Monday, March 14, 2012

PM - L3

1Review of Industrial Revolution¶

1.1Before¶

• 9/10 lived in countryside
• • simpler, not easier, lifestyle
• • aristrotats - big land owners
• • • distributed raw materials
• Began in England, 1760

1.2Jenny¶

• dozens of roles of thread at once
• this dispaced the former lifestyle
• 20,000 being used

1.3changes in agriculture¶

• focus shifted
• agricultural to industrial economy
• wood and cotton production increased (raw materials)
• aristoracts took over commons, fenced them in, started:
• • crop rotations, irrigation methods, breeding of livestock, pest reduction effort,
• went from feed the people -> feed the people at the factories and provide the raw materials to the factories

1.4steam and coal¶

• steam powered motor: greatest technological advance of the industrial revolution
• co2 emmisions increase dramatically
• onset of cars -> burning oil

1.5population¶

• mass migration from country to city
• some cities were built around the factory, i.e. building cities around coal mines
• population increases dramatically, death rate drops, disease stops, eating better, birth rate increases
• industry - getting paid more,
• more potential mates in city
• garbage collection

2Dating Methods¶

• precision vs accuracy
• precision: 'statistical uncertainty that relates to a physical or chemical measurement - it also refers to the ability of the measurement to be repeated under the same conditions'

• 3.1accuracy: 'degree of correspondance between the age and the dating technique, that is how close the dating technique actually comes to the true age of the item being dated'¶

2.1Radiometric¶

• based on radiactive deacy of certain unstable chemical elements or isotopes
• exampels: carbon-14 to nitrogen-14 (40k yrs ago), potassium-40 to argon-40, uranium-238 to lead-206

2.1.1radio carbon dating¶

• 3 carbon isotopes: 12, 13, 14
• 12: most common
• 13: quite rare
• 14: radioactive
• as long as things are alive, the carbon 14 is constantly being replenished. once the thing dies, the radiactive isotope, ie.e carbon 14, starts to break down. carbon 14 is made through cosmic radiation (from nitrogen 14), it is absorbed by living things, then living thing dies, and then it starts to decay.
• measurement is based on half-lifes: amount of time it takes for half of the radioactive isotopes to decay. c-14 has a half life of 5730 $\pm$ 40 yrs
• • i.e. if there are 100 carbon isotopes in a living thing, then it will take 5730 yrs for 50 of those to decay
• • in another 5730 yrs, we'll have 25 left
• look at ratio between carbon 14 of dead thing and carbon 12 (hm?)

2.1.1.1problems with carbon dating¶

• carbon 14 production varies depending on solar activity, during times of increased sunspots, there is less carbon 14. during low sunspot times, there is increased carbon 14
• isotopic fractionation: natural changes between carbon 14 and carbon 12.
• circulation of marine carbon: mixing rate between surface and deep ocean water is slow. so carbon 14 in the deep ocean decays without being replenished. carbon 14 levels in ocean are low
• contamination of organic sediments: younger or older carbon can be added to sample materials

2.2Incremental Dating Methods¶

• based on regular accumulation of materials to organic tissue or sedimentary sequences
• dendrochronology: trees, lichenometry: lichen growth, varves, ice cores

2.2.1dendrochronology¶

• rings of wood are added to the tree every year
• ring width is a reflection of climate: larger during 'favorable' climate, smaller during less favorable times
• cross dating - cross references several samples to create a longer records. the longest record: 8,000 yr tree ring record
• bristle cone pine - oldest living thing

2.2.1.1problems with dendrochrology¶

• standardization: trees grow faster when they are younger and that different tree species grow at different rates - thus it is difficult to compare for cross dating
• complacent and sensitive rings: certain local site conditions that affect tree growth, which will affect tree ring width. things like the slope of the land, the water retention properties of the soil, the amt of shade that the tree is in, genetic characteristics, ...
• missing or partial rings: do not develop as a result of extreme climatic events - 1816: yr w/out a summer
• false rings: occurs in times of extreme climatic events - can cause another ring to appear, if the summer comes to the end, but the fall is mild, then this could cause a false ring

2.2.2lichenometry¶

• lichen: complex organisms whereby algae and fungi live symbiotically. algae provide carbohydrates, fungi provide a safe growing environment
• lichenomtry - dates newly exposed surfaces using variations of lichen size - direct relationship between the size and the age of the lichen
• could grow up to 4,500 yrs, could be limited to 500 yrs
• • specific purpose: most commonly used to date glacial recession
• • been used to establish glacial chronology during the little ice age

2.2.3varves¶

• sediment that develop in the bottom of lakes and ponds: varves are laminations in lake sediments that develop due to annual variations in sedimentation.
• thick layer during spring/summer, thin layer in fall/winter
• established glaciarl chronology of fenoscandian ice sheet - end of last glacial maximum

2.2.3.1errors with varves¶

• adverse weather could create a false varve, slumping or large floods
• can only be cross referenced locally

2.2.3.2ice cores¶

• annual addition of snow to the mass of ice that already exists
• can use the layers to establish a chronology
• also use oxygen isotopes

2.3Age-Equivalent¶

2.3.1paleomagnetism¶

• refers to changes in earths magnetic fields
• 3 aspects of paleomagtism that can be preserved in the sediment: 1) declination: angle between true north and magnetic north, 2) inclimation: the angle of the dip (up or down) at the horizon between zero at the equator and 90 degrees at the pole, 3) intensity: the strength of the magnetic field

2.3.2tephrochronology¶

• uses tephro deposits from volcanic eruptions (Oraefi, Grimsvotn, Laki).
• indiviual tephras are distinguished by their mineral composition - then know which volcano they came from (like a fingerprint)
• create planes in time

2.3.3oxygen isotopes¶

• these are not radioactive isotopes
• two isotopes: 16 and 18 - oxygen 18 is heavier than oxygen 16
• evaporation favors O16, cuz it is lighter
• O16 is more readily evaporated, during nonglaciar periods, this is not an issue, because the O16 returns relatively quickly to the ocean. however, when ice sheets develop, we have enriched O18 in the ocean because O16 is trapped in the ice sheets. when earth's ice caps grow, the snow is enriched with O16, this in turn enriches the oceans with O18 that is left behind when the O16 is evaporated (and then trapped in the ice sheet)

2.4historical data - documentary evidence (proxy data)¶

• stuff written down by humans - 8 basic types
• 1) ancient inscriptions
• 2) annals, chronicles,
• 3) government records
• 4) private estate records (when you planted crops, etc)
• 5) maritime and commercial records
• 6) personal papers, diaries, letters, correspondence
• 7) scientific or quasi-scientific writings
• 8) fragmented early instrumental records
• this is the only method that can give a daily breakdown of weather
• many are firsthand recordings
• more than one calendar in history - can be a challenge
• very much in use during the little ice age
• closeness in time and space to an event recorded is also important
• some authors didn't see things first hand but are recounting things
• so hard to determine specific date, because of the way things are dated

3Environmental reconstruction - Palynology¶

• the use of pollen spores to reconstruct vegetational change through time in a given area
• usually well preserved in lakes, peat bogs, ...
• issues: abudance of pollen spores produced (it varies), productivity is different for wind vs bee, dispersion varies (water vs land and distance)
• each species gets its own chart through time
• "this was a tundra, then over time, trees came in" <- seen through pollen spores