Real Science Radio: Earth & Mercury's Decaying Magnetic Fields

[Stripe]

Why would hot mantle rising to less hot parts suddenly melt, let alone get more dense?

Simple physics is a bit beyond you, isn't it? Mantle material, stuff below about 800km, cannot rise (unless you know of a way to make it colder, which would cause it to become less dense).

You are making it up, Stripe.

Nope.

Rock at pressure becomes more dense upon melting. Fact.

 

[gcthomas]

Simple physics is a bit beyond you, isn't it? Mantle material, stuff below about 800km, cannot rise (unless you know of a way to make it colder, which would cause it to become less dense).

Nope.

Rock at pressure becomes more dense upon melting.

Rock expands as it is heated and/or melts, becoming more dense as it cools. You have been somewhat misled.

Fact.

:rotfl: Ha ha ha ha ha, he he he he. :rotfl: :rotfl:

 

[Stripe]

Rock expands as it is heated and/or melts, becoming more dense as it cools.

Reading is your second language, isn't it?

 

[gcthomas]

Reading is your second language, isn't it?

It is only water ice that becomes more dense on melting. You did know that, right?

If you look at exposed granite batholiths (there is one near where I live) you find all the biggest crystals (the first to slowly form as the melt cools) at the bottom. They'd be at the top if they got less dense on solidifying.

And look at the columnar lava formations, where the cooling lava contracts and forms hexagonal columns as it cools and solidifies.

Or perhaps you'd like to correct what you wrote? You know, to make it more closely match reality.

 

[Stripe]

It is only water ice that becomes more dense on melting.

Nope.

Clearly you aren't willing to check this out for yourself. Rock under sufficient pressure becomes more dense upon being melted.

 

[gcthomas]

Nope.

Clearly you aren't willing to check this out for yourself. Rock under sufficient pressure becomes more dense upon being melted.

I'll accept your claim if you will link to an authoritative source. I like evidence, but you usually seem unwilling to provide it. A link to a forum post might contain sufficient info for me to track down the source myself.

 

[Stripe]

I'll accept your claim if you will link to an authoritative source.

At low pressure, olivine fractionation lowers the density of basic magmas, but above 13-14 GPa this trend is reversed. All of these basic to ultrabasic liquids are predicted to have similar densities at 13-14 GPa, and this density is approximately equal to the density of the bulk mantle in this pressure range. This suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km.

An interesting possibility arises in considering how to use q . Porous shock wave data suggests the form of (19). This form may be overly restrictive, however, particularly for liquids. Note that (19) prohibits y from changing sign. If q were indeed large and if iJytiJV were constant rather than iJlny/iJlnV, then y could become negative at high pressure. Some liquids, most notably water, have negative y in some PT interval. This could be very important for large magma bodies because a negative y implies a negative a., which in turn means that a barrier to convection could exist.

http://authors.library.caltech.edu/33488/1/91JB01204.pdf

 

[gcthomas]

At low pressure, olivine fractionation lowers the density of basic magmas, but above 13-14 GPa this trend is reversed. All of these basic to ultrabasic liquids are predicted to have similar densities at 13-14 GPa, and this density is approximately equal to the density of the bulk mantle in this pressure range. This suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km.

An interesting possibility arises in considering how to use q . Porous shock wave data suggests the form of (19). This form may be overly restrictive, however, particularly for liquids. Note that (19) prohibits y from changing sign. If q were indeed large and if iJytiJV were constant rather than iJlny/iJlnV, then y could become negative at high pressure. Some liquids, most notably water, have negative y in some PT interval. This could be very important for large magma bodies because a negative y implies a negative a., which in turn means that a barrier to convection could exist.

http://authors.library.caltech.edu/33488/1/91JB01204.pdf

Good try, but basic magmas are not mantle rocks - you've got the convection of basic magma mixed up with the convection of mantle rock. (Even if mantle did melt just below a plate, it would produce mafic magma, not basic magma.)

I'll wait while you find a relevent reference ...

 

[Yorzhik]

Whatever the correct description is for what is happening, it will involve fine tuning, not wholesale abandonment of the basics.

I'm not abandoning the basics. There is no need to change any fact. What we do need to question is paradigm that states that what we see today is what has been going on for millions of years.

The only relevance that the icebergs have is to illustrate that what we see sticking up is only a small fraction of what is actually there, just like with continental crust.

I know why you mentioned them. But it's also a good analogy of what the leading edge of 2 crusts do when they meet each other. Although more slab-like icebergs are what I had in mind, it's still not too far off the mark.

I don’t know what the relevance of the “no momentum” qualifier is, unless you are pandering to the ignorant by making the idea of one land mass penetrating another look silly.

That's how it is. Either there is momentum or there is a mechanism to push the slabs. It isn't momentum, thus, they are correctly described as having "no momentum."

