Monday, January 1, 2012

Lecture 6

Lecture 6: Friday, January 27, 2012

Assignment 1

Ice Age Theory, The Players and The Proof (Part 2)

Recap of Ice Age Theory Players
• Jean-Pierre Parraudin: Swiss mountain guide; figured out the weight of the glaciers called the striations on the rocks; recognized because on contemporary glacial recession
• Ignace Venetz: characterized all of the glacier movements; realized it was all of the valleys near where he lived in Switzerland which the glaciers had once occupied
• Jean de Charpentier: did not believe him; when Venetz told him then he started to think about it more seriously; classified and organized all of the evidence for Ice Age Theory
• James and Archibald Geikie: brothers; Scottish geologists; James did not believe Lyell’s theory of tectonic uplift cause of the ice age (happens over millions of years); will talk about Archibald today
• Know these people generally well, do not need to know AS well
• Know their contribution and their relation to each other

Recap of Astronomical Thory
• 11 000 years ago when the Earth is in the same spot we were having summer; now we have winter
• The axis is spinning – takes 21 and 26 000 years to make one complete revolution
• Half way through that cycle it will be tilted the other way
• 1. Precession of the Equinox: Timing of the equinox along Earth’s axis (equal daylight and darkness around all of the earth)
• 2. Eccentricity: 100 000 – 400 000 years (Parihelion: the point at which the Earth is closest to the sun; Aphelion: when Earth is furthest to the sun)
• Axial tilt: how much Earth leans relative to the vertical
• Tropics of Cancer and Capricorn: Shift with axial tilt, equal to axial tilt; lines of latitude

Josph Adhemar
• Proposed that variations in the precession caused ice age
• Precession affects Northern and Southern hemisphere in opposite manner
• 1842: Ice age theory was not widely accepted yet
• French mathematician
• When a hemisphere had a longer winter, it would experience an ice age
• Used the Antarctic Ice Sheet as evidence
• Went on to say this had a force that could pull water from the northern oceans to the southern and create a bulge
• When this ice age ended in the S. Hemisphere, it would create a huge ice laden wave that would go north and engulf the lab
• After 11 000 years the ice age switches to the other hemisphere
• Claimed this was based on the amount of daylight

• Average amount of daylight does not control temperature
• Temperature controlled by energy coming in from the sunlight
• Radiation balance

James Croll
• Thought extra cold winter would cause this to start because more snow would accumulate – happens year after year
• Precession and Eccentricity
• Plotted curve that showed changes in earth’s orbit prior 3 million years
• Deduced that ice ages occurred at times when Earth’s path was more elliptical (oval)
• Eccentricity represents amount of radiation received by Earth each season
• If winter occurs when Earth is close to the sun, winter is warmer and there will be no ice age
• Northern Hemisphere is pointing to the sun = no ice age (increased radiation)
• His theory could be tested by comparing geological information with his astronomical theory

Archibald
• Gave Croll job at Geological Survey of Scotland
• This book got the debate going again for 30 years
• Brothers came out in support of his theory
• Geologsts wanted to see if glaciation occurred in tandom – this would disprove Croll’s theory
•

Milutan Milkanovitch
• Combined all three aspects
• Summer in the northern, high latitudes was the critical season
• Differed because the other two said it was winter
• How much solar radiation strikes the planet at each season, at each latitude
• Showed climate affects variation in angle of tilt was more important than Croll had suggested
• Matheamatical calculations stronimical variations were sufficnet to produce ice ages
• 55, 60, 65 lines of latitude: calculated incoming radiation
• Did calculations for 100 days from morning until night
• Figure 24 in Slides
• Graph aligned well with german Geographers graph 15 years earlier, terracing on the rivers
• The til at each terreace would be progressively older
• If this was an ice age, how would a mollusk grow here?
•

• Vladimer Koeppen: Classified Earth’s climate zones; URL is on Slides! (Active Map)