they are untestable assumptions!!
we cannot test the conditions of the past because we cannot go back there and bring back samples
..........so we have to make assumptions about the past and then proceed
assumptions are by their very nature untestable
So if you read on a pack of burger 'Made from 100% beef' we cannot test that because we cannot go back in the past and see what the animals were chopped up to make the burgers? You couldn't test a claim about the past with say a DNA test?
ok
yes and creationists are correct to do so
losing sight of the assumptions involved in any endeavor is not a good practice - and yet this is what has happened
i looked at the entire category of radiometric dating at wiki and only K-Ar listed the assumptions:
KâAr dating - Wikipedia, the free encyclopedia ....list of assumptions for K-Ar dating - not a creationist source
Lets have a look:
The reference is Ian McDougall and T. Mark Harrison (1999),
Geochronology and thermochronology by the [sup]40[/sup]Ar/[sup]39[/sup]Ar method, Oxford: Oxford University Press. Oxford University Press sounds pretty reputable. Fortunately that book is accessible through Amazon. Lets see how the Wikipedia article compares with the original, see if anything significant is left out. Wikipedia is not a usual place to find quote mining, but you never know. I will go through it point by point and highlight where the wiki article changes the book in blue and when I quote the book, I will use red to show where it differs from wiki.
- The parent nuclide, 40K, decays at a rate independent of its physical state and is not affected by differences in pressure or temperature. This is a well founded major assumption, common to all dating methods based on radioactive decay. Although changes in the electron capture partial decay constant for [sup]40[/sup]K possibly may occur at high pressures, theoretical calculations indicate that for pressures experienced within a body of the size of the Earth the effects are negligibly small.[1]
Here is what the book says, I have added in the bit Wikipedia leaves out in red:
1. The parent nuclide, 40K, decays at a rate independent of its physical state and is not affected by differences in pressure or temperature. This is a well founded major assumption, common to all dating methods based on radioactive decay; the available evidence suggest that it is well founded (Friedlander et al., 1981). Although changes in the electron capture partial decay constant for [sup]40[/sup]K possibly may occur at high pressures, theoretical calculations Bukowinski (1979) indicate that for pressures experienced within a body of the size of the Earth the effects are negligibly small.
Instead of simply claiming the assumption was well founded, as we have in the wiki article, the original say it is supported by all the available evidence and gives a reference for this. Next bullet:
- The [sup]40[/sup]K/[sup]39[/sup]K ratio in nature is constant so the [sup]40[/sup]K is rarely measured directly, but is assumed to be 0.0117% of the total potassium. Unless some other process is active at the time of cooling, this is a very good assumption for terrestrial samples.[5]
This seem to have been extensively re written:
2. The K/K ratio in nature is constant at any given time. As the [sup]40[/sup]K is rarely determined directly when ages are measured, this is an important underlying assumption. Isotopic measurements of potassium in terrestrial and extraterrestrial samples indicate that this assumption is valid, at least to the extent that no authenticated differences greater than about 1.3% have been reported in the 39K/41K ratio. The evidence for the essentially constant isotopic ratios for the potassium isotopes will be presented in more detail subsequently in section 2.3.]
The first bit left out "
at any given time" throws the meaning of the paragraph considerably. It isn't that scientists assume the proportion of
[sup]39[/sup]K was the same in the distant past as it is now, which doesn't make sense since[sup]39[/sup]K is the radioactive isotope. The assumption is that the isotopes of potassium are well mixed and you have the same proportion of isotopes everywhere you go. Again the wiki article leaves out the discussion of how this assumption has been authenticated.
- The radiogenic argon measured in a sample was produced by in situ decay of [sup]40[/sup]K in the interval since the rock crystallized or was recrystallized. Violations of this assumption are not uncommon. Well-known examples of incorporation of extraneous 40Ar include chilled glassy deep-sea basalts that have not completely outgassed preexisting [sup]40[/sup]Ar*,[6] and the physical contamination of a magma by inclusion of older xenolitic material. The ArAr dating method was developed to measure the presence of extraneous argon.
This paragraph is relatively unchanged.
