When did Plate Tectonics begin on Earth, and what came before?
Posted by geosociety under Structural Geology and TectonicsBy Robert J. Stern
Two of my favorite topics of geoconversation are how new subduction zones get started and when in Earth's history did plate tectonics begin? Both are fascinating geoscientific questions but we seem to be making more progress on the first topic than on the second. The plate tectonic revolution changed our science forever but in the excitement of the late 1960's when the paradigm shifted, the question of what makes the plates move was neglected. Yes it was mantle convection, but was convection driven by hot deep mantle rising or cold dense lithosphere sinking? Geodynamicists soon began investigating and now they tell us that it is mostly the sinking of dense lithosphere in subduction zones, pulling the plates and moving them. The most important consideration is that hotter asthenospheric mantle is slightly (~1%) less dense than colder overlying lithospheric mantle, so these want to change places. This sometimes happens during detachment and delamination of lithospheric mantle but generally happens by subduction, the end-on sinking of lithosphere beneath asthenosphere.
Our modern understanding of what drives the plates shows us that the key to understanding how subduction zones form is by understanding the density and strength of oceanic lithosphere. It also tells us that we should be thinking about lithospheric strength and density when we try to answer the question "When did plate tectonics start on Earth?" Certainly the Archean mantle 2.5 to 3.8 Ga was hotter than is the modern mantle. Consequently, Archean lithosphere would have thinner and more buoyant, and on this basis alone a reasonable person would conclude that plate tectonics must have been more difficult back then. In spite of this, most geoscientists think that plate tectonics was underway in Archean time. Regardless of your opinion on this matter, the question of when did plate tectonics start (WDPTS?) is one of the most important – and exciting – unresolved questions in the history of the solid Earth. I find this to be a particularly interesting question because EVERYONE can get involved: graduate students, undergraduate students, K-12 students, professors, amateurs, the media. We can't agree on the answer yet so let's discuss it!
The key to answering WDPTS? must be to reconstruct Earth's tectonic history, using both first-order understanding of how large silicate bodies cool and proper interpretation of the rock record, particularly those mineral and rock assemblages that are diagnostic of plate tectonic records of independent plate motions, subduction and collision. One possibility is that Earth has always had plate tectonics. This follows from a strict interpretation of the Principle of Uniformity, which basically states that "the present is the key to the past". Following strict Uniformitarianist logic, because we definitely have plate tectonics today, Earth must have always had plate tectonics. But strict adherence to Uniformitarianism is ridiculous, as Stephen Jay Gould pointed out in his first peer-reviewed paper (Gould, 1965). Uniformitarianism is very useful when you are trying to explain how the Earth came to be to a bunch of religious nuts who think the Earth is 6000 years old and that humans and dinosaurs coexisted, but it is not useful when trying to understand Earth's tectonic history for the simple reason that it inhibits inquiry.
Earth is the only known silicate planet that has plate tectonics, so plate tectonics is probably a special way that viscous, rocky planets cool. Once we escape the Uniformitarianist straitjacket, we can see that a hotter early Earth may have cooled in a different way than the present Earth. Certainly we all know that there were different conditions in the Precambrian, which makes up 88% of all geologic time. We know that the interior of the early Earth was much hotter than that of today, for a number of reasons. For example, heat production due to radioactive decay at 4 Ga was ~3x that of today. Other causes of early heating include heat of accretion, the Sun's T-tauri event (beginning of H fusion), core differentiation, and the Mars-size impact events. How much hotter was the early Earth? We don't know but we do know that there are vanishingly few rocks from the first 800 Ma of Earth's history, as expected for a hot early Earth.
Earth cooled sufficiently that 3.8 Ga rocks are fairly common (e.g. Greenland, Africa) but still, Earth must have been much hotter in the Archean than it is today. How did a hotter mantle affect our planet's style of heat loss, i.e. tectonic style? Some conclude that a hotter mantle would have resulted in a greater total length of global spreading ridges, which means smaller plates and faster moving plates. Certainly a hotter Earth would have caused more extensive melting and thicker oceanic crust – komatiitic oceanic crust seems likely. It is also likely the oceanic lithosphere would have been thinner and more depleted and that the underlying asthenosphere would have been hotter. I surmise that Archean lithosphere would have been hotter, thinner, and less dense; it also would have been weaker and more prone to necking and breaking. These characteristics would have made it easier for sufficiently dense Archean lithosphere to trade places with buoyant Archean asthenosphere but this would have made subduction – which requires coherent plates – more difficult. We can (and should) stake out an opinion, but who knows for sure? Each of us should consider what we know about how our planet operates today and mentally explore how the hotter early Earth would have been similar or different than the plate tectonic Earth of today.
