On the evidence of moving continents

[Jeff Corey]

Newton's laws worked well enough for us to get around parts of our solar system and we really don't understand the mechanism, do we?
Well, I don't, not at the level of plate techtonics.

 

[Travis]

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.

Just as a thought experiment....what if granitic rock was denser than basalt. In that case what would we expect the ocean topography to look like? Granted we'd need a new explanation for the existence of continents altogether but let's ignore that bit for the moment.

 

[Dinwar]

Just as a thought experiment....what if granitic rock was denser than basalt. In that case what would we expect the ocean topography to look like?

The opposite of what it looks like today.

The problem is the early Earth, not today's. The Earth was molten for a while. Then it began to cool. The thing is, liquids cooling and hardening is actually a fairly complex issue. I've helped make a phase-diagram for salt water, and it's remarkably weird, far more complex than simply "It got colder, then froze". In fact, pure (or nearly pure) water-ice formed first, leading to more salt in the rest of the water. Obviously at a certain point it all freezes, but up to that point the freezing process was a type of fractional distillation. This is why the last bites of Popsicles taste horrible, and I've seen it used to enhance alcoholic drinks (put them in the freezer for a while, scoop out the ice; it concentrates the alcohol).

In the early Earth this was happening as well. As the rocks cooled, the heavier material settled to the center--more or less the reason we have an iron core. Lighter materials rose to the top. And by "materials" I mean "minerals"--uranium is very, very heavy, but uraninite is fairly light (for a mineral), so most of the uranium is at the surface of the Earth. Mafic material, being intermediate, bounces around (over hundreds of millions of years) between the plastic (not liquid, oddly enough) mantle and the solid crust. Felsic material, being too light to sink readily into the mantle, tends to stay put a the top.

If we reversed it--if mafic material was lighter than felsic--the felsic material would sink into the mantle and the mafic would float on top. Given the ratios on Earth I'd guess we'd see broad, relatively shallow oceans with little in the way of landmass and very little in the way of tectonic activity (not enough room to move things around).

All of that is irrelevant if we decide to assume that ultramafic material is really light as well. If that happened, the felsic material would sink and we'd have a crust a hundred miles thick or more.

Newton's laws worked well enough for us to get around parts of our solar system and we really don't understand the mechanism, do we?

Difference is, Newton's laws made predictions, they weren't just a collection of really interesting observations. Without a mechanism, Wagner's idea was more or less untestable. The only way TO test it would be to go back in time.

 

[Correa Neto]

There is a paralell in geology's history, I hinted at it at a previous post. Its the "age of the Earth" controversy (no, not the YEC crap) and it is a hell of an analog situation to continental drift.

On this side, we have a team of scientists led by Lord Kelvin. Based on available (theoretical and experimental) data and thermodynamic equations, he calculated 20My as the age of the Earth.

On the other side, we have a team of geologists like Tyndall, Huxley and Geike. Based on available data (Huttons' uncorfomities, Darwin's evolution, etc.) they say 20My is a time interval way too small. Let the debate begin!

Kelvin says- So, you say I am wrong and Earth is much older than 20My. So, do the math and show me wrong.

Geos say- OK, your math is sound but we think its not time enough for all those changes...

Kelvin says- Well, if you think its not enough time, then tell us why.

Geos say- We can't explain. We just think its not enough, based on the time estimates we have for sedimentation rates, for example...

Kelvin says- Then present an alternative for my equations! Do you think I missed something? Can you show evidence for some extra heat source to allow Earth reaching its present heat flow rate and temperature in more than 20My? Would you happen to have another model for Earth's formation?

Geos say- No, but we still think you are wrong...

Decades later enters Rutherford.

Rutherford- So, I propose Earth is at least 40My old, based on radiogenic decay rates. I also propose heat produced by the recently discovered radiogenic decay phenomena is whay avoids Earth to cool down at the rates and time frames calculated by the Lord Kelvin. Lord Kelvin himself previously hinted that the only way his calculated figures could be wrong would be the presence of an unknown heat sources. Here I present you this unknown heat source, previously predicted by Lord Kelvin - radioactive decay.

