On the evidence of moving continents

[Travis]

We all know the story's basics: Alfred Wegener proposes the idea of Continental Drift to explain a great many things about geology. Skeptics challenged him to come up with a mechanism for how it worked. In this he failed (or got bored and went to other things) and the idea languished. Until undersea mapping discovered subduction and rifting. Then the new idea of plate tectonics comes into play that explains those drifting continents.

What I'm wondering is; Wegener brought forth an awful lot of evidence that seemed hard to explain unless now greatly separated continents had once been joined. Among this were chemically identical basalt formations, fossils and extant flora and fauna.

How was this explained if the idea of moving continents wouldn't be accepted until after a mechanism for their motion was discovered? I had always thought it might have been explained as part of catastrophism but it seems many of those that most opposed to moving continents were not catastrophism advocates. Or am I wrong in that?

 

[bjornart]

They pretty much didn't explain it. I think you're overestimating the philosophical purity of science at the time and the speed with which unpopular ideas spread.

 

[Travis]

Of course that would be like coming across a wrecked car and refusing to believe the car exists until someone explains how it got wrecked.

I'm sure some people live in a cognitively dysfunctional cloud that would allow that but I'm skeptical that so many geologists could do it.

 

[Tim Thompson]

Moving Continents

How was this explained if the idea of moving continents wouldn't be accepted until after a mechanism for their motion was discovered?

It remained unexplained. The problem with Wegener's idea was actually quite serious: He had continents plowing through the crust like ships plowing through the sea, and that is obviously impossible. So absent an understanding of how the continents were supposed to move, there really was no choice but to reject the idea of continental drift, and keep looking for a better answer.

Plate tectonics was that better answer, allowing the continents to drift without plowing through the crust. Rather, the crust moves and takes the continents along for the ride.

 

[Correa Neto]

Basically Wegener's evidence were:

1.The fit of some continental margins.
2. Similar fossil terrestrial fauna and flora in South America and Africa and between Africa and India.
3. Similar rock units at both sides of the Atlantic.
4. Matching paleoclimatic zones when the continents were brought togheter.

As a sidenote, he was not the first person to suppose the continents once were joined. Francis Bacon, Snider-Pellegrini, Mantovani and Pickering made similar proposals, but Wegener's was the one with the better foundations.

This put, let's see his opponents's points of view. First, context. By Wegener's time, people already knew Earth's crust was not static. Faults had already been studied, mapped and understood to a certain point; the same could be said about folds and unconformities. Scientists believed, however, that these things were created by dominantely vertical movements. Check the geosyncline theory, for example, created by Hall and Dana to explain mountain building.

Horizontal movements, given what was known back then about the Earth, could only happen due to shrinkage of the Earth as it cooled down, and this could not account for breaking Africa from South America, for example. This would require an area increase instead of a decrease (see now where the expanding Earth story starts?).

With this in mind, we can now try to look at Wegener's evidence with the eyes of those who lived at his times.

Vertical movements could create and later destroy island bridges between continents, allowing fauna and flora interchange. Remember, island hopping is a fact.

Matching coastlines? A mixture of coincidence and mistaken interpretations, coupled with the fact that a detailed look will show the fit (along present-day shorelines) is not as perfect as you would think. Similar lines of reasoning could be followed for the other pieces of evidence.

Yes, the whole package created lots of genuine "WTF?! Makes a lot of sense but I can't explain that!" moments. Some people went over the line in the debates? Yes. Would that be unexpected? No. Why? Hey, we fight about soccer! Now, here comes a crucial point- was he ignored by the whole or most of geological community? No. Among his supporters, for example, was Arthur Holmes, a kick-ass geologist, pioneer of geochronology.

So, why wasn't his theory adopted quickly? Simple. It was imperfect, it had big flaws and problems. Here's some- the lack of a driving force for continental drift, the mechanisms he proposed (such as the escape to the poles) were not feasible and there were alternative explanations. Among the evidence he gathered, there was nothing as compelling as the zebra pattern of magnetic anomalies at the sea floor, the age variations at the sea floor or the variations in "polar wandering" paths. There were no technologies available at his times to acquire those pieces of data. Thus its no surprise that what we have nowadays is called plate tectonics and not continental drift. They are actually two diferent theories.