I already faulted Walt Brown earlier for stooping to that level of discourse. So before I decide, can you supply sources showing that geologists believe that the momentum is a significant player in, say, the northern migration of India into the Asian continent?

There isn't any momentum, but somehow they crashed. I'd say writing off the idea that momentum played a part just because dogma says so isn't accurate science. Another way of putting it is that since they look like they've crashed with momentum, then what is your evidence against the obvious?

I agree that if icebergs did end up getting squished together, they would essentially “sink to the same level as (they) had been.” Are you implying that is not the case in Asia?

I'm saying that the energy to push a slab sideways into the Himalayas without momentum, since the raised portion wants to sink, should take other possibilities into account. I'm not even saying that Dr. Brown's idea is the one to take into account. But I am saying that catastrophe is more likely than the idea that the same process we see today has been going on for millions of years.

the plate tectonic community... don’t have an answer.

Then look at other possibilities. A catastrophe would explain *some* features we see better.

Real informative response. Kinda like the Japanese word “Hai”, which can mean anything from “Yeah, I hear ya” to “You bet, I understand and will get right on it.”

I'm glad you understand the word. It's exactly what I meant since this is not being my area of most studied interest. I think there is a good rebuttal but I don't know it well enough yet to say. And after I find what I'm looking for in a rebuttal, I may turn out to be wrong. So "OK" is perfect.

Let’s see, this caused the largest earthquake ever known to have hit Japan, and this was the 5th largest earthquake in the world in the last century. And you think this one might be in the norm?

No. Does the edge go up or down as the norm is the question.

But now to backtrack to something you have avoided responding to. Back in post 90, in response to my explaining which type of crust subducts, and why, you responded with:

Based on your very concise and unambiguous statement, it certainly sounded like you, like tens of thousands of others, recognized a rational scientific explanation for some important aspects of plate tectonics.

Right. Some aspects are well understood.

But when, in my response, I pointed out that immense spans of time were required, suddenly you realized that would violate an ultra-literal reading of the creation account that was recorded by nomadic tribes thousands of years ago, tribes whose scientific knowledge was below that of many modern elementary school children today. So given the choice between science and ancient tribal dogma, you recanted your assertion that the science was acceptable, and sided with goat herders as your gurus.

That's simply not true. I didn't "suddenly realize" my personal belief of a short time of life on earth would be violated. I responded, as more of a student than a teacher, that there were features that don't fit the scientific explanation. The fact that there was a worldwide flood is a scientific statement. Just because it is consistent with the bible should be no concern of yours.

And just because I mentioned a world wide flood does not directly mean that I'm appealing to Walt Brown. It is only mentioned to remind you that a catastrophe happened. How that affected the crusts is what I'm trying to learn about in this discussion, which it might turn out to be very little.

You didn’t even pretend that your change was due to science, but due to an ancient religious account. I asked you what about the scientific account was wrong, that would justify your changing your mind. Silence has been your answer.

Your radar on detecting why I've responded the way I did is inaccurate. So far, I've only concentrated on the science of the matter. If I'm silent on a point it is because you made a good point or because I'm verifying what you said to make a response.

 

[Stripe]

Good try, but basic magmas are not mantle rocks - you've got the convection of basic magma mixed up with the convection of mantle rock. (Even if mantle did melt just below a plate, it would produce mafic magma, not basic magma.) I'll wait while you find a relevent reference ...

:darwinsm:

 

[gcthomas]

:darwinsm:

Yes, you are funny.

What TOL needs is a 'I haven't a clue since Walt doesn't mention it in his book' emoticon. Then you'd be sorted.

 

[DavisBJ]

Wow, another "strong scientific" argument, not.

Very good. I am pleased to see that you finally responded, and that you correctly saw that I was not offering a scientific argument. I was asking a question. But you did not answer, so I will repeat. Your original post that I responded to said a number of things that showed a serious lack of scientific understanding. Are you conversant with science enough to defend the ideas you mentioned?

 

[Stripe]

Yes, you are funny. What TOL needs is a 'I haven't a clue since Walt doesn't mention it in his book' emoticon. Then you'd be sorted.

Meanwhile, mantle convection is dead in the water.

What source of energy powers your plates?

 

[gcthomas]

Meanwhile, mantle convection is dead in the water.

You have shown that in some circumstances MAGMA convection might be limited. That is MAGMA, not mantle rock. DIfferent stuff, don't you see? The words are even spelt differently, for ease of identifiction.

What source of energy powers your plates?

Laern to read, Stripey. Learn to read. :thumb:

 

[DavisBJ]

Yes, you are funny.

What TOL needs is a 'I haven't a clue since Walt doesn't mention it in his book' emoticon. Then you'd be sorted.

