earth 96 million yrs Charles Darwin mid 1800s traveled on HMS Beagle and observed nature (finches in Galapagos) Book Origin of the Species 1859 theory of evolution, natural selection occurs very slowly = very old Earth Estimated age of the earth 300, 000, 000 (3 hundred million yrs) Darwin 300 million yrs Phillips 96 million yrs Joly 95 +/- 5 million yrs Very fundamental science establishes estimates preciseness comes later all are lower bounds not precise estimates Cooling of the Earth Isaac Newton Book Philosophiae naturalis principia mathematica 1687 a red hot iron equal to our earth, 40 million ft in diameter could cool the earth in 50, 000 yrs Georges-Louis Leclerc Book Histoire 1749 evolution of the earth in 7 stages: 1. Formation of molten earth 2. Cooling to hand-hot 3. Enveloped in univeral sea 4. Great volcanic activitiy 5. Emergence of land animals 6. Configuration of land masses 7. Humans appear (as for biblical scholars) Book des poques de la nature 1778 built large spheres, heated then measured how long it took to cool Estimated age of the earth 86,667 yrs Adjusted value cool to touching temp. = 22, 911 yrs. Cooling to present temp = 74, 832 yrs William Thomson (Lord Kelvin) physicist (absolute zero, laws of thermodynamics, refrigerator), calculations based on heat arguments and conservations of energy 3 processes which will end over time 1. Earth spins how fast could it spin at birth without breaking apart? 2. Heat felt in mines earth is losing heat & no unknown heat source. 3. Sun still shines earth is not older than the sun sun emits heat and light, suns energy is being used up, sun will extinguish Calculation: maximum age of sun = maximum energy available x rate of energy lost Estimated age of the earth = younger than the sun = 2, 200 yrs P.G. Tait compression of solar gas under its own weight Estimated age of the Earth = less than 20 millions yrs th Two Opposing views at end of 19 Century Geologists: Earth is at least 100 millions yrs old from observations and estimates Physicists: Earth is less than 20 million yrs old from theoretical calculations Lecture 8: Radiometric Age Dating T.C. Chamberlin early 1900s - said the confidence of the physicist is unwarranted Radioactivity Wilhelm Conrad Roentgen late 1800s discovered X-rays won first Nobel Prize in 1901 Antoine Henri Becquerel late 1800s discovered natural X-rays was looking for glowing among naturally fluorescent minerals uranium emits x-rays without external source of energy (left plates out in the sun but it was cloudy so the plates didnt get any energy from the sun but they developed anyways) Marie and Pierre Curie radium gives off heat naturally and indefinitely Calculations of the age of the Earth by cooling must be wrong! Ernest Rutherford 1900s New Zealand 1909 developed model of atom 1902 Rutherfords law of radioactive decay: parent isotope becomes a daughter (1/2 life) said the Earth was alive much before Lord Kelvin thought 1904 age of rocks the amount of helium trapped in igneous rocks must originate from Uranium decay Helium/Uranium ratio Arthur Holmes mid 1900s Edinburgh geochronology 1911 oldest rock = 1,640 Million years plotted data as isochrones lines meet at 3,500 million yrs Estimated age of the Earth: 3,500 millions years Geologists: 3,000 Myrs old Physicists: 2,000 Myrs old (from expansion of the universe) But 1950 Physicists thought 10,000 Myrs old 1958 Allan Sadge proposed big band at 13,000 Myrs ago (from spectral characteristics of stellar clouds) Clair Patterson mid-late 1900s iron meteorites contain lead but no uranium 1953 isolated primeval lead from meteorite Estimated age of the earth: 4,500 Myrs old 1956 paper lead in meteorite is same age as the earth best age of the earth determined from dating of meteorites at UofT Lecture 9: Early Views on Mountains 1. Ancient Greece, Middle Ages til 18 Century Thales 660BC 19yr cycle of lunar eclipse, Earth floats on immense ocean, EQs are wobbles of this island Anaximander 550BC what is holding up the water? Xenophenes 540BC earth and water as 2 fundamental principles hydrological cyclePythagoras 500BC Earth has a central fire Plato and Aristotle 350BC earth is a ball with surface hallows from which passages lead into the earth water can flow back and forth pushing air with it (breathing analogy) moist exhalation causes rain EQs: Earths dry exhalation causes EQs Jean Buridan early 1300s land mostly one hemisphere erosion moves material from land to ocean earth shifts towards ocean hemisphere because centre of earth is centre of universe land becomes ocean Da Vinci late 1400s earth has more water on one side solid parts of earths interior might collapse to centre to maintain balance other side will bulge up EQs solid parts of earths interior might collapse in centre Mountains to maintain balance other side will bulge up Athanasius Kircher mid 1600s teacher of 100 arts German 1637 measured the dimensions of the crate of Vesuvius Book The Underground World 1665 2 systems of channels: water and molten rock Volcanic Activity because of the interaction between water and molten rock Descartes mid 1600s mechanical theory of the universe Book Principia Philosophiae 1644 Earth formed in 4 stages = layered structure Earth made of shells: fire, water, air, rock Oceans and Continents material from inside escaped out during hot weather and did not return cavities formed in the outer shell of rocks cracked and collapsed into water Thomas Burnet Late 1600s thought biblical account always had to be part of science modified Descartes theory crust on top of water Biblical flood caused the collapse of the crust into the ocean Oc
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