Make the best samples for the k/ar dating method

K-Ar dating calculation - Life on earth and in the universe - Cosmology & Astronomy - Khan Academy

So let's say that this is our volcano. And it erupts at some time in the past. So it erupts, and you have all of this lava flowing. That lava will contain some amount of potassium And actually, it'll already contain some amount of argon But what's neat about argon is that while it's lava, while it's in this liquid state-- so let's imagine this lava right over here.

It's a bunch of stuff right over here. I'll do the potassium And let me do it in a color that I haven't used yet. I'll do the potassium in magenta. It'll have some potassium in it. I'm maybe over doing it. It's a very scarce isotope. But it'll have some potassium in it. And it might already have some argon in it just like that. But argon is a noble gas. It's not going to bond anything. And while this lava is in a liquid state it's going to be able to bubble out. It'll just float to the top. It has no bonds.

And it'll just evaporate. I shouldn't say evaporate. It'll just bubble out essentially, because it's not bonded to anything, and it'll sort of just seep out while we are in a liquid state. And what's really interesting about that is that when you have these volcanic eruptions, and because this argon is seeping out, by the time this lava has hardened into volcanic rock-- and I'll do that volcanic rock in a different color. By the time it has hardened into volcanic rock all of the argon will be gone. It won't be there anymore. And so what's neat is, this volcanic event, the fact that this rock has become liquid, it kind of resets the amount of argon there.

So then you're only going to be left with potassium here. And that's why the argon is more interesting, because the calcium won't necessarily have seeped out. And there might have already been calcium here.

K-Ar dating calculation

So it won't necessarily seep out. But the argon will seep out. So it kind of resets it. The volcanic event resets the amount of argon So right when the event happened, you shouldn't have any argon right when that lava actually becomes solid. And so if you fast forward to some future date, and if you look at the sample-- let me copy and paste it. So if you fast forward to some future date, and you see that there is some argon there, in that sample, you know this is a volcanic rock. You know that it was due to some previous volcanic event.

You know that this argon is from the decayed potassium As Paul Giem notes: Thus one could pick the dates that fit one's expectations and create a very impressive list of dates with close agreement without there being more than a general correlation of most dates with one's expectations. It should be remembered that these researchers are not being dishonest in their actions. They think of the long age scenario of evolution as being fact. They do not believe that there is any alternative way to look at history.

So when the data does not come out right, it is only natural that they assume that there is something wrong with the dates that do not fit the long age viewpoint. However, when they turn around and say that the data supports the evolutionary viewpoint and not the Creationary viewpoint. This is not right! The data does not support long ages. So, many people try to say something like: But this is not true either, the weight of evidence does not prove anything.

We do not have an issue of weight of evidence. Rather, what we have is weight of interpretation! This controversy is not over data. The data can go either way. Very intelligent people believe in the long history of the earth and they have good data to support them. There is no question about it.

However, I look at that same data and I come to very different conclusions. This process is legitimate! There is such a thing as multiple interpretation to the data base. There is no proof for either position. On this web page I want to discuss a possible scenario that would allow K-Ar dates to indicate a short age chronology.

Such a discussion might never be allowed in normal scientific circles because of the assumptions they choose to believe as being true. There is such a strong consensus of opinion on K-Ar dating and other similar topics that deal with the history of the Earth that alternative viewpoints are probably viewed as being counterproductive. Before we start, lets look at the specific K-Ar dating assumptions. The rate of decay half-life , and the branching ratio, of K have not changed.

The material in question lost all its argon at an identifiable time, the reset time. No argon has been lost since the time the rock was reset, or set to zero. No potassium has been gained or lost since the reset time, except by decay. The ratio of K to total K is constant. The total K, Ar, and Ar in the material in question can all be measured accurately.

The seventh assumption is one that scientists are doing their best to fulfill. We should also be able to safely make this assumption. The sixth assumption is also fairly secure. When the concentrations of the various K isotopes are measured, the results are always the same.

The fifth assumption is fairly safe. There are some cases where K has been gained or lost; However, the mineral itself has been noticeably altered. The fourth assumption is probably satisfied for most samples. However, this is an assumption that could be challenged. If the rock was heated in the presence of Argon from the earth's mantle, or perhaps in some primordial Argon which might have had a higher concentration of Ar 36; we might have problems making this assumption.

According to most texts on Potassium-Argon dating, the third assumption is fairly commonly violated. Metamorphism, weathering, and reheating are some of the processes that are mentioned to cause a loss of Argon in the crystal of a rock. Most sedimentary rocks are thought to lose Argon because the crystal structure leaks Argon. A loss of Argon would cause the rock to date younger than it should according to evolutionary thought.

This is probably the assumption that scientists make when they choose to present filtered data in a scientific paper. They see the young dates as those samples that have lost Argon. It is an assumption that they probably view as having no alternatives, yet if this same issue was ever pursued, it might uncover other possibilities suggesting a short age time scenario.

Another possibility is that the second assumption is being violated rather than the third.


