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Earth Sciences

Mid Term #2 Review Lecture 7 : Empirical Measurements Battle in Geology: England 2nd half of 19th Century between 2 people Charles Darwin vs Lord Kelvin Charles Darwin: Evolutionist Observations and common sense Lord Kelvin The Physicist theory Precise Calculations TWO DIFFERENT WAYS OF SCIENCE 1. sea-level fall Benoit de Maillet (1656-1738) o french diplomat and naturalist o Telliamed (published 1748, written as conversation between an Indian philosopher and a French missionary) o supported evolutionary sequence for plants and animals (both having originated in the ocean) o argued that Earth is drying over time because water is lost into space o sea-level drops 3 inches per century o estimated Earth to be over 2 billion year old 2. glacial boulders Edward Lhwyd (1660-1709) best known for his cataloguing of fossils at Oxford Univ. Museum and publishing a book on those also worked on archaeology and language noted that high peaks in Britain support alpine flora (the Snowdon lily Lloydia seratina was named after him) noted rocks (glacial boulders) at Llanberis pass in Wales there are but two or three that have fallen in the memory of any man now living [...]we shall be compelled to allow the rest many thousands of years more than the age of the world calculation: 1 every 20 years, 10,000 boulders Estimate Earth must be more than 200,000 years but boulders could have been thrown down the slopes by the Flood 3. saltiness of the ocean Edmund Halley (1656-1742) prominent scientist, Astronomer Royale comet named after him in 1715 suggested that salt content of oceans could be used to determine age of the world paper was rediscovered in 20th century John Joly 1857-1933, Irish physicist developed radiotherapy to treat cancer patented 1st method for colour photography calculated age of Earth from sodium content in oceans; three (uniformitarian) assumptions: o (1) oceans were freshwater at beginning o (2) sodium supplied at constant rate from dissolution of rocks o (3) no process has removed salt from oceans result: 95 +- 5 million years notes: o estimate accompanied by error estimate ex: 95 million years with an error which has a 95% chance of being less than 5 million years in size error shows precision of true value given inaccuracies of input values (here known inaccuracies from flow of river water, and estimating mean river saltiness) o systematic errors can make result meaningless (here wrong assumptions: first ocean from salty water released by magma; salt does get removed, thick layers of rock salt) 4. accumulationerosion of sediments Herodotus (~484-425 BC) Nile and Red Sea analogous deposition of silt in Nile valley Red Sea would fill up with silt in 5,000 years John Phillips o 1800-1874 o nephew of William Smith geology professor in London and Dublin o calculated how long it took sedimentary rocks to accumulate in Ganges basin o result: 96 million years Charles Darwin 1809-1882 circumnavigated the world on HMS Beagle 1831-36 and observed nature (ex: finches on Galapagos) brought with him the first volume of Lyells Principles of Geology 1859: The Origin of Species o lays out theory of evolution: natural selection occurs slowly,need very old Earth lived ~50 miles NW of Dover erosion of the Weald Dome (in: The Origin of Species) Hence, under ordinary circumstances, I conclude that for a cliff 500 feet in height, a denudation of one inch per century for the whole length would be an ample allowance. At this rate, on the above data, the denudation of the Weald must have required 306,662,400 years; or say three hundred million years. not accurate, but at the time no-one even knew how many digits (thousands, millions, or billions) order of magnitude estimate: hundreds of million Three examples of geologic estimates Darwin 300 million years (minimum bound) Phillips 96 million years (minimum bound) Joly 95 (+- 5) million years note: similar order of magnitude all are lower bounds, not precise estimates aside: much very fundamental science just establishes orders of magnitudes; precise values come later. ex. How many light-years, atoms, neurons, genes? An error of an extra digit (+1000% ) or one less digit (-90% ) is trivial at this initial level of science 5. cooling of Earth Isaac Newton (1643-1727) o mathematician and physicist o one of the foremost scientific intellects of all time o 1687 Philosophiae naturalis principia mathematica o a red hot iron equal to our earth, that is, about 40,000,000 feet in diameter, would scarcely cool in above 50,000 years Georges-Louis Leclerc, Comte de Buffon (1707-1788) studied botany, math, medicine in Angers duel in 1730, left for Dijon; there he met Duke of Kingston with whom he traveled, returned to estate near Dijon in 1732 1749 first volume of Histoire Naturelle (39 volumes in all) 1774 member of Academie Royale Buffon postulated evolution of Earth in 7 stages: 1. formation of molten Earth 2. cooling to hand-hot 3. enveloped in universal sea
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