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The results of the glacials and interglacials in the ice age

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  1. Dec 23, 2016 #1
    Hi,
    I have read that the Earth has undergone five ice ages, the latest one is the Quaternary glaciations. I know that in the ice age there are glacial periods and interglacial periods, and we are currently in an interglacial, I want to make sense what is the effect of those succsessive periods on the life on Earth. Because in my text book I read that the soil has grown and become fertile since 20 thousand years ago, since the interglacial period started. But what made this change in the soil? and why it becom suitable for farming? And will we undergo a glacial in the future? And is it a costant thing that the soil become rich and good in the interglacials of all ice ages?
     
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  3. Dec 23, 2016 #2

    FactChecker

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    A lot of life forms can live in very harsh environments. They can certainly break down rocks and make fertile soil on 20 thousand years. I think that even my front yard could become fertile in that long a time. ;>)
     
  4. Dec 23, 2016 #3

    Drakkith

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    Is your textbook more specific than this? Does it give any other details? More fertile in an absolute sense? More fertile than it was during the glaciation?
     
  5. Dec 24, 2016 #4

    1oldman2

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    In my area (the former bed of https://en.wikipedia.org/wiki/Lake_Missoula) the top 18 to 20 inches of soil is very rich black soil, this is mainly due to organic matter settling out of the water, not a direct result of the glaciation however, that material is fine silt/clay layered in Varves and doesn't support much plant growth.
    An interesting side note on the lake. https://en.wikipedia.org/wiki/Missoula_Floods
    During the last deglaciation that followed the end of the Last Glacial Maximum, geologists estimate that a cycle of flooding and reformation of the lake lasted an average of 55 years and that the floods occurred several times over the 2,000-year period between 15,000 and 13,000 years ago. U.S. Geological Survey hydrologist Jim O'Connor and Spanish Center of Environmental Studies scientist Gerard Benito have found evidence of at least twenty-five massive floods, the largest discharging ≈10 cubic kilometers per hour (2.7 million m³/s, 13 times the Amazon River).[2] Alternate estimates for the peak flow rate of the largest flood include 17 cubic kilometers per hour[3] and range up to 60 cubic kilometers per hour.[4] The maximum flow speed approached 36 meters/second (130 km/h or 80 mph).[3]
     
  6. Dec 25, 2016 #5

    davenn

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    Which textbook ... name and author please?
     
  7. Dec 25, 2016 #6
    Hi, my text book is in Arabic, and it is a text book of the high school students, so I will try to give a translation to what it contains about the ice age, here we are:
    "Ice age (one million years ago):-
    The ice cab has spread to the south in the northern hemisphere resulting in the existance of the glacial periods, and these periods were accompanied by a heavy rain periods in the south of the northern hemisphere, and when the ice cab retreated to the north during the interglacial periods there were drought periods in the southern part of the northern hemisphere.
    The rising and falling of the sea level affected the environmental circumstances, which resulted in the flourishing of the vegetation and reproduction of the animal groups which feed on it during the heavy rain periods, wherease the vegetation has detriorated in the drought periods and that resulted in the dcrease of the animal groups.
    These periods lasted since the start of the ice age and ended more than 20 thousand years ago, the soil has grown during them ( I don't know about any "them" he speaks here, is it through the 20 thousand years ago or during the successive periods of glacials and interglacials) especially in the northern regions of the Great Sahari,and it developped farms with rich production for the welfare of the mankind."
     
  8. Dec 25, 2016 #7
    I posted a translation of this part about the ice age.
    My textbook of Geology and Environmental sciences, I posted the paragraph about the ice age.
     
  9. Dec 25, 2016 #8

    Drakkith

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    Unfortunately I cannot give you an answer. Hopefully someone else here on PF will be able to help you. I'm curious to know the answer myself.
     
  10. Dec 25, 2016 #9
    IIRC, after glacial retreat and the degree-day count improves, you're usually left with bare rock plus glacial moraines. You need lichen to start disassembling the sterile rock surface, bird droppings for essential fixed-nitrogen, bacteria, seeds etc etc. Fast-forward via patchy growth to tundra, to scrub etc.

    IMHO, a fair example would be Surtsey. Though volcanic, it lies on the fringes of the Arctic, so is a viable analogy. Colonisation began almost as soon as the main eruption eased. Still, it will take a long, long time for a significant layer of 'humus' to develop...
     
