Expanding Earth Theory - WTF???

gdnp said:
First of all, they haven't. Cut out a picture of South American and one of Africa and try to fit them together. Are there gaps? Yes? Then the shape has not remained constant.

Second, as previously posted, the continents are made of lighter rock and thus float on top of the mantle, which is recycled under them.
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Relatively consistent.

...and you knew that was the meaning.


:gnome:
 
JEROME DA GNOME said:
I see how you can see this.

Why do the processes that you properly described tend to cause the crust to move towards the same "land" masses so consistently?
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The pieces of continental crust are not moving “towards the same land masses”. There are no “fixed points” at the Earth’s crust when we take the geological timescale in to account. All points over the crust are moving all the time. Island chains formed over hot spots such as the Hawaii and linear volcanic chains within the continents show this (I’m not updated on hotspots, last time I read about them there were discussions regarding how “fixed” they are).

What happens is that along the 4.5 Gy of the history of our planet, at certain periods the continental masses merged, in different ways each time, forming a number of “supercontinents”, each one with a different configuration. The masses -be them the supercontinents or the "blocks" that build them (island arcs and continents) do not retain their original shape during and after each cycle; they are constantly being deformed and locally increasing in volume. The contours of present-day configurations are shown at the reconstructions (especially in animations and charts aimed towards the general public) for the sake of clarity, providing a familiar reference. I think this may have caused in you the wrong impression that they retain their shape.

The surface of the Earth has a fixed area; it is no wonder that in 3 billion years or so of plate tectonic activity most continental masses would lump together and form a single mass a couple of times. I think this is the only connection I can see between your questions and the expanding Earth “theory”.

JEROME DA GNOME said:
Are you in agreement with Pangaea?


:gnome:
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The evidence I am aware of is quite convincing regarding the existence of supercontinents in our past (Pangea, Gondwana, Laurasia, Pannotia, Nuna, Rodinia, etc). Of course, we have less informations preserved about the older ones, so the reconstructions are less precise. I’m not very sure, however of the relevance of this to the topic in question
 
JEROME DA GNOME said:
What constant of physics rules out an expanding planet?


:gnome:
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It depends on the mechanism you are using to make the earth enlarge. It seems to me that either the size of atoms or the spacing between them would have to change, and either would involve changing the unit charge on an electron. If you have some other theory, explain it and I'll find out.
 
JEROME DA GNOME said:
shadron said:
Do you mean the way they seem to create a whole landmass, and then separate and then comeback together eventually? No idea really, perhaps it's just a coincidence, or an artifact of the imprecisely understood mantle conveyor.

If you mean something else, you've lost me. There are evidences of earlier super-continents than Pangaea, which broke up and reassembled multiple times in the past. See www.scotese.com .

I also don't know what you mean by "Are you in agreement with Pangaea?". As espoused by whom? That it once existed? Sure.
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How did the land mass Pangaea form according to the accepted theory?
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Ummmm.... having trouble reading? I said, "Do you mean the way they seem to create a whole landmass, and then separate and then comeback together eventually? No idea really, perhaps it's just a coincidence, or an artifact of the imprecisely understood mantle conveyor." What part of "I don't know" doesn't work for you?

I do have one phenomena that may be of use understanding it (or it may not). If you fill a oily baking dish with water (say, prior to cleaning it) and you just add a drop of detergent somewhere on the surface, the surface tension change caused by the determent's surfactant effect drives away all the oil. If there is no edge to the dish (as would be the case on a globe), it would drive all the oil scum into a single clump. Perhaps it is something analogous to that.

ETA: Would not the initial formation of the Earth necessitate relative uniformity of the crust?
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First of all, why? The crust is between 3 and 30 miles thick, more or less. Compared to the 7000 mile radius of the Earth, that *is* relatively uniform.

Even if the crust started out perfectly uniform, the actions of spreading and subduction would introduce non-uniformities which would cause the lighter continental crust material to heap at places and stretch at others. And then, of course, there are both volcanic flows and continuing incoming material which introduce their own non-uniformities. Guesses, of course, off he top of my head - perhaps the right answer here would also be, "I don't know."

Perhaps you may consider that a copout, but its not, because 1) I'm not a geologist, and 2) I don't know.
 
JEROME DA GNOME said:
So how did India slide across the ocean floor?

