Guest “Did you know?” by David Middleton
An upwelling of rock beneath the Atlantic may drive continents apart
The Mid-Atlantic Ridge may play a more active role in plate tectonics than thoughtBy Maria Temming
FEBRUARY 4, 2021
An upsurge of hot rock from deep beneath the Atlantic Ocean may be driving the continents on either side apart.
The Americas are moving away from Europe and Africa by a few centimeters each year, as the tectonic plates underlying those continents drift apart. Researchers typically think tectonic plates separate as the distant edges of those plates sink down into Earth’s mantle, creating a gap (SN: 1/13/21). Material from the upper mantle then seeps up through the rift between the plates to fill in the seafloor.
But new seismic data from the Atlantic Ocean floor show that hot rock is welling up beneath a seafloor rift called the Mid-Atlantic Ridge from hundreds of kilometers deep in Earth’s mantle. This suggests that material rising up under the ridge is not just a passive response to tectonic plates sliding apart. Rather, deep rock pushing toward Earth’s surface may be driving a wedge between the plates that helps separate them, researchers report online January 27 in Nature.
A better understanding of plate tectonics — which causes earthquakes and volcanic eruptions — could help people better prepare for these natural disasters (SN: 9/3/17).
[…]
Science News
Spreading centers drive continents apart? Who could have guessed? Uhm… Just about everyone since at least the late 1960’s.
What drives the plates?
From seismic and other geophysical evidence and laboratory experiments, scientists generally agree with Harry Hess’ theory that the plate-driving force is the slow movement of hot, softened mantle that lies below the rigid plates. This idea was first considered in the 1930s by Arthur Holmes, the English geologist who later influenced Harry Hess’ thinking about seafloor spreading. Holmes speculated that the circular motion of the mantle carried the continents along in much the same way as a conveyor belt. However, at the time that Wegener proposed his theory of continental drift, most scientists still believed the Earth was a solid, motionless body. We now know better. As J. Tuzo Wilson eloquently stated in 1968, “The earth, instead of appearing as an inert statue, is a living, mobile thing.” Both the Earth’s surface and its interior are in motion. Below the lithospheric plates, at some depth the mantle is partially molten and can flow, albeit slowly, in response to steady forces applied for long periods of time. Just as a solid metal like steel, when exposed to heat and pressure, can be softened and take different shapes, so too can solid rock in the mantle when subjected to heat and pressure in the Earth’s interior over millions of years.The mobile rock beneath the rigid plates is believed to be moving in a circular manner somewhat like a pot of thick soup when heated to boiling. The heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again. This cycle is repeated over and over to generate what scientists call a convection cell or convective flow. While convective flow can be observed easily in a pot of boiling soup, the idea of such a process stirring up the Earth’s interior is much more difficult to grasp. While we know that convective motion in the Earth is much, much slower than that of boiling soup, many unanswered questions remain: How many convection cells exist? Where and how do they originate? What is their structure?
Convection cannot take place without a source of heat. Heat within the Earth comes from two main sources: radioactive decay and residual heat. Radioactive decay, a spontaneous process that is the basis of “isotopic clocks” used to date rocks, involves the loss of particles from the nucleus of an isotope (the parent) to form an isotope of a new element (the daughter). The radioactive decay of naturally occurring chemical elements — most notably uranium, thorium, and potassium — releases energy in the form of heat, which slowly migrates toward the Earth’s surface. Residual heat is gravitational energy left over from the formation of the Earth — 4.6 billion years ago — by the “falling together” and compression of cosmic debris. How and why the escape of interior heat becomes concentrated in certain regions to form convection cells remains a mystery.
[…]
USGS
From the time I graduated from college in 1980, up until a few minutes ago (when I read the Science News article), I assumed that every geoscientist knew that mantle convection drove seafloor spreading, which in turn drove continents apart.
However, it appears that this was turned bass-ackwards while I was busy looking for oil & gas, rather than reversing cause and effect. In much the same manner that atmospheric CO2 suddenly became the geological driver of climate change in 1988, subduction apparently became the driver of seafloor spreading…
Until the 1990s, prevailing explanations about what drives plate tectonics have emphasized mantle convection, and most earth scientists believed that seafloor spreading was the primary mechanism.
Cold, denser material convects downward and hotter, lighter material rises because of gravity; this movement of material is an essential part of convection. In addition to the convective forces, some geologists argue that the intrusion of magma into the spreading ridge provides an additional force (called “ridge push”) to propel and maintain plate movement. Thus, subduction processes are considered to be secondary, a logical but largely passive consequence of seafloor spreading. In recent years however, the tide has turned. Most scientists now favor the notion that forces associated with subduction are more important than seafloor spreading. Professor Seiya Uyeda (Tokai University, Japan), a world-renowned expert in plate tectonics, concluded in his keynote address at a major scientific conference on subduction processes in June 1994 that “subduction . . . plays a more fundamental role than seafloor spreading in shaping the earth’s surface features” and “running the plate tectonic machinery.” The gravity-controlled sinking of a cold, denser oceanic slab into the subduction zone (called “slab pull”) — dragging the rest of the plate along with it — is now considered to be the driving force of plate tectonics.
We know that forces at work deep within the Earth’s interior drive plate motion, but we may never fully understand the details. At present, none of the proposed mechanisms can explain all the facets of plate movement; because these forces are buried so deeply, no mechanism can be tested directly and proven beyond reasonable doubt. The fact that the tectonic plates have moved in the past and are still moving today is beyond dispute, but the details of why and how they move will continue to challenge scientists far into the future.
USGS
Another inexperienced wet-behind-the-ears science journalist with a “participation” degree who has zero real world experience but can write 2,500 words about anything and everything to satisfy what the editor wants.
Alfred Wegner will be happy again 😀
The great man’s name was Alfred Wegener.(just saying).
Sorry for typo, ….happens
Modern “scientists” are a product of a modern “college”, formerly “kindergarten”. I support Kamala Harris’s effort to make the college education free. It is already worth every penny.
Nick, notice that the failure of the pull hypothesis is in the obducted plates, where oceanic crust rides up and over the continental plate instead of undergoing downward subduction. This realization supports the null hy0pothesis for the pull theory. I grew up in Oregon on the obducted Klamath Terrain, and it was the center for nickel and chrome production for the US, these elements coming from the ultramafic intrusive rocks contained within the mafic oceanic rocks.
Geology is full of paradoxes.
The theory which they call the Tectonic Plate theory is missing a force to move the plates.
“Alfred Wegener’s theory of continental drift died in 1926, primarily because no one could suggest an acceptable driving mechanism. In an ironical twist, continental drift (now generalized to plate tectonics) is almost universally accepted, but we still do not understand the driving mechanism in anything other than the most general terms”2.”
Do the tectonic plates move?
Yes, absolutely.
However, it is a fact that the plates are moving and have moved in complex ways (dozens and dozens of hard observational paradoxes that killed the mantel deep convection theory)…
…that are absolutely impossible for the “mantel deep convection’ and Slab to cause/explain.
Geology is an odd field. It is constrained. There absolutely must be a real, physical force to move the massive tectonic plates.
The ocean plates are pushed apart at the ocean ridges.
https://www.newgeology.us/presentation21.html
“In recent years, the kinematics of continental drift and sea-floor spreading have been successfully described by the theory of plate tectonics.
However, rather little is known about the driving mechanisms of plate tectonics, although various types of forces have been suggested”14. Seven years later, in 1982, the assessment was:
“At the present time the geometry of plate movements is largely understood, but the driving mechanism of plate tectonics remains elusive”3. By 1995 we find that:
“In spite of all the mysteries this picture of moving tectonic plates has solved, it has a central, unsolved mystery of its own:
What drives the plates in the first place? ‘[That] has got to be one of the more fundamental problems in plate tectonics,’ notes geodynamicist Richard O’Connell of Harvard University.
‘It’s interesting it has stayed around so long’ “25. In 2002 it could be said that: “Although the concept of plates moving on Earth’s surface is universally accepted, it is less clear which forces cause that motion.
http://www.davidpratt.info/tecto.htm
“The driving force of plate movements was initially claimed to be mantle deep convection currents welling up beneath midocean ridges, with downwelling occurring beneath ocean trenches.
Since the existence of layering in the mantle was considered to render whole-mantle convection unlikely, two layer convection models were also proposed.
Jeffreys (1974) argued that convection cannot take place because it is a self-damping process, as described by the Lomnitz law.
Plate tectonicists expected seismic tomography to provide clear evidence of a well-organized convection-cell pattern, but it has actually provided strong evidence against the existence of large, plate-propelling convection cells in the upper mantle (Anderson, Tanimoto, and Zhang, 1992).
Many geologists now think that mantle convection is a result of plate motion rather than its cause and that it is shallow rather than mantle deep (McGeary and Plummer, 1998).”
“The driving force of plate movements was initially claimed to be mantle deep convection currents welling up beneath midocean ridges, with downwelling occurring beneath ocean trenches.
Since the existence of layering in the mantle was considered to render whole-mantle convection unlikely, two layer convection models were also proposed.
Jeffreys (1974) argued that convection cannot take place because it is a self-damping process, as described by the Lomnitz law.
Plate tectonicists expected seismic tomography to provide clear evidence of a well-organized convection-cell pattern, but it has actually provided strong evidence against the existence of large, plate-propelling convection cells in the upper mantle (Anderson, Tanimoto, and Zhang, 1992).
Many geologists now think that mantle convection is a result of plate motion rather than its cause and that it is shallow rather than mantle deep (McGeary and Plummer, 1998).”
https://www.newgeology.us/presentation21.html
Plate Tectonics: too weak to build mountains
“In 2002 it could be said that: “Although the concept of plates moving on Earth’s surface is universally accepted, it is less clear which forces cause that motion. Understanding the mechanism of plate tectonics is one of the most important problems in the geosciences”8. A 2004 paper noted that “considerable debate remains about the driving forces of the tectonic plates and their relative contribution”40. “Alfred Wegener’s theory of continental drift died in 1926, primarily because no one could suggest an acceptable driving mechanism. In an ironical twist, continental drift (now generalized to plate tectonics) is almost universally accepted, but we still do not understand the driving mechanism in anything other than the most general terms”2.”
“The advent of plate tectonics made the classical mantle convection hypothesis even more untenable. For instance, the supposition that mid-oceanic ridges are the site of upwelling and trenches are that of sinking of the large scale convective flow cannot be valid, because it is now established that actively spreading, oceanic ridges migrate and often collide with trenches”14.
“Another difficulty is that if this is currently the main mechanism, the major convection cells would have to have about half the width of the large oceans, with a pattern of motion that would have to be more or less constant over very large areas under the lithosphere.
This would fail to explain the relative motion of plates with irregularly shaped margins at the Mid-Atlantic ridge and Carlsberg ridge, and the motion of small plates, such as the Caribbean and the Philippine plates”19.
