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Thread: Continental Drift

  1. #1 Continental Drift 
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    Can someone please explain to me how continental drift works without the planet falling apart/collapsing in on itself? What I mean is if, say, the land mass of Africa is moving north, what happens to the south, where it used to be? Do we get underwater volcanoes and such? And if this is the case, wouldn't there be underwater volcanoes in the wake of all land masses that are moving? And what happens at the 'front', the direction in which the continent is moving?

    What causes these land masses to move? The continents aren't just 'floating' on the earth's crust - are they?

    I have been reading about the hypothesised 'super-continent' Pangea. All the continents in their present, above-water images would fit together pretty well to form Pangea, but the continents look very different with variations in sea levels. Were sea levels the same at the time of Pangea as they are today?

    I feel like a dummy as most people seem to be able to grasp this concept.


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  3. #2  
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    The land masses ARE the crust - look up 'Continental drift' on google and save me typing out 15 pages.....

    THe subject is called 'plate tectonics'

    Also words like 'Subduction Zone' will also help you.

    along with 'mid-atlantic ridge'

    and then 'Gravity'

    Welcome to the forum!


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  4. #3  
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    Thanks for your welcome and your reply, Megabrain.

    Ok, so by looking at the basics of subduction zones, this would eliminate the concept of Pangea, since bits of land mass 250 million years ago would by now look very different due to subduction zones and divergent boundaries. Or am I wrong?
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  5. #4 Re: Continental Drift 
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    Quote Originally Posted by avs76
    Can someone please explain to me how continental drift works without the planet falling apart/collapsing in on itself? What I mean is if, say, the land mass of Africa is moving north, what happens to the south, where it used to be? Do we get underwater volcanoes and such? And if this is the case, wouldn't there be underwater volcanoes in the wake of all land masses that are moving? And what happens at the 'front', the direction in which the continent is moving?

    What causes these land masses to move? The continents aren't just 'floating' on the earth's crust - are they?

    I have been reading about the hypothesised 'super-continent' Pangea. All the continents in their present, above-water images would fit together pretty well to form Pangea, but the continents look very different with variations in sea levels. Were sea levels the same at the time of Pangea as they are today?

    I feel like a dummy as most people seem to be able to grasp this concept.
    A prof tried to get our heads around this 'way back' in my first year of geology. One variable that helps is perspective of the surface features of the Earth in relation to the size of the Earth. Diagrams showing a cross section are exaggerated. The crust is quite a bit thinner than thinking of a peel of an orange. In fact, if a globe was created with topographic features to true scale then you couldn't feel Mt. Everest with your finger tips. the topographic model would be more or less smooth. What we think of the crust and the land continents are just 'barely there'. Think of puting an orange peel over a candle flame and it's hard to imagine the amount of heat energy impacting the movement of the peel. But put the tiniest of feathers over the flame and it might start to lift. The Earth doesn't put out a lot of energy in relation to surface area but the crust is so miniscule that even the amount of energy the Earth generates is enough to cause energy flows. Moving the crust around is like that little feather. All the mountains and quadrillions of tons of matter on the surface of the mantle go along for the energy ride. Once a perspective of size is obtained then other forces start to make sense.
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    The Earths' mantle, which the crust rests on, acts as a very slow moving liquid. As this liquid moves in currents it carries the different tectonic plates along. Think of a pot of soup with a crust on top. As the convection currents in the soup move the liquid portion, it also moves the crust on top.
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    Quote Originally Posted by DarcgreY
    The Earths' mantle, which the crust rests on, acts as a very slow moving liquid. As this liquid moves in currents it carries the different tectonic plates along. Think of a pot of soup with a crust on top. As the convection currents in the soup move the liquid portion, it also moves the crust on top.
    That's a good analogy. To understand perspective, however, make sure it's a really big pot...enough to feed an army with a few bits of onion skin thickness of crust on top.
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    I grew up in a family of mostly miners, mining engineers and geologists. This is how my mother explained continental drift to me when I was a kid.
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  9. #8 Earths mantle 
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    The earths mantle is liquid and this is what the earth's crust sits on and floats around on, no undersea volcanoes or geothermal vents would not stand in the wake of the movement of landmasses because they actually are landmasses covered in water. The upper mantle as I said is liquid but has the same viscosity of glass. (If you go into any very old building you will notice that the glass is thicker at the bottom than it is at the top - due to decades of being under gravity's pull; and it is this sort of viscosity that we are talking about; which is why the landmasses (or tectonic plates) move very slowly.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  10. #9 Re: Earths mantle 
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    Quote Originally Posted by leohopkins
    If you go into any very old building you will notice that the glass is thicker at the bottom than it is at the top - due to decades of being under gravity's pull; and it is this sort of viscosity that we are talking about; which is why the landmasses (or tectonic plates) move very slowly.
    LMAO! That is complete myth, if it were true then mountains would have deformed under their own weight, and there would be gap at the top(of your windows in the old buildings"!

