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Thread: causal factors for the mid Pleistocene transition

  1. #1 causal factors for the mid Pleistocene transition 
    Forum Radioactive Isotope sculptor's Avatar
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    causal factors for the mid Pleistocene transition
    Early periods of glaciation were in the range of 41ka, recent glacial cycles are in the range of 100ka.

    This transition is sometimes known as the ‘mid-Pleistocene revolution.

    I have yet to read anything proposing a realistic causal factor for the transition.
    Does anyone have any insight into this phenomenon?


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  3. #2  
    Forum Radioactive Isotope sculptor's Avatar
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    No takers?
    Heck guys, I'd even enjoy a wild guess or 2


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  4. #3  
    Time Lord
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    You're looking for what ended the Pliocene era (which apparently had temperatures just slightly higher than now) and started the Pleistocene era (which was a cold era)?

    Pleistocene - Wikipedia, the free encyclopedia

    It seems the Pleistocene era lasted a very long time, about 2.5 million years. Ending only about 11,000 years ago.

    Wiki gives an interesting possibility of a supernova from a star that was close enough to affect Earth. It seems that, by "close enough" they mean 130 light years away. But the Milky way is about 100,000 light years across, so it would have been inside the Milky Way.

    Pliocene - Wikipedia, the free encyclopedia
    Some clocks are only right twice a day, but they are still right when they are right.
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  5. #4  
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    Another possible cause is that maybe there is a central cause for all the transitions - which is that the Earth is not yet at thermal equilibrium and won't be for a long time. It's possible that the core has been cooling ever since the planet started out as a big ball of molten lava, and just plain isn't done cooling yet.

    So from time to time it hits critical points in the cooling process, which then causes a shift in the atmosphere where too little moisture is evaporating, which takes down the greenhouse a notch, and it just becomes a feedback system for a while as ice forms on the upper latitudes, reflecting sunlight and cooling the Earth further. But the cooling stops once it reaches deep enough under the crust, because there's still a big pool of heat left down there. Also heat transfer depends on the difference in temperature, so once the surface is cold enough, more heat than normal will transfer from below. The Earth can't completely freeze until the core freezes.

    So in that case, the ideas is that the Earth just plain goes through cycles. We here on the outer crust are caught in the middle of a much bigger heat exchange.
    Some clocks are only right twice a day, but they are still right when they are right.
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  6. #5  
    Forum Radioactive Isotope sculptor's Avatar
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    Thanks for the answer kojax.
    However, I actually did mean what it was that i posted.
    The mid Pleistocene transition was when we went from a glacial period lasting about 41000 years to our modern approximate 100000 year cycles.
    This is variously stated to have been a short transition (almost a snap of the fingers) following mis25 with a small, almost interglacial, burp at mis23:
    See chart:


    Alternately, the Alfred Wegener institute guys think the transition was a tad more gradual, lasting roughly from mis25 to mis21.

    After this transition, we've had much colder temperatures during the glacial phase of the glacial/interglacial cycles. And, have had only 3 interglacials which matched the high interglacial temperatures common for the pre-mid Pleistocene transition.

    I've read many discussions on the transition, and many divergent opinions as to the potential causal factors, and come away with no identifiably clear conclusion(s?). The most radical of which postulated a change in orbit governed by the larger planets.
    If the premise that the milankovitch cycles govern the glacial cycles, then one is faced with the questions of why the change, and why did we enter this ice age.
    The latter has been postulated to be governed by our position within our arm of the galaxy.

    Confusion reigns supreme and there seem more questions that reliable postulated answers.

    Ergo my posting as to the causal factors for the mid Pleistocene transition.

    If indeed, everything is governed by pattern, and we can identify pieces of the pattern, and interactions of varied patterns
    then.............................................. .....................maybe a fewer of these (?) and some more of these(!)

    The journey continues.
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  7. #6  
    Time Lord
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    I think the suddenness is the result of temperature change being a feedback effect. Drop just a few degrees, and then moisture drops out of the air, reducing the greenhouse effect and causing temperatures to drop a few more degrees - which causes more moisture to drop out of the air, which reduces the greenhouse effect even more, which causes temperatures to drop a few more degrees......... etc....

    Then once ice starts to form at the poles (or expand its territory) you lose even more degrees, causing more ice to form, causing even more heat loss, causing more ice to form...... etc.

    The feedback effect stops before it gets insane because there are things that will stop it from getting too far out of hand, but it would lead to a situation where the temperature is kind of polarized at two extremes, without a whole of middle ground. Drift just one degree too far out of the high range, and you almost immediately fall into the low range. Or vice versa. Drift one degree too far out of the low range, and we may quickly accelerate toward the high range.
    Some clocks are only right twice a day, but they are still right when they are right.
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  8. #7  
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    Then once ice starts to form at the poles (or expand its territory) you lose even more degrees, causing more ice to form, causing even more heat loss, causing more ice to form...... etc.
    And never underestimate the albedo effect of increasing ice and retention of snow cover. If you start out with conditions that promote sea ice expansion, that expansion itself will promote colder conditions as more and more insolation is directly reflected rather than becoming part of the surface absorption and subsequent release as infrared. Which leads to colder conditions ... That eventually results in Snowball Earth conditions unless/until you have enough volcanic activity to release non-water vapour greenhouse gases.
    "Courage is what it takes to stand up and speak; courage is also what it takes to sit down and listen." Winston Churchill
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