The two opposing models of plate tectonic motion are a false dichotomy. But wait! It’s both!
It’s driven by both top-down (slab-pulled) and bottom-up mantle convection (upwellings and plumes). The interior actively drags the surface and vice versa.
Relies on modeling, but appropriate in this application. From 2019:
What drives tectonic plates?
https://advances.sciencemag.org/content/5/10/eaax4295
Abstract
Does Earth’s mantle drive plates, or do plates drive mantle flow? This long-standing question may be ill posed, however, as both the lithosphere and mantle belong to a single self-organizing system. Alternatively, this question is better recast as follows: Does the dynamic balance between plates and mantle change over long-term tectonic reorganizations, and at what spatial wavelengths are those processes operating? A hurdle in answering this question is in designing dynamic models of mantle convection with realistic tectonic behavior evolving over supercontinent cycles. By devising these models, we find that slabs pull plates at rapid rates and tear continents apart, with keels of continents only slowing down their drift when they are not attached to a subducting plate. Our models show that the tectonic tessellation varies at a higher degree than mantle flow, which partly unlocks the conceptualization of plate tectonics and mantle convection as a unique, self-consistent system.
I suggest that the writer, a 1980 grad, reread Forsyth and Uyeda (1975), which demonstrated that plate forces (and gravity) are the primary drivers of plate motion (i.e. “geodynamics”), and that convection is a secondary consequence, and is not itself the primary driver.
https://academic.oup.com/gji/article/43/1/163/586101
Also, since we’re talking about plate tectonics here, it’s important to keep in mind that the original theory of plate tectonics by McKenzie, Le Pichon, et al. was entirely kinematic, i.e. it merely described plate motion and was entirely agnostic with respect to the cause.
So you think one paper “demonstrates” anything?
\it appears that soft tectonic plate (warm, out of the oven cookie-like) movement on a much hotter mantle preceded hard plates, with deeper subduction:
Like you David this is the first that I heard of it if 50 yrs in POil business. I don’t see the mechanism for heavy crust sinking. Isn’t it lighter? I thought it was but no matter. For subduction drag you would need to invoke plates being strong in TENSION. Since transform faults indicate weakness in shear, strength in Tension would seem to me to be unlikely. Funny that we never heard of any discussion on spreading paradigm given our good links with Geol Soc and other bodies, and academia in general. Perhaps this might just be a loose cannon journo with a “Scientists say Plate Tectonics is worse than we thought” narrative.
Alastair Gray,
Agree. Rocks are very weak in extension, and especially so if fractured and faulted as are the seafloor bedrocks.
In extension, many solid rocks have a strength of only about 200 psi if not full of cracks and faults. Not very much. You can not drag a 10 km thick mass of rock like that across the seafloor by pulling on one end that is ~ 1500 km away. Two options: gravitational sliding or being moved by a conveyor belt comprised of the mantle convection.
Any other ideas?
You’re considering surface rock, not fluid filled strata underneath tremendous weight.
Robert,
Correct. I described the surficial and shallow structure and know that plastic or viscous fluid mantle material underlies the thin oceanic crust.
I understood the author to suggest that magma was pushing on the oceanic crust at the ridge and driving it toward the subduction zone. I do not believe in that but I do support the idea that there is mantle convection that drags the thin crust along for the ride, possibly down slope, i.e. a gravity assist. I agree with your statement elsewhere in this blog that we must consider the entire system and not just part of it.
I’m just an engineer with a passing familiarity with rock structure and characteristics, but I figured they weren’t very different than unreinforced concrete. I couldn’t imagine how the subducted portions of surface crust were pulling the rest of the continental train behind them.
Well stated from another professional point of view.
Because the crust is literally floating on the mantle. Where the mantle is sinking the crust sinks and pulls crust behind it, where the mantle is rising the crust rises and pushes crust in front of it. The crust only influences plate tectonics, but it is the mantle that drives it.
Do not disagree. Well stated. Separately, I do not believe in magma push as stated in the title paper.
I suggest you get a good text on geology to help with your confusion.
The “denser” phase that causes this alleged pull is something like a high pressure/low temperature phase, say eclogite, in the cool portion of a descending slab.
Nope.
Now you sound like Mosher.
The buckling up of the western margin of the Americas is compression at work transmitted by the pushing of the plates away from the upwelling mantle material at the mid-Atlantic Ridge. The ‘pull’ of the subducted Pacific plate as a mechanism is hard to accept as having forces and integrity of material sufficient to ‘tow’ the masses of the continental plates, buckle up the western mountains AND drive the upwelling in the mid Atlantic!
Here is a definitive thought experiment. How did this ‘towing’ start before there was a slab of Pacific oceanic crust under the western margin of the Americas to tow it? No! The idea is silly. Morover, the continents themselves would be a network of failures in tension of which there is no sign.
Actually there is little “bulking up” of the western margin of NA due to compression, The overwhelming force is extension (Hello Basin and Range). The western margin of NA has “bulked up” due to docking of exotic terranes which do show some compression after being run over by the NA plate (well actually a combo collision but less mass is always the looser). As to lack of evidence of failure of conventional crust as support, keep in mind that continental crust is very thick (average 70 KM) and mostly granitic and gneiss which, although prone to faulting and fracturing at the “surface” are very competent at depth. BTW thin-skin deformation should not be mistaken to reflect deeper lithosphere behavior.
Oops sorry I misread bucking as bulking. I should wear my glasses. Nevertheless, the western margin of NA is not “buckling up”. The overwhelming process is extension.
You ignore the remnants of the formerly vast Farallon Plate, now largely subducted under the NA Plate, causing at least some of the Rocky Mountains, and possibly the whole chain.
The Cascadian Subduction Zone is a triple juntion, where the Farallon remnant Juan de Fuca, mighty Pacific and North American Plates meet. The JdF is also fragmented into sub-plates.
The Cocos Plate off Central America and the Nazca Plate off South America are other remnants of the Farallon Plate.
Those plates are part of the Pacific sea floor, and are/were moving west to east. North America is moving east to west.
Obviously a plate in the Pacific that is moving west to east did not cause the Atlantic mid ocean ridge to form 90 million years ago and continue to spread to this day.
Any ideas that try to explain everything have to explain everything, in all places, all the way back in time.
At various times the continents had all joined together and then split apart again.
How on Earth is subduction any explanation for the forces that split the supercontinents up and propelled them around the planet?
Or caused them to accrete into a supercontinent to begin with?
India broke off from Antarctica and sprinted northwards clear across the Indian ocean. When it hit Asia, it kept going and underran it, creating a new mountain range two contents thick…which is still rising today as India continues to move north.
Subduction did that?
Where exactly is the subduction that is moving Africa and South America in opposite direction?
Where is the subduction that is forcing North America and the western margin of Eurasia in opposite directions?
What is thrusting Africa under Europe and raising up the alps and causing all the Mediterranean volcanoes?
How can subduction ever explain how sea floor crust winds up accreted onto continents?
The truth is all of the process and forces at work interact in complex ways, and what happens is the result of ALL of the things going on.
Anyone who thinks there is no appreciable mantle convection, is poorly informed and likely not very smart.
There was a line in the second Alien movie, where Sigourney Weaver inquires about how IQ’s have changed in the years she was in cryosleep.
Evidently it can happen in way less time than that.
I wonder when the new breed of glaciologists will assert that it is the terminus of glaciers moving downhill that pulls snow out of the sky and accumulate into the cirques that are the origin point for many of those glaciers, then sucks it down the mountain?
The fatal flaw of “subduction tectonics” is that oceanic lithosphere fails under extension.
See Doglioni et al. (2007).
151.100.51.154/sites/default/files/doglioni/2007DoglionietalSubductionKinematics.pdf
Subduction is a fact. Repeating what I’ve already commented, it’s observable and measurable.
No one disputes that subduction is a thing.
The issue at hand is whether or not subduction causes rifting and upwelling at spreading centers on the other side of the planet…IOW, is it the cart or the horse?
Where is the subduction that is dragging N.A. to the west a few inches every year?
That a more recent hypothesis explaining “continental drift” of tectonic plates, ie “subduction pulling”, cancelled the previously found fact of seafloor spreading (SFS), then revived by new evidence in favor of SFS, is a complete misstatement of the history of geology. Only reason I can see for this claim is to make the new paper appear more important, rather than just another confirmation of well-established SFS.
Here is what her link to the effect of sinking plates (subduction) has to say:
“Abundant new seismic data and amped-up computing power, meanwhile, led to insights about the mysterious regions where Earth’s tectonic plates were sinking back into the planet’s interior, dubbed “subduction zones.” A heavy, sinking slab of lithosphere, researchers discovered, can exert an extremely powerful pull on the rest of the plate — the first suggestion that subduction might be one of the main engines keeping plates on the move. Scientists also found that those plates might descend much deeper into Earth’s interior than once thought, and could play a big role in stirring up circulation of dense, hot rock within the mantle, the 2,900-kilometer-thick layer between the planet’s rigid outer layer and its superheated, metallic core.”
Even should such a pulling effect be confirmed, it wouldn’t invalidate the repeatedly-observed fact of seafloor spreading from mid-oceanic volcanic ridges. This fact has been repeatedly confirmed by a variety of evidences, not just observation of deep sea volcanic eruptions, but such further findings as the age of seafloor rocks, with younger close to the ridges and oldest near the continents. Little oceanic crust predates the beginning of the breakup of Pangaea, ~200 Ma.
Rifting can be seen around the world today, akin to that which caused the supercontinent to start splitting apart at the Triassic-Jurassic boundary.
We suggest the pressure of subduction elevated the Andes, it’s pressure, not gravitational head.
I remember reading many years ago, a theory that the Rockies were caused by the Pacific plate initially diving under the N. American continent, and then rising back up to strike, and crinkle the continent.
The Canadian Rockies were probably lifted by subduction of the Kula Plate and accretion of terranes.
Formation of the farther inland southern Rockies is more controversial. One hypothesis is subduction of the Farallon Plate. Another involves subduction of a hypothetical oceanic ridge.
https://en.m.wikipedia.org/wiki/Laramide_orogeny
T. rex witnessed the middle of it.
I saw a documentary yesterday that talked about how the rise of the Rocky Mountains caused the elimination of the inland sea that split the North American continent in two.
I had a National Geographic map I got out of the magazine one time, that showed the world when that inland sea was splitting the U.S. and it looked like my particular living area would be right on the eastern shore. I guess that means if all the ice on Earth melts, I will still be high and dry.
I heard an interesting tidbit tonight that said the amount of water ice on the north pole of Mars is equivalent to the amount of ice on Greenland.
The disappearance of the inland sea probably resulted both from the land rising and sea level retreating.
“Another involves subduction of a hypothetical oceanic ridge.”