I discussed some of these issues with an eminent geoscientist, who argued that plate tectonics has always been operating on Earth. I asked him why he thought this and he replied "How else can you generate magmas and deform rocks?" There is no doubt that the Archean Earth witnessed a lot of igneous activity and deformation, maybe more than experienced by the modern Earth, but this does not require plate tectonics. This is vividly demonstrated by the examples of Venus and Mars, which today suffer intense deformation and magmatic activity but without plate tectonics.
For me, the most important evidence that Plate Tectonics operated at a given time interval is the preservation of ophiolites, blueschists, and ultra-high pressure (UHP) metamorphic terranes from a given time period somewhere on the globe. For those unfamiliar with what I call the "Smoking guns"* of Plate Tectonics' (Fig. 1): ophiolites are fragments of oceanic crust and upper mantle (lithosphere) emplaced on continental crust (where geologists can study them). Ophiolites should have but sometimes lack extensive gabbros or sheeted dike complexes, but at a minimum an ophiolite should include tectonized harzburgitic mantle and pillowed tholeiite.
Figure 1: Histograms showing ages of preserved plate tectonic indicators for the last 3 Ga
of Earth history. Histograms are grouped into three types of plate-tectonic indicators: (a)
oceanic lithosphere (ophiolites), (b) subduction zone metamorphic products (jadeitites,
blueschists, and lawsonite eclogites), and (c) continental margins and collision zones
(gem corundum, UHP metamorphic rocks, and passive continental margins. Modified from Stern et al. (in press).
Blueschists are fragments of oceanic crust that have been metamorphosed 40-60 km deep in the distinctive high-P, low T environment of a subduction zone. This produces the diagnostic Na-amphibole known as glaucophane. UHP terranes are slivers of continental sediments which have been subducted even deeper than blueschists, to depths of 100 km. Pressures like this are required to produce UHP-diagnostic phases of diamond or a high-P polymorph of SiO2 known as coesite. Both blueschists and UHP terranes require a two way ticket, down to be metamorphosed in a subduction zone, and back to the surface to be greeted by enthusiastic geologists. Excepting a few 1.9 Ga ophiolites, all three 'smoking guns' first appear in Neoproterozoic time, less than 1 billion years ago. I am very impressed by the fact that the vast majority of these three primary indicators of plate tectonics are so young, other geoscientists are less impressed (Fig. 2). More details about the nature of these three petrotectonic indicators can be found in Stern (2005) and Stern (2008).
Fig. 2: Different views about Plate Tectonic Smoking guns. My views are on the
left, the views of some/many other geoscientists are on the right.
Thanks to Julian Pearce for cartoon on right.
WTPTS? does not take up much of my research time but it is fun because it keeps me thinking about all the ways that Earth's tectonic history can be interrogated. I wonder if there is some type of ore deposit or other rock association that could be used as a new plate tectonic indicator. Eclogites are also potential plate tectonic indicators. One type of eclogite forms when oceanic crust is metamorphosed at 50 km or more deep in a subduction zone but the term also can be used to describe any garnet-pyroxene rock produce by non-plate tectonic processes, for example in the lower continental crust as high-P cumulates or accompanying crustal thickening. Bob Coleman and colleagues wrote an interesting review entitled "Eclogites and Eclogites" that discussed some of these issues (Coleman et al., 1965). Subduction-related eclogites are a particular variety of clinopyroxene-garnet that contain Pyrope (Mg-Al) garnet and omphacite (jadeite-rich garnet). We need some kind of a "discrimination diagram" to distinguish subduction-related eclogites from those of other origins and then we could compile the distribution in time of subduction-related eclogites and use this as an independent petrotectonic indicator to help answer the question WDPTS? A few years ago, Tatsuki Tsujimori and co-authors looked at another subgroup of eclogites which must be subduction-related, those containing lawsonite (Tsujimori et al., 2006). Lawsonite is a hydrous calcium aluminum silicate that is typical of blueschist facies environments, and all known lawsonite-bearing eclogites are Phanerozoic (Fig. 1).