So, yes, in my opinion, the continental drift tale is not as dramatic as quite often it is told. Its not actually a tale of inertia from mainstream science, prejudice, etc.

 

[shadron]

What I'm wondering is; Wegener brought forth an awful lot of evidence that seemed hard to explain unless now greatly separated continents had once been joined. Among this were chemically identical basalt formations, fossils and extant flora and fauna.

How was this explained if the idea of moving continents wouldn't be accepted until after a mechanism for their motion was discovered? I had always thought it might have been explained as part of catastrophism but it seems many of those that most opposed to moving continents were not catastrophism advocates. Or am I wrong in that?

As was pointed out, geology was between a rock and a hard place. All the evidence for movement was there but no mechanism. This sort of situation, in whcih there is battling evidence, has happened often in science, and it usually is taken to mean that a radical new theory is around the corner.

Look at physics today. Relativity and quantum mechanics both seem to have mountains of evidence, and yet they do not mesh. Something is waiting in the wings to show itself on stage, if we can pry it loose from the woodwork (pardon my mixing). The evidence on both hands is accepted as true. Resolution is coming.

 

[Travis]

Okay, I suppose the heart of my question then is why would you need to understand the mechanism to believe in the movement? Going back to the wrecked car in the woods analogy it just does seem odd to say that because I don't how something is happening I won't believe it is happening.

And I suspect that the real answer is that it was much more nuanced than that. Clearly many were still investigating the idea of moving continents even after Wegener decided meteorology was more interesting.

 

[lomiller]

I haven’t read it myself, but science historian Naomi Oreskes wrote a book on the subject.
http://books.google.ca/books/about/...nental_drift.html?id=EEQdk9GRfkoC&redir_esc=y

In the early twentieth century, American earth scientists were united in their opposition to the new--and highly radical--notion of continental drift, even going so far as to label the theory "unscientific." Some fifty years later, however, continental drift was heralded as a major scientific breakthrough and today it is accepted as scientific fact. Why did American geologists reject so adamantly an idea that is now considered a cornerstone of the discipline? And why were their European colleagues receptive to it so much earlier? This book, based on extensive archival research on three continents, provides important new answers while giving the first detailed account of the American geological community in the first half of the century. Challenging previous historical work on this episode, Naomi Oreskes shows that continental drift was not rejected for the lack of a causal mechanism, but because it seemed to conflict with the basic standards of practice in American geology. This account provides a compelling look at how scientific ideas are made and unmade.

 

[Travis]

Challenging previous historical work on this episode, Naomi Oreskes shows that continental drift was not rejected for the lack of a causal mechanism, but because it seemed to conflict with the basic standards of practice in American geology.

I wonder what those standards of practice are?

 

[Soapy Sam]

There certainly seems to have been a difference of attitude between American and European geologists and geophysicists.
Physicists said there was no mechanism and that was that. Many European geologists said "Yet still it moves" and went on with mapping reality while someone else worried about a mechanism. Some folk (like Arthur Holmes) suggested mantle convection as a driving mechanism.
Eventually the physicists found the magnetic evidence for seafloor spreading and said "Look what we proved!"- and a lot of geologists said , yeah, we've been trying to tell you that for years."
It's an interesting psycho-social history of science. Science, like Soylent Green, is people.

 

[Travis]

I'm going to have to see if I can get that book through an interlibrary loan.

 

[JudeBrando]

Explained.

 

[WhatRoughBeast]

Okay, I suppose the heart of my question then is why would you need to understand the mechanism to believe in the movement? Going back to the wrecked car in the woods analogy it just does seem odd to say that because I don't how something is happening I won't believe it is happening.