Note- Kelvin was actually present at a Rutherford's speech on the Age of Earth wich run pretty much on the lines above (built with some artistic freedom of mine). Its said Kelvin, already of some age, was half asleep for most of it and woke up when Rutherford spoke his age of Earth estimate.

Kelvin accepted Rutherford's work. Case closed, geos win? Yes but not yet. Time for beer came some more years later when Sir Arthur Holmes added more zeros to Rutherford's figures- 1600My. In the 60's, Holmes' estimate grows to 4500My.

See? Its not unlike continental drift. Something very important was missing. As soon as it appeared, the matter was settled (sort of). And the final figure is not very similar to the first one.

 

[DSo]

....and I've seen it used to enhance alcoholic drinks (put them in the freezer for a while, scoop out the ice; it concentrates the alcohol).

Thanks for the tip. It's going to be a great Saturday night!

 

[fuelair]

It's more fun to put dry ice in your alcohol to concentrate it - you get the "smoke" effect and the higher proof alcohol - and it freezes out more water than the freezer as the freezer has warm/cold cycling.

 

[Corsair 115]

The evidence on both hands is accepted as true. Resolution is coming.

Well, I hope it comes in high definition.

 

[JJM 777]

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

Ergo, God?

 

[sphenisc]

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.

For the same reason that, although I can watch the sun come up in the morning, move across the sky and go down at night, having a mechanism to explain its movement means I'm not necessarily seeing what I might think I'm seeing.

 

[Travis]

Hmmm, I like the analogy to the age of the Earth. Too often stories surrounding that get caught up in the religious factors and overlook that there were wide differences in opinion among the scientists that had nothing to do with mythology. You simply had those that showed that the math on thermal conduction said one thing while sedimentation/erosion indicated another.

Another issue surrounds a book I'm reading on the discovery of Chicxulub. There was an effort by some to keep articles about it out of science journals because they thought a crater in Iowa was the K-T event impactor and there was grant money on the line. I guess they thought their money was at risk if an even bigger crater dated to the time period was indicated.

Anyways, they kept articles on the crater out of a few journals but eventually one let it through. And once people saw the evidence--shocked quartz, bedrock deformation and a huge iridium anomaly being key among them--things sorted themselves out. Eventually Manson crater in Iowa was Argon-Argon dated to be too old to be the impact event responsible while Chicxulub would be dated to exactly match it. The rest is history.

 

[randman]

The short answer to the OP is because scientific consensus is generally flawed and not reflective of genuine adherence to facts and logic. Yes, after awhile, it can be corrected so that consensus is congruent with facts due to overwhelming evidence but it can easily assert there is overwhelming evidence when there is none.

It ought to give more pause and consider the group-think psychology involved, but that hasn't sunk in unfortunately.

 

[Correa Neto]

Hmmm, I like the analogy to the age of the Earth. Too often stories surrounding that get caught up in the religious factors and overlook that there were wide differences in opinion among the scientists that had nothing to do with mythology. You simply had those that showed that the math on thermal conduction said one thing while sedimentation/erosion indicated another....snip...

Religious folks will always cherry pick and distort facts. What else can you do when you model your life and perception of the universe on a loose collection of Bronze Age texts loaded with lots of lies and prejudice?

Back to Geology, a real science, note that in both cases (Kelvin x geos and continental drift x vertical movements), new technologies and even a whole new branch of science had to appear to move the debate ahead.

Meanwhile, theologists are still debating things like the Holy Trinity, just like they've been doing since hundreds of centuries ago...

As for the Mexico x Iowa crater issue, I don't know about such debate; never heard about. Maybe Dimwar can shed some light on this.

 

[lomiller]

I wonder what those standards of practice are?