Another rock association that needs to be looked into for the purpose of addressing WTPTS? is the distribution of calc-alkaline batholiths through time. Batholiths mark the exhumed roots of magmatic arcs, exposed by a few km of erosion to remove the volcanic cover, and can be expected to persist as distinctive hallmarks of subduction until they are covered up by sediments. How can we recognize subduction-related batholiths in the rock record? We shouldn't be happy with just a few trace element diagrams as sufficient to identify arc-like igneous rocks. Someone should develop a more robust set of characteristics and use these to define subduction-related batholiths. These characteristics should include a combination of geographic extent (how many km long and wide?), magmatic geochemical characteristics (e.g., K and isotopic gradients, and position relative to where the forearc basin and trench were (inferred from ophiolites, blueschists, and subduction-related eclogites), temporal features (subduction zones and thus magmatic arcs should be active for tens to hundreds of millions of years), and of course igneous rock compositions.
I continue to look for ways to interrogate the rock record for information about WDPTS? This investigation should be as broad as possible. I recently co-authored a Geology paper on the topic Plate Tectonic Gemstones (Stern et al., in press), which identified gemstones that are diagnostic of plate tectonic processes of subduction and collision. The subduction gemstone is Jade, which consists of nephrite (amphibole) and jadeite (pyroxene). Nephrite can form in other tectonic environments but jadeite only forms 25-70 km deep (0.8 – 2 GPa) under the cool (300-500°C) conditions found in subduction zones. All 19 known localities of jadeite are Phanerozoic in age (Fig. 1). The collision gemstone is ruby, which is gem corundum containing ~1% Cr2O3, an impurity that gives the gemstone its deep red color. Rubies form by hot metamorphism (500°- 800°C, 0.2 – 1.0 GPa), especially when passive margin sediments (esp. aluminous shales) get involved in continental collision. We summarized 32 ruby deposits and all but two are Neoproterozoic (Fig. 1). These gemstones are particularly useful because they form so deeply that erosion should reveal, not remove these. Our understanding of the global distribution of the gemstones ruby and jadeite are further indicators that subduction and collision – and therefore plate tectonics – are geologically young phenomena.
There should also be a way to use the temporal distribution of certain ore deposits to answer the question WDPTS? We haven't made much progress in this aspect yet, but maybe someone will figure something out about this record. A while back I thought that porphyry copper deposits, which are clearly related to subduction, might be 'smoking guns' but now I understand that erosion is likely to remove all evidence of these deposits after a few tens of millions of years.
By now you have probably reached a point where you either think that there is some merit in these digital scribblings, or you may have concluded that I am full of unlithified coprolites. Regardless of what you think about WDPTS?, it must have begun at some time after Earth formed. I have shared my opinion about when this was, and some of the reasons for this opinion. Whenever "the great tectonic revolution" happened, there must have been a different tectonic style that it replaced. What was Earth's pre-plate tectonic style?
To better understand Earth's early tectonic style we must start from first principles. We know that the farther we go back in time, the hotter Earth's mantle must have been. The lithosphere must have been correspondingly thinner and weaker and the asthenosphere must have been weaker and melted more extensively. Abundant mafic outpourings have loaded weak lithosphere, depressing it into the eclogite stability field (T>580°C, P>1.3 GPa) where the increase in density due to eclogitization would have stimulated further sinking, ultimately forming detached sinking diapirs, much as happens today during delamination. Archean greenstone belts must have been dominated by downwellings where weak lower crust delaminated and sank. The downwelling zones must have been flanked by mantle upwelling zones (Fig. 3). Hamilton (2007) concluded that dense mafic and ultramafic lavas erupted atop mobile felsic crust during the Archean produced a density inversion that led to the downfolding of volcanic rocks at the same time as domes of felsic middle crust flowed up and around the keel, resulting in the characteristic (keel-and-dome) structure of Archean greenstone belts. The lower panel on Fig. 3 summarizes one idea of what may have happened in the mostly "weak lithosphere vertical tectonics" of the early Earth.
Figure 3: Upper panel shows a simplified version of modern plate tectonics, driven
by the edgewise sinking of strong, dense lithosphere in subduction zones. Lower
panel shows a cartoon of how Earth's tectonic regime might have been before plate
tectonics began. In a hotter Earth, thin, weak lithosphere sank vertically, similar to
modern scenarios of delamination or "drip tectonics".
