Misplaced Pages

Charles Lyell defended uniformitarianism. Uniformitarianism blocked continental drift. Quote; Oreskes, Naomi. The rejection of continental drift: theory and method in American earth science, page 200: "Charles Schubert subscribed to a substantive uniformitarianism: the belief, expounded most famously by Charles Lyell, that the Earth today is more or less as it has always been". --Chris.urs-o (talk) 20:06, 30 August 2010 (UTC)

comment added by Jpvandijk (talkcontribs) 10:05, 31 August 2010 (UTC)): Oreskes, N. (1999); The Rejection of Continental Drift: Theory and Method in American Earth Science. Oxford University Press, 420 pp.

Very interesting the opinion expressed by Oreskes, and it stimulates surely some discussion. As promised, yesterday I checked all three volumes of Charles Lyell in the original form. In fact, he rejects any type of specific process that does anything else than impose vertical movements upon the Earth crust, to make sea where once land was and opposite (so its not really the Earth which has always been as it was, it are the Processes and Agents that have remained the same) infinitely and without any clearly defined regularity, which is the basis of his type of uniformitarianism. He doesn't speak at all about anything related to shifting continents. The only thing I noticed he talks a little bit about is the resemblance between the directions like N-S on the Globe of some volcanic chains as was used by his forerunners to expose other ideas, but he assigns this to merely accidental. The argument can be exposed more in detail elsewhere, on the page dedicated to Charles Lyell. I would say that in terms of Plate tectonics, he, therefore, doesn't play a role in development or early proposals of the concepts. We must, on the other hand, not forget that also Plate Tectonics is a sort of uniformitarianism if we suppose that the Processes related have been active always in the same way. So it's not the problem of uniformitarianism that "blocked" the acceptance of continental drift I would say. Anyway thats not the question here. comment added by Jpvandijk (talkcontribs) 10:05, 31 August 2010 (UTC))

Tectonic Plate movement

The below paragraph is quite weak:

Tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. Dissipation of heat from the mantle is acknowledged to be the original source of energy driving plate tectonics. The current view, although it is still a matter of some debate, is that excess density of the oceanic lithosphere sinking in subduction zones is the most powerful source of plate motion. When it forms at mid-ocean ridges, the oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age, as it conductively cools and thickens. The greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate motions. The weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. Although subduction is believed to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the North American Plate which are moving, yet are nowhere being subducted. The same is true for the enormous Eurasian Plate. The sources of plate motion are a matter of intensive research and discussion among earth scientists.

Some objections:

1. Density is NOT the main issue; the issue is that the mantle is molten and the crust is solid.

2. If we look at the Mid-Ocean Ridge, we see that there is rising magma from the mantle. This pushes upward. So, it is CONVECTION that drives the movement.

3. "Sinking" is NOT the real issue here. We only see "subduction" zones where one plate goes under another. We don't see sinking, but instead a being forced downward.

So, the bottom line is, the above paragraph is a violation of common sense, and poorly sourced to boot. Ryoung122 10:27, 29 April 2010 (UTC)

This is not the whole story, if something gets more dense and sinks, something has to come up instead in a globus. --Chris.urs-o (talk) 10:32, 29 April 2010 (UTC)

That paragraph can be improved. However, #1 is wrong on both counts (mantle is solid, and its convection is density-driven) and #3 is partially right (the reason one goes up and the other goes down is density). For #2, it is true that "ridge push" is important. But this is because of the dynamics topography produced at ridges which creates a gravitational potential energy high there. When considering oceanic crust, it's not that mantle convection pushes it along. It is the upper boundary layer of the convection system.

So I see your point that convection must be mentioned, and I agree, but it might be worthwhile doing a little more reading about the topic before changing it. Awickert (talk) 16:53, 29 April 2010 (UTC)

Well, the ultimate driving force is the heat. If the subducted plate is not melted down, then the machine would stop. --Chris.urs-o (talk) 04:35, 30 April 2010 (UTC)

Yes and no. Heat drives convection. But the subducted plate is not melted (a small bit of it may be); it does change phase, however. Awickert (talk) 07:35, 30 April 2010 (UTC)

Giant impact hypothesis

I seem to recall hearing something about the possibility that the hypothesized Mars-sized planet that impacted the early Earth and created the Moon may have something to do with plate tectonics. I haven't had a chance to do any research into this, but the idea I read about or saw on some documentary is that the impact could have cracked the crust of the early Earth like an egg leading to the plates. Has this been discredited? Does anyone know of any research into this notion? Mego2005 (talk) 14:28, 18 May 2010 (UTC)

I've never heard anything about it, and I doubt it. The impact would have been more cataclysmic than to just fracture the upper layers. Plus, oceanic lithosphere is the upper part of mantle convection cells, and that seems to be what drives plate tectonics. Google Scholar is a good first step if you want to give it a search. Awickert (talk) 15:11, 18 May 2010 (UTC)

Giant impact hypothesis/ Theia (planet). It has something to do with the Earth's core and its magnetic field. --Chris.urs-o (talk) 09:28, 6 July 2010 (UTC)

I finally had some hazy recollection of where I heard about the impactor leading to plate tectonics -- it was in an article or documentary regarding the Rare Earth hypothesis. The Wiki article mentions it briefly: "The impact that formed the Moon may also have initiated plate tectonics..." but doesn't cite any reference about this particular point. Mego2005 (talk) 17:17, 22 July 2010 (UTC)

A more likely suggestion (as I naïvely see it) is that the crust before the impact was all continental; the impact punched an ocean-sized hole, allowing movement. —Tamfang (talk) 04:49, 30 July 2010 (UTC)

Grammar

"Plate tectonics (from the Late Latin tectonicus, from the Greek: τεκτονικός "pertaining to building") is a scientific theory which describes the large scale motions of Earth's lithosphere. It is vital for the existence of life on earth because of the role that it plays in the global cycle that maintains the balance of carbon between the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere".

