Plate Techtonics!

[Nyril]

Several years ago (more then one, less then ten thousand) the idea that the Earth was not the center of the Universe was high in the ranks of things we argued about. Neatly behind that would be the age of the Universe, age of the Earth, the Earth goes around the sun, Earth is flat, etc. In time, a number of these ideas were accepted by pretty much everyone. By that I mean that I doubt even YEC will argue the point that the Earth is the center of the Universe and in addition to being flat also has the sun and everything else revolve around it.

On that line of thinking, I'd like to ask what you think of plate tectonics in that regard. It isn't brought up much on these boards, but because it neatly explains how we get fossils and strata on opposite sides of the Ocean all neatly lined up (such as the shore between Africa and South America), I imagine there must be some controversy surrounding it.

So, plate tectonics, is it like the Earth being round, or closer to evolution in terms of the amount of public debate surrounding it?

[YEC]

Once again, no one is denying creep rates....you need to show how it folds rocks.
To date you have failed to do this.

[MagusYanam]

Once again, no one is denying creep rates....you need to show how it folds rocks.
To date you have failed to do this.

If the marble bench example wasn't good enough, I guess I just need some more examples with which to bludgeon this thread.

Read this website:

http://www.dukeresearch.duke.edu/databa ... ?992633017

Specifically, these lines:

During their trip south from San Francisco, itself the scene of a famous 1906 San Andreas quake, Malin's students visit both creeping and locked segments as they follow a series of state roads along a largely rural inland corridor east of California's coastal ranges. At various stops along the way, students learn how to read evidence of the fault as Malin leads the way on foot. During intervening van rides, Malin points out features via radio. Just northwest of the quaint mission town of San Juan Bautista, a line of fencing has been bent by aseismic creep of about 7 millimeters a year. In the town of Hollister, creep has offset curbs, walls, streets, sidewalks and parts of a nearby winery.

In this particular area along the San Andreas fault line, fences have been displaced, streets and walls offset et cetera - not by fracturing of the supporting rock, but by aseismic creep. If the rock isn't bending, then pray tell, what is happening here?

And if this isn't evidence enough, what more does there need to be?

[otseng]

The can't get that far, of course, because they crash into each other again only half-way around. It's a large distance, all right, but it's also a long time.

What do you mean by "crash"? The plates have already "crashed". That is, all plates have always abutted next to each other. It is not like if the plates are giant pieces of wood floating on top of a large pool of water. All the plates are adjoining to one another. If one plate moves, it already "crashes" into another. So, another question, why do we not see this evidence of "crashing"?

One cannot generalize a single mechanism from one example, or from three examples, or from a hundred examples.

Let's put it this way. Let's assume "modern" stratas to be 1 million years old. And let's go back into the geologic record for 600 million years placing us in the Precambrian era. What we should see are evidence of folds/faults in old stratas on the order of 600 to 1 compared to folds/faults in modern stratas. So, the evidence should be overwhelming, yet surprisingly, it is underwhelming.

Let me go more into detail of what I'm asking for.

Let's just pick one period, the Ediacaran period. If plate tectonics happened during this period, then there should be some evidence of folds or faults.

Perhaps it would look like my drawing here:

Figure 1

Now, if another layer got deposited on top of this, what should it look like?

Would it look like this?

Figure 2

Or would it look like this?

Figure 3

What would make the most sense to me is figure 3. So, I would expect to see stratas similar to figure 3, not figure 2, throughout the rock record.

[MagusYanam]

What do you mean by "crash"? The plates have already "crashed". That is, all plates have always abutted next to each other. It is not like if the plates are giant pieces of wood floating on top of a large pool of water. All the plates are adjoining to one another. If one plate moves, it already "crashes" into another. So, another question, why do we not see this evidence of "crashing"?

Perhaps 'crash' isn't the correct term to use - there's a connotation of distance that seems unproductive. But we do see evidence of plates moving in relation to each other - seismic activity. Subduction zones (and the volcanoes they produce) are evidence of one plate being pushed beneath another - lithospheric material is melted here and becomes part of the asthenosphere or is forced upward into an eruption. At places where plates diverge (places like the Mid-Atlantic Ridge), plate material is emerging. There is ample evidence of this (Surtsey).

What would make the most sense to me is figure 3. So, I would expect to see stratas similar to figure 3, not figure 2, throughout the rock record.

Yes, that would make sense, were the strata at the surface as they were being deformed. Remember that this is a gradual process we're talking about.

So, suppose that during the Ediacaran period, the sediments or surface matter that made up figure one would have just been deposited. They aren't likely to turn into rock for awhile - at least, not until there has been some precipitation of cementing material (the last stage in the formation of sedimentary rock).