OK, enough ramblings. This brief essay has hopefully stimulated the reader's interest in the grand question of when Earth's modern tectonic regime was established. I encourage the reader to join the fun and excitement of this investigation. It's easy to join and contribute to the discussion; we are just feeling our way around this problem. One route forward is to identify those rocks that, in your opinion, most likely formed by plate tectonic processes, and make these your "smoking guns" for plate tectonics. The occurrence of these through time may be an important indicator. It will also be fun to watch how this line of inquiry evolves and what new ideas are advanced over the next few years.
*'The term "smoking gun" was originally, and is still primarily, a reference to an object or fact that serves as conclusive evidence of a crime. In addition, its meaning has evolved in uses completely unrelated to criminal activity: for example, scientific evidence that is highly suggestive in favor of a particular hypothesis is sometimes called smoking gun evidence. Its name originally came from the idea of finding a smoking (i.e., very recently fired) gun on the person of a suspect wanted for shooting someone, which in that situation would be nearly unshakable proof of having committed the crime (from Wikipedia).
References:
Coleman, R.G., Lee, D.E., Beatty, L.B., and Brannock, W.W., 1965. Eclogites and Eclogites: Their Differences and Similarities. Bull. Geological Society America 76, 483-508.
Gould, S. J. 1965. Is Uniformitarianism Necessary? American Journal of Science 263, 223-238.
Hamilton, W.B., 2007, Earth's first two billion years—The era of internally mobile crust, in Hatcher, R.D., Jr., Carlson, M.P., McBride, J.H., and Martínez Catalán, J.R., eds., 4-D Framework of Continental Crust: Geological Society of America Memoir 200, p. 233–296
Stern, R.J. 2005. Evidence from Ophiolites, Blueschists, and Ultra-High Pressure Metamorphic Terranes that the Modern Episode of Subduction Tectonics Began in Neoproterozoic Time. Geology 33,7, 557-560.
Stern, R.J. 2008. Modern-Style Plate Tectonics Began in Neoproterozoic Time: An Alternative Interpretation of Earth's Tectonic History. Condie, K., and Pease, V., eds, When did Plate Tectonics Begin?: Geological Society of America Special Paper 440, 265-280.
Stern, R.J., Tsujimori, T., Harlow, G., and Groat, L. A., in press. Plate Tectonic Gemstones. Geology
Tsujimori, T., Sisson, V.B., Liou, J.G., Harlow, G.E., and Sorensen, S.S., 2006, Very low-temperature record in subduction process: a Review of worldwide Lawsonite eclogites. Lithos, doi:10.1016/j.lithos.2006.03.054.
And that's why I wrote www.solvingthemajorextinctions.com and published it on the internet. Check it out.
From: Kim Noyes <kimnoyes@gmail.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Monday, April 29, 2013 1:10 AM
Subject: Re: [Geology2] Re: The Earth Moved
That's all fine and dandy but you have to prove there are impacts where your "hypothesis" claims there are and that they are big enough for the job and that they are of the right timing.... and that is just for starters.