    Now before you respond with "Ah but mounains look triangular so I'm right" - look up glaciation. But don't spell it as glaziation.
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  11. #10 the gap 
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    Yes there would be a gap at the top.

    I read that this is the case, infact in Bill Bryson's short history of nearly everything. so.........umm........ill have to research from other sources.

    ....Okay so I have just looked up glaciations.....erm,... mountains do look triangular so i must be right, yes.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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    As I remember reading BB's Book he exposed it as a myth.
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  13. #12 Oh...... 
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    Oh......

    Page 270 (Dangerous planet, Fire Below)

    No, he does not expose it as a myth at all.
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  14. #13  
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    Well take it from me it's a myth! - As I said before mountains would have flowed into pancakes if it were true.

    Just type 'glass myth' into google and judge for yourself.

    http://www.sciencenews.org/pages/pdf...2/15322-07.pdf
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  15. #14 Okay. 
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    Okay, I have just read it and yes its a myth. Beinning to wonder what else in that book is not true ?! Is his name even Bill ?!?!?
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  16. #15  
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    It is the world as he see's it, his interpretation of things. No more no less - I read it cover to cover found about a dozen or so mistakes/errors [in my opinion of course] - but all in all a good read only a dozen mistakes in 400-600 pages? - So don't take it as accepted science on google type 'Errors A short history of nearly everything' - it might pull something up...
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  17. #16  
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    googled it. Nothing.

    Which erors did you find ?
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  18. #17  
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    To be honest with you it's so long ago I read the book I really cannot remember any specific point but I do remember it had errors. Remember as he states in his book he is not a scientist he's a travel writer who interviewed people, did some elementary research then expressed it in his own words - a good read, full of dry humour (the bit about the guy who put lead in petrol to make thins 'better' and CFC'c into fridges to make them safer and then died in a home-made contraption springs to mind). I liked the style found the book interesting But I treated it as Sci-fi 'loosely based on fact'. I would not treat anything in the book as fact unless I either already knew it or could check it's validity. If people read it and believed it was a real scince fact book then they simply failed to read the first 20 pages (info preface background etc).
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  19. #18  
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    yes i know........

    ive also read Stephen Hawkings a briefer history of time. but there is so MUCH i disagree with; like when he keeps going on about strings and extra dimensions. i mean WTF ?
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  20. #19  
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    Why do you disagree with it?
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    w/o a long story, the idea of a giant continent and the drifting of split off sections, was first published in 1903 and received little acceptance. to explain minor or small shifts the theory has held on. try looking up "continental drift" in a encyclopedia form and you should have results...

    currently a National Oceanographic Survey of the ocean floors is working on the issue. it has to do with what should be after a drift, primarily on ages of material, and iron-silica remnants. they also are investigating island formations with this subject in mind.
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  22. #21 Okay a prime example......... 
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    Okay a prime example in the book okay, picture of a space shuttle, the earth and the sun. the shuttle is between the earth and the sun. the shadow cast on the earth of the shuttle is curved. and he uses this to argue that must mean that space-time is curved.....um NO !! the shadow is curved becasue the earth is a sphere !! (numbnuts)
    The hand of time rested on the half-hour mark, and all along that old front line of the English there came a whistling and a crying. The men of the first wave climbed up the parapets, in tumult, darkness, and the presence of death, and having done with all pleasant things, advanced across No Man's Land to begin the Battle of the Somme. - Poet John Masefield.

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  23. #22 Re: Earths mantle 
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    Quote Originally Posted by leohopkins
    The earths mantle is liquid and this is what the earth's crust sits on
    No, the Earth's mantle is solid. The asthenosphere is visco-elastic which basically means that it can flow, but it is still not a liquid.

    As for the original post: Crust is continually being created, so where your continents are drifting apart rather than leaving behind a great big hole new crust is formed by material that has upwelled from the mantle below. Crust is also being subducted (pushed down into the mantle), this is what is going on at the 'front', this is necessary for the conservation of mass.
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  24. #23 Re: Earths mantle 
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    Quote Originally Posted by billiards
    Quote Originally Posted by leohopkins
    The earths mantle is liquid and this is what the earth's crust sits on
    No, the Earth's mantle is solid. The asthenosphere is visco-elastic which basically means that it can flow, but it is still not a liquid.