3. The radiogenic argon measured in a sample was produced by in situ decay of [sup]40[/sup]K in the interval since the rock crystallized or was recrystallized. Violations of this assumption are not uncommon. Well-known examples of incorporation of extraneous 4[sup]40[/sup]Ar include chilled glassy deep-sea basalts that have not completely outgassed preexisting radiogenic argon and the physical contamination of a magma by inclusion of older xenolitic material. Further examples will be discussed later, as the [sup]40[/sup]Ar/[sup]39[/sup]Ar dating method allows the presence of extraneous argon to be recognized in some cases.
However the next paragraph was completely left out.
4. "Corrections can be made for nonradiogenic [sup]40[/sup]Ar present in the rock being dated. For terrestrial rocks the assumption generally is made that all such argon is atmospheric in composition with 40Ar/36Ar = 295.5, and although this commonly is so, there are exceptions. Various ways of assessing this assumption are available including the use of isotope correlation diagrams. Extraterrestrial samples such as meteorites and lunar rocks have nonradiogenic argon of quite different composition to that of atmospheric argon, but corrections often can be made satisfactorily, particularly as the nonradiogenic contributions usually are minor."
The following chapter in wiki is not from the book at all.
- Great care is needed to avoid contamination of samples by absorption of nonradiogenic [sup]40[/sup]Ar from the atmosphere. The equation may be corrected by subtracting from the [sup]40[/sup]Ar[sub]measured[/sub] value the amount present in the air where [sup]40[/sup]Ar is 295.5 times more plentiful than [sup]39[/sup]Ar. [sup]40[/sup]Ar[sub]decayed[/sub] = [sup]40[/sup]Ar[sub]measured[/sub] − 295.5 × [sup]39[/sup]Ar[sub]measured[/sub].
Wiki continues...
- The sample must have remained a closed system since the event being dated. Thus, there should have been no loss or gain of [sup]40[/sup]K or [sup]40[/sup]Ar*, other than by radioactive decay of [sup]40[/sup]K. Departures from this assumption are quite common, particularly in areas of complex geological history, but such departures can provide useful information that is of value in elucidating thermal histories. A deficiency of [sup]40[/sup]Ar in a sample of a known age can indicate a full or partial melt in the thermal history of the area. Reliability in the dating of a geological feature is increased by sampling disparate areas which have been subjected to slightly different thermal histories.[7]
The last two sentences are not in the book and look like the wiki writer is expanding on the previous sentence.
5. The sample must have remained a closed system since the event being dated. Thus, there should have been no loss or gain of of potassium or radiogenic argon, other than by radioactive decay of 40K. Departures from this assumption in fact are quite common, particularly in areas of complex geological history, but such departures can provide useful information that is of value in elucidating thermal histories.
Notice how (1) we can tell if there has been loss or gain of these isotopes and (2) how that tells us even more about the history of of the rock? The wiki article leaves out the next paragraph, which while it is not a numbered paragraph is pretty important as the conclusion of the section:
"These basic assumptions must be tested and assessed in each study that is undertaken. This is usually best done by measuring a suite of rocks or minerals from the area under study. The consis[bless and do not curse]tency or lack of consistency of the results, together with knowledge of the geology of the area, allows assessment of some of these assumptions, and provides the basis for conclusions as to the reliability and meaning of the measuredages. As will become evident later, animportant advantage of the [sup]40[/sup]Ar/[sup]39[/sup]Ar dating method is that the assumptions underlying calculation and interpretation of an age are more readily assessed than is the case for conventional K-Ar age measurements."
You see, you want 'assumption' to mean something completely unverifiable. But what McDougall and Harrison meant by assumption, at least in the original version, was a basis for the dating method that needs to be, can be, and has been, verified.
Looking at the history of the Wikipedia page, the reference was added, and further edited down, by a user called Christian Skeptic, whose account has been blocked as a sockpuppet of another user blocked for 'abusive use of one or more accounts'. Your evidence for radiometric dating being based on unverifiable assumptions may be a case of
wikiality.
this link below may be a creationist source but that does not mean the info presented is not valid
Radiometric Dating
Few people realize it but all radiometric dating methods require making at least three assumptions. These are:
1) The rate of decay has remained constant throughout the past.
As we have seen this had been tested and confirmed.
2) The original amount of both mother and daughter elements is known.
3) The sample has remained in a closed system...
Isochron dating deals with these.