Thursday, January 25, 2012
L5 - Alternate
January 25 Lecture
Assignment 1 handed out next class
Drew, TA, will hold office hours to help with assignment
Topics for today:
1Exists an Ice Age - How did this idea develop¶
-- !! understand theory and the thought process that went into it
1.11: Louis Agassiz¶
-- Was not the first to theorize Ice age theory
-- He didn't believe it at first.
-- -- he believed in the !!biblical flood - most people did
2Other people played roles¶
-- 1787 - Bernard Friederich Kuhn
-- 1794 - James Hutton - Scotland
-- Jean-Pierre Parraudin
-- Ignace Venetz
-- Jens Esmark
-- Jean de Charpentier
-- Reinhard Bernhardi
-- Note: The swiss (living in mtns) probably first to figure it out
3back to Louis¶
-- !! Why does he get credit for ice age theory?
-- !! other people presented papers (Venetz - systemized, Charpentier - categorized the evidence), but Louis Agassiz was a spokesperson
-- !! Agassiz didn't believe it until Charpentier showed the evidence in person
-- !! still took 25 years before it was widely believed
4Ice rafted boulders¶
-- boulders carried on ice, then dropped when ice melts
-- ice rafting is a real thing, but it doesn't explain boulders
4.12: Revered Prof Will Buckland¶
-- ardent believer that "objective of geology was to confirm the evidence of natural religion and to show that the facts developed by it are consistent with the accounts of creation and deluge recorded by the mosaic writings of the bible"
-- i.e. geologists should show proof that the Biblical flood (Noah's flood) is responsible for the landscape
-- a little eccentric, but one of the most well respected geologists of england at the time
4.23: Initial Evidence¶
4.2.1erratic boulders¶
-- erratic boulders - carried by ice and brought down and dropped somewhere
-- erratic boulders - don't match the bedrocks in their immediate surrounding bedrocks
4.2.2erratic vs ice-rafted boulders¶
-- erratic is rounded -- glaciers are "like a river of ice", so they mix and move the boulders around, and smooth them out
-- ice-rafted are sharp - not caused by boulders
4.2.3striated rocks¶
-- caused by debris inside the glacier moving over the rock and scratching it
4.2.4polished rocks¶
-- the ice and smaller debris will "polish" the rocks
-- the basic weathering process will erode the rocks
-- so, polished rocks are seen when rocks were recently uncovered
4.2.5moraines¶
--- unsorted debris that accumulates at the terminus and sides of glaciers and in the middle where two glaciers meet
-- two glaciers meet - like coming from a fork in the road - when they meet, on the edges of the intersected path, there is all this unsorted debris
-- there is also debris at the "terminal", like everything gets dumped by the glacier "like a conveyor belt"
-- the "till", before the "terminal" is where all the debris is dumped as the glacier melts
-- the "recession" moraine is before the till
-- "lateral moraine" is on the edges
-- the "medial" moraine is in the center
-- they all demonstrate the extent of glaciers
-- Cape Cod is a terminal Morain! (we know because the make-up of the till, it doesn't match the bedrock)
4.3what is Ice Age Theory?¶
-- "Ice age theory states that in the past, glaciers and ice sheets occupied a much larger area than they do today"
4.44: Charles Lyell¶
-- considered himself a pupil of Buckland
-- most renowned geologists of the time (while buckland was just 'respected'
-- developed ice raft theory, in 1833, 4 years before Agassiz said "no, this is all caused by glaciers"
-- in order for the "deluge" to happen in the alps, the water would've had to have happened from somewhere else
-- so many cultures experienced rising sea levels
-- Buckland convinced Lyell by taking him out to some Moraines. Lyell said that ice age theory turned out to explain things that he couldn't explain before
-- a year later, 1860, all 3 of them presented these results at the some geological conference
-- said that tetonic activity could've caused an ice age (colder at higher elevations)
-- James Gykee disproved that tetonic activity was responsible because that sort of tetonic activity would've taken millions of years
-- -- for example, ice land is on a plate boundary, spreading center, it grows an inch every 100 years.
-- -- so, for an uplift to occur would've been impossible
4.5what could explain the ice ages?¶
-- sunspots (their impact is so minimal)
-- dust particles (some said that it created cooling, because they reflect)
-- co2 levels (low levels of co2 could've caused an ice age, but no one knew co2 levels would've dropped)
-- volcanic eruptions (but they're temporal)
4.65: The Energy Source¶
-- the energy that keeps the climate machine running - winds, currents - comes from the sun
-- when sun its directed, the energy is over a smaller area than if it was more tangental - why it is hotter equator than at the poles
4.76: Astronomical Theory¶
-- astrological reasons caused an ice age.
-- a theory that explains the ice age theory
-- 3 aspects of astronomical theory explain the earth's revolution around the sun
-- -- 1) precession of the equinox
-- -- 2) eccentricity of the orbit
-- -- 3) obliquity
4.7.1precession of the equinox¶
-- equinox - 12 hours of daylight, 12 hours of sunlight at every place in the earth (fall and spring equinox)
-- !! solstice -- make distinction between winter and summer solstice around the world
-- !! figure 14 in book
-- takes 21 years to return to the same axis
-- right now, in the winter, we are closest to the sun, but we point away from it
4.7.2eccentricity¶
-- gravitational from sun and moon changes eccentricity of earth's orbit
4.7.3obliquity¶
-- earth axis tilts between 21.5 and 24.5 degrees - over 41 year cycle
-- tropic of cancer and tropic of capricorn - lines of latitude that mark the tropics - 21 deg north and 21 deg south since earth axis is at 21 - the tropics change over cycles
4.7.4relation between the three of them¶
-- eccentricity is slowest, then tilt, and then precession wrt amount of isolation
-- there is a threshold of insulation, caused by these 3 things, that that can introduce an ice age