Notices
Results 1 to 10 of 10

Thread: How did the oceans form?

  1. #1 How did the oceans form? 
    ox
    ox is online now
    Forum Professor
    Join Date
    Mar 2009
    Posts
    1,476
    Did the oceans condense from the atmosphere and/or the earth struck repeatedly by comets? Did the atmosphere once extend much further into space?


    Reply With Quote  
     

  2.  
     

  3. #2  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    There is some debate as to how much of the oceans are derived from the water in impacting comets and how much is derived from degassing of the mantle. The Earth, like the other terrestrial planets is essentially dry (The average ocean depth is 3.7km, which is only 0.06% of the Earth's width.) and this favours a cometary source for at least some of the water.

    I recently read of a study on isotope ratios in ocean water that strongly indicated no more than 30% could have been derived from cometary impact.

    Either way, the water would start out as water vapour. At some point in the Earth's history the surface and atmosphere became cool enough for liquid water to exist. That must have been quite a rainstorm!

    I don't see any reason for the atmosphere being sginificantly more extensive in the past. It would have contained much more carbon dioxide. That has been trapped into carbonates and organisms. There would have been almost no oxygen. On balance I don't think it would have made a big difference.

    Kingjacob's point about the water content itself is a valid one, but again if you are thinking in terms of an atmospher extending out to say five hundred miles rather than fifty, I wouldn't have thought so.


    Reply With Quote  
     

  4. #3  
    Forum Sophomore kingjacob's Avatar
    Join Date
    Jun 2006
    Location
    between time and timbuktu
    Posts
    131
    I've always heard the oceans formed when the earth cooled and the air condensed. That could mean that the atmosphere used to extend further or just that it was the same size but more dense.
    Reply With Quote  
     

  5. #4  
    Moderator Moderator
    Join Date
    Apr 2007
    Location
    Washington State
    Posts
    8,416
    Even as the crust cooled enough to condensate and start to form the oceans, there was probably lots of outgasing of water vapor from the interior--a process that continues today.
    Reply With Quote  
     

  6. #5  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by Lynx_Fox
    Even as the crust cooled enough to condensate and start to form the oceans, there was probably lots of outgasing of water vapor from the interior--a process that continues today.
    Much, if not most, of the water being outgassed today is recycled water carried into the mantle by subduction.
    Reply With Quote  
     

  7. #6  
    WYSIWYG Moderator marnixR's Avatar
    Join Date
    Apr 2007
    Location
    Cardiff, Wales
    Posts
    5,810
    i was under the impression that the collision event that created the moon virtually left the earth free of substantial amounts of volatiles - meaning that most of the water now on earth comes from subsequent cometary material (remember, there was still a substantial bombardment going on until about 3.9 billion years ago)
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
    Reply With Quote  
     

  8. #7  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by marnixR
    i was under the impression that the collision event that created the moon virtually left the earth free of substantial amounts of volatiles - meaning that most of the water now on earth comes from subsequent cometary material (remember, there was still a substantial bombardment going on until about 3.9 billion years ago)
    The surface volatiles were all, or nearly all lost, but degassing of the mantle was still able to generate significant volumes of water and atmosphere.
    The notion that most of the oceans came from impacting comets was popular for a decade or so, but I sense that tide has swung away from these as being the principal source and reverted to degassing.
    Reply With Quote  
     

  9. #8  
    Administrator KALSTER's Avatar
    Join Date
    Sep 2007
    Location
    South Africa
    Posts
    8,231
    IOW, degassing of both H<sub>2</sub> and O<sub>2</sub>, among others, but specifically those two that formed much of the water?
    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  
     

  10. #9  
    Moderator Moderator Dishmaster's Avatar
    Join Date
    Apr 2008
    Location
    Heidelberg, Germany
    Posts
    1,624
    And don't forget the carbonaceous chondrites. They contain a lot of water, although some scientists seem to think they might not be that important for the water content on earth.
    Reply With Quote  
     

  11. #10  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by KALSTER
    IOW, degassing of both H<sub>2</sub> and O<sub>2</sub>, among others, but specifically those two that formed much of the water?
    Didn't see this earlier. The hydrogen and oxygen were probably already in the form of water. At the temperatures we are discussing the water would have been gaseous, so degassing is the appropriate term.

    Much of that water would have come from the carbonaceous chondrites that contributed most of the mass of the Earth during its accretion. Later impacts were likely dominated by icy comets. I haven't checked Dishmasters link yet to see if it is the isotope study I have been trying to track down.
    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
  •