GCThomas,

As you may know, Stripe sings hymns of praise to Walt Brown. Many of the unusual ideas in geology that Stripe proposes can be found pretty literally presented in Walt’s book. Stripe’s recent allusions to sinking magma are in that category. However, there are some interesting details that Stripe has been remiss on.

Let me quote what Walt Brown says about magma sinking in the current on-line edition of his book. Walt’s initial handling of sinking magma is this:

Magma’s Compressibility. Magma (melted rock inside the earth) is more compressible than the solid rock from which it came.2 Rock that melts under the extreme pressures more than 220 miles below the earth’s surface will contract and occupy a smaller volume than before melting! At depths of about 220 miles, melted rock occupies nearly the same volume as the original rock. At atmospheric pressure, rock expands by 7–17% when it is heated and melts. The density where the rock’s volume does not change as it melts is called the crossover density. The exact crossover depth depends on the minerals present. Because of magma’s compressibility, magma below this depth of about 220 miles is too dense to rise, so magma cannot circulate inside the mantle,18 contrary to what has been taught for 50 years!​

​

The primary endnote Walt references is #18, which says this:

18. “The basaltic magma could not ascend from a position deeper than 200 km in the Earth’s interior.” Satoru Urakawa et al., “Anomalous Compression of Basaltic Magma,” Research Frontiers 2006, p. 114. Also available at www.spring8.or.jp/pdf/en/res_fro/06/113-114.pdf. **“Magmas are normally less dense than coexisting crystals at atmospheric pressure, but they are more compressible than crystals. More than two decades of experimental studies have shown that the density of magmas can be higher than that of coexisting crystals at high pressure.” Ibid, p. 113. **When the mineral perovskite (Mg,Fe)SiO3 melts at high (mid-mantle) pressures, the mineral’s iron and magnesium preferentially leave the solid and enter the melt, making the magma denser. [See Ryuichi Nomura et al., “Spin Crossover and Iron-Rich Silicate Melt in the Earth’s Deep Mantle,” Nature, Vol. 473, 12 May 2011, pp. 199–202.] **These experimental results, by themselves, should kill the idea that the mantle as a whole circulates as a convecting fluid.

​

I have, and have carefully read, the study Walt references by “Satoru Urakawa et al”. it appears Walt saw something in that study that he grasped into without a very firm understanding. And of course Stripe, acting as a mindless parrot repeating whatever Walt says, could not be expected to critically look at Walt’s take on the study.

First, I note that the nearest thing Urakawa says about magma convection is the line Walt quotes:

The basaltic magma could not ascend from a position deeper than 200 km in the Earth’s interior.​

Nowhere in the study is any mention made of circulation or convection. But even more interesting, neither the study nor Walt Brown say the magma below 200 km will sink as a result of the density changing. That appears to be a conclusion (an incorrect one) that Stripe drew based on the “could not ascend” statement in the study. I am not going to detail the reasons typical magma would not sink just yet. Stripe has said that it will sink (“at pressures found at relatively shallow depths, rock contracts upon melting -- thus it becomes more dense and sinks”), and I want to give him a chance to show why he thinks it will.

As to the technical article that Stripe quoted from recently (“This suggests that melts derived from a peridotitic mantle may be inhibited from ascending from depths greater than 400 km. … a barrier to convection could exist.”), I seriously doubt Stripe really understands what the article was saying. Specifically, on almost every occasion when I have had to grind through some non-trivial mathematics to investigate a question, at the end (as well as most intermediate steps) the information in the mathematical equations can be expressed in fairly succinct English, such as “this shows the temperature varies as the inverse of the elapsed time”. The material Stripe is relies directly on equations 19 and 20. I invite Stripe to show he actually understands the material by expressing, in layman’s English, what those equations actually say.

 

[gcthomas]

Thanks. It is interesting that Walt attacks the straw man of a liquid convecting mantle, when it is clear from the transmission of earth-quake s-waves that the mantle is solid.

Stripe needs to read a primer on the topic instead of repeating Wally's 'work' without understanding.

 

[Stripe]

It is interesting that Walt attacks the straw man of a liquid convecting mantle.

:darwinsm:

 

[Stripe]

As you may know, Stripe sings hymns of praise to Walt Brown.

You should surely be able to point out where I have mentioned him in this thread them.

Neither the study nor Walt Brown say the magma below 200 km will sink as a result of the density changing.

Wrong.

I invite Stripe to show he actually understands the material by expressing, in layman’s English, what those equations actually say.

Or perhaps you could stop playing silly games and just have the conversation. :thumb:

 

[gcthomas]

The mantle is solid, Stripe .

 

[Stripe]

The mantle is solid, Stripe .

The sky is blue, moron.

You can't even understand what DavisBJ writes. What hope do you have of understanding anything from a source not adherent to your religion?