There is nothing hypothetical about subducted ridges .The southern extent of one of them is plainly evident. It underlies the Gulf of California and extends southward from the mouth of that gulf, where it is called the East Pacific Rise.
This spreading center is pushing sea floor crust eastwards towards South America, which nonetheless continues to move towards the west. This collision is what has raised up the Andes.
The downwards directed forces of the subducting Pacific sea floor under South America is causing continent-sized masses of rock to be forced up into the sky several miles?
Or is the source of that energy the force(s) that is(are) driving North and South America to move to the West?
Convection currents in the mantle, or anywhere else, consist of a rising portion, a sinking portion, and two (or more) laterally moving portions, one at the top and one at the bottom. At least that is an idealized model of such a process. In reality, the Earth is a sphere, and is spinning, and many things are going on at once.
(A similarly idealized diagram of the primary circulation pattern of the atmosphere, shows the Hadley cells as lateral zones extending east and west around the whole planet, but that does not actually exist anywhere. Instead various other forces cause the belts to be broken up into discrete cells, and alternating zones of high and low pressure.)
A Lava Lamp may be a way to visualize what happens, although at far different scales of time and velocity, as well as size and shape of course.
Where subduction is the only source of energy and plate motion, such as is seen along the northern margins of the Pacific ocean, the result is island arcs.
Curved lines of volcanoes.
Everything that is happening in any location is the result of all of the factors, not one or another of the many.
If there were people who at one time thought that subducting plates did not go very far into the mantle, that is simply a failure of imagination on the part of those people, and lack of any way to be able to visualize it at the time.
It is impossible to understand geology as a series of disconnected events and processes.
“it wouldn’t invalidate the repeatedly-observed fact of seafloor spreading from mid-oceanic volcanic ridges”. Exactly; from the evidence we “see”, and which you describe, we can tell that the seafloor is spreading, but it’s harder to tell if the spreading is caused by push (at the mid-ocean ridges), pull (from the subducting plates), a current in the mantle (upwelling at the ridges splits so as to cause viscous flow to each side of the ridge, pushing the crust along with it), or some combination of these.
Pushing is a compressive force which would show reverse faulting (shortening). All evidence from active spreading ridges (axial riffs) and obducted oceanic plates show extension (normal faulting) and the dominate actor in oceanic plate formation. Sear-floor spreading is not caused by “pushing”
If I push my car, it may compress a little at first, but once it is moving, it is just rolling along in front of me.
There is no subducting portion of the North or South American plates to be doing any pulling.
There may have been at one time, perhaps when the Atlantic first opened up.
As a thought experiment, consider what might occur if North and South America stopped moving to the West, and began moving to the East again?
(We know that North American has been either stationary or moving eastwards several times in the past, each time ending in one or another of the orogeny’s that have shaped and built up the the Eastern parts of North America.)
Which part of the Atlantic would begin to subduct?
I think the oldest, thickest, and hence densest and heaviest part of the Atlantic would subduct eventually. Those would be the parts along the continental margins.
Would there be two subduction zones in the Atlantic, one in the east and one in the west?
I tend to doubt it. More likely one side or the other would detach from the adjacent continental crust and subduct, and the opposite side of the ocean basin crust would remain welded to it’s adjacent continental crust. And the mid Atlantic Ridge may in fact remain active in this scenario, adding new oceanic crust up until the point in time the spreading center itself was subducted.
Islands and small pieces of continental crust would be accreted onto existing continents.
Florida might end up at the top of a mountain range, with volcanoes here and there, and Cuba and the Bahama shelf crumpled alongside and beneath it.
Do I understand that right; the subduction of seafloor (f.e. western South America) is first, and the spreading in the middle of the Atlantic follows ?
Subduction plate pulling may have some effect, but IMO the ultimate cause of continental drift, ie tectonic plate splitting and subsequent motion apart, is first, volcanic rifting, leading to seafloor spreading from mid-ocean ridges.
Residents of the North American Atlantic Seaboard live on rocks of the Triassic-Jurassic Newark Supergroup, a feature of the Central Atlantic Magmatic Province (CAMP), during the formation of which their continent split apart from Africa and Europe, leading to the Central Atlantic Ocean. The massive CAMP eruptions are a likely cause of the End Triassic major extinction event, after which Jurassic dinosaurs inherited most of Earth’s land surface.
“Subduction plate pulling may have some effect, but IMO the ultimate cause of continental drift, ie tectonic plate splitting and subsequent motion apart, is first, volcanic rifting, leading to seafloor spreading from mid-ocean ridges.”
I would say tensional strength rock is not a lot as compared to it’s compressive strength.
And Earth is generating heat in couple way but mostly, it’s nuclear energy.
IMO, internal heat is presently about 50:50 residual thermal and nuclear.
Being more massive, we’ve so far avoided Mars’ fate.
You’re massively underestimating the nuclear. Uranium is more abundant than both gold and silver… in just the Earth’s crust. More dense too; now extrapolate how much is diffused into the core & mantle.
Then we have a ridiculous amount of potassium, not to mention all the lathanides just below the abundance of Pb.
Residual is more likely <20%
No, I’m not.
About equal amounts from the two heat sources, as per Turcotte and Schubert, Geodynamics, Cambridge U, 2002:
https://books.google.cl/books?id=-nCHlVuJ4FoC&q=primordial&pg=PA286&redir_esc=y#v=snippet&q=primordial&f=false
Map of heat flow to the surface:
A lot of heat in Antarctica.
If current theories are right and a Mars sized planet crashed into the earth a few billion years ago, then the Earths core is a lot larger compared to it’s over all mass.
The question becomes, what force caused the rifting?
That is what initiated the series of events and subsequent motions.
Rifting is not a cause, it is an effect.
No W of South america goes with mid pacific ridge system. Google Hazeen and Tharp pictures
You are right, of course 🙁
The East Pacific Rise spreading center is sending sea floor crust to the East.
I am unclear how anyone might think this somehow cause a rift to form and begin to spread and become an entire ocean, clear around the planet, when the effect of the E.P.R is to tend force the crust together in that location, not rip it apart.
See here:
http://2.bp.blogspot.com/-ERgmSc7P3bg/Vk4USTXmbMI/AAAAAAAAHCg/vu1F4X0u9j0/s1600/Destructive%2BMargin%2BDiagram%2BWhen%2Bdid%2Bthe%2BAndes%2Bmountains%2Bform-geology.jpg
Here is a somewhat different rendering:
226B-Image+Subducting+Plates.jpg (565×319) (bp.blogspot.com)
Clearly subduction in the Pacific has nothing at all to contribute to the current movements of North or South America, nor to the rifting that is ongoing for the past 90-some million years at the mid Atlantic Ridge.
That subduction is actually in opposition to all of those other processes.
That’s the currently accepted view, aka “subduction tectonics.”
Thanks for the posting, David. I was in on the start of plate tectonics in Graduate School and have been a believer in the spreading ridges being the driver ever since. Maria Temming has degrees in Physics, English, and Science Writing, none in geology. I think the regularity of the magnetic striping, produced by normal and reversed magnetic poles, suggests the driving force is the spreading ridge, other wise how can they be so regular?
Just how old are you?
There are a few of us still around.
I had Flint, who older geologists will recognize, for my first geology text, still us biologists came away at the time with the somewhat modern view that the continents fit, as did some fauna and flora back when. Recently an ocean modeler, I posted this way back, this millennium+ a decade finally discovered that the oceans were 3 dimensional, having done two for decades. I learned about the need for 3-d models about 46 years ago according to my calculator, about the same time plate tectonics began to be better understood. Van Andel’s Science at Sea–Tales of an Old Ocean (1977) should be required reading.
And we’re hoping you stick around for a few more aeons! Your contributions to WUWT are always enlightening. Thanks!
Phil,
You’re welcome.I am hoping that our next contribution on Venus makes the grade.
As of 1976-1980… The 97% plate tectonics consensus was still in its formative years. In Historical Geology, we learned all about the geosynclinal evolution of the Appalachian Mountains. The “funny thing” is that a lot of geosynclinal principles actually do apply to salt tectonics.
74. In college 64-67, in the Army 68-69, back to college, BSc , then continued through Graduate School for MSc.
The start of plate techtonics would have been about the time the earth cooled down enough to have a crust. Multiple billions of years ago.
Until the ’60s Alfred Wegener’s theory of “Continental Drift” was considered radical and had not been generally accepted. It wasn’t until the early ’60s that the term “Plate Tectonics” was coined an the theory rapidly gained ground. Sadly Wegener was never vindicated in his lifetime and suffered the same sort acrimony and viciousness, over his theory, that skeptics do today.
Provided that the theory is valid (very likely), you’re right, it has been around since Earth cooled enough to have a crust.
Of course Ron meant at the start of the theory of plate tectonics…
Actually the start of PT is a hotly debated topic for those that study the Precambrian. There is no consensus from the researchers although earlier rather than later seems to be the current flavor. There are several other types of planet tectonic behavior that could be candidates for the very young earth. I’m no expert but there is a very good presentation by Robert Stern “How and when did plate tectonics start on Earth, what came before and why does it matter?” that might help.
Unfortunately evidence in the really old rock is very poor (because the earth recycles it’s crust and there doesn’t appear ether to have had much or maybe most of it was destroyed by PT). Certainly by the late Archean (2.5 BY) we do see strong evidence of pate tectonics culminating in the assembly of the supercontinent Rodinia at around 1.3 BY.
Evidence from last year supports the early startup of plate tectonics:
https://www.sciencedaily.com/releases/2020/04/200422151310.htm
Is some new theorizing really what counts as “evidence” in science?
I think not.
Even evidence is only tentative, and ought to be discounted until it is confirmed by multiple lines additional of converging evidence, as well as consisting of a repeatable and reproducible result.
IOW…a paper could be published tomorrow describing how some rocks were dug up and analyzed and accompanied by some new ideas about what that evidence means.
But none of that by itself proves or “demonstrates” anything. It is just an idea and an assertion of a result.
All of the theorizing in the world will never add up to evidence.
“a believer in the spreading ridges being the driver”: I don’t see how the regularity of magnetic striping bears on the question of push (from the ridges) vs. pull (from subduction). Suppose for a moment that the plates were strong enough to be dragged across the mantle (or maybe the mantle is flowing in each direction from the mid-ocean ridges too). Where the crustal plates do break apart–in what we now call spreading zones–there is less pressure on the underlying mantle, so it wells up as molten rock, gluing itself to the receding plate edges rather like honey sticks to a biscuit. Wouldn’t that result in the same striping?
As for the question of push vs. pull, why not both? Otherwise the mid-ocean spreading has to be shoving the plates to each side *down*, and that seems unlikely.