On Sun, Apr 28, 2013 at 9:57 PM, Ben Fishler <benfishler@yahoo.com> wrote:
[Attachment(s) from Ben Fishler included below]Dear Vic & Lin,The Wegener article is certainly apropos to our current situation.Although the basics of Wegener's Theory were eventually accepted, this acceptance didn't occur until 30 years after Wegener died. The biggest problem was the fact that Alfred Wegener lacked an acceptable mechanism for his theory of continental drift.It was not until after World War II that the mid-ocean ridge was discovered and the basis for a mechanism was established. At that point Wegener's Theory could be properly considered.I find myself in what I think is a similar situation in discussing my theory with you ... except that I do have a mechanism. And it is a mechanism that has been used and proven on a small scale in manufacturing plants for years.Why would two intelligent geologists have so much trouble with the geological mechanisms that I propose (i.e. the concept of continental uplift being regarded as "science fiction")?The problem may be a lack of familiarity with analogous processes that are used in industry today. I worked in the cold heading business for 16 years earlier in my life. Impact heading and its use of extrusion at the antipode of an impact is old hat for someone like me. However, it may be unfamiliar to you.Impact heading (where a mild steel cut off piece is trapped in a die) forces extrusion at the end of this solid steel piece through a hole in the die when this cut off piece is hit by a punch.This impact heading process is almost a direct analog to the event of a very large object impacting the Earth. In this much larger scenario, the pulverized weak area at the impact's antipode (due to a natural spherical concentration of earthquake waves) acts as the hole in the die, while the liquid mantle transfers the shock impact pulse (resulting from a temporary deformation of the Earth's crust at the impact point) to the antipodal area. The Earth's solid crust and the force of gravity act as the trapping agents.If the impact is large enough, then even a raging hotspot won't relieve enough of the pressure and continental uplift (similar to stamping or embossing in industrial processes) through forced crack propagation can occur.Extruding liquid rock or shearing rock through crack propagation is much easier than extruding solid steel, and yet extruding solid steel is an everyday manufacturing occurrence.I located a 12 page cold heading brochure that includes diagrams of impact heading. The brochure shows how the cold heading process works and the types of parts that can be formed by extruding solid steel at the antipode of an impact. Pay particular attention to the "1st Blow" picture under the "Two Die, Three Blow Process" heading on page 3. It illustrates impact heading. Lots of pictures. Easy to read. I am attaching this brochure to my email.Once Wegener's critics had the evidence of the mid-ocean ridge, it led to an understandable mechanism by which they could evaluate his theory.Maybe, once you understand the analogous industrial processes, my theory won't sound so much like science fiction.The real question is not whether an impact from a meteor would cause deformation at the surface of the Earth and some kind of extrusion at the antipode, but rather, how big would the impact have to be? Would a six-mile-in-diameter meteor traveling at 24,000 mph relative to the Earth be big enough to uplift the continent of India 65 million years ago? The evidence says that it would.Science is a self-correcting mechanism. While existing theory should be given a certain deference because it has become accepted, it should not automatically overrule challenges merely because of that deference.Eventually the facts will win out and theories will be revised or discarded if that is necessary. Otherwise, we would still be discussing epicycles and listening for the music of the spheres when studying astronomy.Regards,Ben Fishler
From: Lin Kerns <linkerns@gmail.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Saturday, April 27, 2013 11:06 AM
Subject: Re: [Geology2] Re: The Earth Moved
LOL!On Sat, Apr 27, 2013 at 9:23 AM, sactovic <sactovic@yahoo.com> wrote:
Fascinating piece. My only criticism: He omits any discussion of Wegener's opinons about antipodal continent creation.Vic> *This is a story I wrote for the June issue of Smithsonian Magazine. The
--- In geology2@yahoogroups.com, Lin Kerns wrote:
>
> The Earth Moved
>
> Posted by Richard Conniff on May 22, 2012
>> disagree in the comments:*
> editors there asked me to write a different lead, to make it seem more
> timely. You can read that version
> here .
> But I think the historical account stands on its own. Feel free to> arm. Hospital time gave him a chance to extend his idea into a book, *The
>
>
> Alfred Wegener
>
> On November 1, 1930, his fiftieth birthday, a German meteorologist named
> Alfred Wegener set out with a colleague on a desperate 250-mile return
> trip from the middle of the Greenland ice pack back to the coast. The
> weather was appalling, often below minus-60 degrees Fahrenheit. Food was
> scarce. They had two sleds with 17 dogs fanned out ahead of them, and the
> plan was to butcher the ones that died first for meat to keep the others
> going.
>
> Less than halfway to the coast, down to seven dogs, they harnessed up a
> single sled and pushed on, with Wegener on skis working to keep up. He
> was an old hand at arctic exploration. This was his fourth expedition to
> study how winter weather there affected the climate in Europe. Now he
> longed to be back home, where his wife Else and their three daughters
> awaited him. He dreamed of "vacation trips with no mountain climbing or
> other semi-polar adventures" and of the day when "the obligation to be a
> hero ends, too." But he was also deeply committed to his work. In a
> notebook, he kept a quotation reminding him that no one ever accomplished
> anything worthwhile "except under one condition: I will accomplish it or
> die."
>
> That work included a geological theory, first published a century ago this
> year, that sent the world woozily sliding sideways and also outraged fellow
> scientists. We like to imagine that science advances unencumbered by messy
> human emotions. But Wegener's brash intuition threatened to demolish the
> entire history of the Earth as it had been built up step by step by
> generations of careful thinkers. The response from fellow scientists was a
> firestorm of moral outrage, followed by half a century of stony silence.
