Thursday, January 27, 2012

L6

Geo
1/27/2012
Assignment 1 - due feb 17
part 1 - literature search
part 2 - read one of the papers and answer 4 questions in 2 paragraphs (first 3 in one paragraph)

1ice age theory - the players and the proof (part 2)¶

-- 1) recap of the ice age theory players
-- 2) recap of astronomical theory
-- 3) joseph adhemar
-- 4) james croll
-- 5) milutan milkanovitch
-- 6) astronomical theory controversies

2ice age theory players¶

-- ! recognize them, know who they are, know their contribution, and their relationship to each other
-- ! also know jean-pierre parraudin, ignace venetz, jean de charpentier, james and archibald geikie

-- jean-pierre parraudin - swiss mountain hunter - weight from glaciers caused striations. he knew this because of contemporary glacier recession
-- ignace venetz - characterized all the glacier movements, he realized that it wasn't just one valley that glaciers occupy
-- parraudin told chaprentier, didn't believe him, but ignace made charpentier believe. carpenter catalogued everything
-- agincy didn't believe de charpentier until charpentier showed him personally. then agincy was the main guy
-- james geikie - disproved that techtonic was responsible for the ice age

3the energy source¶

-- the energy that keeps the climate machine running - that causes teh winds to blow and the currents wtto flow - comes from the sun
-- its all about the sun and the earth spinning

4astronomical theory¶

-- 11,000 years ago, the earth was tilted the other way (winter becomes summer)
-- !3 aspects of astronomical theory (procession of equniox, timing of the quinox; eccentricty of the orbit - is orbit circular or not; obliquity - axis tilt - 41,000 year cycle)
-- !equinox - equal daylight and darkness everywhere
-- !perihelion - the point at which earth is closest to the sun
-- ! aphelion - the point at which the earth is furthest from the sun
-- ! axial tilt - how much earth axis is tilting (away from vertical)
-- ! tropic of cancer and capricorn - changing lines of latitude that shift with the axial tilt , i.e. if the earth is 20 degree tilt, the cancer and capricorn is at 20 degree north and south latitude

5atronomical theory players: joseph adhemar¶

-- variations in the precession caused the ice age
-- worked on jean pierre someones work 100 year earlier
-- since procession affects norther and souther hemishpere differently, adhemar predicted that the northern and southern hemispheres would be out of phase with each other - i.e. winter in northern means summer in southern

6james croll¶

-- precession and eccentricty caused the ice ages
-- speculated that the tilt was important
-- he thought an extra cold winter would cause an ice age to start

7milutin milankovitch¶

-- milankovitch cycles
-- he said that procession, eccentricity, and obliquity
-- summer in the norther high lattitudes was the critical season

8joseph adhemar in depth¶

-- ! figure 14 in book
-- 1842, french mathematician, said that variations in pression caused ice age
-- he said " if hemisphere in precession would have a longer winter (arc length)
-- he knew - earth orbit ellipse, 25 degree tilt, and seasons occur because axis is fixed in space
-- "because there are 168 more hours of daylight in the north hemisphere, and 168 fewer hours of daylight in the souther hemisphere, he believed that the southern hemisphere was caused a ice age, which he said explained the ice sheets in the south. he also said that gravitational pull of sheets did something which was wrong"
-- since axis switches every 11 thous years, ice eage would happen in both hemispheres
-- figure 16 in book - not entirely accurate cuz our calendar is fixed.
-- june 26, something, something, solstice
-- i.e. the solsitice moves around, but the dates don't change. the dates don't change.
-- since the procession affects the northern and southern hemisphere in a different way, the ice agae would happen in different years
-- !he claimed that this was based on the amount of daylight
-- his colleagues overlooked all of the crazy ocean talk
-- but they did examine the astronomical theory of it, which is wrong, because the energy that moves in is balanced "humbolt brought this up, he said "one hemisphere isnot heating up while the otehr is cooling, the average temp is not controlled by the hours of daylight, it is controlled by the average amount of radiation and how it is transferreed - it is always ballanced out on an annual basis. ! radiation balance is balanced."
-- his theory was disproven because he thought extra hours in winter would cause differences in temp, or something
-- adamer had the eccentricty as a constant, which it isn't