    As for the original post: Crust is continually being created, so where your continents are drifting apart rather than leaving behind a great big hole new crust is formed by material that has upwelled from the mantle below. Crust is also being subducted (pushed down into the mantle), this is what is going on at the 'front', this is necessary for the conservation of mass.
    If you want to get technical the mantel is a sludge. How the hell can it be a solid, i ask you what comes out of volcanoes?
    Come see some of my art work at http://nevyn-pendragon.deviantart.com/
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  25. #24 Re: Earths mantle 
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    Quote Originally Posted by Nevyn
    Quote Originally Posted by billiards
    Quote Originally Posted by leohopkins
    The earths mantle is liquid and this is what the earth's crust sits on
    No, the Earth's mantle is solid. The asthenosphere is visco-elastic which basically means that it can flow, but it is still not a liquid.

    As for the original post: Crust is continually being created, so where your continents are drifting apart rather than leaving behind a great big hole new crust is formed by material that has upwelled from the mantle below. Crust is also being subducted (pushed down into the mantle), this is what is going on at the 'front', this is necessary for the conservation of mass.
    If you want to get technical the mantel is a sludge. How the hell can it be a solid, i ask you what comes out of volcanoes?
    The mantle is a crystalline solid, if it were a liquid s-waves wouldn't be able to get through it and any seismologist will tell you that s-waves do travel through the mante. Over very long timescales the mantle can flow, but not quickly enough for it to be considered a liquid, although perhaps geophysical fluid dynamicists could put forward a good argument that it is a fluid, it is certainly not a liquid or even a 'sludge'.
    What comes out of volcanoes, well if you want to discuss that we could go into details seeing as there are different types of volcanism. Suffice to say that what comes out will probably be a mixture of liquid, solid and gas; besides, the properties of most materials will vary immensely as a function of pressure and temperature, clearly the mantle has different pressure/temperature conditions to the base of the atmosphere.
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  26. #25 Re: Earths mantle 
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    Quote Originally Posted by Nevyn
    If you want to get technical the mantel is a sludge. How the hell can it be a solid, i ask you what comes out of volcanoes?
    Decompressional melting, variable chemistry and in some cases temperature can cause cause melting (or more commonly partial melting) of the mantle at some localities confined to the very upper mantle, but for the most part it is solid as Biliards says.
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  27. #26 Re: Earths mantle 
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    Quote Originally Posted by The Matt
    Quote Originally Posted by Nevyn
    If you want to get technical the mantel is a sludge. How the hell can it be a solid, i ask you what comes out of volcanoes?
    Decompressional melting, variable chemistry and in some cases temperature can cause cause melting (or more commonly partial melting) of the mantle at some localities confined to the very upper mantle, but for the most part it is solid as Biliards says.
    Whilst this is a common perception it is not necessarily entirel true. One of the papers I recommended you in our little PM exchange talks about a melt layer at about 410 km depth, at the Wadsleyite/Ringwoodite transition. Some seismologist claim that there is a bit of a velocity drop here which supports this claim, although to be fair nobody really knows and the data set is underdetermined.
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  28. #27  
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    With a very low percentage interstitial melt component, such as would obtain in conditions of partial melting, you can get quite significant mobility of the entire rock mass. Also note that water, which will be present in large quantities in subduction zones , will lower the melting temperature considerably.
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  29. #28 Re: Earths mantle 
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    Quote Originally Posted by billiards
    Whilst this is a common perception it is not necessarily entirel true. One of the papers I recommended you in our little PM exchange talks about a melt layer at about 410 km depth, at the Wadsleyite/Ringwoodite transition. Some seismologist claim that there is a bit of a velocity drop here which supports this claim, although to be fair nobody really knows and the data set is underdetermined.
    I'll read it in the coming few days. I've not really had chance yet as I've been swamped with other work.
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  30. #29 Re: Earths mantle 
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    Quote Originally Posted by Megabrain
    Quote Originally Posted by leohopkins
    If you go into any very old building you will notice that the glass is thicker at the bottom than it is at the top - due to decades of being under gravity's pull; and it is this sort of viscosity that we are talking about; which is why the landmasses (or tectonic plates) move very slowly.
    LMAO! That is complete myth, if it were true then mountains would have deformed under their own weight, and there would be gap at the top(of your windows in the old buildings"!

    Now before you respond with "Ah but mounains look triangular so I'm right" - look up glaciation. But don't spell it as glaziation.
    Mountains do collapse under their own weight, so to speak! Mt. Everest is roughly as high as a mountain can get on Earth before the gravity of the planet begins to pull the rock masses back in toward the centre.

    Regards,
    Rv. Jon
    :-)
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