The proof is that liquid rock is a very poor solvent for gases like argon. If an atom of potassium-40 decays to argon in soup, the argon escapes. If it decays in a crystal in a rock, it has a difficult time breaking out.
If the rock gets melted (or near-melted) with trapped argon in it, the argon can escape and the clock gets reset to zero.
You're correct, sorry about that. I misread "magmatic" as "magnetic" and thought he was making a different argument.
But Pressie is still just providing simple factual information. Gas escapes easily from molten rock, resetting the K/Ar and Ar/Ar clocks.
It works like this. Say there's a buried rock layer containing K, some of which has decayed to Ar. If we had access to this rock layer, maybe by obtaining a core sample, we could date its age. But now let's say the layer becomes heated and molten, so all the Ar escapes. The K/Ar and Ar/Ar clocks are now reset since there is no accumulation of Ar left. When the layer cools and solidifies then Ar will again begin to accumulate and these clocks will begin again.
What if the argon is being made in the molten state?
Actually, there is probably some argon dissolved in all magma. The question is, where does it go when minerals form. Some minerals, such as pyroxene will admit argon into its lattice, while others such as biotite and orthoclase do not. This is know empirically.
So, it doesn't really matter when the argon is generated, or where.
Yet it is produced in the magma state. And looking at Zircon crystals, it looks as though the noble gases are formed very fast. I just wonder if the noble gas is in there bouncing, and not wanting to react to crystal rock.
Argon is a "noble gas" or an "inert gas". It has a full shell of valence electrons. It reacts chemically with pretty much nothing at all, even under pretty extreme conditions. It may well be very stable "in its containment" but only if it is trapped in a cage of atoms that are bonded to each other. It will not form bonds of its own in any plausible geological setting.
Ar is a noble gas; therefore it can't partcipiate in the chemical reactions resulting in the formation of the crystal lattices. Thus; Ar won't be present in the crystal lattices directly after formation of crystals. Basic chemistry.
I wasn't clear. Is it unstable in its containment? Does it bounce around in the rock?
Obviously not. What does "unstable in their containment" and "bounce around the rock" even mean?
"not wanting to react"? I wasn't clear. Is it unstable in its containment? Does it bounce around in the rock?
It is somewhat to very mobile, depending very strongly on temperature. That's why dating using helium (produced as part of the decay or uranium and thorium) is very difficult and very rarely used. The very first radiometric date, in 1904 by Lord Rutherford, was based on helium. He wrote that almost certainly some helium had escaped and therefore his age was a lower bound.
If you are referring to Humphreys' work with zircons as part of the RATE group, again you need to learn a lot before you can discuss it.
Standard U-Pb dating of zircons does not use helium, how much helium there is or is not in the zircon doesn't matter.
Curiously, I don't think that site supports what you think it does ...
quote:Third is an argument which is perhaps the most definitive falsification of the idea that trees grew more than one ring per year in ancient history. Here is a greatly condensed version of this argument.
Our sun occasionally goes through periods of quiescence. During these periods few sunspots are seen on the sun's surface and the solar wind is reduced. This lets more cosmic radiation into the upper atmosphere of the earth, which allows more radiocarbon to be produced in the atmosphere. These periods of quiescence occur in two varieties, one lasting an average of 51 years, and the other lasting an average of 96 years.
How does this relate to tree-rings? During these periods of quiescence, atmospheric radiocarbon concentrations are higher. This difference in radiocarbon concentration is recorded in tree rings which are growing during the period of quiescence. If trees were growing two or three rings per year at the time one of these episodes occurred, two or three times as many rings would be affected than if trees were only growing one ring per year. In other words, if trees were growing one ring per year, a 51-year period of solar quiescence would affect 51 tree rings. If trees were growing three rings per year, a 51-year period of solar quiescence would affect about 153 rings. Thus, a record of ring growth per year is preserved in the number of rings affected by these periods of solar quiescence.
In fact, at least 16 of these episodes have occurred in the last 10,000 years.These 16 episodes are more or less evenly distributed throughout those 10,000 years. In all cases, the number of rings affected is grouped around 51 or 96 rings. Thus it is clear that, for at least the last 10,000 years, trees have been growing only one ring per year. The suggestion that dendrochronology is invalidated by growth of multiple rings per year is thus falsified.
Bold added. So thanks, I'll be happy to add them to my list of references.
AND I have other evidence that shows how accurate tree-ring counting is. See also the evidence that Lake Suigetsu varves accurately record annual layer events and that gets back to the limits of 14C dating. Then there are ice layers ...