Travis, call it inertia, but not in a dismissive way. To accept Wegner's hypothesis would have tied together a number of puzzling questions, but at the cost of actually throwing out a bunch of solid understanding, and substituting a number of just outrageous problems. Continents plowing through the crust like the ocean liner in Speed 2? The idea was so far beyond what folks understood that they simply wouldn't accept it without a mechanism. And how would the crust fill in behind the moving continent? It's like one of the problems with believing in The Deluge: where did the water come from and where did it go? I've never seen an answer that was even remotely credible, short of invoking a miracle.

Science works by elimination. You keep trying to answer questions and getting proved wrong. So when you finally get an answer that holds up, there is considerable motive to hold on to that answer. In this case, tossing out pretty much everything people understood about rocks in order to clear up some puzzles just wasn't going to happen without a really good explanation, and Wegner's idea couldn't provide it.

And, as has been mentioned, Wegner was wrong. Close, yes, but still wrong.

 

[WhatRoughBeast]

Deleted - inadvertent and unexplained duplication.

Sorry. The system doesn't like me today.

 

[Wowbagger]

Explained.

That video is a few decades old, and in all that time, I don't think any of those "explanations" has lead to any significant new scientific discoveries about geology. The video is vacuous at best, inaccurate at worst.

 

[Travis]

Travis, call it inertia, but not in a dismissive way. To accept Wegner's hypothesis would have tied together a number of puzzling questions, but at the cost of actually throwing out a bunch of solid understanding, and substituting a number of just outrageous problems. Continents plowing through the crust like the ocean liner in Speed 2? The idea was so far beyond what folks understood that they simply wouldn't accept it without a mechanism. And how would the crust fill in behind the moving continent? It's like one of the problems with believing in The Deluge: where did the water come from and where did it go? I've never seen an answer that was even remotely credible, short of invoking a miracle.

Science works by elimination. You keep trying to answer questions and getting proved wrong. So when you finally get an answer that holds up, there is considerable motive to hold on to that answer. In this case, tossing out pretty much everything people understood about rocks in order to clear up some puzzles just wasn't going to happen without a really good explanation, and Wegner's idea couldn't provide it.

And, as has been mentioned, Wegner was wrong. Close, yes, but still wrong.

Of course back then nobody knew what the bottom of the oceans looked like. So for all they knew the topography of the ocean bottoms would have proved the "continents plow through ocean crust" idea. As it turns out mapping the ocean bottom didn't show that but it did, instead, point to how they do move.

 

[RecoveringYuppy]

Continents plowing through the crust like the ocean liner in Speed 2? The idea was so far beyond what folks understood that they simply wouldn't accept it without a mechanism.

In fact they may have seen the crust as a mechanism for preventing motion.

 

[fuelair]

Basically Wegener's evidence were:

1.The fit of some continental margins.
2. Similar fossil terrestrial fauna and flora in South America and Africa and between Africa and India.
3. Similar rock units at both sides of the Atlantic.
4. Matching paleoclimatic zones when the continents were brought togheter.

As a sidenote, he was not the first person to suppose the continents once were joined. Francis Bacon, Snider-Pellegrini, Mantovani and Pickering made similar proposals, but Wegener's was the one with the better foundations.

This put, let's see his opponents's points of view. First, context. By Wegener's time, people already knew Earth's crust was not static. Faults had already been studied, mapped and understood to a certain point; the same could be said about folds and unconformities. Scientists believed, however, that these things were created by dominantely vertical movements. Check the geosyncline theory, for example, created by Hall and Dana to explain mountain building.

Horizontal movements, given what was known back then about the Earth, could only happen due to shrinkage of the Earth as it cooled down, and this could not account for breaking Africa from South America, for example. This would require an area increase instead of a decrease (see now where the expanding Earth story starts?).

With this in mind, we can now try to look at Wegener's evidence with the eyes of those who lived at his times.

Vertical movements could create and later destroy island bridges between continents, allowing fauna and flora interchange. Remember, island hopping is a fact.

Matching coastlines? A mixture of coincidence and mistaken interpretations, coupled with the fact that a detailed look will show the fit (along present-day shorelines) is not as perfect as you would think. Similar lines of reasoning could be followed for the other pieces of evidence.

