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Author | Topic: Earth science curriculum tailored to fit wavering fundamentalists | |||||||||||||||||||||||||||||||||||||||||||
Tanypteryx Member Posts: 4451 From: Oregon, USA Joined: Member Rating: 5.0
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The issue would be the presence of significant unconformities beneath or above the lava flows. I would be very careful about either unless I was in a fairly continuous sequence of sediments briefly interrupted by a volcanic event. In the case of a sill, the only relationship would be intrusive younger than sediments on either side. Sure, that makes perfect sense. I assume that ash layers are the best, from a geology dating standpoint, because they can cover much wider areas than lava flows.What if Eleanor Roosevelt had wings? -- Monty Python One important characteristic of a theory is that is has survived repeated attempts to falsify it. Contrary to your understanding, all available evidence confirms it. --Subbie If evolution is shown to be false, it will be at the hands of things that are true, not made up. --percy
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RAZD Member (Idle past 1435 days) Posts: 20714 From: the other end of the sidewalk Joined:
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I assume that ash layers are the best, from a geology dating standpoint, because they can cover much wider areas than lava flows. Indeed, and each volcano has a "signature" mix of minerals and elements so they can be compared and correlated. An ash layer in a peat bog in Japan is from the same volcanic eruption as one in Lake Suigetsu, and this can be used to validate the age of the layers in Lake Suigetsu or vice versa. In addition sometimes artifacts or footprints are found in the tuff (Laetoli being a famous example) or killed by the ash cloud (as occurred at Pompeii) and thus they can be dated directly by the tuff. Major eruptions also leave ash on glaciers or ice fields, and this allows those dates to be correlated. Creationists love to intentionally do science badly because they know that they will get bollixed results which they can then foist on the gullible as "evidence" that the science is wrong. Time and again it is shown that all they have done is gotten the science wrong, as seen in the article TAD posted at the beginning of this subthread. Enjoy Note: you can follow subthreads by using the thread index and searching it for the subtitle (why subtitles are important?) -- click the little icon at the top left -- for this post I have changed it to
and on this thread it takes you to EvC Forum: Earth science curriculum tailored to fit wavering fundamentalists Message Listby our ability to understand Rebel☮American☆Zen☯Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
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Admin Director Posts: 13044 From: EvC Forum Joined: Member Rating: 2.3
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Precipitation and sedimentation are two different things. Precipitation is the result of a chemical reaction. Sedimentation is when solids suspended in a liquid fall out of suspension. The only way they're related is that after solids precipitate out of a solution via chemical reaction, those solids are then suspended in the liquid, and they will over time fall out of suspension, but they are called precipitates, not sediments.
There's an experiment anyone can perform that's been described to you many times. Take a few tablespoons of dirt and stir them into a large glass of water, then let it sit. While being stirred the dirt will remain suspended in the active and energetic water. Once the stirring stops there is no longer sufficient energy to maintain the larger particles in suspension and they will fall to the bottom, the larger first. Over time smaller and smaller particles will fall of suspension. The end result will be the dirt sorted by particle size, with the largest particles on the bottom and the smallest on the top. It would be very unlikely for there to be no chemical reactions taking place in our dirt, but certainly not anything particularly noteworthy. There wouldn't be any expectation of noticeable precipitates. In other words, the Earth's sedimentary layers consist primarily of sediments, not precipitates.
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NoNukes Inactive Member
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Precipitation and sedimentation are two different things. Precipitation is the result of a chemical reaction. I am tutoring several young folks in chemistry this semester, so perhaps I am overly sensitive, but I think your definition is just a tiny bit narrower than the one used in chemistry. From the wikipedia artilce (emphasis added by me). Precipitation - Wikipedia(chemistry)
quote: As I understand it, even a non-ionic substance, when coming out of a solution due to change in solubility or temperature may be precipitation. However in the case of a non-ionic substance no chemical reaction has taken place. Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846) History will have to record that the greatest tragedy of this period of social transition was not the strident clamor of the bad people, but the appalling silence of the good people. Martin Luther King If there are no stupid questions, then what kind of questions do stupid people ask? Do they get smart just in time to ask questions? Scott Adams
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Admin Director Posts: 13044 From: EvC Forum Joined: Member Rating: 2.3 |
Yes, of course, there's also supersaturation - salt deposits, for example. But they're not sedimentary. If you think it's relevant to what Faith was trying to say then go ahead and work it into the discussion, but from context it seemed to me that Faith was using the wrong term. What she said was, "...both must have precipitated out of water as all the other sediments did," and the vast majority of sediments in the geological record are not precipitates but just erosion products washed and blown down from higher elevations.
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petrophysics1 Inactive Member |
Percy,
A precipitate is a sediment and as such it is sedimentary. Limestone can be the result of chemical precipitation, biological activity, or clastic deposition or combinations of these. So salt, anhydrite, gypsum, limestone and dolomite are sedimentary. Read your geology glossary on what a sediment is. Thanks
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ThinAirDesigns Member (Idle past 2403 days) Posts: 564 Joined:
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So cool the stuff I learn here just watching the back and forth.
