Notices
Results 1 to 25 of 25

Thread: dispersal of Gondwana

  1. #1 dispersal of Gondwana 
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    came across the following site showing the break-up of Gondwana

    the animation's a bit fast, but still neat


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  2.  
     

  3. #2  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    Wow, look how India shoots off! Pretty cool.


    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  4. #3  
    Forum Freshman
    Join Date
    Feb 2008
    Location
    Texas
    Posts
    21
    that is pretty darn cool...
    i wish that they could do it a litle slower...
    I AM GOING TO SHOW THAT TO ALL THE PEOPLE THAT LIKE SCIENCE THAT I KNOW...
    which is unfortunately, only me...
    SCIENCE BOWL RULES AND SO DOES FUEL CELL CAR RACE
    IF ANY OF YOU HAVE HEARD OF IT
    Reply With Quote  
     

  5. #4  
    Forum Professor Pendragon's Avatar
    Join Date
    Jan 2005
    Location
    Nederland
    Posts
    1,085
    Seems that we're heading for another pangea in the far future.

    Some other nice maps here
    Reply With Quote  
     

  6. #5  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    in our current understanding of plate tectonics, do we actually know enough to predict when a passive continental margin becomes an active one, when mid-ocean ridges become inactive and when new subduction zones form ?

    if not, are the images for +100MYA and +250MYA any more than pure guesswork ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  7. #6  
    Forum Sophomore
    Join Date
    Jan 2007
    Posts
    158
    I got the impression that it was educated guesswork, but guesswork none the less
    Reply With Quote  
     

  8. #7  
    Forum Professor Pendragon's Avatar
    Join Date
    Jan 2005
    Location
    Nederland
    Posts
    1,085
    Quote Originally Posted by marnixR
    in our current understanding of plate tectonics, do we actually know enough to predict when a passive continental margin becomes an active one, when mid-ocean ridges become inactive and when new subduction zones form ?

    if not, are the images for +100MYA and +250MYA any more than pure guesswork ?
    Guesswork: probably yes, to some extent. It doesn't seem difficult to extrapolate current plate movements, which we can measure very accurately. But when new mid-oceanic ridges form it's very hard to predict what will happen. For example the mid-Atlantic ridge was just one of many candidates to split the Americas from Africa and Europe, it could easily have had a different shape. For example the Mississippi valley was one side-'crack' attached to the mid-Atlantic ridge, but I don't see a reason why it couldn't also have become the main route for the ridge. In that case the Eastern half of the US would've stayed attached to Europe and the Mississippi valley would've been the center of the Atlantic ocean, giving the continents quite different shapes. It's like cracking an egg-shell, it's impossible to tell beforehand how the cracks will run exactly.

    On the other hand it doesn't seem a crazy idea that one way or another we'll end up with a new Pangaea. According to one theory we've had several 'pangaeas' already in Earths long history. There's some evidence that the earth has had about 6 or 7 pangaeas already in it's history, so it would almost be strange if there wouldn't be one in the future.
    Reply With Quote  
     

  9. #8  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    One of the delights and benefits of predicting what will happen in 100 million years time is that its difficult to prove you wrong.
    Reply With Quote  
     

  10. #9  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    How do they know there was nothing on the other side of the planet, just one mass on one side? Could there have been lots of land and it sunk?
    Reply With Quote  
     

  11. #10  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    clues from geomagnetism and paleobiogeography (oh, and rock formations too, obviously)
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  12. #11  
    Forum Sophomore
    Join Date
    Jan 2007
    Posts
    158
    Quote Originally Posted by Orleander
    How do they know there was nothing on the other side of the planet, just one mass on one side? Could there have been lots of land and it sunk?
    Sunk to where? continents don't just bob under the surface randomly. They're not dense enough to do that.
    Reply With Quote  
     

  13. #12  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    Quote Originally Posted by The Matt
    ...Sunk to where? continents don't just bob under the surface randomly. They're not dense enough to do that.
    LOL, I don't mean sink like a boat. I mean sink like New Orleans or Port Royal.

    OK, this may be a stupid question, but that never stops me, so here goes.

    Hawaiian Islands are basically vents for the earth's core. If the plates over the vents shift, the vents will spring up else where right? The islands will stop growing. Wind/erosion could wear down the islands over millions of years. That land is gone and with it all evidence of civilization. Does that make sense?
    Reply With Quote  
     

  14. #13  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    Hawaiian Islands are basically vents for the earth's core. If the plates over the vents shift, the vents will spring up else where right? The islands will stop growing. Wind/erosion could wear down the islands over millions of years. That land is gone and with it all evidence of civilization. Does that make sense?
    Actually, this is sort of what happens. There is what is called a hot spot over which the continental plate moves, creating new islands along the way.

    See HERE.

    Edit: Only thing is, there were no Homo sapiens sapiens millions of years ago. :wink:
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  15. #14  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    No, I don't think civilizations disappreard during that time, but the land could have.
    Reply With Quote  
     

  16. #15  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    That land is gone and with it all evidence of civilization.
    What did you mean by this? Anyway, I am sure that does happen as you said. Another possibility is landslides. I think ones big enough to plunge a large city into the sea can and do happen from time to time.
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
    Reply With Quote  
     

  17. #16  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    i suppose you're aware that the chain of islands ends up with underwater sea mountains, caused by sinking of the sea floor as the islands move away from the bulge of the hot spot

    likewise islands can sink as they move away from the centre of mid-ocean ridges

    it is, however, still a big step from a sinking sea floor with some sinking islands dotted around on it to whole continents sinking without a trace - as someone said before, continents are too light compared with the ocean floor to sink as oceanic islands do + evidence of sunken islands is still with us, while as far as i'm aware there's none for sunken continents
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  18. #17  
    Forum Sophomore
    Join Date
    Jan 2007
    Posts
    158
    Quote Originally Posted by Orleander
    OK, this may be a stupid question, but that never stops me, so here goes.

