ESS102H1 Study Guide - Midterm Guide: Mesozoic, Cenozoic, Neogene

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14 Dec 2010

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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:
Observations and common sense
Lord Kelvin
The Physicist theory
Precise Calculations
1. sea-level fall
Benoit de Maillet (1656-1738)
ofrench diplomat and naturalist
oTelliamed (published 1748, written as conversation between an Indian
philosopher and a French missionary)
osupported evolutionary sequence for plants and animals (both having
originated in the ocean)
oargued that Earth is drying over time because water is lost into space
osea-level drops 3 inches per century
oestimated Earth to be over 2 billion year old
2. glacial boulders
Edward Lhwyd
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
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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
calculated age of Earth from sodium content in oceans; three (uniformitarian)
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
oestimate 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)
osystematic 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. accumulation/erosion 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
onephew of William Smith geology professor in London and Dublin
ocalculated how long it took sedimentary rocks to accumulate in
Ganges basin
oresult: 96 million years
Charles Darwin
circumnavigated the world on HMS Beagle 1831-36 and observed nature
(ex: finches on Galapagos)
brought with him the first volume of Lyell's Principles of Geology
1859: The Origin of Species
olays out theory of evolution:
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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)
omathematician and physicist
o"one of the foremost scientific intellects of all time"
o1687 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
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
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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