There may well be both push and pull effects, mcswell. However you can’t pull an oceanic crust slab that far, it would break apart, so for me the push starts the process. These spreading centers/ridges have a long life, they even survive in segments if transform faulting starts to move them into different angles. However, the real evidence for the push being the controlling mechanism is the obduction plates. These occur when the oceanic plate rides up over the continental crush, instead of going into the subduction mode. I grew up in SW Oregon near the northern limit of the Klamath Terrain, an obducted plate. The area produced both nickel and chrome from cumulate layers in ultramafics contained with the mafic crust.
It does actually require the appearance of push, pull, slide and other motions. The cause of the motions was mantle convection back in the 70’s, with seafloor spreading driving some continental plates apart untill they mashed together. Most of the plate collisions feature some form of subduction zones, particularly where oceanic plates collide with continental plates.
My head hurts.
Non-Science News, I suggest. Deep movement of mantle material has been detected and located beneath the spreading center.
Simple test for the author: what is the structural style astride the mid-ocean ridge, the spreading center? The structural style gives a clue as to the forces involved.
For decades, it has been known that the structural style is extension, pull-apart faults; central graben and tilted blocks. This evidence from imaging of the seafloor indicates that the oceanic crust is being pulled away from the mid-ocean ridge. The physical evidence disproves the idea that the sea floor is being pushed apart at the ridge. This is not a secret. What evidence supports the largely discarded hypothesis that the ocean crust is being pushed apart?
A look at the bathymetry shows that the mid-ocean ridges are, well, ridges. Depths gradually increase towards the edges, Surely if the seafloor was pulled apart, the mid-ocean ridges would be trenches?
Yes, the Mid-Atlantic Ridge is the longest mountain range on the world and it is mostly under water except for Iceland,etc. It also has a very high heat flow because the crust is thin and magma exists at shallow depth.
The Mid-Atlantic Ridge has a “central rift valley”, i.e. a graben which is a block of rock that is faulted downward relative to either side. This indicates extension which means that both sides have moved away from the center thereby allowing the block in the middle, the graben, to drop downward.
Same thing at Central Rift Valley in the highlands of Africa where the continent is being split apart, a rift valley on a high-elevation plateau. The central African rift valley contains some “interesting” fossils.
The overall hypothesis is that the oceanic crust is being pulled apart allowing mantle-derived magma to move upward and fill the void. Magma push does not seem like a viable process for seafloor spreading.
The entire mechanism is driven by the laws of thermodynamics, which starts with heat from the core moving to space. Mantle upwelling is the force pushing up the midocean ridges and mantle upwelling is not because the subduction zones are pulling continental slabs. The convection cycle can only be described as a whole – you can’t just have one part of a whole and say that’s what describes the whole thing. Subduction is due to the downwelling of the mantle, spreading due to the upwelling, but the whole thing is caused by mantle convection process as a whole. The continental and oceanic crust arrangement then has a feedback on the mantle convection which then leads to the Wilson Cycle.
Robert Turner,
Sounds good to me. Geothermics causing mantle convection which drags things around and also creates gravitational instability and adjustments. But, not magma push at the ridge as if pushing on the end of a thin carpet.
You are missing the flow of magma underneath the plate to where the downwelling occurs.
Upwelling is just the start of the surface flow.
Magma flow across the entire plate finally downwelling at the subduction zone is why subducted plate portions are driven many miles deep.
Magma dragging along the bottom of the tectonic plate build immense force.
Exactly.
The lateral component of mantle convection seems to be overlooked by many.
The continents are far thicker than the sea floor, which adds to the push they get from lateral currents in the mantle.
As well, if there is deep subduction, there of course has to be deep upwelling in an equal volume, and lateral movements between the two.
However, the shape of the planet precludes the possibility of any stable and regular arrangement of such currents.
At some point it will become discontinuous and eventually chaotic.
“Mantle upwelling is the force pushing up the midocean ridges and mantle upwelling is not because the subduction zones are pulling continental slabs.” How would we know that? If the plates are being pulled apart, then that leaves a gap in between them, i.e. deeper water or lower elevation (relative to the margin on each side). A rift, in other words. And magma is going to flow up into that rift because of the relief of pressure.
If you’ve ever cut a hole in thick ice (to go ice fishing, or scuba diving under the ice), you know that the water, which was previously up to the level of the bottom of the ice, flows up into the hole to almost the top. (The fact that it does not flow all the way to the top of the hole is because ice is slightly lighter than water–which is one reason we’re here. But I digress.) Analogously with mid ocean spreading, if it is pull: the magma is just rising up to fill the gap left by the receding plates.
You’ve got the ice/water relationship wrong.
Ice is only slightly less dense than water. It is why the bulk of icebergs are under water.
Continuous ice firmly attached to shore may form a structure when water drops.
Broken discontinuous ice with open water expanses, often where water inflows, means all floating ice is still mostly submerged.
Your cut a hole in the ice example proves that relationship.
Disputin
Take a trip to Iceland and visit the actual site of the plate boundary. It is located right here. Looks like a rift valley to me
I wish! (a stroke does slow one down a bit) But I have seen photographs of parts of Iceland, including the plate boundaries
But the main point of my posting is that if the mid-ocean ridges were pulled apart, one would expect them to be deeper, rather than shallower than areas further from the middle, because the infilling rock has to be squeezed up to fill the gap.
I am going to toss a fly into the ointment here, David, if I may. If convection of the thermal variety drives plate tectonics, then it is a heat engine that must obey the laws of thermodynamics. That is, the available work in this engine cannot exceed the efficiency set by the second law times world heat flow. Only a rough estimate of second law efficiency is possible, but available work is actually pretty small. Maybe only 10% of heat flow.
There are two other possible sources of the driving force of plate tectonics. Long ago I suggested that tidal drag from the force couple of Moon-and-oblate-Earth provides more available work than does heat flow. I published this speculation in a 1976 issue of “Tectonophysics”. In other words the Moon stirs the Earth mechanically, and the kinetic energy being converted to work (the slowing of the Earth’s rotation) is 100% available, not subject to the 2nd Law limit.
More recently I have wondered if the ongoing evolution of the core-mantle-crust might also provide more available work than does heat flow. In effect more dense materials are still settling downward, and less dense materials rising. The Earth has not reached a mechanical lowest energy configuration yet. Since this is mechanical potential energy being converted to work, it is 100% available, not subject to the 2nd Law.
The Americas and Eurasia are moving in opposite directions. How can this be caused by the moon?
I have observed stirring move materials in opposite directions. How does your observation preclude anything? What frame of reference do you propose to use?
I challenge your observation. Besides, the moon isn’t stirring the earth.
The Moon is slowing the Earth’s rotation. How do you suppose it does that? Well by putting a force couple on our planet — i.e. a torque. That’s how. This torque is applied preferentially to the crust, tidal drag, etc. Don’t take the term “stir” too literally. It stirs in much the same manner as a rotational viscometer.
Once again, that force is uniform all over the planet. It would be impossible for it to cause one continent to accelerate spinward, while causing another continent to accelerate anti-spinward.
It is not uniform over the earth. Please look up what a tide raising force is. In addition the earth has an oblate shape which makes the Moon’s influence not uniform.
I don’t suppose that you know the tides rotate around nodal points in the ocean basins? This is the Moon actually stirring the Earth’s oceans. Or have you heard of precession of the axis? Another example of stirring the earth.
But not literally stirring?
And you are the one getting snippy?
In a scientific discussion of a physical process, there is that which is meant to be taken literally, and that which is…?
So where is the guide to what parts of what you say should be taken literally, and which parts…not?
You’re not the only one to think along those lines. There is some thought that the moon is responsible for the Earth’s magnetic field and thereby makes the planet habitable. link
Venus has a magnetic field.
And Mars doesn’t have a magnetic field in spite of the fact that has two moons.
It seems to me that the article I linked makes a cogent argument. I think you have to apply a sharp pencil to the data.
I simply encountered a paywall, so couldn’t read the argument.
Here’s a much better link.
Mars’ moons are miniscule compared to Earth’s Moon. If there were oceans on Mars, there would be no significant tides because those moons are so small.
Indeed. My point was that MarkW’s argument was simplistic.
What argument?
I see only a one sentence observation from Mark.
I am wondering why you agreed with the statement that Venus has a magnetic field?
Of the inner planets, only Earth has much of a magnetic field.
Venus and Mars have almost zero detectable magnetic field…unless there is some secret conspiracy to keep that information out of the minds of the general public and even textbooks.
Mercury has a very weak field.
Mar’s moons are more like small asteroids that got captured by the gravity of the planet.
One is only 8 miles across, and looks about as bright as Venus does from Earth.
The other is not much bigger, at 14 miles across, but is only 3700 miles above the surface of Mars, an so it looks rather large, almost one third the size of our moon.
But if our moon was only 3700 miles up, instead of nearly 250,000 miles away, it would look big.
Real big.
Really very big, and large, and bright.
Very bright and big.
How big and how bright?
BIG big, and BRIGHT bright.
And fast…did I mention fast?
Venus’s field intensity is 40nT. Earth’s is 60,000.
Its magnetic field is induced, not internal, however.
Referring to Venus.
Yes. Not long after my paper appeared in print I got a cryptic note from Leon Knopoff who I think was at UCLA at the time. I believe he was trying to tell me he had been thinking along the same lines in something he had published in the early 1960s — but Leon did not always make himself very clear.
I had not heard about the Moon, magnetic field hypothesis. That is interesting.
If the energy for plate tectonics is provided by the Moon, why doesn’t the Earth–which has far more mass–cause plate tectonics on the Moon? The tidal forces caused by the Earth on the Moon are significantly larger than the tidal forces caused by the Moon on the Earth.
For one thing, Moon has no equivalent of the asthenosphere. The soft layer within the earth between the harder tectosphere above on which the crust rides, and aharder layer of mantle below. The bigger factor, though, is that the Moon rotates very slowly, once per month, which means it has the same face always toward the earth.
The bigger factor is that it has no metallic molten core.
Really?
I’m waiting for a day when they announce that this thing up there in the sky is not just a torch-light
How much heat is this adding to the Atlantic Ocean?
William
Pretty much the same as last year, and the year before that, and the year before that, etc.
This reminds me of when I first heard of plate tectonics back around 1968-69. I was young and read one of my father’s 1950’s geology books (yes, I have always been a NERD) which flat out made fun of the theory of Plate Tectonics. Imagine my surprise about 5 or 6 years later to find out it was a well established and accepted theory. This was the beginning of my skepticism about anything I read or hear – I like to check the facts now.
I must have missed the turn-around in the 1990’s – of course geology is not my field but just a hobby.
Unlike AGW, Plate tectonics actually makes sense. I m sure there are multiple explanations for why various plates move about – it’s nature and all it’s complexity – and each will apply more or less to every area affected. Depending on where you study the movement, you may come up with different forces in action. I had not realized there was any question about the mid-ocean ridges.
