I've been working through Humphreys' recent article presented at ICC#5 ...
http://www.icr.org/research/icc03/pd...CC_7-22-03.pdf
... and I've found some minor problems and errors, some of which are detailed in this thread.

But the big, fatal flaw has eluded me until now. Here it is:

Humphreys measured the helium diffusion rate in zircons from 750 meters down in a borehole in New Mexico, then calculated what diffusion rates would generate the observed levels of helium in zircons collected from various depths (and temperatures) in the same borehole.

He produced two models, one assuming the diffusion took place over only 6000 years, the other over 1.5 billion years. The diffusion rates predicted by the two models differ by a factor of about 100,000. The Creation model predicts diffusion rates very close to what was actually measured, at least for the zircons collected from depths with temperatures close to the range of temps for which diffusion rates were measured. The Uniformitarian model requires rates to be lower by the factor of 100,000 mentioned above. Figure 8 from the article shows this graphically.

Simply put, the factor of 100,000 is almost entirely explained by the fact that diffusion rates depend not only on temperature, but also on the amount of helium in the zircon. The zircons for which diffusion rates were measured contained far more helium than the zircons at the bottom of the hole (point 5 from figure 8) - maybe a thousand time more or possibly even higher.

The diffusion rate SHOULD be far lower for point 5 compared to zircons from near the surface (assuming the same temp, of course), because they contain so much less helium.

There are other factors, such as a graphing error, increased uranium content near the surface, and selective data massaging that account for some of the remaining difference. But these are small in comparison.

The Creation model, when adjusted for actual helium content, fails miserably. The Uniformitarian model is deadly accurate.

Is this argument ready for AIG's "do not use" list?

Please comment, critique, etc...

Today @ 01:52 AM post located here
wehappyfew:

...

Simply put, the factor of 100,000 is almost entirely explained by the fact that diffusion rates depend not only on temperature, but also on the amount of helium in the zircon. The zircons for which diffusion rates were measured contained far more helium than the zircons at the bottom of the hole (point 5 from figure 8) - maybe a thousand time more or possibly even higher.

Good point. If there is no gradient, there will be no diffusion. In fact, if the zircons happened to be lower in He content, diffusion would occur in the opposite direction.

So much for YEC "peer review"...

First, even if everything in that article was true, they'd still have to account for the reported 1.5 billion year isotopic dates using standard radioisotopes.

Secondly, no geochronologists use helium retention to tell the age of a rock (or a zircon crystal), because it is known to be subject to all kinds of problems. However, they do use it for "thermochronology" studies (to learn when and how much the rock was heated or cooled).

While lead is retained well in zircon, even up to remarkably high temperatures, helium is very small and non-reactive, so it leaks out of zircon crystals quite quickly, especially if the zircon is even slightly heated. When warm, the zircon expands slightly, and becomes very permeable (leaky) with respect to helium, although not so with respect to lead and uranium. Above the critical closure temperature, zircon is "open" (leaky), whereas below, it is "closed" (or sealed). However, zircons also become quite leaky merely by sitting around for a while since they cooled below their closure temperature, because the decay of uranium atoms blasts tiny holes in the zircon (literally, the explosive expulsion of helium ions from the uranium creates (surprise) holes just large enough for helium to escape through.

Because helium escapes readily whereas lead and uranium don't, it is not a problem to say that the zircon has a certain number of years worth of helium but is a different number of years old by uranium-lead dating. Nor is it a problem to say that the zircon has a high closure temperature for lead but a low closure temperature for helium, or that it is closed with respect to lead but simultaneously open with respect to helium.

Humphreys and his colleagues mention that the Jemez Granodiorite is about 1.5 billion years old. However, it sits next to volcanic intrusions that have pumped up the temperature considerably. The rise in temperature has allowed all the helium to escape from the deeper zircons, and they remain warm enough to be open, so that helium escapes pretty much at the same rate at which it is produced.

When you look at zircons nearer the surface, they are cooler, so they have closed and have started to accumulate helium. The ones nearest the surface closed the longest ago, so they have the most helium and thus the oldest "apparent ages".

You can play around with calculations involving the recency of heating, the degree of heating, and multiple episodes of heating to see what best explains the distribution of helium in the zircons at various depths. (That's basically thermochronology.)

The only real puzzle here is that the zircons at the surface reportedly contain 58% of the helium that should have been produced, if you assume that all the lead in the zircon decayed from uranium (inevitably producing a set amount of helium in the process). One would have expected the loss of much more than 42% of all the helium that the zircon presumably ever contained due to (a) leakage prior to the first closure after formation of the zircon, (b) radiation damage in the time since the first closure, (c) any reheating due to magmatic intrusions in the caldera, and (d) radiation damage since event "c".