:gnome:
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A rift opened between two parts of the proto-African continent; the eastern part, India, traveled on the piece of plate broken off of Africa pushed by the spreading rift (note that the current rift valley through eastern Africa represents another possible piece of Africa, a little farther north, starting to move farther east as well). Of course, a rift in one place demands a subduction somewhere else, and that happened, it is estimated, at the edge of Asia. The result was the fastest relative documented plate motion known (about 20 cm/yr during the Cretaceous relative to Asia; see http://www.nature.com/nature/journal/v449/n7164/abs/nature06214.html), and the India plate delivering India up to the Asian plate. In this case the crust is being scraped off the subducting India plate, piled up to build the Himalayas. Perhaps some perspective will assist in drying up some of the scorn in the source of your amusement: the Himalayas are, at most, 6 miles high, set upon a crustal depth of 30 miles. It doesn't take much scraping to result in that much material piling up, no matter how huge that may seem to us. You may take note that the Himalayas contain no volcanoes, so the source of their mass is not upwelling lava, as it is in the Pacific northwest.

I do wish you would be more specific in your questions - I just that had a thought that perhaps you were asking about the mechanism of any plate's movement. The plates consist of upper mantle and accompanying crust that are conveyed away from spreading centers towards subductions. The more rigid outer mantle/crust rests upon a more plastic inner mantle which moves from upwellings towards downwellings of mantle material associated with heat convection plumes. The inner mantle acts like very viscous liquid; the outer mantle acts like more rigid plates. The crust acts like floating detritus. Nothing slides. All parts are affected by gravity which severely limits vertical movement at the surface while supporting convection (convection requires gravity; remember that if you ever need to light a match in weightless space).
 
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JEROME DA GNOME said:
Than how have the "land masses" retained their consistently in shape?

:gnome:
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They haven't. They've been pushed, prodded, crushed, ground, piled one atop another, stretched, sunk, raised, slip-struck, kneaded, slivered. melted and torn asunder by immensely powerful, but slow, constant forces. All the crustal pieces and parts, as well as the mantle plates, are constantly, if slowly, changing.
 
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How much validity is there to the Plume Theory as a driver of plate tectonics as opposed to convection currents?
 
I would say plumes and convection cells are not competing because mantle plumes may also be formed by convection. The size, shape and location of the cells are different, however. Plumes may be the driving mechanism for plate movement insome cases while in other they just heat the spot above them (generating volcanism and/or basin formation) without actually causing plate movement. Something else is moving the plate (a "standard" convection cell). The Earth's mantle, I think, could be described as a turbulent mess. Big and small cells are inteferring with each other while here and there "jets" shot upwards and downwards, caused by cells with broader amplitude, reaching down the mantle/core interface.
 
Travis said:
How much validity is there to the Plume Theory as a driver of plate tectonics as opposed to convection currents?
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What is the difference? In a finite sphere, convection currents competing with their downdraft counterparts tend to dice the surface up into regions of relative upwards movements vs relative downwards movements. The upwards ones can be considered plumes; fluctuating intensity will tend to focus a convection "cell". For example,

The breakup of the supercontinent Gondwanaland into Africa, Antarctica, Australia and India about 140 million years ago, and consequently the opening of the Indian Ocean, is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the Marion, Kerguelen and Réunion plumes. [op cit]
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I could be wrong (of course), but I don't think there is a meaningful dichotomy to be drawn.

Edit: Reading Correa Neato and upon further consideration, yeah, I'm perhaps at least partly wrong. For example, there are the Hawaiian and Yellowstone plumes that happen right in the middle of their respective plates. Then again, if they were stronger they might initiate spreading by inducing the typical threeway split pattern in the plates they occupy. Wouldn't that make Wyoming interesting?

I don't think plumes or convection cells rule each other out; they both occur and provide their bits, and are mainly a difference in emphasis.
 
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Yes, if the plume is big enough it will create an extensional environment which may start a rift big enough to divide a plate in two. This is the basic mechanism which may have been reponsible for the break-up of the supercontinents. If the heat flow is high enough, there will be a mantle upwelling and basically the continental crust will "slide" through the sides of the elevation. Oceanic crust will be formed and bingo! Now you have two continents. Of course, I am making several oversimplifications.

A nitpick regarding the "typical threeway split pattern in the plates":
There are several possible triple junctions or triple plate boundaries, not all of them will be on of extensional nature (RRR - "R" for "rift"). Plate boundaries can be:
(a) divergent - extensional environments (rifts, mid-oceanic ridges)
(b) convergent - compressional environments (subduction complexes -Andes and island arcs such as Japan, continent-continent collisions - Himalayas)
(c) transform - transcurrent or wrench movment - plates pass sliding besides each other (California). This type is actually more complex, since transcurrent movement is almost always associated with some degree of extension or compression (transtraction -or transtension, but I don't like this particular name- and transpression).