Logically, the "It" which begins the second sentence refers to the noun "theory". Thus the paragraph is telling us that the theory is vital for the existence of life on earth, which seems unlikely. Intelligent Mr Toad (talk) 08:38, 3 June 2010 (UTC)

Removed the "vital for..." sentence. Unsourced and nothing appears in the article body to support its place in the lead. Vsmith (talk) 12:31, 3 June 2010 (UTC)

Development of the Theory

Is there a reference for the sentence "It was at this point that Wegener's theory became generally accepted by the scientific community", since it seems to be referring to the mid 1950's, which is at least ten years too early. Even one of the references (number 35) at the end of the paragraph indicates that the theory was only built upon after 1961:

"The result was the famous magnetic anomaly map (Mason and Raff, 1961; Raff and Mason, 1961) demonstrating the existence of bands of anomalously high and low magnetization having continuity over hundreds of miles-the fundamental building blocks of seafloor spreading and its successor plate tectonics."

It's not a major thing, but unless there is a reference, I think the sentence could just be deleted. Ersby (talk) 09:12, 18 August 2010 (UTC)

Agree and removed the sentence. "At this point..." seems quite out of place and as Ersby says, a decade too early. Vsmith (talk) 13:22, 18 August 2010 (UTC)

Possible flaws?

• Earth Rotation related Driving Forces
  • Quote: "Global reghmatic shear patterns". Is this a typo or is there a simpler word for this sentence?
• Mantle Convection related Driving Forces
  • Quote: "In that theory the mantle flows not in cells but in large scale channels, and the direction of the flow is strongly influenced by the Earth's rotation (see below)." Where is the see below?
• Ridge spreading, Subduction rediscovered, and Plate tectonics were born
  • Quote: "(the former published the same idea one year earlier in Nature; However, priority belongs to Hess, since he had already distributed an unpublished manuscript of his 1962 article by 1960)" Capital letters and brackets is this allowed? --Chris.urs-o (talk) 18:40, 6 September 2010 (UTC)

I removed the first thing in parentheses; that word seems to be all but unused. Its paragraph may be quite a bit of WP:OR as well. The second issue is in a sentence about something that is fringe and physically implausible, so I saved us the trouble and just deleted it. That whole section though ("Mantle Convection related Driving Forces") will need quite a bit of work; it will go on my to-do list. For the third, the "However" should not have been capitalized, but I just reworded. Awickert (talk) 07:13, 7 September 2010 (UTC)

Thx ;) You are quite a roadrunner (Geococcyx velox) :D --Chris.urs-o (talk) 07:17, 7 September 2010 (UTC)

A "lesser roadrunner"? Well, isn't that a backhanded compliment :). I finally took a paleontology course last Spring, but still don't know much about life, so thanks for the link. Awickert (talk) 07:22, 7 September 2010 (UTC)

Some comments:

• The surge tectonics theory is still much quoted. Its not physically unplausible, as it was tested against mantle tomography models and maybe its not to us to bother about physical plausibiliy, there are lots of models and mechanisms cited here that are seen by many as plausible and by others as unplausible. Jpvandijk (talk) 16:16, 7 September 2010 (UTC)
• Its actually strange there is not yet a Misplaced Pages page on the surge tectonics model, which was quite popular in a certain time span during the ninetees and certaintly not less important than the latest mantle plume models. We could say that it is just one of the variations of mantle flow and delamination modes. We should put back the references. Jpvandijk (talk) 16:16, 7 September 2010 (UTC)
• I will give some more information on the regmatic patterns. They are used a lot by Storetvedt, and also others revived them in their 21st century models. There is quite some literature on this subject refering to the first half of the nineteenth century, but this is out of the Plate Tectonic concepts page I would say. It is only cited to show the relationship between the observed kinematics and the later developed ideas. I will give some more information. Jpvandijk (talk) 16:16, 7 September 2010 (UTC)

Ok. Plate tectonics is at 75 kBytes, quite a lot I'd say. A page needs to be kept manageable in order to be able to achieve a good quality. Surge tectonics theory and Global reghmatic shear patterns might be out of scope of the broad view of this page. I liked that you showed the link between hotspot, mantle plume, plume tectonics and plate tectonics. We have geos on Misplaced Pages, they might help reach a consensus: User:Awickert, User:Vsmith, User:Mikenorton, User:Geologyguy, User:DanHobley. --Chris.urs-o (talk) 06:15, 8 September 2010 (UTC)

Thanks for all of the info, Jpvandijk! I will stay out of your way for the moment, as you clearly know more about the history of this than I do. I had never heard of surge tectonics (in spite of doing quite a bit of geodynamics), but that may just be my young-ness. Awickert (talk) 07:13, 8 September 2010 (UTC)

Thanks for the feed back, and actually the page plate tectonics is getting a little long, but its also quite an important issue in Earth Sciences, a sort of unifying theory everything is linked to nowadays. As many call it's "a paradigm". Well the link between all the items related to mantle dynamics is actually one of the main issues nowadays amongst us geoscientists, and the request to create some order is therefore justified. I'll try to do something here, so that also some of the background information can be transported to other pages more dedicated to the arguments.Jpvandijk (talk) 10:21, 8 September 2010 (UTC)