Plate Tectonics: A Paradigm Under Threat?

earthseed · Nov 28, 2004

Plate tectonics theory is the modern explanation of the behavior of the Earth's oceans and continents over time. Its constant recycling of the Earth's crust and the buildup of continents is essential to life as we know it. The "Rare Earth" hypothesis claims that plate tectonics may be relatively unique to Earth, making life elsewhere less likely to occur. So what if it is all an illusion? That is the claim being made by this website. This is not the usual Creationite rubbish; an ancient Earth and all the techniques of modern geology are fully accepted. The basic premise is plate tectonic theory was based on insufficient information, that more detailed data that came later refutes the theory but no one wants to abandon the status quo. So what do I make of this? Lets start with a credibility check on the author, one David Pratt, who appears to have no relevant qualifications, other than to promote Theosophy. The paper itself has plenty of references, some of them rather old, eg. Gregory (1929) and Bucher (1933), many turn out to be college textbooks, and a lot of the refer to a single author, A. A. Meyerhoff. We have enough red flags here for a May Day parade, but I found the content itself to be well written, demonstrating a thorough knowledge of plate tectonics. I prefer to discuss ideas on their own merit, rather than appeal to authority or lack of it. I find it difficult to pick these arguments apart, so I am looking for a little help (Jon Clarke, are you still around?). Lets start with his first topic, Plates in Motion. The claim here is that continents are up to 600 km thick (as shown in the attached picture), thus cannot slide about on the asthenosphere as the theory predicts. I found this hard to believe, but then I locate

spacechump · Nov 28, 2004

Plate Tectonics: A Paradigm Under Threat? Hardly....remember mountain ranges and subduction zones? The "Rim of Fire" in itself is evidence of plate techtonics.

kmarinas86 · Nov 29, 2004

Tectonic plates exist no doubt about that.... what exactly are you arguing about? In any case, there is probably more than one way that mountains can form geologically.. Volcanoes are one example. Subduction causing the Mountains of Nepal and Everest. No God is needed... just a whole lot of energy to move accelerate the continents so that they do not decelerate so much under so much massive resisting friction forces. http://www.google.com/search?sourceid=navclient&ie=UTF-8&q=define%3Atectonic+plates

spacechump · Nov 29, 2004

Subduction causing the Mountains of Nepal and Everest. What's your point? I already mentioned subduction as evidence for plate tectonics. Tectonic plates exist no doubt about that.... what exactly are you arguing about? What exactly am I doing to argue? I was only providing a counterstatement to the poster.

Maddad · Nov 29, 2004

earthseed "The basic premise is plate tectonic theory was based on insufficient information http://www.maddad.org/earth-science-exam-III.doc The people at that website are probably well meaning, but our information is quite sufficient. The clincher is that we can see the plates moving. "The claim here is that continents are up to 600 km thick (as shown in the attached picture), thus cannot slide about on the asthenosphere as the theory predicts. He believes that it should not be able to happen, but we see that it is. However lettered he is, I will accept actual measurements over his belief.

mooware · Nov 29, 2004

"The "Rare Earth" hypothesis claims that plate tectonics may be relatively unique to Earth, making life elsewhere less likely to occur. " What do they base this on? How can they say plate techtonics are going to be relatively unique to earth? Considering we have very few examples to derive that kind of conclusion.

silylene old · Nov 29, 2004

First let me state that the evidence for the plate tectonic theory is quite strong. I am not debating whether plate tectonics is operant on Earth. "The "Rare Earth" hypothesis claims that plate tectonics may be relatively unique to Earth, making life elsewhere less likely to occur. " What do they base this on? How can they say plate techtonics are going to be relatively unique to earth? Considering we have very few examples to derive that kind of conclusion. There is a hypothesis that Earth's plate tectonics are rather unique, because their origin is the outcome of the collision between a primordial Earth and a planetoid. According to this hypothesis, the collision stripped off much of the Earth's crust and this matter largely ended up forming the moon. Then plate tectonics began because the remaining crust was thinner and had an uneven distribution on the Earth's surface. Plate tectonics should be helpful for the maintainenece of life, because it recycles the lithosphere, repleneshing minerals and CO2. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

centsworth_II · Nov 29, 2004

There's also the possibility that plate tectonics relies on the presence of a substantial hydosphere to act as a lubricant. I have to mention that arguments put forward in "Rare Earth" may be suspect to the extent that there may be a creationist agenda behind them. Not to say that they are not scientific, just that there is a bias, as there is in much of science. Its just important to know what the bias is when there is one. <div class="Discussion_UserSignature"> </div>

JonClarke · Nov 29, 2004

Good old Meyerhoff! Funeral by funeral science advances! <img src="/images/icons/smile.gif" /> Jokes aside, while PT is a very useful paradigm, it does not explain everything. Vertical movements also appear very important, possibly related to mantel plumes - themselves very contraversial. In particular the connection between mountains as plate movements is very poorly understood. Sites of plate collision are places of strong deformation, but uplift may occur later. Mountains require uplift, but not neccessary deformation. Some mountains are cut into flat-lying rocks. Uplift seems more related into intraplate readjustment of stress, others to crustal underplating, yet others we don't know. But there are more people out there sceptical of PT than you might think. I have several colleagues in this category. Some might be older scientsists who will carry their scepticism to the grave but not all of them. The problem is that, because of its apparently all encompassing explanatory power, many people accept PT uncritically. As an aside regarding comments later in the discussion, I don't think it is helpful to label views we regard as suspect (such as rare earth) as being possibly "creationist". The rare earth argument has nothing to do with "creationism", itself a badly misused and misunderstood term. Cheers Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

Saiph · Nov 29, 2004

plate tectonics: It exists, because it is observed. We can measure and observe the motion of various plates. The question is: Why do they move? 1) They ride mantle convection currents. But is this enough? Why doesn't Venus have a similarly complicated plate structure? 2) Thermal Plumes, similar to convection but not as "organized". Also they are more forceful. 3) Gravity. Various bulges and depressions caused by the different weight of various plates (or parts of a plate) may allow the plates to slide "downhill" also fostering motion. There were a few others mentioned in my geology class a month or so ago, but I can't remember them. Each has it's camp, but many believe a mixed bag prevails (the question is, what are the proportions?) <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

earthseed · Nov 29, 2004

First, I would like to note that the practicing geologist here sees the most limitations of plate tectonics. The existance of mountain ranges and fault lines do not in themselves prove the correctness of plate tectonic theory. Let me make clear, I believe the theory is basically right, but science is not about belief. By taking on this critique my knowledge will get better. Unless someone sets me straight, I am going to concede the thick continent argument to Pratt. We have several competing theories (whole and layered mantle convection, ridge push, slab pull, etc) of what drives the plates, but no clear idea. This does not affect the reality of the theory one bit. Whether it occurs or not is a matter of observation - are the continents moving as it describes, or not?. A nice complete explanation is only icing on the cake. Unlike Wegener in the 1920's and plate tectonics people in the 1960's, today we no longer need to rely on indirect evidence. As maddad said, "we can see the plates moving." To me, that means if we take a set of measurements between points on different plates, there should be consistent evidence of movement in the direction that plate tectonics theory suggests. Let me quote Pratt's take on that (from here):<blockquote>Measurements using space-geodetic techniques -- very long baseline interferometry (VLBI), satellite laser-ranging (SLR), and the global positioning system (GPS) -- have been hailed by some workers as having proved plate tectonics. Such measurements provide a guide to crustal strains, but do not provide evidence for plate motions of the kind predicted by plate tectonics unless the relative motions predicted among all plates are observed. However, many of the results have shown no definite pattern, and have been confusing and contradictory, giving rise to a variety of ad-hoc hypotheses (Fallon and Dillinger, 1992; Gordon and Stei</blockquote>

earthseed · Nov 29, 2004

I did not really want to discuss Rare Earth in this thread. A good summary of the relationship of the moon and plate tectonics is found here. But as for this being an amazingly lucky coincidence, this article suggests the impactor that caused the moon's formation developed at a Lagrange point on the Earth's orbit, and is thus a likely outcome of planet formation. As for the "creationist" influence on Rare Earth, read this article. Guillermo Gonzalez, the "influence" in question, believes in life only on Earth, but is not a creationist, by which I mean 7,000 year old Earth. I think Ward and Brownlee's excellent book still stands on its own merits, no matter what impact Gonzalez had on it. Anyway, if we want to talk Rare Earth, please lets start another thead.

bobvanx · Nov 29, 2004

Over in my thread with the giant circles, one idea I hadn't posted was that PT could be called into question. So, thanks, earthseed! The entire western US really stands out, to me, in that it has a vast, sparsely settled "mantle." Look at he night picture, and you can see there's a center ring, and outer "dead" area, and then the outer rim (which California shows a really nice chord of the circle). Intraplate movement to rumple the Rockies looks pretty evident. But I am imagining, where did the rock come from in the first place? What if it's the shell of an ancient planetismal that "landed" rather than "impacted?" Other areas are eastern China, and northern South America, all showing various circular morphology, on a very big scale.

spacester · Nov 30, 2004

I was surprised (or confused) to read that intraplate deformation was somehow radical thinking. To assume otherwise would be equivalent to what I know of as a "solid body" assumption, used in basic stress analysis in Mechanical Engineering. It's one of those useful assumptions engineers make to get a handle on a complicated situation, but it is too simple to really tell what's going on. It would seem obvious to me that the mass of the continent would stretch and torque and warp as a secondary effect of the movement at its margins. Primary effect: gross movement, secondary effect: topological variation. <div class="Discussion_UserSignature"> </div>

centsworth_II · Nov 30, 2004

"...this article suggests the impactor that caused the moon's formation developed at a Lagrange point on the Earth's orbit, and is thus a likely outcome of planet formation." Thanks for the links. As we get the chance to study more and more planetary systems, we may find that the series of events that seem to have made Earth a unique planet are not so unlikely after all. <div class="Discussion_UserSignature"> </div>