Yes, the whole package created lots of genuine "WTF?! Makes a lot of sense but I can't explain that!" moments. Some people went over the line in the debates? Yes. Would that be unexpected? No. Why? Hey, we fight about soccer! Now, here comes a crucial point- was he ignored by the whole or most of geological community? No. Among his supporters, for example, was Arthur Holmes, a kick-ass geologist, pioneer of geochronology.

So, why wasn't his theory adopted quickly? Simple. It was imperfect, it had big flaws and problems. Here's some- the lack of a driving force for continental drift, the mechanisms he proposed (such as the escape to the poles) were not feasible and there were alternative explanations. Among the evidence he gathered, there was nothing as compelling as the zebra pattern of magnetic anomalies at the sea floor, the age variations at the sea floor or the variations in "polar wandering" paths. There were no technologies available at his times to acquire those pieces of data. Thus its no surprise that what we have nowadays is called plate tectonics and not continental drift. They are actually two diferent theories.

So, yes, in my opinion, the continental drift tale is not as dramatic as quite often it is told. Its not actually a tale of inertia from mainstream science, prejudice, etc.

And, in the early fifties a number of young kids looked at globes and realized that NA/SA would fit just about perfectly against EurAfrica. I know because I was one of them and some of us talked about it from time to time. When I found they had and heard the Wegener story I was royally not happy. He did what he could at the time and there is a rather large distance between "looks like you could be right but how might it have happened?" and "we don't know any way that could happen so regardless of your evidence go pound sand!!"

 

[Robrob]

Okay, I suppose the heart of my question then is why would you need to understand the mechanism to believe in the movement? Going back to the wrecked car in the woods analogy it just does seem odd to say that because I don't how something is happening I won't believe it is happening.

I suspect at that level of novelty, not being able to deduce the cause from the results as being similar to a "blind spot."" Also similar to the machinations astronomers went though before Galileo, trying to explain the the planets' movement in the sky as they supposedly orbited the Earth.

 

[Dinwar]

Okay, I suppose the heart of my question then is why would you need to understand the mechanism to believe in the movement?

Because geology, simply put, is weird. It's entirely possible to have chemically identical rocks form in different geographies. HIGHLY unlikely, but possible. The rest of the evidence is similar. Even the hippo-like animals he used as evidence--there are numerous bottom-feeding fish that get transported in ships' ballasts, for example, because their larva migrate to the surface at different points throughout the day. We've also found crinoids attached to the underside of wood (found them attached to the wood, near some truly weird trace fossils). Animals are odd, and it takes very, very careful study to rule out all the possibilities.

More significantly, without a mechanism all Wagner had amounted to "Gee whiz, guys, this sure looks like something is happening!" That was the state of geophysics for about a hundred years by the time Wagner proposed his idea--it wasn't new. What Wagner did that WAS new was to propose an idea that was actually worth debating. It was wrong--it had deep flaws, such as felsic rock plowing through mafic rock (put a marshmellow and a gram cracker is some chocolate fondue and see what it takes to push the marshmellow through the gram cracker)--but at least it was scientific, which was a major step forward.

So for all they knew the topography of the ocean bottoms would have proved the "continents plow through ocean crust" idea.

No. Mafic crust is much denser than felsic--that much was known (I have hand-samples of both, and I've never been to the bottom of an ocean; it would be easy to test). That's why continents are made of felsic rock--it floats higher than oceanic crust. The idea of continents plowing through the crust was an ad-hoc explanation for something that Wagner didn't understand.

The thing is, it's not just Wagner that was wrong. The idea of continents moving because of convection within the mantle is equally wrong--and for many of the same reasons. For example, if the convection-cell idea was right, you should be able to map the convection cells. It's incredibly obvious and should be the first test of the idea. Unfortunately, we cant do it. There's no way to make convection cells that fit with the Earth's tectonic activity. Ridge push/slab pull is more accepted, with hot-spot volcanism playing a role. Mantle plumes have also been invoked, with varying degrees of success. My point is that yeah, Wagner's ideas were rejected--but they were discussed, and that's all part of the scientific process.

JB, thanks for the laugh. Unfortunately for your side, any good geophysics or structural geology textbook can show the problems with it.