    Hawaiian Islands are basically vents for the earth's core. If the plates over the vents shift, the vents will spring up else where right? The islands will stop growing. Wind/erosion could wear down the islands over millions of years. That land is gone and with it all evidence of civilization. Does that make sense?
    That's a fair question actually. The thing is erosion mostly happens above, at and immediately below sea level. Once you're below the wave base there's not generally a whole lot that can erode material, so you tend to end up with an oceanic plateau or continental shelf which may well accumulate sediment. These won't wear down the further 2-4km that would be needed to bring them down level with the deep oceans. I'm pretty sure that (just like today) there were such areas around, which is why there are marine sedimentary rocks dating from the time of Pangea, but it looks like all of the continental crust that was around at the time was all in the same place.
    I get the feeling I'm not being as clear as I'm trying to be, so ask if you don't understand or want to know more.
    Reply With Quote  
     

  19. #18  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    [quote="The Matt"]
    Quote Originally Posted by Orleander
    ...The thing is erosion mostly happens above, at and immediately below sea level. ....
    But over the time span it took for Pangaea to evolve, wouldn't it be possible? All the plates moving under other plates, earthquakes causing underwater mt. ranges to crumble...

    I just wanna know why was there land on only 1 side?
    Reply With Quote  
     

  20. #19  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    Quote Originally Posted by Orleander
    I just wanna know why was there land on only 1 side?
    pot luck ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  21. #20  
    Forum Bachelors Degree
    Join Date
    Mar 2008
    Location
    Canada
    Posts
    414
    Quote Originally Posted by Orleander
    Quote Originally Posted by The Matt
    ...Sunk to where? continents don't just bob under the surface randomly. They're not dense enough to do that.
    LOL, I don't mean sink like a boat. I mean sink like New Orleans or Port Royal.

    OK, this may be a stupid question, but that never stops me, so here goes.

    Hawaiian Islands are basically vents for the earth's core. If the plates over the vents shift, the vents will spring up else where right? The islands will stop growing. Wind/erosion could wear down the islands over millions of years. That land is gone and with it all evidence of civilization. Does that make sense?
    Or..... Atlantis?
    Reply With Quote  
     

  22. #21  
    Forum Sophomore
    Join Date
    Jan 2007
    Posts
    158
    [quote="Orleander"]
    Quote Originally Posted by The Matt
    Quote Originally Posted by Orleander
    ...The thing is erosion mostly happens above, at and immediately below sea level. ....
    But over the time span it took for Pangaea to evolve, wouldn't it be possible? All the plates moving under other plates, earthquakes causing underwater mt. ranges to crumble...

    I just wanna know why was there land on only 1 side?
    Continental crust is made of fundamentally different stuff to oceanic crust. Oceanic crust is largely basalt, gabbro and similar, where was continental is largely granite. No matter how much you wear down a mountain range, you will still be able to tell that it is continental crust as its granite foundations will remain, even if they are underwater. Granite is much less dense than basalt/gabbro, which means that when an oceanic and a continental plate collide, the oceanic one is always the one to subduct.

    The reason all the continental crust was in the same place was probably down to chance to some degree- all those plates wandering around, they're bound to bump in to each other sooner or later. Once they're properly joined they are essentially one giant plate and probably won't split along the old join when they eventually break up.. I think there's still some argument about how they do break apart- some say mantle plumes (like at Hawaii), others say after long periods, supercontinents become naturally unstable because of the heat they trap under them. Either way, if there's no sizable mantle plumes or the continent hasn't been there long enough then it's pretty hard to break up.

    It's worth mentioning that even though all the continental crust was in the same place, this doesn't mean all land was joined. There may have been seas on the continental shelves separating islands from the mainland, and there were probably oceanic islands like Hawaii kicking around somewhere too.
    Reply With Quote  
     

  23. #22  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    Quote Originally Posted by The Matt
    ....Continental crust is made of fundamentally different stuff to oceanic crust. ....
    yeah, NOW. But was it always so?
    Reply With Quote  
     

  24. #23  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    Quote Originally Posted by Orleander
    Quote Originally Posted by The Matt
    ....Continental crust is made of fundamentally different stuff to oceanic crust. ....
    yeah, NOW. But was it always so?
    presumably so - at least, there's no evidence to suggest that things were different 250 million years ago
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  25. #24  
    Forum Sophomore
    Join Date
    Jan 2007
    Posts
    158
    Quote Originally Posted by Orleander
    Quote Originally Posted by The Matt
    ....Continental crust is made of fundamentally different stuff to oceanic crust. ....
    yeah, NOW. But was it always so?
    Seems so. Very little continental crust is young (even geologically). Continental crust with Precambrian sediment on it isn't rare & it still behaves in much the same way.
    Reply With Quote  
     

  26. #25  
    Forum Freshman
    Join Date
    Mar 2008
    Posts
    89
    <sigh> oh. darnit.
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •