Notes on 'Ice Ages: Solving the Mystery' - English CC-BY-NC

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ice age:
- 22,000 yrs ago, sea level fell by 350 ft, 11 million sq miles
- began retreating 14,000 years ago, ended 7,000 yrs ago
- glaciers left moraine

1part 1, chapter 1: Louis Agassiz and Glacial Theory

1.1Louis Agassiz

  • erratic boulders could only be interpreted as evidences of past glaciation, and "at a certain epoch all of the north of europe and also the north of asia and america were covered by a mass of ice"
  • others came to same conclusion earlier, in order: Bernard friederich Kuhn, James Hutton, Jens Esmark, Reinhard bernhardi
  • Charles Lyell argued that boulder-laden icebergs and ice rafts drifted about in the great flood

1.2leading up to Agassiz presenting the theory

1) Jean-Pierre Perraudin (swiss mountaineer) observed rocks that do not weather had scrapes - must've been from the weight of glaciers. compared similarities between southern boulders to recently unveiled boulders
2) Perraudin presented to Jean de Charpentier (naturalist, later advocate), who didn't believe it
3) Perraudin presented to Ignace Venetz (engineer, published results comparing moraine in the south vs moraine on current glaciers), Venetz believed it after some time. No one believed Venetz
4) Jean de Charpentier believed Venetz. Charpentier collected the data
5) Agassiz believed Charpentier when Agassiz visited him

2chapter 2: triumph of the glacial theory

2.1reverand william buckland

  • super smart, super well respected
  • strong supporter of flood theory
  • the purpose of geology is to "confirm the evidences of natural religion; and to show that the facts developed by it are consistent with the accounts of the creation and deluge recorded in the Mosaic writings"
  • flood: 5000-6000 yrs ago - fossil evidence and bible

2.2contradictions in flood theory

  • erratic boulders
  • perhaps boulders in glaciers were transported, but then water must've risen 5000 ft


  • agassiz eventually convinced buckland
  • buckland eventually convinced lyell
  • papers included " glaciers and the evidence of having once existed in scotland, ireland, and england",

2.4james croll

  • "drift deposists contained marine fossils, fossilized sea shells are simply erratic boulders in minature, transported from their submarine homes by glacial ice"

2.5agassiz in america

  • american scientist conrad said "m agassiz attributes the polished surfaces of the rocks in switzerland to the agency of ice, an d the diluvial sctarches, as they have been termed, to sand and pebbles which moving bodies of ice carried in their restless course. in the sammer manner i would account for the polished surfaces of rocks in western new york"


  • mid 1860s, 30 yrs after proposed, both sides of atlantic agreed.

3chapter 3: exploring the ice age world

3.1glacier science

  • lodegement till
  • ablation till
  • glaciers are like a conveyor belt, the bottom melts and the top grows with snow, stuff gets deposited on the bottom of the glaciers
  • terminal moraines
  • 1875: glacier map
  • Laurentide Ice Sheet: Hudson Bay

3.2land depression and ocean lowering

  • during ice age, sea level dropped around 350 ft. land, under heavy ice, depressed
  • when ice sheets melted, sea level immediately rose and land gradually rose - deglaciation resulted in flooding the depressed areas, but eventually those depressed areas rose

3.3loess (silt)

  • when melting occurred at south of ice sheet, silt was deposited by outwash streams
  • these deposits were easily blown away by high winds
  • silt is in farm belt

3.4several glaciations

  • Geikie argued that plant fragments between layers of scottish tills were clear evidence that sustained intervals of warm climate intervened between different glacial ages


  • Amerika was Wetter in the past than it is today

4Part 2 - explaining the ice ages

5chapter 4: the ice-age problem

5.1earth system

  • ocean, ice sheets, atmosphere : all interconnected
  • energy that keeps climate machine running (wind blowing, current moving) is from the sun
  • gain energy: absorption. lose energy: radiation and reflection
  • exact balance between gains and loses: 40 deg north and 40 deg south
  • equator: land and sea absorb energy, days are long, sun is high
  • poles: ice and snow reflect sun energy, sun angle is low
  • winds and currents are negative feedback at poles and equator, keeps temps more constant

5.2radiation feedback

  • growth of ice sheet causes more reflection, causes temps to drop, feedsback

5.3theory 1: decrease in sun radiation

  • in limbo, no way to see how intensity of solar radiation varies through time

5.4theory 2: uneven distribution of dust in space

  • unable to accurately predict concentration of dust in space over time

5.5theory 3: concentration of carbon dioxide

  • co2: transparent to shortwave radiation entering atmsophere, opaque to longwave radiation reflected back in space: insulator
  • unable to find reason why co2 would drop

5.6theory 4: epochs of valances

  • incoming sun is reflected by dust
  • krakatoa in 1883 caused temp to drop
  • hard to test

5.7theory 5: vertical movements in crust (Charles Lyell)

  • James Geikie argued against, said it couldn't happen fast enough
  • fail

5.8theory 6: abrupt sliding of ice sheet into ocean (Wilson, 1964)