Saiph · Nov 30, 2004

steve: Earthseed is actually being pretty reasonable and rational about this, so ease up. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

centsworth_II · Nov 30, 2004

"...plate tectonic theory. Let me make clear, I believe the theory is basically right, but science is not about belief. By taking on this critique my knowledge will get better." -- earthseed "ES is at it again, very clearly. This person is full of beliefs which are false and yet strongly believed in, yet persist despite the facts & all reason." -- stevehw33 ES's statement seems reasonable, exemplary even. Have the posters at SDC really become so rational that you are reduced to jumping on someone who states general agreement with a widely accepted theory, but wants input regarding possible problems with that theory? There are really no better targets out there for you? <div class="Discussion_UserSignature"> </div>

centsworth_II · Nov 30, 2004

"Plate tectonics is an established fact. The theory works and is very well substantiated." -- shw33 Yes, but there is plenty of room for improvement. And it is definately not a Theory of Everything. Every geologic happening on Earth is not necessarily explained by plate tectonics and there is still plenty of work to do to determine what is and what is not due exclusively or in part to PT. Not neat, not cut and dried. Plenty of room for discussion. <div class="Discussion_UserSignature"> </div>

Saiph · Nov 30, 2004

steve: 1) This is earthseed, not extrasense 2) He's saying plates move, and flex 3) He's merely discussing the cause of the motion and flex, which is a more controversial and undecided than you'd think. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

spacester · Nov 30, 2004

So it's true that PT theory basically assumes that the plates are rigid bodies that don't flex and bend? If true, I am astonished at the simplicity. Many simplifying assumptions are made in the early days of trying to understand a complicated natural phenomenon. But a robust theory needs to go back and address those assumptions. Are they just now starting to do that with PT? <div class="Discussion_UserSignature"> </div>

Saiph · Nov 30, 2004

Now they're doing a more thurough job. You start with simple things, and work your way up, filling in the cracks as you go. So to begin with, they treated the plates as rigid, or mostly so (maybe some bowing in the center). Actually, they probably just didn't address it. Now that the science behind it has matured, they look at the flexing and mid-plate stresses. You have to, in order to explain earthquakes in nebraksa, various land formations, rift valleys. So the theory treats them as mostly rigid, though many geologists make a living studying the exceptions (which are many). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

earthseed · Nov 30, 2004

I am glad most people understand what I am trying to say here. I personally think that plate tectonics is by far the best description we have of the large scale behaviour of the Earth. "Established fact" is a bit strong for something we can't directly see and has mostly occured in the distant past. Of course, forty years ago stevehw33 would be telling us that "Continents Can't Move" was an established fact, and wonder about the motiviation of those damned Continental Drifters. As for this statement:<blockquote>There are NO volcanos in Tibet or Nepal. There is no subduction going on there. There is no oceanic crust. There is massive collision between two plates, just as in the Swiss Alps as Italia pushes into southern Europe.</blockquote>Well, not quite. The Himalayas have a long history of magmatic activity due to the subduction of the Tethyan oceanic crust (see this article). There is also good evidence for some subduction of continental crust, which has been returned to the surface as metamorphic rock. There are no active volcanoes today. The comparison to sourthern Europe is good, as that is extremely complicated as well. The Earth is a very complex place, and no single theory can explain all of it. While I don't think plate tectonics will ever be replaced, there are many parts of the theory that need refinement. That will occur only by challenging the theory, not by blindly accepting it as gospel truth.

bobvanx · Dec 1, 2004

I wonder what swh33 does during an earthquake.

bobvanx · Dec 1, 2004

<blockquote>In reply to:<hr />the presumed role of water in plate tectonics<hr /></blockquote>I recall a Japanese researcher who had worked out that the zones were lubricated by hydrated minerals, and as the earth cooled, it continued to sop up water. He suggested that the oceans were in fact, disappearing, and that we had some wildly short amount of time left before the water was all trapped. I wonder if I can track any of that down...

bobvanx · Dec 1, 2004

Well, it wasn't a Japanese reseacher that I found:link "... Nolet points out that in coming eons, as the interior of Earth cools, mantle plumes may occur less frequently. Then more water will go down than comes up. The surface oceans will gradually drain into Earth's interior, making our planet a dry world like Venus or Mars." In the same article, it talks about deep subducted water (250 miles!) acting as a lubricant.

Plate Tectonics: A Paradigm Under Threat?

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