There seems to be some information here.
http://historyweb.ucsd.edu/oreskes/Papers/Continentaldrift2002.pdf

Third, Americans rejected continental drift because of the legacy of uniformitarianism. By the early twentieth century, the methodological principle of using the present to interpret the past was deeply entrenched in the practice of historical geology. Many believed this the only way to interpret the past, that uniformitarianism made geology a science, for without it what proof was there that God hadn’t made the Earth in seven days, fossils and all? Historical geologists routinely used faunal assemblages to make inferences about climate zones, but according to drift theory, continents in tropical latitudes did not necessarily have tropical faunas, because the reconfiguration of continents and oceans might change matters altogether. Wegener’s theory raised the specter that the present was not the key to the past—that it was just a moment in Earth history, no more or less characteristic than any other. This was not an idea Americans were willing to accept.

 

[Dinwar]

Back to Geology, a real science, note that in both cases (Kelvin x geos and continental drift x vertical movements), new technologies and even a whole new branch of science had to appear to move the debate ahead.

I'd say that's one of the unique features of science: as new data become available, these highly-contested issues become resolved. Sure, there was hot debate over the age of the Earth--but the facts are what they are, and decided the debate. Lord Kelvin made a very good interpretation of the data, but lacked (as everyone did) sufficient knowledge of the system in question to understand that he was working with incomplete data. Once we had the data, science corrected the error.

lomiller: Nice link, but it doesn't get the idea of uniformitarianism correct. Uniformitarianism has four parts: U. of Rate, U. of State, U. of Process, and U. of Law. The first says that everything moves slowly and steadily, the second that things are as they've always been, the third that the only processes we can use to account for the past are those we observe today, and the last that laws of physics are identical across time and space. (Yes, I know, I'm simplifying, but that's what they boil down to.) The real issue isn't the last two--those are more or less correct (with the caveat that we may not have been around long enough to observe all the processes, though astronomy is fixing that issue rapidly). The problem isi that the first two--U. of Rate and U. of State--are mere assertions, without any actual justification. There's no reason to assume, a priori, that all processes are slow and steady, nor is there any reason to conclude (and ample reason to reject) the idea that the Earth is as it always was. The thing is, Uniformitarianism was a reaction to Catastraphism, which argued that changes occurred quite rapidly and in devistating manners. Catastraphism was wrong, and obviously so--but so was Uniformitarianism. The fear of tainting one's research with Catastraphism kept people from examining the issue too closely for a long time.

Currently stratigraphers have a paradigm called Neo-Catastraphism, which states that slow and steady processes dominate sedimentology temporally, but those sediments frequently get re-worked by high-amplitude, low-frequency events (storms, landslides, rodents making burrows, etc).

 

[Travis]

Darn rodents. Also worms.

 

[Dinwar]

Yeah. It's hard to imagine considering a worm a high-energy event, but stratigraphers are weird.

 

[lomiller]

lomiller: Nice link, but it doesn't get the idea of uniformitarianism correct.

Keep in mind that it’s not an overview of uniformitarianism, rather, it’s a historical perspective on how uniformitarianism was being used/misused at the time and the implications this and several other issues had for the acceptance of continental drift.

 

[Dinwar]

My point was that Uniformitarianism is yet another example of science advancing. Uniformitarianism sensu stricto is clearly wrong, and in fact not really scientific--it's a form of package-dealing that scientists really should know better than to do, but do it anyway, and shows how influential a really well-respected scientist can be. Once we learned more, we advanced, and discarded the pieces of Uniformitarianism that didn't make sense.

 

[Travis]

They argued against the mass extinction events too didn't they? Granted we have way more fossils now to better define the extinction events.

 

[Dinwar]

They did. Originally the idea was that God wouldn't allow His creations to die out, but later that it violated Uniformitarianism because it was too fast. That idea really held sway until 1981, I believe, when Louis and Walter Alvarez demonstrated that either the K/Pg boundary was a few tens of millions of years long, all over the world, and had the same depositional rate all over the world, or it was a LOT faster than was originally thought.