My guess (which is not very well informed, so I'll be happy to bow to superior knowledge here) is that after annealing (healing) of the now near-surface crystals in event "c", the crystals once again became open due to the accumulation of radiation damage, and since then have been taking in a lot of excess helium. First, the last active phase of the Valles Caldera probably effectively emptied the near-surface zircons of any argon that they may have contained at that point. Second, there must be a lot of helium seeping up from the depths, due to the intrusions and the warmed and open zircons nearby. Third, a crystal that is open to leakage is equally open to inflitration. Fourth, some crystals in some locations are known to be very susceptible to the infiltration of gas, sometimes in excessive quantities. My understanding is that there are quite a few examples in the literature of argon-argon and potassium-argon dates on feldspars and micas that got screwed up because of excess argon. Excess argon is apparently something to be especially wary of next to intrusions, dikes, veins, and vapor-carrying fractures.

I haven't heard of studies of this happening with helium and I certainly can't be sure that that's what went wrong here, but (a) the chemistry etc. is comparable so why not, (b) helium hasn't been studied as much as argon because argon problems are generally managable (making detailed studies of problems helpful), whereas helium problems aren't (so almost no one bothers with it), and (c) this isn't my field, so I could be quite ignorant of a lot of pertinent work.

Thanks for your thoughtful reply, Sed...

However, I think that much of your objections to Humphreys' article are missing the mark. To play the Devil's advocate, and since not a single YECer has deigned to take notice of this thread, I will jump to the other side of the fence and attempt to refute your points.

Yesterday @ 05:27 PM post located here
SedRocks:

First, even if everything in that article was true, they'd still have to account for the reported 1.5 billion year isotopic dates using standard radioisotopes.

This one is easy...
Accelerated decay has compressed 4.55 billion years of decay into only a few thousand years, at least for most radioactive isotopes. This generated 1.5 billion years worth of lead and helium in the rocks (which must, therefore, be significantly younger than the Earth). The lead, being relatively immobile, remains in the zircons at these temperatures, and gives consistent U/Pb ages of 1.5 billion years. The helium has leaked out to some extent, depending on temperature.

Secondly, no geochronologists use helium retention to tell the age of a rock (or a zircon crystal), because it is known to be subject to all kinds of problems. However, they do use it for "thermochronology" studies (to learn when and how much the rock was heated or cooled).

Humphreys is not claimnig the U/He "ages" are meaningful as actual chronological ages, but that the amount of He retention is controlled primarily by temperature. So modeling the diffusivity at various temperatures can be used to calculate the time required for helium to reach its observed values.

While lead is retained well in zircon, even up to remarkably high temperatures, helium is very small and non-reactive, so it leaks out of zircon crystals quite quickly, especially if the zircon is even slightly heated. When warm, the zircon expands slightly, and becomes very permeable (leaky) with respect to helium, although not so with respect to lead and uranium.

The rate of leakage is measureable, and is dependent on temperature, so the amount remaining is a function of the initial amount, the amount added since, time elapsed, and temperature.

Above the critical closure temperature, zircon is "open" (leaky), whereas below, it is "closed" (or sealed).

Humphreys wrote a detailed explanation of how leakage can still occur, even at temperatures below the closure temp. It's pretty close to accurate. Read section 10.
http://www.globalflood.org/papers/2003ICChelium.html

To be completely accurate, we should say that "closure temperature" is the temperature of the crystal at the time in the past given by its apparent age. At that time, helium is still leaking out quite rapidly, and continues to leak out as it falls lower. To say the diffusion stops when the closure temperature is reached is wrong.

However, zircons also become quite leaky merely by sitting around for a while since they cooled below their closure temperature, because the decay of uranium atoms blasts tiny holes in the zircon (literally, the explosive expulsion of helium ions from the uranium creates (surprise) holes just large enough for helium to escape through.

Humphreys does not address this process directly in his article. I think this is a major shortcoming of his effort. There are two effects that compound his error here:
1. As you mentioned, at lower temps, radiation damage can easily accumulate. The zircons which were measured for diffusivity were collected at 750 meters, shallower (and colder) than all the other zircons. This means their radiation damage should be annealed the least - thus leading to a higher measured diffusivity.
2. There is a strong trend of higher uranium content at shallower depths in the samples. The deepest zircons have far less U and Th than the shallow zircons which had their diffusivity measured. Again, more radiation damage, higher diffusivity for the shallow zircons.