Triple points will be combinations of them (most are unstable and only a handfull of them are stable- sorry, memory is failing right now and lazyness avoids me to think and figure out how many and which ones). Pure extension may divide a plate in two pieces (note that triple junctions will have to exist somewhere in the plate). Of course, what is nowadays a simple extensional plate limit may have started as a triple junction where one of the rift "arms" became inactive (aulacogens or failed rifts).

More details and sources can be found at physical geology handbooks and at linkies like these:
http://www.mantleplumes.org/WebDocuments/DLAHowManyPlates.pdf (mantleplumes.org- Everything You Always Wanted to Know About Mantle Plumes But Were Afraid To Ask - apologies to Woody Allen)
http://openlearn.open.ac.uk/mod/resource/view.php?id=172193
http://www.le.ac.uk/geology/art/gl209/lecture3/lecture3.html (talks about plumes starting continental breakup)
http://earthednet.org/Support/ODP/UsingODPMan/Ch4.Plate_Tectonics.pdf
http://www.nsm.buffalo.edu/courses/gly481-581/McGuire05_2.pdf
 
Based on the information in the OP, under the expanding earth model, wouldn't the Hawaiian Island chain be impossible? If the earth were expanding away from the rift zones, it would seem to me that the location of the hot spot would move radially with the islands, resulting in just one big volcano rather than a chain of little ones.
 
Hokulele said:
Based on the information in the OP, under the expanding earth model, wouldn't the Hawaiian Island chain be impossible? If the earth were expanding away from the rift zones, it would seem to me that the location of the hot spot would move radially with the islands, resulting in just one big volcano rather than a chain of little ones.
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Dunno; the earth expansion people are really cagey with their mechanisms. I standard tectonics, the Hawaiian hotspot is not sufficiently strong to cause it's own rift to start, so it just dimples the plate riding above it.
 
Correa Neto said:
A nitpick regarding the "typical threeway split pattern in the plates":
There are several possible triple junctions or triple plate boundaries, not all of them will be on of extensional nature (RRR - "R" for "rift"). Plate boundaries can be:
(a) divergent - extensional environments (rifts, mid-oceanic ridges)
(b) convergent - compressional environments (subduction complexes -Andes and island arcs such as Japan, continent-continent collisions - Himalayas)
(c) transform - transcurrent or wrench movment - plates pass sliding besides each other (California). This type is actually more complex, since transcurrent movement is almost always associated with some degree of extension or compression (transtraction -or transtension, but I don't like this particular name- and transpression).
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Thanks for the help, Correa. Always like to hear from a professional.

More details and sources can be found at physical geology handbooks and at linkies like these:
http://www.mantleplumes.org/WebDocuments/DLAHowManyPlates.pdf (mantleplumes.org- Everything You Always Wanted to Know About Mantle Plumes But Were Afraid To Ask - apologies to Woody Allen)
http://openlearn.open.ac.uk/mod/resource/view.php?id=172193
http://www.le.ac.uk/geology/art/gl209/lecture3/lecture3.html (talks about plumes starting continental breakup)
http://earthednet.org/Support/ODP/UsingODPMan/Ch4.Plate_Tectonics.pdf
http://www.nsm.buffalo.edu/courses/gly481-581/McGuire05_2.pdf
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And thanks for that. Lots of good reading there.
 
shadron said:
Dunno; the earth expansion people are really cagey with their mechanisms. I standard tectonics, the Hawaiian hotspot is not sufficiently strong to cause it's own rift to start, so it just dimples the plate riding above it.
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Hmm, even if it could form its own rift, Kilauea and Loihi would be centered in the islands rather than dangling off the end if their theory were true, I would imagine.
 
MattusMaximus said:
No, he isn't. I think he's just trolling, as usual.
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I think it's good that he asks questions about things. He's like Simplicio in Galileo's dialogues. He gives experienced people the opportunity to explain phenomena, which then becomes a learning resource for readers.

I think his role on the forum is to question assumptions. And that's normally a good thing, isn't it? Jerome questions those things that most of us take for granted, and forces us to think about why we assume those things.

I for one welcome his presence in this thread. He's elicited a lot of very good information from knowledgeable people. And I see the net effect as positive.

Thanks Jerome. Keep doing what you're doing.
 
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