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: http://zebu.uoregon.edu/1996/ph123/l13i.html
Дата изменения: Tue May 21 02:23:11 1996
Дата индексирования: Tue Oct 2 02:56:33 2012
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Break up of Pangea
Climate results from the uneven distribution of heating over the
surface of the earth caused by the earth's tilt. This tilt is
the angle between the earth's rotational axis and its orbital
plane around the sun. Currently this angle is 23.5 degrees.
Long term climate is also affected by the heat balance of the earth
which is driven mostly by the concentration of CO2 in
the atmosphere.
Climate change can result if the pattern or solar radiation is changed
and/or if the amount of CO2 changes. There is abundant
evidence that the earth does undergo climatic change. Climatic
change can be a limiting factor for the evolution of many species.
Climate Change:
- Periodic Ice Ages ---> Glacial-Interglacial Periods
- Major Period: ---> 100,000 years; 9 degree F decrease
- Minor Period: ---> 12,000 years; 5 degree F decrease
- Smaller Periods??: ---> 1,000 years; 3 degree F decrease
We currently are nearing the end of a small, minor interglacial period
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Major Ice Ages: Most of the Planet is Covered
-
Minor Ice Ages: 40o Latitude and Above. The most
recent one of these occurred about 15,000 years ago and the
coverage of the ice sheet is shown here
-
Little Ice Age: (1000-1850 AD; Irish Potato Famine; Nisqually Glacier)
Effects of Ice Ages
-
Changes sea level by 100 meters exposes continental shelfs
-
changes continental shelf composition due to increased deposition
during melt
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changes hydrological cycle through less evaporation
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changes landscape Great Lakes; Seattle; Stoss and Lee
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Changes drainage patterns
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changes topsoil characteristics
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massive flooding episodes --> Eastern Washington
Causes of Ice Ages -->
needs to be PERIODIC!
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Solar Cycle --> no evidence
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Volcanic Dust in Atmosphere --> why periodic?
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CO2 Cycle --> why periodic? --> factor 2 reduction
causes 7 F drop --> Record of CO2
and temperature variations
-
Increased precipitation at poles due to changing orientation of continental
land masses
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Changes in mean temperatures of ocean currents --> what mechanism?
The most Probable Cause:
-
Orbital Variations of the Earth!
- Eccentricity variation 90,000 years 5 variation
around mean value. This is due to Jupiter.
- Change of tilt of axis 24,000 years
More About Ice Ages
More about orbital mechanics and Ice Ages
Next Lecture
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The Electronic Universe Project
e-mail: nuts@moo.uoregon.edu