Monday, February 3, 2012

L7 - Alternate

Feb3
Review from last time.

1revival of Milankovitch¶

1.1shoreline terraces¶

-- shoreline terraces happen in the tropic zone
-- each terrace was tested with thorium dating
-- broecker led the effort
-- the dates he collected from terraces didn't align with milankovitch's calculations
-- 125,000 years ago, we had high sea level terraces (less ice)
-- sea level drops cuz of glacial period (at 105,000 yrs), but also land is being uplifted
-- terraces formed by the weight of the water

1.2geologists needed a concrete date to compare the data from around the world to the same data¶

-- Bernard Brunhes discovered that when bricks cooled, the iron rich material aligned with the magnetic field
-- Brunhes finds this in lava
-- notices that in ancient lava, the poles are aligned in opposite direction
-- Japanese geologist Matoyama discover same thing
-- others tried to explain this away by showing that they could do self reversal in the lab
-- lava flows provided correlation technique needed: potassium argon dating, that works well in lava. found specific date when field polarity changed
-- now they have universal date
-- geologists want to know if they can find magnetic reversals in deep sea cores
-- john hayes picked high altitude cores
-- 'date for pliestoscene'
-- applying cold water dating to the oldest cold water fossil dated the start of the 'pliestoscne'

1.3loess¶

-- "wind blown sediment, up to 20% is clay, the remaining 80% is split between sand and silt. it is derived from glacial outwash streams"
-- cockla found this.
-- 1968, cookla finds 5 magnetic reversals.
-- he tears apart old river system
-- found a way to account for the 100,000 yr cycle that is from this evidence
-- they believe that eccentricity plays a part, and the intensity of radiation in a given season is controlled by the procession and the amplitude of the procession is proportional to the eccentricity
-- cockle believes croll (winter), and grad student believes milankovich (summer)

1.4CLIMAP¶

-- john hayes, john imbrie
-- 2 main goals, 'map earths climate during last ice age', and something else
-- deep sea cores, a variety of dating methods, calculations,…
-- climate oscillations occur as 4 distinct cycles: 100,000 cycle for eccentricity, 40,000 yr cycle for axial tilt, and 2 something cycles for the procession
-- imbrie showed that the ice sheets lagged 8,000 yrs behind axial tilt
-- confirmed astronomical forces caused the ice age

2climate and environmental changes as a result of the ice ages¶

2.1dates¶

-- earth 4.6 billion yrs old, oceans 3.8 billion yrs old
-- 65 million yrs ago, KT boundary, extinction of dyonosours
-- 1.8 million yrs ago, Pleistocene
-- end of Pleistocene, beginning of Holocene. Holocene begins 10, yrs ago with the recession of the ice sheets

2.2holocene¶

2.3recession of the lorenchint sheet¶

2.4ice ages have changed the global biospheres¶

2.5landscape changes and new land features from receding lorientian ice sheet¶

-- !terminal moraine: pile of till that marks the furthest extent of the ice sheet or glacier
-- !kettle ponds: spots were icebergs have been carried by the outwash streams and they land. i.e. melted icebergs that formed a lake
-- !esker: form where streams flowed under the glaciers, like tunnels, then as glacier receded, the deposit left by streams (sand, rocks) stayed.
-- !drumlin: almond shaped mound of till. formed in response to a receding glacier, or highly pressurized subglacier flooding

2.6alpine glaciers¶

-- !Arete: thin ridge of bedrock usually scoured on both sides by a glacier
-- !Horn: rock outcrop that has been carved to a point by glaciers
-- !Cirque: valley head that has been carved out by a glacier to a rounded pot or bowl shape
-- !Hanging values: values enter the glacial trough. often have waterfalls
-- !glacial lakes: form in cirques or behind or between or behind recessional moraines
-- !terminal, medial, recessional, lateral moraines

3eustasy and isostasy¶

4eustasy¶

-- is a global rise in sea level which occurs due to fluctuations in the polar ice caps
-- global scale
-- as sea level rises, florida will disappear

5isostasy¶

-- can also be referred to as isostatic rebound
-- refers to the rebound of the lithosphere (land) in response to the weight of the ice sheets begin removed. local event based on the crust response to receding ice sheets

6champlain sea¶

-- lake champlain used to be salt water
-- land kept rising, flushed out salt water

7cordilleran ice sheet¶

-- jo(umlats)kullhlaup
-- columbia river basin
-- hugefloods.com/LakeMissoula
-- scours the land tremendously

8black sea¶

-- many cultures have giant floods in history

9Humans on the move¶

10homo sapien migrations¶

-- environment 35,000 yrs ago in europe is very different than it is today

11"refugia"¶

-- area untouched by climate change
-- becomes stores for plants + animals - migrate into these areas

12south america was the last continent that humans got to¶

-- 10,000 yrs ago

13islands¶

-- hawai'i wasn't populated till 300 AD
-- 1500BC in Fiji
-- New Zealand - 1000 AD (vikings adapting christianity)