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Admin Director Posts: 13044 From: EvC Forum Joined: Member Rating: 2.3 |
petrophysics1 writes: A precipitate is a sediment and as such it is sedimentary. Yes, of course, but the point I was making to Faith is that the sedimentary layers we're usually discussing (e.g., Grand Canyon layers) did not originate as precipitates, and so did not precipitate out of solution as Faith describes. Layers like the Tapeats and the Muav and the Coconino and so forth are the ones usually being discussed. Can the sediments making up those layers be accurately described as precipitates? I don't think so, and so when Faith in her Message 914 postulated that diatomite and volcanic tuff layers "precipitated out of water as all the other sediments did," I provided correct information. Those layers were not formed (for the most part) from material precipitating out of solution and falling as sediments to the bottom. They were formed (for the most part) by suspended material falling out of suspension. I appreciate the additional detail, and I understand the desire for accuracy and precision, but the approach I'm trying to take is to coax the other side out of the crawling stage of understanding before asking them to walk or run. I understand there will be other opinions about the best approach, but that's the one I've chosen.
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Faith  Suspended Member (Idle past 1474 days) Posts: 35298 From: Nevada, USA Joined: |
So they fell out of suspension, they dropped out of the water anyway. But limestones may precipitate out as petro said, and that would be the Tapeats and the Muav.
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edge Member (Idle past 1736 days) Posts: 4696 From: Colorado, USA Joined: |
So they fell out of suspension, they dropped out of the water anyway. But limestones may precipitate out as petro said, and that would be the Tapeats and the Muav.
I don't think you intend to mention the Tapeats here. I've seen the Muav described as precipitated, but I'm not sure that's entirely accurate since few limestones are 'pure' and usually have a fine siliciclastic component. Indeed, 'precipitate' would be a nonstandard usage in the rocks we are discussing, but it is also kind of vague. Often, I try to use the phrase 'chemical sediment' to avoid ambiguity. I think that, for a layman, the confusion is understandable. ETA: I have no problem with making the clarification, however. Edited by edge, : No reason given.
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Faith  Suspended Member (Idle past 1474 days) Posts: 35298 From: Nevada, USA Joined: |
You are right, the Tapeats is sandstone and I shouldn't have included it.
I think that, for a layman, the confusion is understandable. I would think so. One way or another it appears that the sedimentary particles dropped out of water, whether by precipitation or by falling out of suspension.
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Dr Adequate Member (Idle past 314 days) Posts: 16113 Joined: |
A precipitate is a sediment and as such it is sedimentary. Limestone can be the result of chemical precipitation, biological activity, or clastic deposition or combinations of these. So salt, anhydrite, gypsum, limestone and dolomite are sedimentary. But we were talking about diatomite and volcanic tuff. They didn't precipitate. Percy's reply: "Precipitation and sedimentation are two different things. [...] The Earth's sedimentary layers consist primarily of sediments, not precipitates" is perfectly accurate. If he had said "THERE ARE NO PRECIPITATES IN THE GEOLOGICAL RECORD YOU FOOL", then he would have needed putting right. Edited by Dr Adequate, : No reason given.
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NoNukes Inactive Member |
If he had said "THERE ARE NO PRECIPITATES IN THE GEOLOGICAL RECORD YOU FOOL", then he would have needed putting right. There is no question that Faith's statement was imprecise. However Admin's correction lacked some precision as well (cleared up for the most part in his subsequent posts). I think petrophysics1 could rightly take issue with the following:
Admin writes: It would be very unlikely for there to be no chemical reactions taking place in our dirt, but certainly not anything particularly noteworthy. There wouldn't be any expectation of noticeable precipitates. What does in our dirt refer to? It appears to me not to refer to just the grand canyon, but to sedimentation in general. But even if we limit it to the GC, surely we can find gypsum, limestone and metal carbonates and sulphates in places in the Canyon. For example the Redwall and Muav includes limestone layers which are in part chemical sediments. Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846) History will have to record that the greatest tragedy of this period of social transition was not the strident clamor of the bad people, but the appalling silence of the good people. Martin Luther King If there are no stupid questions, then what kind of questions do stupid people ask? Do they get smart just in time to ask questions? Scott Adams
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Faith  Suspended Member (Idle past 1474 days) Posts: 35298 From: Nevada, USA Joined: |
But we were talking about diatomite and volcanic tuff. So how do you explain the layering of the diatomite and tuff? The layers look like all the other layers which were deposited from water.
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Admin Director Posts: 13044 From: EvC Forum Joined: Member Rating: 2.3 |
The interest in accuracy and precision is laudable but isn't contributing to the discussion and may easily be causing confusion. My comments were made in the context of the discussion, where Dr Adequate asked Faith her reaction to an image that included diatomite and volcanic tuff layers:
In her reply Faith said that "both must have precipitated out of water as all the other sediments did." That is incorrect. It is untrue that all other sediments precipitated out of water. In fact, almost the opposite is true. The vast majority of sedimentary deposits around the world are not precipitates but ordinary sediments. I was only communicating this information to Faith. If my manner of expression lacked accuracy or precision in the eyes of some, then please while correcting me at least keep one eye on the topic and put the corrective information in context.
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