>
> Wegener's revolutionary idea was that the continents had started out massed
> together in a single supercontinent and then gradually drifted apart. He
> was of course right. Continental drift, and the more recent science of
> plate tectonics, are now the bedrock of modern geology, helping to answer
> life-or-death questions like where earthquakes may hit next, and how to
> keep San Francisco standing. But in Wegener's day, drift was heresy.
> Geological thinking stood firmly on solid earth, continents and oceans were
> permanent features, and the present-day landscape was a perfect window into
> the past.
>
> The idea that smashed this orthodoxy got its start at Christmas 1910, as
> Wegener (the W is pronounced like a V) was browsing through "the
> magnificent maps" in a friend's new atlas. Others before him had noticed
> that the Atlantic Coast of Brazil looked as if it might once have been
> tucked up against West Africa like a couple sleeping in the spoon
> position. But no one had made much of this matchup, and Wegener was hardly
> the logical choice to show what they had been missing. At that point, he
> was just a junior university lecturer, not merely untenured but unsalaried,
> apart from meager student fees. Moreover, his specialties were
> meteorology and astronomy, not geology.
>
> But Wegener was not timid about disciplinary boundaries, or much else: He
> was an Arctic explorer and had also set a world record for endurance flight
> as a balloonist. When his mentor and future father-in-law, one of the
> eminent scientists of the day, advised him to be cautious in his
> theorizing, Wegener replied, "Why should we hesitate to toss the old views
> overboard?" It would be like heaving sandbags out of a gondola.
>
> Wegener proceeded to cut out maps of the continents, stretching them to
> show how they might have looked before the landscape crumpled up into
> mountain ridges. Then he fit them together on a globe, like jigsaw puzzle
> pieces, to form the supercontinent he called Pangaea. Next, he pulled
> together biological and paleontological records showing that, in regions on
> opposite sides of the ocean, the plants and animals were often strikingly
> similar: It wasn't just that the marsupials in Australia and South America
> looked alike; so did the flatworms that parasitized them. Finally, he
> pointed out how layered geological formations, or stratigraphy, often
> dropped off on one side of the ocean only to pick up again on the other.
> It was as if someone had torn a newspaper sheet in two, and yet you could
> still read a sentence across the tear.
>
> Wegener presented the idea he called "continental displacement" in a
> lecture to the Frankfurt Geological Association early in 1912. The meeting
> ended with "no discussion due to the advanced hour," much as when Darwinian
> evolution made its debut. He published his idea for the first time in an
> article later that year. But before the scientific community could muster
> much of a response, World War I broke out. Wegener served in the German
> army on the Western Front, where he was wounded twice, in the neck and
> Origin of Continents and Oceans*, published in German in 1915. Then, with> according to Naomi Oreskes, author of *The Rejection of Continental
> the appearance of an English translation in 1922, the bloody intellectual
> assault began.
>
> Lingering anti-German sentiment no doubt aggravated the attack. But German
> geologists also scorned the "delirious ravings" and other symptoms of
> "moving crust disease and wandering pole plague." Wegener's idea, said one
> of his countryman, was a fantasy "that would pop like a soap bubble." The
> British likewise ridiculed Wegener for distorting his jigsaw-puzzle
> continents to make them fit, and, more damningly, for failing to provide a
> credible mechanism powerful enough to move continents. At a Royal
> Geographical Society meeting, an audience member thanked the speaker for
> having blown Wegener's theory to bits–then also archly thanked the absent
> "Professor Wegener for offering himself for the explosion."
>
> But it was the Americans who came down hardest against continental drift.
> Edward W. Berry, a paleontologist at Johns Hopkins University called it
> "Germanic Pseudo-Science" and accused Wegener of cherry-picking
> "corroborative evidence, ignoring most of the facts that are opposed to the
> idea, and ending in a state of auto-intoxication." Others poked holes in
> Wegener's stratigraphic connections and joked that an animal had turned up
> with its fossilized head on one continent and its tail on another. They
> argued that similar species had arrived on opposite sides of oceans by
> rafting on logs, or by traveling across land bridges that later collapsed.
>
> At Yale, paleogeographer Charles Schuchert focused on Wegener's lack of
> standing in the geological community: "Facts are facts, and it is from
> facts that we make our generalizations," he said, but it was "wrong for a
> stranger to the facts he handles to generalize from them." Schuchert
> showed up at one meeting with his own cut-out continents and clumsily
> demonstrated on a globe how badly they failed to match up, geology's
> equivalent of O.J. Simpson's glove.