My grade school science text books referred to plate tectonics as a controversial theory. This was back in the 60’s.
Continental drift was still controversial during the 1960s and I do not think plate tectonics yet existed as a scientific term. Maybe by the end of the 60s. Marine geophysics showed the central graben, fault block structure, and axi-symmetric magnetic stripes astride the mid-ocean ridges. Dating of the sediments (microfossils) resting directly on those areas of seafloor showed that the age of the seafloor lavas and dikes increased away from the mid ocean ridge in both directions. At the ridge, the seafloor was being actively created by submarine extrusions of lava-not very old at all! A conveyor belt with the conveyed rocks increasing in age away from the mid-ocean ridge.
Grade school textbook are usually 10 years behind the times.
I had read of, accepted, and was fully acquainted with continental drift/plate tectonics/sea floor spreading by the late 1960s when I was in third grade.
That was around when I started reading old copies of SciAm I found in a closet…ones from the 1950s and early 1960’s, when it was an actual science magazine.
And books. I was always in libraries reading. In school, after school, at home…libraries full of books everywhere.
And BTW…it was only the geological scientific establishment that discounted the ideas put forth by Wegener.
He made an airtight scientific case. Multiple converging lines of evidence.
There was literally no other possible explanation.
Lack of a known mechanism is no a reason to doubt an idea that is proved by evidence.
It was like doubting the guy holding the gun was the one that done it, because there was no know motive.
Not having a mechanism is cause to look for one, not to be dismissive.
And besides, for most of the time between Wegener publishing his ideas and the first mapping of the ocean floor which showed the mid ocean ridge system, much of the objection pertained to the belief that the crust and upper mantle were to stiff to allow any motion.
Scientific establishments have always been hard headed.
Up until WWII, the idea that rocks could, let alone did, fall from the sky was scoffed at and ridiculed, even when the evidence, in the form of actual chunks from space that people had seen falling and then went and looked for and found, was all over the place. People were mocked for suggesting it.
And then there was them Martian canals.
It is shocking to consider how recently many people, including scientists, believed they could see them and that it was proof of a civilization there.
Continental drift was disbelieved out of hard headedness and stupidity, no other reason.
An upsurge of [divisive] hot rock from deep beneath the Atlantic Ocean may be driving the continents on either side apart.
There that’s more PC
Hot rocks are Republican?
So massive reshaping of of the seafloor doesn’t affect sea levels?
No.
Not on a year to year basis.
Over geologic time… Yes.
Over human time… No… But the Climatariat invokes seafloor subsidence because sea level rise measurements are insufficient to explain their assumptions about ice melting.
Of course it does. Suppose that the plate tectonic engine were to slow down and new sea floor were to be produced at a slower rate for a time. This has actually occured. Because cooling oceanic crust sinks, taking islands beneath the waves with it, then the depth profile of the ocean shifts toward more area at greater depth. If the ocean waters are a more or less constant volume, this would lead to lower sea level. The opposite is also true.
And over geologic time there is little else to explain the main transgressive-regressive sequences than major changes in ocean bathymetry. The global magnitude of these sea level changes is far too great to be explained by glaciation. They happen to correlate with the hothouse/icehouse cycle which happens to correlate with marine chemistry which is best described by long-term variability in hydrothermal circulation with the sea floor and especially at mid ocean ridges.
I think they add in a value to account for basin enlargement. I believe that means they add the odd extra mm to the data for spreading, but don’t take one off for isostatic rebound. Similar to the way that adjustments to the temperature record are only made in one direction. The actual sea level (tide gauges) only matters to people, not to the “scientists”.
Depends on how you define sea levels – worldwide or local? Scandinavia was weighted down by a massive layer of ice during the recent ice age and pushed down into the mantle. At the same time, sea levels went down, of course. Then the ice melted relatively rapidly, and sea levels rose. However, with the oppressive weight lifted, Scandinavia started to rise again and is still rising. This means sea levels in Scandinavia are going down, a local matter, and contrary to the rising sea levels fearmongering of the alarmists. Of course, the rising of Scandinavia just might in itself have an effect on sea levels elsewhere . . .
Otzi what you are saying. [/groan]
Could anthropogenic CO2 somehow be finding its way from the oceans into the earth’s crust, where the added pressure of the gas amplifies the movement of the tectonic plates thus increasing the risk of major damage from seafloor earthquakes and their resulting tsunamis?
In a word. No.
Nuts. Another opportunity for getting a government grant to study an absurd and thoroughly ridiculous question bites the tectonic dust.
Oh dear God. I think I may have just read the next Climate Science research study abstract!
You probably have. A graduate student at Gaia University majoring in Politically Correct Environmental Geology might just decide that CO2-driven plate tectonics is a worthy area for research.
Only in a few of “carbon capture” schemes.
NO!
Best troll I’ve seen in months … 🙂
Having taken a number of geology courses half a century ago while in college, the temptation to troll this article was just too much to resist.
Only if it can be shown to disproportionately disadvantage certain demographics.
If that can be shown to be the case…then yes, of course it does.
I was taught that 50 years ago.
I first heard it in the late 60’s.
Odd. It was not “Consensus Science” then, yet I still heard of it in a science class. (I don’t remember if it was in grade school or high school.)
No, the volume-based publication mill drives plate tectonics and the climate. It’s just that climate has tapped into the world economy and treasuries to propel it past tokamak levels.
There is an interesting backstory to Wegener’s continental drift theory. He was a meteorologst, not a geologist. He first published his Kontinentalverscheibung theory in a 1912 paper. Followed up with a book in 1915. By the book’s third edition in 1922, he had amassed massive physical evidence of three basic sorts: rock stratigraphy, fossil matches in those rocks (eg in eastern south America and western Africa), and climate (tropical fern fossils in coal found on Spitsbergen in the Arctic). Yet when he died on a meteorological expedition to Greenland in 1930, he was still mocked everywhere by geologists. It wasn’t until the late 1960’s and the discovery by geologists of magnetic reversal striping at the mid Atlantic spreading center that Wegener’s idea became accepted as plate tectonics.
There are many analogies to global warming adherents versus sceptics. All the former have is models that because of parameterization cannot distinguish between anthropogenic and natural change.Yet they dismiss all the observational evidence sceptics have for natural change (MWP, LIA) and models being wrong because they run hot because of that fundamental problem (absence of predicted tropical troposphere hot spot, Energy budget ECS and TCR).
I wrote about this both in the Recognition and in the Climate chapters of my ebook The Arts of Truth.
Funny aside. I sent the manuscript to MIT’s Lindzen for a critique of the climate chapter. Over a long day and delightful lunch he critiques the whole thing. He picked on Spitzbergen, which forced me to add a long footnote to the Wegener recognition example.
The Japanese Prof who is quoted seems to have some standing and maybe we should consider what he actually postulates.
Does anyone remember Warren Carey of Tasmania University? His hypothesis in the sixties was ” I recognise the creation new oceanic crust at a rate of of X Sq km per year for Y years. However I do not see the evidence for subduction on that scale. Therefore the earth must be expanding, and here is some evidence where on my picture the jigsaw fits better”
That argument did not make me a believer as it would necessitate dickering with a few basic Constants of physics.
I then read an interesting book by Carey called “Fact and dogma in the geological sciences” pointing out where breakers of the consensus like Neptunists vs Vulcanists, Agassiz and ice ages, Wegener and continental drift etc the consensus will brutally attack the mavericks with ad hominem attack, appeal to authority, and all the dirty tricks that the AGW brigade so love.
Carey said “Accept my theory or not as you wish. That is your right but do not try to bully or ridicule me for having contrary views. So let us give this Japanese fellow a hearing with open mind otherwise we are little better than the Mikie Mann or Gavin Schmidt who showed such an arrogant ass to Roy Spencer rather than enter scientific debate. Tempting target for a kick.
Mind you There is a lot about this subduction pull that I don’t like but let the man have his say.
The earth has been measured, very accurately for over a century. If the Earth was actually expanding, there would be evidence of it by now.
On the other hand, how accurate were Carey’s measurements of the amount of plate area being created and subducted.
Finally, for the Earth to expand, there would need to be something that causes that expansion. What is it?
I reject the claims of the climate catastrophists precisely because the data does not match their theory.
Why should I accept anyone else’s theory that is equally lacking in data?
Evidences of the expanding Earth from space-geodetic data over solid land and sea level rise in recent two decades
“According to the space-geodetic data recorded at globally distributed stations over solid land spanning a period of more than 20-years under the International Terrestrial Reference Frame 2008, our previous estimate of the average-weighted vertical variation of the Earth’s solid surface suggests that the Earth’s solid part is expanding at a rate of 0.24 ± 0.05 mm/a in recent two decades.”
“Finally, for the Earth to expand, there would need to be something that causes that expansion. What is it?” .
Consider water: as it freezes, it expands. What happens to magma as it becomes lava and then solid rock?
What happens to lava as it cools, is that it shrinks. Water is one of very few materials that expands when it goes from liquid to solid. Water shrinks while cooling, until it gets a couple of degrees above the freezing point. Ice shrinks as it cools.
That’s why when the surface of a magma pool cools and solidifies, it sinks.
There was never any evidence that Earth expanded to break up Pangaea, and all the evidence in the world against that baseless speculation, including the volume of subducted crust.
We can now measure tectonic plate movements, which has led to the discovery of many small plates.
There is no oceanic crust older than about 180 my.. Has the subduction process been so complete, that there is no trace of it for 4.3 billion years of Earth history? Zip, zero.
The prevailing wisdom is that there is relatively little oceanic crust left except that which is still in the ocean and all of that is young, as you say. It was destroyed, recycled, in a subduction zone. A lot can happen in 4 billion years! Some remnants of oceanic crust were obducted which means pushed upward along the edge of a land mass and over younger rocks thereby escaping destruction in a subduction zone. Fragments of ancient oceanic crust are found as the ophiolite suite comprising a distinctive association of rocks: submarine basaltic lava (pillow basalt) with sea floor sediment and sheeted dikes; gabbro (coarse-grained solidified basaltic magma), and coarse-grained ultramafic rocks (rich in iron and magnesium) which crustallized at depth from the mantle-derived magma).
Oman, Cyprus, west coast of USA.