9james croll - in depth¶

-- he thought eccentricty and something would cause something
-- "extra cold winters would cause ice age to start because more snow would accumulate"
-- very versitle - got a job as a janitor at the college where he had acess to a library
-- he came across adamar's book in the library, published 25 yrs before
-- croll recognized what adamar's mistake, but he still believed that some astronomical component was responsible
-- adamer had the eccentricty as a constant. croll plotted a curve which showed teh changes in orbit over the last 3 million years. he concluded that the changes in eccentricty (orbit) and showed that it varied
-- croll showed that the eccentricty affects very strongly the amount of radiation recieved by the earth each season,
-- croll said the amount of sunlight favored the amount of snow
-- !!!! croll said " additional snow accumulated reflected the amount of light coming in, positive feedback"
-- "if winter occurs when earth is close to the sun, then winter will be warmer, less snow, no ice age. if further, then ice age
-- today, eccentricty is about 1%.
-- if earth is close to sun, no ice age
-- if earth is far from sun and northern ice age is pointing away, then ice age (!! aphelion), if northern point towards, then no ice age (!! parahelion). because the ice sheets grew tremendously in the north. !! hemispherical ice age
-- he said oceans also contribute
-- exists a current toward brazil is deflected north - he wanted to know if there was a mechanism to cause the current to flow to the south, moving the warm water/moisture/air away from the north towards the south, hence amplifying an ice age affect
-- croll's theory could be tested by comparing geological data, which is where archibald geiki comes in - croll wrote "cliamte in time"
-- but, if the ice ages occured in tandem in both hemispheres croll would be disproven
-- charles lyell (back in teh picture), did some measurements around niagra falls, came up with estimate of 30,000 years of erosion of years, but in minnasota, 8,000 years, which was much more recent than what croll was saying (croll said 120 or something thousand years ago)
-hence, disproven

10milankovitch¶

-- combined all 3 aspects into ice age theory
-- summer in "northern high lattitudes" was critical season, differed from the others in this regard
-- !! he was going to develop a "mathematical theory capable of describing the climates of earth, mars, venus today and in the past"
-- wanted to calculated the temp at each point in earth
-- 30 years to complete (apparently he completed them)
-- !! he found that the 3 orbital properties determined how the suns radition is distrubted over earths surface (croll was mising axial tilt, but milankovitch didn't)
-- someone had already done these calculations
-- goal #1: describe geometry of orbit and show how it evolved and changed throughout time
-- goal #2: calculate how much solar radiation strikes each surface of the planate for each season, each lattitude
-- he showed climate variations in the tilt were important (more important than croll expected)
-- !! he complteted #2 in a book, groundbreaking for modern climate, it also showed that astronomical variations were sufficient to produce ice ages
-- could calculate amt of sunlight for any time in the past
-- gets the help of some very important scientists (vladamir koeppen/koeppen (responsible for climate zones), alfred vagner (continental drift))
-- vagner was koeppen's son in law, working on a book together
-- vagner said that continets were like floating around in water, but didn't know the mechanism that was driving it
-- when V and K talked to mil, mil was working on goal 3
-- goal #3 - mathematical models for earths past climates
-- milankovitch had to decide which lattitudes to do, since each one had a unique radiation history
-- croll said winter, Mil wasn't convinced. He talked to Vlad, Vlad said "the reduction of heat during the summer was the decisive factor in causing glaciation". i.e. mild summers don't melt the previous winter's snow.
-- milakovitch calculated the curves for going back 650,000 years (3 lines: 55, 60, 65, latitude), calculated the incoming radiation - see fig 24
-- aligned well with german geologists work 25 years earlier
-- fig 24 was published and vagner presented it at a conference - controversy stirred up again1
-- milankovitch did more work on more alltitudes, and published in koeppen's manual of climateology
-- showed that the strength of these effects varied
-- tilt had greatest influence at the poles, but towards equater, 20,000 year procession had the most effect
-- goal #4 - feed back mechanism defined by croll - amount of ice sheets.. something, gave geologists a graph to obtain a estiamte of the lattitude of ice sheet at any time over last 650,000 years, i.e. how far down the ice sheet was down in latitude
-- after this happened, geiki had a team of scientsts look for effects of glaciation
-- Mil said ice ages 115, 72k, somethingk ago. very hard to date ice agaes
-- problems with Milkankovitch: german gelogists said till of each terrace would get older at higher heights, but someone found mollusks that were warm environment creatures
-- also, geologiests said that Mil didn't consider ocean currents
-- mathematicians had problem that 6.7 degree difference than they are today
-- milankovitch was disproven ultimately by radiocarbon dating
-- richard flint from yale, sends them to reuben, results show that the drift from the samples, at 2 glaciations, had supposidly been a single glaciation - Flint and reuben showed that last ice age was 18k-10k years ago.
-- then, peet found in illinois 25k years ago, which only happens in the warm climates