  11. Dec 25, 2016 #10
    I think soil (and other sediments) can come from a variety of sources.

    Some would be:
    • glacially ground up rock (fine silts)
    • debris that was carried off by the glacier and dropped when it melted (piles of sand, for example in areas like the Upper Peninsula of Michigan). Not ground up to powder.
    • material from chemical weathering of newly uplifted mountains (like the Himalayas; I am sure someone else (like @CapnGranite) could explain this better)
    • debris (eroded by a variety of mechanisms) deposited from flowing water (like in Glacial /Lake Missoula as described by @1oldman2 (an extremely interesting geological event or series of events)). The Glacial Lake Missoula floods also deposited 350 feet of sediments in the Willamette valley (where I live which is now good farm land). When the water was flowing out the Columbia river basin (and turning it into the Columbia Gorge), it ran into some flow limitation and was diverted to backfill the Willamette valley (multiple times) and dropped sediment there. Portland was under 300-350 feet of water and much of Portland is now built on sediment piles.
    • There are also "erratics" (rocks out of place in the local geology) from the Missoula floods. These are huge chunks of rocks were carried down stream from the glacial dam by the ice chunks (small icebergs?) they were embedded in.
     
  12. Dec 25, 2016 #11

    1oldman2

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    One of the most interesting erratics would have to be the...
    http://www.usgennet.org/alhnorus/ahorclak/WillametteMeteorite.html

    Between 12,500 and 15,000 years ago, the last ice age included the formation of the Cordilleran Ice Sheet, a mass of ice that covered northern-most America west of the Rocky Mountains; the glacier lifted and shifted boulders (such as the Willamette Meteorite) that lay beneath it. When the ice age ended, over a period of 2000 years, ice-melt created Glacial Lake Missoula, an unimaginably huge reservoir which repeatedly flooded the northwestern continent. As ice dams reformed and broke, the floods created walls of water 2000 feet high that swept at 65 miles per hour all the way to the sea.
     
  13. Dec 31, 2016 #12
    Let me try. I'm a retired farmer in the Canadian province of Saskatchewan which is mostly
    excellent farmland in the southern third. Most of it (3/3) was glaciated the last time around
    with the exception of a bit of the south-west corner. The best soil was formed in shallow
    lakes which were flooded by glacial melt in the spring. This water carried considerable soil
    which settled out during the summer with the coarser particles first, then the finer and darker
    clay particles later in the summer. This created the Varves which are about 2 inches thick
    near here. These soils are very fertile and drought resistant. These clay soils were formed
    under semi-arid conditions and really don't want more than 20 inches annual precipitation.
    Much of this area has loam soils which you could describe as glacial till with a fair bit of
    clay and rocks too. There's some poor land that's mostly sand. It was carried down by
    glacial meltwater. and don't yield well unless it's a rainy year. All of these soils benefited
    from several thousand years of plant growth putting organic matter into the topsoil.
     
  14. Jan 1, 2017 #13
    Back again. The simple answer to your first question is that the ice was a mile (estimated) thick here during the last glacial, so the soil has definitely improved. The loess soils in the Cornbelt south of the ice sheet were formed by wind erosion at the base of the ice sheet and are some of the most fertile on earth. The dust storms that originated at the base of the glacier and carried over 100 feet of topsoil south must have made the dust storms of the 1930's Dust Bowl look pretty mild by comparison.

    I should say that I agree with everything posted above, but different conditions exist in different places. The landforms here don't permit a Missoula size flood and most of the rocks here were ground to powder by the glacier so we can skip the lichen stage.

    The last glacial period ended about 7000 years ago in Hudson's Bay, Canada. The land is still rebounding there. Rebounding means that the land is rising now that the weight of the ice is off it. The glacier was gone from here about 10,000 years ago, but it's only 700 miles to Hudson's Bay, and the climate here must have been cooler until the bay melted out.

    Some recent research indicates that the previous interglacial was warmer than this one by about 4°C, but the Polar Bears survived the ice free summers. The Qu'Appelle Valley, 15 miles south of here, is about 2-3 miles wide and 150 feet (50 meters) deep, but the river channel is only 50 meters wide on average. The valley got that big by draining glacial melt. The Hatfield Valley which drained the melt at the beginning of the last interglacial is under the Qu'Appelle Valley. It was 700 feet (210 meters) deep and 10 miles wide.

    The northern 2/3rds is Saskatchewan is boreal forest on a poor acidic soil. I was at an agricultural conference some years ago when someone said that it's unfortunate the soil was too poor there for profitable farming. My old Soils professor said "If we had a climate, we'd have a soil". That may be the shortest and most complete answer to your question.

    Hopefully I haven't muddled things completely.
     
  15. Jan 6, 2017 #14
    To address the last question: will Earth have future Ice Ages / Interglacial periods? The short answer is yes as long as a nearly continuous circle of land surrounds the Arctic Ocean. The combined effect of Canada, Greenland, Scandinavia and Siberia is to prevent warm currents from the equator from carrying this heated water all the way to the North Pole. Consequently, a permanent ice cap can form over the Arctic Ocean and allow glaciers to extend southward into Europe, Asia and North America. In the Southern Hemisphere, Antarctica covers the South Pole and holds a permanent ice cap as well.
    Millions of years in the future, the positions of the continents will shift due to tectonic forces (continental drift), and Ice Ages will become a relic of Earth's geological history.
     
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