But yes, the surface sediment would indeed have been at a roughly even level. We see that today, in the topsoil, which tends toward a flat surface. But the cementation that occurs nearing the end of the process of forming rock is liable to take place underneath several additional layers of sediment, and under considerable pressure.

It seems to me that what would happen is that the rock being formed would conform more to the layer below it as it was continually being weighed down by the layers of sediment above, and much of the porous quality to the sediment is lost in the process of cementation, so the layer being formed would go from looking like Figure 3 to looking more like Figure 2 (albeit with the yellow layer being much thinner).

[ST88]

What do you mean by "crash"? The plates have already "crashed". That is, all plates have always abutted next to each other. It is not like if the plates are giant pieces of wood floating on top of a large pool of water. All the plates are adjoining to one another. If one plate moves, it already "crashes" into another. So, another question, why do we not see this evidence of "crashing"?

Oh, hold on, but they are "floating." This I remember from Physics. The plates are all solid objects that are floating on a molten part of the earth's mantle called the aesthenosphere. The "crashing" comes in several different forms, such as was discussed earlier, like the buckling that is forming the Himalayas and the subduction that happens in the ocean.

A primary factor is the relative bouyancy of the continents and plates on top of the aesthenosphere. This is a vast oversimplification, but because the ocean plates are made up of heavier elements -- megnesium, iron -- and the landmasses are made up of lighter elements -- silicon, aluminum -- the continental plates are more bouyant than the ocean plates. This principle is called isostacy. This is why continental plate boundaries are not subducted. You will only find subduction in ocean plate boundaries, and this is due to gravity.

Plates also spin, which accounts for the movements of the South American tip and the northward migration of the land to the west of the San Andreas fault (on a geologic scale).

Here are some interesting discussions:
http://people.hofstra.edu/faculty/j_b_b ... nics3.html
http://web.earthsci.unimelb.edu.au/Teac ... 1/rp2.html
http://www.ldeo.columbia.edu/edu/dees/e ... /lec7.html
http://darkwing.uoregon.edu/~dogsci/kays/bouyancy.html

[otseng]

For completeness, I've also thrown some diagrams together illustrating faults.

The figure below shows a fault occurring. The fault line goes all the way from the bottom to the top.

Figure 4

Now, if a layer got deposited on top of this, what would it look like?

Would it look like figure 5 or figure 6?


Figure 5 (the new layer has a fault line in it)


Figure 6 (the new layer does not have a fault line in it)

Again, figure 6 is the most logical to me.

Plate tectonics says that plates have been moving for over 600 million years. And the movement is strong enough to even form the largest mountain ranges (Andes, Rockies, Himalayans, etc). We would expect that there should also exist many folds/faults forming throughout all the stratas (esp ones that are not so pronounced as the major mountain ranges). It would be hard for me to conceive that land masses would've been able to move for hundreds/thousands of miles without any evidence of any folding or faulting. I would expect to see folding/faulting in every single sedimentary layer. But, even if there was no folding/faulting in every layer, there should exist some.

Therefore, it would make sense to me that figures 3 and 6 should be quite common in the rock record. So, I'm asking for this evidence to be presented.

[MagusYanam]

Again, otseng, you seem to be making the assumption that sedimentation and cementation are concurrent (or nearly so). If they were, then yes, we would see a lot of layers like Fig. 3 and Fig. 6 in the geological record. But as it happens, this is a gradual occurrence (taking place over many millions of years) and there is a period of some duration between sedimentation and cementation during which more sediment is inevitably deposited and by the time the layer in question becomes cemented there is enough pressure to make it conform to the layer beneath. Allow me to put it this way.

When you step in dry sand (a porous material much like the sediment in question), the footprint you make doesn't keep its shape very long because you haven't held your foot there, supplying the pressure to keep the sand in that form and at the same time preventing erosion of the print. But when the pressure is supplied, the sand conforms to the shape of the foot above it.

Now, the accumulation of sediment applies pressure via gravitation to everything beneath it, and the sediment nearest the bottom is most subject to this pressure. Being so, it should conform by the time of cementation more to the shape of the rock beneath than to the shape of the layers of non-rock above it.

[otseng]

When you step in dry sand (a porous material much like the sediment in question), the footprint you make doesn't keep its shape very long because you haven't held your foot there, supplying the pressure to keep the sand in that form and at the same time preventing erosion of the print. But when the pressure is supplied, the sand conforms to the shape of the foot above it.

I do not understand your illustration here. Are you saying that if you have a footprint in one layer, then immediately put another layer on it, then apply pressure, then there will be a footprint on the new layer?

