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Was the cycle of supercontinent formation and destruction initiated by the Theia...

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enotechris | College Teacher | (Level 2) Senior Educator

Posted December 23, 2009 at 7:46 PM via web

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Was the cycle of supercontinent formation and destruction initiated by the Theia collision?

The name "Theia" has been given to the Mars-sized object that appears to have struck the Earth and consequently caused the formation of the Moon (Theia, in Greek mythology, being the mother of the moon-goddess Selene.)  Since the continents and the Moon have nearly the same density and appear to be made up of similar material, did that impact also initiate the first supercontinent formation?  Did the matter ejected in the collision both become the Moon (if it reached escape velocity) and the continents (if it fell back to Earth?)

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pohnpei397 | College Teacher | (Level 3) Distinguished Educator

Posted December 23, 2009 at 8:54 PM (Answer #2)

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That's pretty intriguing, but I don't see how it would ever be provable one way or the other.  The jury seems to be in favor of the giant impact idea of the Moon's origin.  That theory seems to hold up given the evidence we have now.

But to connect that to plate tectonics and supercontinents is surely beyond our (yours and mine) ability and probably beyond any hope of proof.

The reason I say it can't be proved is that I don't see that there's any way to know what would have happened (in terms of continent creation and plate tectonics) had the impact not occurred.  Do we have any reason to believe that plates would not have been created?  Do we have reason to believe that the earth's core would not have been hot enough to drive plate tectonics without the impact?

It's an intriguing idea, but given that it happened so long ago and so much of the evidence has been recycled through plate tectonics, I don't know how we could ever know.

If your school has access to ProQuest, check out this article -- might be of interest

The planet that stalked the Earth

Marcus Chown.

New Scientist

.

London:

Aug 14-Aug 20, 2004

.

Vol. 183

, Iss. 2460;

pg. 27

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enotechris | College Teacher | (Level 2) Senior Educator

Posted January 27, 2010 at 8:50 AM (Answer #3)

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The first theorized supercontinent, Vaalbara, apparently formed 3.1 to 3.6 billion years ago (http://www.statemaster.com/encyclopedia/Vaalbara)  The Theia collision is assumed to have occured 4.5 billion years ago (http://www.newscientist.com/article/mg18324605.200-the-planet-that-stalked-the-earth.html?page=1)  Although there appears to be a billion year difference between these 2 events, they are both sufficiently in the past that and close enough in geologic time that there may be causal relationship -- that the Theia impact in fact began the cycle of supercontinent formation.  At 1 billion years of age, the Earth, in its molten state, being struck with a much smaller and denser object, would have experienced 2 phenomena -- enough terrestrial material would have been ejected to coalesce into the Moon, and other terrestrial material would have been driven from one side of Earth to the other -- shoving a section of the planet to one side.  Although that may not have immediately caused an uprift of material to cool into continents, it may have moved enough material to one side of the planet, below escape velocity, which would have separated, circled around, and coalesced -- perhaps repeating the reverberation many times until the molten surface cooled enough to form land masses. If the strike had been severe enough, not only would matter be ejected from the side of the strike, but material pushed through the center of the Earth may have been ejected on the other side -- either coalescing into the Moon, falling back to Earth, or both.  Could the falling matter also create, or augment, a reverberation that would force surface material to compress and start the continent formation cycle? Surface matter on the Earth and Moon are the same density; could they have originally been located together? Are the Moon and continents the same material? Plate tectonic theory is based upon the currents formed by Earth's hot interior.  The basis for the heat is due to the radioactivity found below, but could it be that the cataclysmic Theia impact, which is now supposed to have given Earth its molten iron core, is responsible for the heat generation to move continents?  Since supercontinent formation and destruction seems to have occurred several times in Earth's history, could they actually be the long, slow reverberations of that ancient impact?

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