Humphreys and his colleagues mention that the Jemez Granodiorite is about 1.5 billion years old. However, it sits next to volcanic intrusions that have pumped up the temperature considerably. The rise in temperature has allowed all the helium to escape from the deeper zircons, and they remain warm enough to be open, so that helium escapes pretty much at the same rate at which it is produced.

Humphreys' argument is that the deep zircons still contain more helium than they should, based on extrapolating the measured diffusion rates. The equilibrium amount (where the production equals the diffusive loss) at the diffusivity he measured in the shallow zircons would predict that the deep zircons should have thousands of times less helium than what they actually have.

The only real puzzle here is that the zircons at the surface reportedly contain 58% of the helium that should have been produced, if you assume that all the lead in the zircon decayed from uranium (inevitably producing a set amount of helium in the process). One would have expected the loss of much more than 42% of all the helium that the zircon presumably ever contained due to (a) leakage prior to the first closure after formation of the zircon, (b) radiation damage in the time since the first closure, (c) any reheating due to magmatic intrusions in the caldera, and (d) radiation damage since event "c".

Your model presented here - involving substantial heating of even the near-surface zircons - should leave no more than a few million years worth of helium. Instead we find nearly a billion years worth. So either your model is wrong, or the age of the Earth is only a few thousand years.

My guess (which is not very well informed, so I'll be happy to bow to superior knowledge here) is that after annealing (healing) of the now near-surface crystals in event "c", the crystals once again became open due to the accumulation of radiation damage, and since then have been taking in a lot of excess helium.

I think you are implying that the zircons absorb helium from other sources, not just internally generated from U and Th decay. Humphreys refutes this model by pointing out that the helium levels in the borehole are essentially zero. There is insufficient partial pressure of helium to force it into the zircons.

First, the last active phase of the Valles Caldera probably effectively emptied the near-surface zircons of any argon that they may have contained at that point.

Do you mean helium? Not "argon"?
If so, then the near surface zircons should contain very little helium - only a few hunderd thousand or a few million years worth. They have a thousand time more than that.

Second, there must be a lot of helium seeping up from the depths, due to the intrusions and the warmed and open zircons nearby.

There is no significant partial pressure of helium in the borehole, so your model must fail, unless you can show that the helium pressure must have been much higher in the past. I don't see how it could be.


I think the radiation damage is the best point of your post. It is another aspect of Humphreys' pattern of comparing apples to oranges in his measurement of helium diffusivity. The shallow zircons shoud have higher difusivity because they are more damaged, having higher levels of uranium and being colder, which prevents annealing of the damage.

Add that to my previous observation that the helium levels of the shallow zircons are thousands of times higher, then it becomes obvious why this graph (figure 8) SHOULD have a discrepancy of 100,00 times between the diffusion rates measured for one zircon compared to a completely different zircon found deeper in the same hole...


http://www.globalflood.org/graphics/...s/image069.jpg

The deeper zircons (point 5) have less helium, less uranium, and less radiation damage. That is why its diffusivity is 100,000 times less, as shown on the graph.

Can any YECreationist find fault with this analysis?

If not, then can any YECreationist deny that the helium diffusion argument is seriously flawed?

Thanks for your critique, Wehappyfew. Your point about differing concentrations of uranium in the zircons is well taken.

Beyond that, although I could quite easily be wrong here, I'm not yet ready to throw in the towel. Excess argon is common enough that we should be suspicious about the possibility of excess helium. I'm not convinced that low modern helium concentrations in the borehole have any relevance for concentrations in the past. (Incidentally, yes, I meant helium instead of argon in that one sentence you noted.)

First, one would expect the many ignous rocks in the area to contain reasonable quantities of uranium. Secondly, the area is a caldera, which implies a complex history of opening of fractures, hydrothermal fluid circulation, complex near-surface groundwater flow, and reblocking of fractures by mineral precipitation. Even secondary concentrations of uranium are possible. Helium certainly accumulates naturally in gas fields, and gas and oil fields can change easily enough over time as rock seals fracture or are eroded away, or as groundwater conditions change. A caldera is quite active geologically, and should certainly offer lots of analogues to normal natural gas traps, so I wouldn't be surprised if helium built up in one place for a while, and then escaped through a new fracture, only to get get trapped some place else for a while. Thus there might well have been an interval or two when partial pressures of helium were high enough to saturate some of the zircons.

If only there were a YECist chemist around here who could give us his opinion on the matter of Helium and Zircon and how it applies to the age of the Earth?

Take care.