Toss in some flysch, and you get fubarite… 😉
It is well known that some form of PT has been in place since the Protozoic (say around 2 BY) by may researchers (but not all). We have a relatively good record in the rocks but details are somewhat obscure. Because oceanic crust is consumed in subduction zones O plate residence time is limited (approx 180 MY is the oldest based on age dating to date). Prior to 2 BY the evidence of “modern PT” activity is not as strong. Review of other “rocky” planets in our solar system (that aren’t dead) like Venus and Mars provide a look at types of active planet modes that the early Earth might have had. The one that seem most likely is called the Stagnant Lid model where active crust is modified by volcanic plumes but “crust” is rapidly overturned and recycled (Venus) (Io, a moon of Jupiter). Obviously this type of activity doesn’t lend itself to rock (crust) preservation. So 2.5 BY of Earth’s history has no real evidence of what the “crust” would have been. We do see the granitic and high grade metamorphic rocks left behind in the Precambrian “basement” much of which is older than 2.5 BY. The origin of those rocks suggest a modern PT setting, but more detailed evaluations does not point directly to analogues from modern PT. Its a very interesting subject and their are some good reviews available under a Google and/or YouTube search.
There is older oceanic crust on both land and the sea floor. Just not much of it.
Subduction has indeed been extensive. The vast slab of the Farallon Plate can still be detected in the mantle under the Americas.
https://www.newscientist.com/article/2100988-worlds-oldest-ocean-crust-dates-back-to-ancient-supercontinent/
Oldest well-dated at 340 Ma in the Med, but much older, though less well constrained, on land mountains.
Yes that is true. Mass balance looking at new crust cremation (oceanic) with rates of subduction (O plate destruction) shows that the rates are mostly balanced with almost a wash between destruction and creation (it is actually slightly under balanced to loss but these types of analyses have a lot of assumptions).
Yes sir. Professor Uyeda is a most respected scientist in the history of plate tectonics and its subsets. No question about that.
Rud,
My understanding was that Alfred Wegener based his ideas on direct observation of the movement of ice floes when visiting Greenland.
He reasoned that polynya are rifts and that ice pressure ridges have deep buoyancy roots just like fold mountains do, The real joke is that his conceptual model of floating ice requires a fluid layer of sea water underneath for the ice floe to move over and was therefore discounted.. The semi-plastic Asthenosphere is the now recognised as the required weak ductile layer below the more rigid crust that makes his model work.
I did not find that in researching his recognition example for my book. Perhaps true and I just did not dig enough. The book has over 100 ‘truth’ examples, some very short paragraphs (Ramen soup calories) and others very long (standardized education testing, LENR—longest is the climate chapter that runs about 87 pages depending on your ebook font size). Was researched, written, and published in just under a year, Christmas 2011 to Nov. 2012. I was inspired and worked long hours, as was completely coincidentally a ‘lull’ time in both my then businesses. One possible acquiror was running clinical trials in Arizona, the other was building a pilot line in Austria. Other than some travel, had lots of free time.
What I found was that his interest was initially peaked by the complementarity in coastal complementary shapes of eastern South America and Western Africa. That led him to stratigraphy match comparisons (1912 paper). That led him to fossil match comparisons (1915 book). Spitzbergen was in his 1922 third edition.
A geology ‘ridicule’ subreason I did not mention was that his data was Atlantic centric. Ironic that it was the mid-Atlantic spreading ridge that finally proved him right 60 years later.
It should be noted as well that Wegener was the son-in-law of Wladimir_Köppen.
Koppen was probably the originator of most of the ideas that Wegener had.
Koppen was extremely prolific and had a wide range of interests and published in many fields, over 500 papers in his lifetime.
He took Wegener on long treks around the world, starting when Wegener was still barely more than a student.
I think he wanted his son in law to publish the continental drift theory for several reasons, not the least of which was, Koppen was already a man with a solid legacy of scientific accomplishment.
And as an aside…Wegener knew about the mid Atlantic ridge system, although likely not the full extent of it.
He even wrote and lectured about it.
But he seems to have never incorporated the ocean ridges into his continental drift work.
Rud,
Like you I have not previously been able to find confirmation of this online, but I am confident that this was understood to be the case in the 1960s when I believe that I first read it in my brother’s geology textbook.
Anyway, I have done some digging and this from the great man is pretty close:
Search for floe Page 17
Just saying…
“In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) in 1989, and is still the deepest artificial point on Earth.”
=======
Barely a pinprick.
Couldn’t even depict it on that image.
Just saying.
A better understanding of plate tectonics — which causes earthquakes and volcanic eruptions — could help people better prepare for these natural disasters
But wait! Doesn’t “Anthropogenic Global Warm…Ahh We really meant Climate Change all along” Cause earthquakes and Volcanoes? If they haven’t tagged them to Man Made because fossil fuel yet, they will soon enough.
The bureaucrats are into their 3rd generation of bypassing critical thinking education in order to dumb down the ‘chillun.’ So Anthropogenic Volcanoes and Earthquakes because fossil fuel will be easily digestible to the hive minded.
Does this have anything to do with the fact that earthquake-prone California is so loaded with human-caused climate change believers?
Not sure, but if the worst happens and California, along with its residents, undergoes a massive catastrophe then the average IQ of the human race may actually increase!
Both the upwelling and the downwelling in the mantle control tectonics, it’s a push pull mechanism. Localized mantle upwelling causes hotspots and localized downwelling causes continental basins and deep continental roots. Linear upwelling at ocean ridges push the crust and subduction of cooler material pulls the crust, you need both for plate tectonics.
Seems logical to my uneducated eyes. If it was just down to spreading, wouldn’t we see more buckling of the crust moving away from the rift?
If it was just pushing from the spreading centers and pulling from the subduction zones, then what we see would not be what we see.
There are lateral mantle currents, and also factors related to momentum.
Bad and wrong ideas are common.
Some people think that sinking cold water around Greenland causes the Gulf Stream.
Plate tectonics-Again? How about that. Wegener’s hypothesis always lacked a driving mechanism until…
Maurice Ewing and Bruce Heezen identified and described mid-ocean ridges, 1950’s; Robert Deitz Sea-floor Spreading,1961; Harry Hess History of Ocean Basins, 1962; Vine and Matthews, Magnetic Anomalies over Ocean Ridges,1963. By the mid 60’s the theory was getting legs and by the late 60’s had J. Tuzo Wilson and others pronounced it good. In 1968 as an undergraduate in Geology and we were reading the above papers as paper copies as there were no textbooks yet published that described this Plate Tectonic theory. Those were the days. Plate tectonics sunk the old geosynclinal theories of continents and ocean basin formation. The true value of Plate Tectonic theory is that it provides an elegant framework for the geologic features, both modern and ancient, that are recorded in the rock record
Readers may recall that about a year ago I posted a comment on a post about sea level rise in which I stated that sea levels cannot rise or fall because we have just a given amount of water on this planet, plus a given amount of other substances. I referred to the fact that the earth’s tectonic plates and the crust float upon the mantle which is in liquid form, therefore Archimedes principle applies. Evidence will show that whilst parts of a tectonic plate may rise and fall, overall they and the ocean levels will remain the same and have done so as far as we know having remained the same since sea levels began being measured.
To give you a crude example, take a fully loaded cargo ship that comes into a harbor to unload. Does the sea level in the harbor rise? No it doesn’t. Unload that ship and take the cargo away. Does the sea level in the harbor drop? No it does not. This admittedly is only a very tiny scale but should tell us what is happening world wide.
So Archimedes was wrong? Displacing water does not cause the water level to change?
Sailing a ship into a harbor does not cause the level of the water in the harbor to rise, because there is no change in the amount of water being displaced. Just in the location of the displacement. However when you unload the ship, the amount of water being displaced does change. It’s just that the size of the displacement compared to the size of the ocean is to small to be measured with any instruments we can build at present.
When there are miles thick ice sheets sitting on North America and Eurasia, and continuous ice along the Rockies and Andes than was tens of miles wide and very thick as well…sea level does indeed change…by a lot.
As it did when the ice sheet formed over Antarctica and another one over Greenland.
Also, mass wasting processes are continuous, but mountain building and continental uplift are episodic events.
Poor Ms Demming. She has basically quoted verbatim from a web page of the US Geological Survey (the link is the little red “USGS” at the end of the post), which gives a simplified account of mantle convection, as the driver of plate tectonics. It’s actually the last of a series of web pages in a teaching module about plate tectonics called This Dynamic Earth. The last page is titled Some Unanswered Questions, with a sub-caption: What drives the plates?. She skipped all the previous pages, which give a very good account of plate tectonics, what it is, how it works and and how the theory evolved. Anyone interested in learning about it, should visit
https://pubs.usgs.gov/gip/dynamic/dynamic.html
What exactly goes on in the mantle is still a bit mysterious, because we only have indirect evidence of it. Convective circulation is the driver, but exactly what it looks like and how it operates are still subjects of discussion and research, hence the “unanswered questions”.
Poor journalist missed all the really interesting aspects of plate tectonics, the parts that all us working geologists know about, which is how it affects the crust. We now know that new oceanic crust is created at mid-ocean ridges from magma coming up from the mantle, and destroyed in subduction zones. And we know that the continents, which are made of lighter rock (so they can’t sink) just ride along on the top.
Sorry for the gross simplifications. Geology is a fascinating subject, and it became much more fascinating after the plate tectonics revolution of 1964-65. Every educated person should know something about plate tectonics, something about evolution, and something about ice ages.
I quoted the USGS passage. The quoted passages are individually attributed to the sources.
I’ve been puzzled by references to Wegener’s theories not being accepted and taught until the late 1960s early 1970s. I left school in 1968 and changed secondary schools in 1966. I have a clear memory of learning about and discussing Continental Drift in a prefabricated classroom which makes it pre-1966, and more likely 1964. I think that in Scottish schools (possibly just one) at least Continental Drift was being taught in the early 1960s.
Ben Vorlich,
Very interesting bit of history you describe.
In fact, probably because Professor A. Holmes of Edinburg Univ. was a very early and effective proponent of continental drift. He published a text book in 1945 and suggested thermal convection to be the driving mechanism. In his text book of physical geology he wrote: ” … speculative ideas of this kind, …, can have no scientific value until they acquire support from independent evidence.”
Marine geophysics and geology provided the first independent evidence that was widely accepted; Vine and Mathews, Harry Hess, Dietz and stated above by rocdoctom.
David
Nice review.
In 1962 a good friend graduated in Geological Engineering. At U. Sask.
That year Tuzo Wilson reviewed plate tectonics to a large audience in a large lecture hall.
All in the Geology Dept sat at the back, and when the lecture was over did not ask any questions.
But in silent disapproval stood as a bloc and left.
And today, if you check the USGS website you will see that it promotes CO2 as causing global warming.
Bob Hoye,
Interesting bit of history you describe. By the time I read J. Tuzo Wilson and his new paper including triple junctions, the concept of sea floor spreading, continental drift and subduction zones was like a snow ball rolling downhill and increasing velocity.
But, we are still waiting to see the evidence that CO2 is the control knob for the climate.
Is this the state of science today? I think that the “Institutions of Higher Education” owe us a massive refund! The idea that upwelling and subduction are inextricably linked has been known since I was young (a very long time ago).
Known,perhaps, but not proven. There is no consensus in science.