  • Argon Geochronology Methods.
  • K-Ar dating calculation (video) | Khan Academy.
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Some samples will not be fully reset, initially. Thus these rocks give a date which is older than what normally would happen if the rocks were fully reset. These older dating rocks give the kind of dates as expected by the scientific community. On the other hand, those rocks that date younger, would not need to have had Argon leak from the crystal after the time when the reseting process occurs. Instead, the rock was probably more completely reset when it was molten.

This means that there was less Argon in the rocks to begin with, because the younger dating rocks were more fully set to zero in the reseting process. The second assumption sounds logical at first. Many text books say it is self-evident.

Radiometric dating

The Age of the Earth. Stanford University Press, p. This is because Ar 40 is an inert gas that does not combine chemically with any other element and so escapes easily from rocks when they are heated. Thus, while a rock is molten the Ar 40 formed by the decay of K 40 escapes from the liquid.

Potassium-argon (K-Ar) dating

There are reasons and evidences for challenging the second assumption. The first assumption is often challenged by some creationists. They think that the radioactivity could have speeded up during the flood producing dates with long ages. But there is no known mechanism to explain or predict the increased rate of radioactivity. However there may be a new development in the field of nuclear reactions that could change this situation. People around the world are working on active "Cold Fusion" reactions. There is another group that has been conducting experiments for the express purpose of speeding up the transmutation process thus changing the half-life characteristics of radioactive materials.

Some of these reactions occur under admittedly extremely mild conditions, However, it is another question to suppose that these newly discovered processes can occur or did occur in natural conditions, in the history of our world. Dating mechanisms such as Carbon, work within the creationary paradigm without the need of having a change in half-lives. So since the time of the flood, there is no evidence that there has been any change in half-lives of radioactive materials.

K/Ar Dating

On the other hand, It is possible that the creation event could have caused changes in the half-lives of nuclides. For more on Cold Fusion and the creation event click on Extinct Nuclides. The majority of the fossils are found in the phanerozoic from Cambrian up to the Pleistocene layers of the Geologic column. This includes the Paleozoic, Mesozoic, and Cenozoic layers.

These are considered by most Creationists to have been laid down during the time of the flood. It is possible that the sedimentary layers in the upper Precambrian are also flood deposits See my Geology page. So the volcanic rock and ash within these layers would have been been produced during the flood event. Only the rocks in the precambrian layers could have been affected by the creation event. Everything else would have been redeposited or re-melted in the global flood. When a scientist needs to measure the amount of Argon that is trapped in a rock, the first step in the process is to get the Argon out of the rock.

That is done by heating the rock in a vacuum. In a vacuum, virtually all the Argon comes out of the heated rock. What conditions could have been present when igneous and volcanic rock was formed? Were the rock layers laid down in a vacuum?

Potassium-argon (K-Ar) dating (video) | Khan Academy

Or might we suggest that molten rock was intruded at very high levels of pressure. Within the Creationary flood model, we also might expect layers to be made underwater. Would all the Argon come out of the heated rock under these high pressure conditions? Since K-Ar dating is so widely used, we might expect that many experiments would have been done to see how well Argon is released under various heated conditions.

We might also expect that hornblende and biotite, the most reliable types of rocks from an evolutionary perspective, would have been tested. But this kind of work has not been published.


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  5. One has to wonder why these kinds of experiments were not originally done. It is always possible that these kinds of experiments were done, but the results never worked out, thus it was never published. I do not know.


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    5. I do know that there have not been too many experiments to determine what really happens to the Argon in various conditions; But there are a few. Dr Giem see references below has been able to find only two published papers. Synthetic introduction of argon into mica at high pressures and temperatures. Isv Akad Nauk S. R Geol Ser ; 8: Argon, being a noble gas , is a minor component of most rock samples of geochronological interest: When 40 K decays to 40 Ar argon , the atom typically remains trapped within the lattice because it is larger than the spaces between the other atoms in a mineral crystal.

      Entrained argon—diffused argon that fails to escape from the magma—may again become trapped in crystals when magma cools to become solid rock again. After the recrystallization of magma, more 40 K will decay and 40 Ar will again accumulate, along with the entrained argon atoms, trapped in the mineral crystals.

      Measurement of the quantity of 40 Ar atoms is used to compute the amount of time that has passed since a rock sample has solidified. Despite 40 Ca being the favored daughter nuclide, it is rarely useful in dating because calcium is so common in the crust, with 40 Ca being the most abundant isotope. Thus, the amount of calcium originally present is not known and can vary enough to confound measurements of the small increases produced by radioactive decay.

      The ratio of the amount of 40 Ar to that of 40 K is directly related to the time elapsed since the rock was cool enough to trap the Ar by the equation. The scale factor 0. In practice, each of these values may be expressed as a proportion of the total potassium present, as only relative, not absolute, quantities are required. To obtain the content ratio of isotopes 40 Ar to 40 K in a rock or mineral, the amount of Ar is measured by mass spectrometry of the gases released when a rock sample is volatilized in vacuum.

      The potassium is quantified by flame photometry or atomic absorption spectroscopy. The amount of 40 K is rarely measured directly. The amount of 40 Ar is also measured to assess how much of the total argon is atmospheric in origin.