11-13-2003 @ 01:10 AM post located here
wehappyfew:

Thanks for your thoughtful reply, Sed...

I think you are implying that the zircons absorb helium from other sources, not just internally generated from U and Th decay. Humphreys refutes this model by pointing out that the helium levels in the borehole are essentially zero. There is insufficient partial pressure of helium to force it into the zircons.

How was this He partial pressure measured and how important is it under conditions of diffusion? Unless the diffusion rates are extremely high, I wouldn' t imagine that He concentrations would be measurable in a borehole after drilling.

We know that the interior of the earth is a source of He and that there is a constant flux through the crust into the atmosphere. So there are sources and there are measureable amounts. How do such concentrations compare with actual He measurements in zircon? Is there any 3He in the zircon crystals?

There is no significant partial pressure of helium in the borehole, so your model must fail, unless you can show that the helium pressure must have been much higher in the past. I don't see how it could be.

However, we do know that in some places the He pressures are significant enough to allow production. And we know that 3He/4He varies in space. Is it that unreasonable to assume that it cannot likewise vary with time and result in different patterns of He concentration?

Today @ 06:31 PM post located here
aniso:

How was this He partial pressure measured and how important is it under conditions of diffusion? Unless the diffusion rates are extremely high, I wouldn' t imagine that He concentrations would be measurable in a borehole after drilling.

Iirc (and I'm not reading that report again!) the rocks around the zircons had low He concentrations.

However, we do know that in some places the He pressures are significant enough to allow production. And we know that 3He/4He varies in space. Is it that unreasonable to assume that it cannot likewise vary with time and result in different patterns of He concentration?

Once again, iirc the He in gas fields is attributed to partitioning between water and gas phase in reservoirs - He concentrates in the gas resulting in high partial pressures.

3He/4He varies in space (I simplify, and assume you mean in the Earth's interior) primarily due to two processes: variable efficiency of degassing and generation of 4He by radioactive decay. In essence, everywhere evolves to lower 3/4 ratios because degassed 3He is not replaced while 4He is generated continuously, the rate depending on U and Th concentrations.

So (broadly speaking) to raise the partial pressure to a high enough level for the zircons to acquire He from outside, would you not need a source region with U + Th concentrations as high or higher than in the zircons?

Humphreys has published a new article (Impact No. 366) with more experimental diffusion data. He makes the obligatory pompous claims of "powerful evidence against the long ages of uniformitarianism"... that "resoundingly confirm" the Creationist predictions... and ... "emphatically repudiating the Evolution model".

The new data extends the temperature range of experimentally measured diffusion rates down to 175degC, thus overlapping the range found in the borehole from which Gentry extracted zircons.

In reality, this new data confirms the old age paradigm, not the YECreationist one. The reason for this vast disconnect between claims and reality is very simple. Humphreys once again compares zircons with very high levels of helium to zircons with very low amounts of helium. The new data is from zircons recovered from a depth of 1490 meters. This is closest to the shallowest zircons of Gentry's data set - point 1 from this graph:

http://www.icr.org/research/rate/hel...s/image041.jpg

The diffusion rate measured is quite high, almost as high as the previous measurement of zircons from 750 meters depth. The same three factors are responsible:

1. The zircons from 1490 meters depth have retained a large percentage of the helium generated within. Humphreys does not provide this datum in the article, but we can estimate that it will fall between the values for zircons from 960 meters and 2170 meters - the two closest points from Gentry's data. That is, it should be less than 58% and more than 27%.

2. The zircons from shallower depths generally have much higher levels of uranium. This leads to both more absolute amounts of helium, and more radiation damage - both of which increase diffusion rates.

3. Shallower, and thus colder zircons can accumulate more radiation damage, while the deepest zircons are annealed by the high temperatures.

When these shallow zircons are compared to the deepest zircons (point 5 in the graph above), the diffusion rate should be much higher. The deepest zircons have retained several hundred times less helium due to their higher temperature, they may have an addition reduction due to their lower uranium content - perhaps as much as 64 times lower, and their radiation damage is annealed by the high temps.

The new data is presented by Humphreys in a very similar graph:

http://www.icr.org/newsletters/images/impact1203-2.jpg



Consider two of the zircons being compared by Humphreys:

Zircon 5 (from point 5 in the first graph above) is the deepest - 3930 meters, has retained a very small proportion of its helium (0.1%), is the hottest (277degC - high enough to anneal radiation damage), and contains very little uranium - perhaps as low as 83 ppm*.