Having graduated in 79 and 82 with geology and geophysics rectangular sheets of paper, I thought I had learned everything about the evolution of continental drift to plate tectonics at that time. However, the name Arthur Holmes is new to me. Thanks. You’ve contributed to my goal of learning something new every day.
Some geologists predict the formation of another single super continent in the far future. The Pacific northwest has a Paciic plate diving under a North American plate and the N. American plate is dragged downward until the pressure builds and results in a snap back ….earthquake…followed by a tidal wave….it is almost clock work for long term geology. Drill cores can be taken near the coast and sand layers indicate the tidal waves.
As long as we are telling tales about plate tectonics (Sea Floor Spreading) I may as well add one about a disappointed scientist. Morley was a Canadian geologist who had gotten stuck in the administration of scientific grants and programs as I recall. About a year before the famous Vine and Matthews paper, he had noticed the odd pattern of remanent magnetism in sea floor data, and sent a short note to Nature or perhaps it was science, outlining the idea of sea floor spreading which was rejected as too speculative. I see now that the Vine and Matthews hypothesis is occasionally called the Matthews Morley hypothesis. There is some justice after all.
Civil Engineering 101: No matter what your structural analysis might come up with, you can not push on a rope or cable. If you’ve got a solution that has a cable or rope in compression, you did something very wrong.
I’ll also add that putting concrete in tension is also usually very bad idea unless it has lots of rebar and possibly pre/post-tensioning.
I suspect the same is true for Earth’s plates.
Rocks are not very similar to rope… But if they were, mantle convection cells would be pulleys.
See the Pattern raises serious questions about the mechanics of plate tectonics https://youtu.be/8qoTs7w22r4
This brings to mind a study I read as an undergrad way way back in the early ’80s. It was titled something like ‘What kind of tool do we need to pick up Texas?’ It was an analysis from a rock mechanics point of view. Small scale rocks can be brittle and strong, but scaled up hugely they are very much weaker. Various hypothetical tools were examined for lifting Texas, such as drilling holes, putting in pins and lifting it with a gigantic crane. Not surprisingly, it would crumble. Turns out the only way to lift it is with a giant shovel.
Now applying this lesson to plate tectonics we should see that a tectonic plate is too weak to be pulled or pushed, it needs support (or force) applied all over, like Texas, i.e. a convection cell.
Bravo.
Is the circular movement of earth’s molten interior a 3-dimensional Coriolis effect due to the rotation of the earth, analogous to the 2-dimensional Coriolis effect as seen on storms on earth’s surface?
There are about 40,000 miles of mid-ocean ridges all over the Earth. For example, there is a mid-ocean ridge that surrounds Antarctica and so on.
The physical evidence for mid-ocean ridges is robust and overwhelming.
The physical evidence for subduction is much less robust.
There are two locations, one in the North Pacific and one in the South Pacific Ocean off the Americas where observations and measurements have shown that the plates go back and forth (East and West).as measured after moderate earthquakes in the areas.
The pressure needed to “push” the plates under the continents would be huge.
So much that a back and forth motion would only happen with tremendous counter forces and resulting huge earthquakes, not moderate ones.
Geology has a limited knowledge of what goes on below the Earth’s surface.
Consider: the Earth grows.
There is a jump up and down ‘breakthrough’ in geology. I kid you not. The earth is changing in real time. See observations below that the mid ocean ridges all over the planet suddenly started to increase their spreading rate in 1997. 300% increase in mid-ocean earthquakes at the ocean ridges all over the planet.
All over the planet. How is that even possible?
The explanation of tectonic plate motion is the same explanation for the origin of the water that covers 70% of the surface of the earth.
The tectonic plates are moved by CH4 that is extruded from the liquid core of the earth when it crystallizes. The CH4 at high temperatures and pressure binds with metals. That property created a sheath around the liquid CH4 that is extruded from the liquid core.
The sheath keeps the CH4 in a tube like structure that cares the CH4 and the force from the core to the surface of the planet.
The earth’s core started to crystallize about 1 billion years ago. That started the massive increase in CH4 that was pushed up to the surface of the planet.
The start of core extruded CH4 created the earth’s deep oceans. And explains why advanced life did not appear on the earth until after core crystallizations and at the time of the first appearance of deep oceans on the earth.
Why deep oceans gave life to the first big, complex organisms
What happened on 570 million years ago for the earth ….
To produce the ‘first’ deep oceans on the earth?
There is an old unsolved paradox to explain Cambrian Explosion of advance life, 570 million years ago.
https://www.sciencedaily.com/releases/2018/12/181212134354.htm
Why deep oceans gave life to the first big, complex organisms
Why did the first big, complex organisms spring to life in deep, dark oceans where food was scarce? A new study finds great depths provided a stable, life-sustaining refuge from wild temperature swings in the shallows.
In the beginning, life was small. For billions of years, all life on Earth was microscopic, consisting mostly of single cells.
Then suddenly, about 570 million years ago, complex organisms including animals with soft, sponge-like bodies up to a meter long sprang to life. And for 15 million years, life at this size and complexity existed only in deep water
All over the planet starting in 1994, there was suddenly a 300% increase in the frequency of earthquakes of magnitude 4 to 6 all along the ridges where the sea floor is being pushed apart.
The mid-ocean ridges are thousands of miles long. At these very long regions, the ocean ridge is pushed apart in two directions. At ridges where there is sufficient force (Pacific ocean) to move the ocean plates apart fast, there is constant magma coming up at the ridge.
This increase in the frequency of mid ocean earthquakes, physically absolutely must have a cause and the only physically possible cause is there must be a physical system in the earth that suddenly can cause unbelievably massive ocean ridges to be pushed apart.
So, what we have ‘discovered’ (this is an observational discovery not a theory): There is mysterious unknown ‘force’ that Geology has not found that is moving the ocean plates and …
This is the logical implications of the observations, kicker. This mysterious force that moves the ocean plates can increase by a 300%. The mysterious force is changing in real time.
Curiously and unbelievably, It is a fact that Geology does not have an explanation as to what ‘moves’ the massive ocean plates and what moves the massive continental plates.
“As detailed in those studies, increasing seismic activity in these submarine volcanic complexes is a proxy indicator of heightened underwater geothermal flux, a forcing mechanism that destabilizes the overlying water column. This forcing accelerates the thermohaline circulation while enhancing thermobaric convection [3-6]. This, in turn, results in increased heat transport into the Arctic (i.e., the “Arctic Amplification”), a prominent feature of earth’s recent warming [7-9].”
https://www.omicsonline.org/open-access/have-global-temperatures-reached-a-tipping-point-2573-458X-1000149.pdf
https://www.newgeology.us/presentation21.html
“In recent years, the kinematics of continental drift and sea-floor spreading have been successfully described by the theory of plate tectonics.
However, rather little is known about the driving mechanisms of plate tectonics, although various types of forces have been suggested”14. Seven years later, in 1982, the assessment was:
“At the present time the geometry of plate movements is largely understood, but the driving mechanism of plate tectonics remains elusive”3. By 1995 we find that:
“In spite of all the mysteries this picture of moving tectonic plates has solved, it has a central, unsolved mystery of its own:
What drives the plates in the first place? ‘[That] has got to be one of the more fundamental problems in plate tectonics,’ notes geodynamicist Richard O’Connell of Harvard University.
‘It’s interesting it has stayed around so long’ “25. In 2002 it could be said that: “Although the concept of plates moving on Earth’s surface is universally accepted, it is less clear which forces cause that motion.
“The driving force of plate movements was initially claimed to be mantle deep convection currents welling up beneath midocean ridges, with downwelling occurring beneath ocean trenches.
Since the existence of layering in the mantle was considered to render whole-mantle convection unlikely, two layer convection models were also proposed.
Jeffreys (1974) argued that convection cannot take place because it is a self-damping process, as described by the Lomnitz law.
Plate tectonicists expected seismic tomography to provide clear evidence of a well-organized convection-cell pattern, but it has actually provided strong evidence against the existence of large, plate-propelling convection cells in the upper mantle (Anderson, Tanimoto, and Zhang, 1992).
Many geologists now think that mantle convection is a result of plate motion rather than its cause and that it is shallow rather than mantle deep (McGeary and Plummer, 1998).”
Your 570 Ma is Pre-Cambrian, ie Ediacaran Period (635-541 Ma), last of the Neoproterozoic Era of the Protetozoic Eon. The Cambrian (541-485 Ma) is the first period of the Paleozoic Era of our present Phanerozoic Eon.
The fact of subduction has been observed and can be measured.
Ah, the old slab-pull diagram … allegedly transmitted through fault and joint desiccated crust, above an occasionally partially-melted crustal root … that does not seem to move with it … oh well … the show must go on …
I don’t know whether to laugh or cry.
An upwelling of rock beneath the Atlantic may drive continents apart
The Mid-Atlantic Ridge may play a more active role in plate tectonics than thought – quote
No, really? I learned that in high school back in the Dark Ages when kids were taught Real Science. What happened to that strange idea – teach the REAL stuff instead of twaddle?
Mantle convection does not exist (there is zero evidence for it occurring and there is a computer simulations that show it does not happen in the earth. The mantel motion is from falling slabs and moving plates.) and mantle convection does not move the earth’s plates.
A simple calculation indicates the force moves the ocean plate is orders of magnitude more that the greatest possible force a convection drive system could generate.
“Computer models showed that internally heated (and/or surface cooled) systems have no upwelling sheets or plumes and that all concentrated flow originates in the upper cold boundary layer, which stirs the interior as it sinks.
Thus it became natural to regard plates of lithosphere as driving themselves and, incidentally, stirring the rest of the mantle”5.
“Another difficulty is that if this is currently the main mechanism, the major convection cells would have to have about half the width of the large oceans, with a pattern of motion that would have to be more or less constant over very large areas under the lithosphere.
This would fail to explain the relative motion of plates with irregularly shaped margins at the Mid-Atlantic ridge and Carlsberg ridge, and the motion of small plates, such as the Caribbean and the Philippine plates”19.
Some researchers make the point emphatically: “convection does not drive plates.” Upper mantle convection is a product, not a cause, of plate motions20. Thus the location and orientation of a sinking slab is the best indicator of which way upper mantle flows.”
This is an excellent summary of this issue.
https://www.newgeology.us/presentation21.html
What drives the plates?
Study of the motions of plates is called kinematics, while study of the driving forces is called dynamics. “A key to the simplicity of plate tectonics is that the strength of lithospheric plates enables the analysis of their kinematics to be isolated and treated separately from the dynamic processes controlling plate motions; relative velocities of plates can be analysed without reference to the forces that give rise to them”34.