  • each surge would cause ocean to be more reflective with ice
  • no evidence of resulting rise is found or of sediment on bottom of ocean
  • fail

5.9theory 7: Ewing-Donn - positive feedback from growth in arctic

  • mositure causes snow and glaciation, but then once enough snow, no more moisture and then deglaciation
  • no fossils to show that arctic was once ice-free
  • fail

5.10theory 8: stochastic method

  • large and possible organized random changes cause random ice ages
  • unable to be tested

6chapter 5: birth of astronomical theory

6.1Revolutions of the sea - Joesph Adhemar (mathematician)

  • earth is tilted and orbit is elliptical, axis is fixed (causes seasons)
  • equinox - daylight hours = nighttime hours
  • southern hemisphere contains more hours of darkness each year than daylight (north hemisphere is opposite). explains antartica

6.2variation in earths axis: precession of the equinox

  • over long periods of time, earths axis shifts
  • 26,000 year period
  • "today, winter begins in north when earth is close to one nod of ellipse, 11,000 years ago, winter began when earth was at the opposite end of the ellipse"


  • glacial climates are function of 22,000 year syclce
  • basic idea: one hemisphere heats, other cools was proven wrong by Humbolt because temp is governed by energy of the year, not of the light during each day
  • adhemar is wrong but important since he brought up astronomical evidence

7chapter 6: astronomical theory of james croll

  • adhemar only considered changes in axis, but croll considered changes in orbit eccentricity
  • previous dude named Leverrier" studied eccentricity
  • Leverrier showed that energy during the year is not a function of eccentricity, Croll showed that energy of each season is a function of eccentricity
  • small change in heat during winter could cause positive feedback (more snow, more reflection, more snow, …)
  • combined with precession theory: "if orbit was circular, precession would have no effect at all on climate,e for each season would then occur at the distance form the sun. winters wouldn't be exceptionally cold or warm, but if eccentricity is large, then there are exceptionally warm winters at one end and exceptionally cold winters at the other end"
  • one hemisphere or the other eill experience an ice age whenever there is an exceptionally long orbit and a winter solstice that occurs far from the sun"
  • Glacial Epochs: intervals which eccentricity of orbit is great enough to cause ice age in some hemisphere
  • Interglacial Epochs: time in-between
  • Last glacial epoch began about 250,000 years ago and ended 80,000 years ago. since then, we've been in interglacial epoch

7.1current effects

  • if equatorial currents were shifting, then that could trigger big changes in climate
  • trade winds cause current direction. trade winds are caused by temp in polar regions

8chapter 7: debate over croll's theory

8.1James Geikie

  • layers of glacial sediment separated by non-ice age peet, proved multiple ice ages occurred (as croll predicted)

8.2mapping time

  • lyell separated earth into periods (from Laurentian to Post-Pliocen/Rent) and eras (Precambrian, paleozoic, mesocoic, cenozoic)
  • modern classification of cenozoic period: Holecene - post ice age, Pleistocene - ice ages

8.3evidence against croll

  • evidence at niagra falls shows that last ice age occurred not 80,000 yrs but 10,000 yrs ago
  • amount of variation in radiation might not've been enough to cause big fluctuations

9chapter 8: through distance worlds and times (Milankovitch)

  • Mil sought to explain mathematically the climates of earth, mars and venus today and in the past
  • 3 orbital properties determine how sun's radiation is distributed: eccentricity of orbit, tilt of the axis of rotation, position of equinoxes in their processional cycle
  • claimed it would be possible to calculate the amount of sunlight reaching the earth at any time
  • teamed up with Koppen, a climeatologist. they claimed that it is the decrease in summer, not winter, radiation that caused an ice age. this is cuz the glaciers wouldn't melt as much, making the annual snow budget positive, learning to glacial expansion, whereas decrease in winter radiation doesn't have much of an effect, because it is already cold enough for snow
  • mil's curves of radiation matched with ice ages geological evidence
  • high latitudes are governed by the 41,000 yr tilt cycle, while low latitudes are governed by 22,000 yr precession cycle
  • accomplished 4 objectives: 1) geometry of each planets orbit and how that geometry has evolved 2) how much solar radiation strikes the surface of each planet during each season at each latitude 3) effect of latitude on radiation 4) calculate how much ice sheets would respond to change in solar radiation

10chapter 9: milankovitch controversy

10.1chamberlin and leverett

  • found evidence of 4 ice ages by looking at thickness and extent of the layers of till and soil

10.2penck and bruckner

  • looking at european erosion, found 4 ice ages. koppen verified this with milaknovitch's cycles - matched well

10.3downfall of milankovitch

  • radiocarbon fossil dating of the Pleistocene era
  • discovery of 25,000 yr old peat layer in illinois shattered milankovitch theory (mil said this was a cold period, but deposits happen in warm periods)