>
> The most poignant attack came from a father-son duo. Thomas C. Chamberlin
> had launched his career as a young geologist decades earlier with a bold
> assault on the eminent British physicist Lord Kelvin. He had gone on to
> articulate a distinctly democratic and American way of doing science,
> Drift–Theory and Method in American Science. *Old World scientists tended> historian whose biography, *Alfred Wegener's Life and Scientific
> to become too attached to grandiose theories, said Chamberlin. The true
> scientist's role was to lay out all competing theories on equal terms,
> without bias. Like a parent with his children, he was "morally forbidden
> to fasten his affection unduly upon any one of them."
>
> But by the 1920s, Chamberlin was being celebrated by colleagues as "the
> Dean of American Scientists," and a brother to Newton and Galileo among
> "great original thinkers." He had become not merely affectionate but
> besotted with his own "planetismal" theory of the origin of the Earth,
> which treated the oceans and continents as permanent features. This "great
> love affair" with his own work was characterized, according to historian
> Robert Dott "by elaborate, rhetorical pirouetting with old and new
> evidence." Chamberlin's democratic ideals—or perhaps some more personal
> motivation–required grinding Wegener's grandiose theorizing underfoot.
>
> Rollin T. Chamberlin, who was, like his father a University of Chicago
> geologist, stepped in to do the great man's dirty work: The drift theory
> was "of the foot-loose type … takes considerable liberties with our globe,"
> ignores "awkward, ugly facts," and "plays a game in which there are few
> restrictive rules and no sharply drawn code of conduct. So a lot of things
> go easily." Young Chamberlin also quoted an unnamed geologist's remark
> that inadvertently revealed the heart of the problem: "If we are to
> believe Wegener's hypothesis we must forget everything which has been
> learned in the last 70 years and start all over again."
>
> Instead, geologists largely chose to forget Alfred Wegener, except to
> launch another flurry of attacks on his "fairy tale" theory in mid-World
> War II. For decades after, older geologists quietly advised newcomers
> that any hint of the drift heresy would end their careers.
>
> Wegener himself was exasperated but otherwise undaunted by his enemies. He
> was careful to address valid criticisms, "but he never backtracked and he
> never retracted anything," says Mott Greene, a University of Puget Sound
> Work*comes out later this year. "That was always his response: Just> V ei8 -Volcanoes of the World
> assert it
> again, even more strongly." By the time Wegener published the final
> version of his theory in 1929, he felt certain that continental drift would
> soon sweep aside other theories and pull together all the accumulating
> evidence into a single unifying vision of the Earth's history. He didn't
> pretend to know for certain what mechanism would prove powerful enough to
> explain the movement of continents. But he reminded critics that it was
> commonplace in science to describe a phenomenon (for instance, the laws of
> falling bodies and of planetary orbits) and only later figure out what made
> it happen (Newton's formula of universal gravitation). He added, "The
> Newton of drift theory has not yet appeared."
>
> The turnabout on Wegener's theory came relatively quickly, in the
> mid-1960s, as older geologists died off, unenlightened, and a new
> generation accumulated irrefutable proof of sea-floor spreading, and of
> vast tectonic plates grinding across one another deep within the Earth.
> Else Wegener lived to see her husband's triumph. Wegener himself was not
> so fortunate.
>
> That 1930 expedition had sent him out on an impossible mission. A
> subordinate had failed to supply enough food for two members of his weather
> study team spending that winter in the middle of Greenland's ice pack.
> Wegener and a colleague made the delivery that saved their lives. He died
> on the terrible trip back down to the Coast. His colleague also vanished,
> lost somewhere in the endless snow. Searchers later found Wegener's body
> and reported that "his eyes were open, and the expression on his face was
> calm and peaceful, almost smiling." It was as if he had already foreseen
> his vindication.
> About these ads
> http://strangebehaviors.wordpress.com/2012/05/22/the-earth-moved/
>
> --
>
>
> Webcams
> Roxxfoxx~~Adventures in Geology
> Penguin News Today
> Penguinology: The Science of Penguins
> Gentoo Penguins of Gars O'Higgins Station,
> Antarctica
> Canis lupus 101
> Through Golden Eyes
> Follow me on Pinterest !
>
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