Zircon B (the second one measured in the lab - the black dots in the second graph) has retained a large proportion of its helium (between 27 and 58%), is cool (between 105 and 151degC - thus radiation damaged), and may contain up to 5300 ppm* uranium (yet more helium and more radiation damage).

The "Uniformitarian Model" from Humphreys' graph predicts the diffusion rate for Zircon B should be far higher than Zircon 5 - and that has been experimentally confirmed by Humphreys.

The "Creation Model" predicts the two zircons should have nearly the same diffusion rate, perhaps even a little higher for the zircon with less helium. That prediction flies in the face of the known physical behavior of diffusing gasses in solids.

Can anyone reasonably argue that the zircon with thousands of times more helium and much higher radiation damage should have the same diffusion rate as the low helium, low radiation-damaged zircon? Humphreys makes that claim, but I contend it is not at all reasonable.

His model requires a very helium-rich zircon to have the same or slightly lower diffusion rate than a zircon with very little helium. Is that reasonable?
Humphreys doesn't think so:
"As the amount of helium in the zircon increases, Fick’s laws of diffusion (sect. 3) say the loss rate also increases. "

His model also requires a zircon with more radiation damage to have a lower diffusion rate. Does Humphreys really believe this to be possible?
No:
"The more defects there are, the higher D1 is..."

(both quotes from this article)

Thus his model is discredited by his own statements about how diffusion actually works.

Comments, please, anyone at all? I'm not afraid of criticism, I welcome it, in fact.

* (from Gentry's article in Science, p.296, v216, 16 Apr 1982)

Since few of us are qualified to judge the various arguments, you should direct your comments to Humphreys, who I am sure would be as happy to receive constructive criticism as you are.

wehappyfew:
His model also requires a zircon with more radiation damage to have a lower diffusion rate.

Humphreys makes no such claim nor does his model impose such a requirement. Rather D1 is, as he points out, a "defect parameter" that increases the diffusion rate.

Quoting from his article...

If the crystal has defects such as vacancies in the crystal lattice, impurities, dislocations, or grain boundaries, then the diffusion coefficient equation will have a second term related to the defects:

(equation given in original article)

The defect parameters (D1 and E1) are almost always smaller than the intrinsic parameters (D0 and E0):

...

For a given type of mineral, the location of the knee can vary greatly. It depends on the value of D1, which depends on the amount of defects in the particular crystal. The more defects there are, the higher D1 is. If we increase the number of defects, the defect line moves upward (keeping its slope constant) on the graph, as Figure 4(b) illustrates.

In the case of zircons containing radioisotopes, the main cause of defects is radiation damage, so highly radioactive (“metamict”) zircons will have a large value of D1, causing the defect line to be higher on the graph than for a low-radioactivity zircon.

WHF, perhaps you jumped to your faulty conclusion when you misread where Humphreys states that the "defect parameters...are almost always smaller than the intrinsic parameters."

Today @ 04:13 AM post located here
TheFiveSolas:

Humphreys makes no such claim nor does his model impose such a requirement.

I think it does. The creation model point 5's diffusivity is derived from a zircon with low He and low Uranium assuming a 6000 year age. The diffusion data, black points, are measured from a zircon with high He and high Uranium. Humphrey's point is that these two diffusivities agree. Hence he is asserting that they ought to agree, and thus that U content, defects and He content should have little or no effect on diffusivity.

In fact, the low He zircon point is actually slightly higher than measurements suggesting it has a higher diffusivity, which is what WHF is saying.

Of course Humphreys knows defects do affect diffusivity - the bits you quote show this. He just elides the difference in zircons that WHF points out.

I wonder what temperature those zircons would get to during a few days of accelerated decay, btw, and how long they would stay hot. Does the creation model take that into account? I suspect not.

"Since few of us are qualified to judge the various arguments....."

I think I need a whole new emoticon here.

Today @ 06:18 PM post located here
SedRocks:

"Since few of us are qualified to judge the various arguments....."

I think I need a whole new emoticon here.

You need to recognize that we are not judging a debate but only hearing one side of the story. This is why it would be better to wait until we hear what Humphrey's has to say about some of the statements WeHappyFew made in his posting. If they are substantial then perhaps talk.origins would include them in an article on their website. That would probably induce Humphreys to answer them.

Socratism:
You need to recognize that we are not judging a debate but only hearing one side of the story. This is why it would be better to wait until we hear what Humphrey's has to say about some of the statements WeHappyFew made in his posting. If they are substantial then perhaps talk.origins would include them in an article on their website. That would probably induce Humphreys to answer them.

If only there were someone with a chemistry background out there--who was also a YECist--to help us with the big picture concerning this problem...

Take care.