11chapter 10: the deep and the past

11.1deep sea cores

  • by 1963, ericson, ewing, and woolen had made strides in charting climatic history of pleistocene epoch. found 8 containing a boundary clearly defined by changes in the remains of planktonic organisms. this boundary marked onset of first ice age of the pleistocene

12chapter 11: pleistocene temperatures

12.1isotpoic thermometer

  • Emilani: there have been seven complete glacial-interglacial cycles over the last 300,000 yrs


  • multiple factor technique - showed that carribean temp droped by 2 degrees. emilani said 6 degrees

13chapter 12: milankovitch revival

13.1new dating methods - Broecker improved geological calendar

  • coral reef dating
  • 3 high sea level dates: now, 80,000 yrs ago, 120,000 yrs ago aligned with milankovitch warm periods

13.2Matthews of Brown University and Barbados terraces

  • terrace at 80, 120 k years ago matched with Broecker
  • new terrace at 105k years ago was surprising. it meant that more emphasis should be placed on precession effect of Milankovitch, then it could be explained
  • high sea level = intense summer radiation and high orbital eccentricity

14chapter 13: signal from the earth

14.1magnetic timeline

  • Bernard Brunhes - brickyards/magnetic fields
  • Matuyama, japanese scientist
  • there exist a worldwide synchronous event - the switching of magnetic field polarity
  • possible to date any core that had a magnetic signal
  • international community defined the beginning of the plastocene era - 1.8 million years ago. now scientists could use reversals within the pleistocene - arpticularly the reversal boundary that marks the base of the brunhes epoch 700,000 yrs ago- to establish a calendar convering the portion of pleistocene history for which milankovitch had constructed his theory

15chapter 14: pulsebeat of climate

15.1changes of climate where ice sheets didn't exist

  • central europe was a poar desert when ice sheets were larege
  • ice sheets small: chechoslovakia was warmer and wetter
  • boundary between prairie and forest marched back and forth across nonglaciated corridor of central europe


  • 10 reptitions of the soil-loess cycle recorded
  • average length of each cycle was 100,000 yrs
  • Kukla concluded: "cooling phase of climatic cycle lasted much longer than the warming phase. transitions from dusty polar desert phases to deciduous forest pahses were soabrupt that they appeared in the quarry walls as distinct lines"
  • Kukla went back to irregular alpine terraces discovered by Penck
  • Kukla proved Penck and Bruckner were wrong, and therefore Koppen and Wegner who confirmed Milankovitch were also wrong
  • Conclusion: major ice ages of the Pleistocene were spaced about 100,000 rs apart, developed slowly, termined abruptly.

15.3updating Milankovitch theory

  • Mesolella @ Brown University updated Mil's theory to account for 100,000 yr cycle
  • "intensity of radiation during a season is largely controlled by precession cycle and the amplitude is proportional to eccentricity, …
  • ".. when orbit is unusually elongate, the contrast between seasons is greater. so if temp is critical to expansion or retraction of ice sheets, then 100,000 yr cycle must be reflected in record"
  • Mesolla said summer was responsible. Kukla said winter was responsible.

16chapter 15: pacemaker of the ice ages

16.1james d hays

  • with time scale fixed from magnetic reversals, and paleontological techniques available to track ocean currents and estimate ocean temps, deep-sea cores were instruments for monitoring global climate
  • if time scale could be adapted to the Brunhes Epoch, then definitive test could be made agasint milankovitch theory
  • teamed up with Imbrie, who's multiple factor technique was good at dating things


  • goal 1) map history of north pacific and north atlantic oceans during the brunhes epoch
  • 1976: published global map showing temps of the ocean and distribution of glaciers at the height of the last ice age, 18,000 yrs ago
  • a dude named Shackleton and Opdyke sequences 19 isotopic stages within then 700,000 yr Brunhes Epoch
  • spectral analysis showed that 40,000 yr cycle was dominant on Emiliani's isotopic curve - this was the dominant climatic pulse
  • Imbrie showed that 100,000 year cycle was dominant and two smaller peaks indicating cycles of 40k and 20k years long
  • hays finally found 2 silver bullet cores in indian ocean - analsyis of the cores resulting in the following:

16.3recalculation of astronomical cycles

  • 4 distinct cycles:
  • 41,000 yr tilt curve
  • major precessional cycle of 23k yrs, minor precessional cycle of 19k yrs
  • 100k yr cycle corresponding to variations in eccentricty

16.4spectral test - definitive!

  • imbrue recalculated spectral analysis test with the silver bullet core
  • dominant pulse: 100k cycle
  • isotopic spectrum: 43k, 24k, 19k
  • temp-radiolarian spectrum: 42k, 23k, 20k


  • 41k cycle lagged behind variations in axial tilt by 8k yrs
  • 23k cycle lagged behind variations in precession

17part 3: ice ages of the future

18chapter 16: the coming ice age

18.1definition of ice age

  • pleistocene interglacial age is defined as any interval of time during which oak and other deciduous trees are widespread in europe
  • thus, holocene epoch began 10k yrs ago