Also are you arguing that initially a new layer would look like figures 3 and 6, then given sufficient time, it would look like figures 2 and 5? Actually, this argument is quite hard for me to accept. For one thing, we have many examples where the topmost layer is folded exactly like the layers beneath it. Given pressure of any amount, there is no way to create a parallel layer to the strata beneath if the new layer is flat. Also, how can it explain folds as dramatic as this?


Also, your suggestion cannot explain faults. How can a fault line be created in a layer after a fault has occured?

Another question, when the mid-Oceanic ridge "pushed" the continents apart, exactly what was the plates that got pushed? How big are they? Where are the boundaries of the plates?

[MagusYanam]

A brief caveat before going on - I'm not an expert in this field and I don't pretend to be. Probably half of what I'm saying is valid fact and the other half is me trying to make sense of it. But I'm still trying to work my way through as best I can given my limited scope of knowledge.

I do not understand your illustration here. Are you saying that if you have a footprint in one layer, then immediately put another layer on it, then apply pressure, then there will be a footprint on the new layer?

Pardon, that was a bit of a poor illustration. The point was that the sand could hold its shape because of the obstruction of the foot. The foot was meant to represent the rocky layer, but the entire analogy probably didn't work that well to begin with.

Also are you arguing that initially a new layer would look like figures 3 and 6, then given sufficient time, it would look like figures 2 and 5? Actually, this argument is quite hard for me to accept. For one thing, we have many examples where the topmost layer is folded exactly like the layers beneath it. Given pressure of any amount, there is no way to create a parallel layer to the strata beneath if the new layer is flat. Also, how can it explain folds as dramatic as this?

Suppose a series of strata is at depth, and plate convergence causes uplift - this is a gradual process, remember. Does the resulting deformation affect only the bottom-most strata, or every stratum from the bottom up? Where would the top-most strata go if only the former are deformed? Remember, creep and erosion are working here, too. The strata shown here may not have been either sediment or rock near the surface as they were being deformed.

Also, your suggestion cannot explain faults. How can a fault line be created in a layer after a fault has occured?

The fault keeps occurring, even as the process of cementation is taking place in the new rock layer. It's true that faults move in fits and starts, but they aren't just one-shot phenomena, as anyone living in southern California can bear out. The effects of tectonics are all gradual over geologic time-scales, no matter how sudden the individual actions - your figures would work perfectly if plates moved quickly enough for each layer to be neatly deposited and then deformed. But I don't think it works either that quickly or that sequentially.

when the mid-Oceanic ridge "pushed" the continents apart, exactly what was the plates that got pushed? How big are they? Where are the boundaries of the plates?

You write as though this 'pushing' were some sudden action, which may not be the best way to look at it. The Mid-Atlantic Ridge is constantly causing the plates to diverge, and constantly making plate material. As to the latter questions, I don't think they can be answered - plate material melts into the asthenosphere as it is submerged, or accumulates in mountain ranges as plates converge. The boundaries of the plates, therefore, are gradually changing.

[ST88]

Given pressure of any amount, there is no way to create a parallel layer to the strata beneath if the new layer is flat. Also, how can it explain folds as dramatic as this?


Also, your suggestion cannot explain faults. How can a fault line be created in a layer after a fault has occured?

If you'll notice, in the picture you provided, the topmost part of the fold is worn away. Erosion and exposure does a lot to wear away the layers as they rise. I have no idea where this geological feature is in the world, but when this fold was made, it was most likely far under the surface, where the pressure and heat would have squeezed the layers into this shape. They cooled as the mountains rose, then exposure gradually ripped off the topmost part of it.

I'm not sure what you mean by "faults" when you say that layers created after the fault occurred wouldn't have the fault in it. The areas around faults are constantly moving. In transform faults (& in strike-slip), the two sides run past one another laterally. That is, on one side of a transform fault, the land moves north, and on the other side it moves south. So any layers deposited on top of layers already affected by the fault would themselves eventually also be affected by the fault.

Similarly, in thrust faults, normal faults, and reverse faults, one side of the fault is constantly moving either upwards or downwards (albeit in a punctuated fashion), which means that any layers that get set down upon them are also subject to the fault. This model would predict something about layers and faults that a Creationist model wouldn't predict, namely that the distance between layers on a fault would not be the same. That is, over time, the newest layers would have moved less. Here is an illustration of this principle:

From Torrey Pines State Reserve, right in my own neighborhood near San Diego!
Notice that the layers on one side of the fault correspond neatly with the layers on the other side with regards to color and texture. However, also notice that some of the paired layers are farther away from each other than other pairs. This is due to fault movements that are spread out over time. As the layers get deposited on top of the fault, they are moved only by the most recent fault activity. The layer pairs that are farther apart indicate fault movement farther back in geologic time. (There are many more forces at work in most places, but this particular image illustrates the point quite nicely.)