Around the end of the first decade of dominance by plate tectonics, in 1975, the situation was described this way: “In recent years, the kinematics of continental drift and sea-floor spreading have been successfully described by the theory of plate tectonics. However, rather little is known about the driving mechanisms of plate tectonics, although various types of forces have been suggested”14. Seven years later, in 1982, the assessment was:
“At the present time the geometry of plate movements is largely understood, but the driving mechanism of plate tectonics remains elusive”3.
By 1995 we find that: “In spite of all the mysteries this picture of moving tectonic plates has solved, it has a central, unsolved mystery of its own: What drives the plates in the first place?
‘[That] has got to be one of the more fundamental problems in plate tectonics,’ notes geodynamicist Richard O’Connell of Harvard University. ‘It’s interesting it has stayed around so long’ “25.
In 2002 it could be said that: “Although the concept of plates moving on Earth’s surface is universally accepted, it is less clear which forces cause that motion. Understanding the mechanism of plate tectonics is one of the most important problems in the geosciences”8.
A 2004 paper noted that “considerable debate remains about the driving forces of the tectonic plates and their relative contribution”40.
“Alfred Wegener’s theory of continental drift died in 1926, primarily because no one could suggest an acceptable driving mechanism. In an ironical twist, continental drift (now generalized to plate tectonics) is almost universally accepted, but we still do not understand the driving mechanism in anything other than the most general terms”2.
The problem has always been that it is hard to discern what is going on deep in the Earth, motion is almost imperceptably slow, and different combinations of forces, perhaps varying over time, could apply to particular areas.
“When the concepts of convection and plate tectonics were first developing, many thought of mantle convection as a process heated from below, which in turn exerts driving tractions on the base of a relatively stagnant ‘crust’ (later, ‘lithosphere’) to cause continental drift.
In the early 1970s, more sophisticated understanding of convection led to the opposite view. It was realized that only a fraction of the Earth’s heat flow originates in the core, while most results from radioactivity and/or secular cooling of the mantle.
Computer models showed that internally heated (and/or surface cooled) systems have no upwelling sheets or plumes and that all concentrated flow originates in the upper cold boundary layer, which stirs the interior as it sinks.
Thus it became natural to regard plates of lithosphere as driving themselves and, incidentally, stirring the rest of the mantle”5.
Some researchers make the point emphatically: “convection does not drive plates.” Upper mantle convection is a product, not a cause, of plate motions20. Thus the location and orientation of a sinking slab is the best indicator of which way upper mantle flows.
“The advent of plate tectonics made the classical mantle convection hypothesis even more untenable. For instance, the supposition that mid-oceanic ridges are the site of upwelling and trenches are that of sinking of the large scale convective flow cannot be valid, because it is now established that actively spreading, oceanic ridges migrate and often collide with trenches”14.
I beg to differ with you on your statement that mantle plumes do not exist. Especially using a computer model as one of your primary pieces of evidence. Models, as we all know, will give you any answer you want based on the inputs. Real geology relies hard facts and earth tomography has shown very strong evidence of low density (hot) material rising from the upper mantle into the lower lithosphere. Call it a mantle “plume” of something else, I don’t care but you can call it evidence that a mechanism exists to get hot (possibly melted) mantle rock into high crustal positions (see Yellowstone, etc.)
Ok, so…”Mantle convection does not exist.”
But a few sentences later…
“Upper mantle convection is a product, not a cause, of plate motions.”
Which is it?
The correct answer is, neither.
Both of those assertions are incorrect.
Do not bother thanking me.
I suggest that the writer, a 1980 grad, reread Forsyth and Uyeda (1975), which demonstrated that plate forces (and gravity) are the primary drivers of plate motion (i.e. “geodynamics”), and that convection is a secondary consequence, and is not itself the primary driver.
https://academic.oup.com/gji/article/43/1/163/586101
Also, since we’re talking about plate tectonics here, it’s important to keep in mind that the original theory of plate tectonics by McKenzie, Le Pichon, et al. was entirely kinematic, i.e. it merely described plate motion and was entirely agnostic with respect to the cause.
Demonstrated, or asserted speculatively?
As a geologist I’m not particularly upset with “slab pull” as a mechanism as I am with the wildly uninformed “news report”. All intro geology classes taught include plate tectonics (at least the simplified version). Even someone that has not had intro geology can easily find basic plate tectonics online. Where was the editor?
30 years ago (and as far as I know until recently had remained) the leading candidate for spreading was gravity pull. This was accomplished by the increasing density of oceanic crust as it moved from the thermal inflated spreading center into the deeper ocean basin. Gravity is fairly weak so the process was enhanced by convection in the mantle The idea that magma was “pushing” the plates apart never worked given the divergent/tensional process that it is. All rock evidence from spreading ridges and ophiolite complex investigations showed that the spreading process is overwhelmingly passive (axial riff valleys anyone?).
I am now “woke” to the “slab pull” mechanism idea which has been boosted by sophisticated mantle tomography analysis that shows the intactness (is that a word?) of subducted slabs to great mantle depths. By running-back subduction there has been great insight into former oceanic plate positions and configurations among others. The short answer are slab walls where the subducted piles up like soft-serve ice cream or frozen yoghurt anchoring the subducted slab which provides a new insight as to why continental plates converge on oceanic plate/oceanic plate subduction zones (they appear to remain stationary).
As to the brittleness of oceanic crust, concrete and shallow upper crust rock are very poor analogues for modeling oceanic plate lithosphere behavior. There are many factors involved in the cohesiveness of a 5 KM thick piece of complicated oceanic crust (not all basalt but including gabbro, diabase, etc.). Obviously given time and temperature that crust can bend/flex or we would not have subduction zones mappable in the lithosphere and the mantle.
Part of the reason why people have so many misconceptions is that the diagrams in textbooks are interpreted literally, even though they have hugely exaggerated proportions and are many orders of magnitude out of scale.
If the Earth was shrunk to the size of a cue ball, it would feel as smooth as polished glass if held in in one’s hands.
The crust would be a skin so thin that…
Well, let’s consider that there question.
Oceanic crust is 3 to 6 miles thick, and ocean plates areas are hundreds to thousands of miles in horizontal extent.
Continents are thicker but still mostly many tens to as much as hundreds of times wider than they are thick.
Earth is about 8000 miles wide.
The crust is a skin than is 24,000 miles in circumference, but on average roughly ten miles thick.
So the planet is somewhere around a thousand times wider than the skin encasing it which we call the crust.
So the crust is proportionally as thick compared to the whole Earth, as the curb outside a hundred story high building is to the building itself.
How about if the Earth was an apple?
How thick is the crust compared to the skin of an apple?
Let’s go metric to make this more better to calculate.
An apple is about 3 or 4 inches in diameter.
8 to 10 centimeters of shall we just say 100 millimeters for an apple that is four inches high, roughly.
Skin of an apple is variable, but many have skin about a millimeter thick, and sometimes less than that.
For the Earth’s crust to be the same proportion as an apple skin, the apple would have to have a skin a tenth of a millimeter thick or so.
That is about the same as a human hair…if the person has very thick hair…IOW not a blonde or a redhead.
So the crust of the Earth is proportionally about as thick as hair is to an apple.
And it is far from uniform.
The part where all of the pushing and pulling is going on is far thinner.
The thinnest is near the spreading centers.
We are talking fine haired blonde for the crust in these areas. Silky.
Even the thickest and densest oceanic crust near the subduction zones is thinner than the average used in the above rough calculation. So yeah…the crust is several kilometers thick…but it is thousands of KM wide.
It is weak enough so that a inch a year of motion…as fast and fingernails grow, tears open the whole skin of the planet and let’s the juicy tootsiepop center come pouring out.
And when two pieces run into each other at that velocity (fast as fingernails grow)…it crumples up into miles high jagged mountains of solid rock. Some of them crumples are as high as commercial jets fly.
Ocean floor plate is very weak rock. Just look how easily and cleanly it shears at all of the many transverse faults.
It is weak for one thing b/c of how it forms.
It is like Ritz cracker crumbs held together with spit.
I’m glad you raised this. I get “Science” too – and I thought I was seeing things! (I had to check the cover in case I might have mistakenly picked-up “Woo Scientist”)
I’ve acquired the paper now. (It wasn’t in “Science”, it was in “Nature”.)
It is titled “A thin mantle transition zone beneath the equatorial Mid-Atlantic Ridge”.
The authors are:
Matthew R. Agius (Ocean and Earth Science, University of Southampton, Dipartimento di Scienze, Università degli studi Roma Tre)
Catherine A. Rychert (Ocean and Earth Science, University of Southampton)
Nicholas Harmon (Ocean and Earth Science, University of Southampton)
Saikiran Tharimena1,(Institute for Meteorology and Geophysics, University of Vienna)
J.-Michael Kendall (Department of Earth Sciences, University of Oxford)
FWIW the abstract reads: (emphasis mine)
The location and degree of material transfer between the upper and lower mantle are
key to the Earth’s thermal and chemical evolution. Sinking slabs and rising plumes are
generally accepted as locations of transfer1,2, whereas mid-ocean ridges are not
typically assumed to have a role3. However, tight constraints from in situ
measurements at ridges have proved to be challenging. Here we use receiver
functions that reveal the conversion of primary to secondary seismic waves to image
the discontinuities that bound the mantle transition zone, using ocean bottom
seismic data from the equatorial Mid-Atlantic Ridge. Our images show that the seismic
discontinuity at depths of about 660 kilometres is broadly uplifted by 10 ± 4
kilometres over a swath about 600 kilometres wide and that the 410-kilometre
discontinuity is depressed by 5 ± 4 kilometres. This thinning of the mantle transition
zone is coincident with slow shear-wave velocities in the mantle, from global seismic
tomography4–7. In addition, seismic velocities in the mantle transition zone beneath
the Mid-Atlantic Ridge are on average slower than those beneath older Atlantic Ocean
seafloor. The observations imply material transfer from the lower to the upper
mantle—either continuous or punctuated—that is linked to the Mid-Atlantic Ridge.
Given the length and longevity of the mid-ocean ridge system, this implies that
whole-mantle convection may be more prevalent than previously thought, with ridge
upwellings having a role in counterbalancing slab downwellings.
References 1, 2 & (especially!) 3 are:
1. van der Hilst, R. D. Complex morphology of subducted lithosphere in the mantle beneath
the Tonga trench. Nature 374, 154–157 (1995).
2. Montelli, R. et al. Finite-frequency tomography reveals a variety of plumes in the mantle.
Science 303, 338–343 (2004).
3. Hofmann, A. W. Mantle geochemistry: the message from oceanic volcanism. Nature 385,
219–229 (1997).
This is tantamount to arguing that the streams of rope lava flowing down the slopes of Kilauea are “pulling” the lava up out of the volcano. Nonsense!
Yuppers!
Almost as bad as suggesting glaciers pull snow out of the sky.
A beautiful visualization, uploaded 13 years ago, showing a growing earth.