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Thread: Magma

  1. #1 Magma 
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    I watched National Geographic's Amazing plantet the other night. I didn't realize that earths magma has alot of uranium in it. And that helps it stay hot. I always wondered why the magma didn't cool and turn solid. I'm sure there are other reasons. Filix.


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    Universal Mind John Galt's Avatar
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    You may have partly misunderstood the program. There is very little magma in the Earth. Some small portions of the upper mantle undergo partial melting and generate magam which can then move upwards and either erupt, or slowly cool and crystallise at depth. The heat of the mantle is partially a consequence of the original heat of planetary formation, but also radioactive decay. However, in this respect, potassium is vastly more important than uranium as the source of the heat.


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    Thankyou John. I have to watch those programs several times before I start to get it. Potassium? Thats amazing. I feed my plants potassium. What are the continents drifting on, if there is very little magma? Sorry if this is a dumb question. I also saw a program called snowball earth I think. Saying that the intire earth was covered in snow and ice for millions of years. Is this under debate? Thanks Filix.
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    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by filix View Post
    What are the continents drifting on, if there is very little magma?
    The layer of the Earth which makes up the 'plates' is known as the lithosphere ('rigid layer'), and indeed is predominantly brittle/rigid rock. Beneath this layer is the asthenosphere, characterised by a low velocity zone for seismic waves. The asthenosphere is 1-10% liquid, and the solid portion of it tends to deform plastically (think plastercine).

    Also worth noting is that the entirity of the mantle is thought to convect, despite being almost entirely solid. Convection occurs over geological time, however, not at the rates observed in liquids and gases.

    Quote Originally Posted by filix View Post
    I also saw a program called snowball earth I think. Saying that the intire earth was covered in snow and ice for millions of years. Is this under debate? Thanks Filix.
    I think this is now widely accepted.

    Wikipedia explains it better than I can:
    Snowball Earth - Wikipedia, the free encyclopedia
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    Thankyou very much. Filix.
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    Quote Originally Posted by drowsy turtle View Post
    Quote Originally Posted by filix View Post
    What are the continents drifting on, if there is very little magma?
    The layer of the Earth which makes up the 'plates' is known as the lithosphere ('rigid layer'), and indeed is predominantly brittle/rigid rock. Beneath this layer is the asthenosphere, characterised by a low velocity zone for seismic waves. The asthenosphere is 1-10% liquid, and the solid portion of it tends to deform plastically (think plastercine).
    Well a little bit old fashioned knowledge, if you take a look at africa there is no asthenosphere, the asthenosphere seems to be a consequence of plate motion and not the other way around.

    Quote Originally Posted by filix View Post
    I also saw a program called snowball earth I think. Saying that the intire earth was covered in snow and ice for millions of years. Is this under debate? Thanks Filix.
    I think this is now widely accepted.

    Wikipedia explains it better than I can:
    Snowball Earth - Wikipedia, the free encyclopedia
    that depends on which model of "snowball earth" you are arguing the earth surface to 100% under ice thats not really widely accepted.

    Another word to the elements/isotopes which are generating heat by radioactive decay, those elements are today to the major part in earth crust, the mantle is "depleted".
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    Quote Originally Posted by The Geographer View Post
    that depends on which model of "snowball earth" you are arguing the earth surface to 100% under ice thats not really widely accepted.
    The first difficulty, of course, lies in the precision and reliability of latitudes derived from palaeomagnetism. Because of the age of the minerals there is a greter probability that they have undergone subsequent reorientation. Secondly, I understand there are still a body of workers who argue for a highly oblique axial orientation for the Earth that led to glaciated equatorial and tropical zones, but ice free poles. There is not even universal agreement on the number of neoproterozoic glaciations, nor on their correlation, or extent.

    Quote Originally Posted by The Geographer View Post
    Another word to the elements/isotopes which are generating heat by radioactive decay, those elements are today to the major part in earth crust, the mantle is "depleted".
    Is this correct? Large parts of the mantle are depleted, but large parts (probably the larger part) are still thought to be primordial. I understand this is evidenced by detailed study of key isotope ratios.
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    Quote Originally Posted by John Galt View Post
    The first difficulty, of course, lies in the precision and reliability of latitudes derived from palaeomagnetism. Because of the age of the minerals there is a greter probability that they have undergone subsequent reorientation. Secondly, I understand there are still a body of workers who argue for a highly oblique axial orientation for the Earth that led to glaciated equatorial and tropical zones, but ice free poles. There is not even universal agreement on the number of neoproterozoic glaciations, nor on their correlation, or extent.
    well I just know the argumentation that live couldn't regenerate so fast from biologists, my latest information was that with the new model (please don't ask me any detail) for rodinia things may look different.

    Is this correct? Large parts of the mantle are depleted, but large parts (probably the larger part) are still thought to be primordial. I understand this is evidenced by detailed study of key isotope ratios.
    It's hard to argue against this point, maybe there are those zones ok, but I think the major part of the mantle is depleted (for common MORB thats prooved), and I think even those zones will have much lower concentrations of those elements. Let's say continental crust would result of a 1% melting of the mantle then you would get a 100 times higher concentration of those elements than in primordial mantle.
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    Reptile Dysfunction drowsy turtle's Avatar
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    Quote Originally Posted by The Geographer View Post
    Quote Originally Posted by drowsy turtle View Post
    Quote Originally Posted by filix View Post
    What are the continents drifting on, if there is very little magma?
    The layer of the Earth which makes up the 'plates' is known as the lithosphere ('rigid layer'), and indeed is predominantly brittle/rigid rock. Beneath this layer is the asthenosphere, characterised by a low velocity zone for seismic waves. The asthenosphere is 1-10% liquid, and the solid portion of it tends to deform plastically (think plastercine).
    Well a little bit old fashioned knowledge, if you take a look at africa there is no asthenosphere, the asthenosphere seems to be a consequence of plate motion and not the other way around.
    Consider it an over-simplification.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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