Some of the basic Dating Methods are as follows:
- Samarium - Neodymium. (Sm-Nd)
- Rhenium - Osmium (Re-Os)
- Uranium / Thorium - Lead. ( U/Th-Pb)
- Ribidium - Strontium (Rb-Sr)
- Potassium - Argon (K-Ar)
- Argon - Argon (Ar-Ar)
- Lutetium - Hafnium (Lu-Hf)
All these methods rely on the changing ratio of parent or daughter isotopes in a closed system. Now such a closed system does not really exists, but open system affects can't be determined easily, so it is hoped that they about balance out. These methods all have the same basic assumptions.
- Constant decay rate.
- No gain or loss of parent or daughter isotope.
- Known amounts of daughter isotope at start.
| PI | Parent isotope |
| DI | Daughter isotope |
| DE | Different isotope of same element as daughter isotope |
Realizing the difficulty of dealing with assumptions #2 and #3 above Isochron Dating was developed in an attempt to solve this problem.
According to theory the sample starts out with daughter isotopes ratio with other isotopes of the same element at a constant value, but with the parent isotope is arbitrary. As a result is forms a strait horizontal line on a graph. As parent decays to daughter, the ratios change and the straight line remains but becomes angled. The slope of the line equals the number of half-lives of the parent isotope has passed sense solidification.
If there occurs a gain or loss of parent isotope the point moves horizontally. If it is a gain the point moves right. If it is a loss the point moves left.
If a gain or loss of daughter isotope the point moves vertically. A gain moved the point up and a loss moves the point down.
Take this set of data points.
A shift from contamination can take place in all of the data points, but such contamination does not affect all data points equally, so it can cause the data points to shift off the true isochron completely. Given this when one looks at an isochron plot how can one really tell where the true isochron line should be. Sufficient contamination can produce any isochron pattern regardless of the true isochron.
It is even possible to get a negative slope, this would be equivalent to a negative or future date.
Potassium-Argon and Isochron Ages
When you look at actual isochron plots such as the ones
at above link, there seems to be room for subjectivity. Some are
better than others but there is often room for multiple plot
lines. Even uniformitarian geologists recognize the existence of
false isochron. So how do they distinguish good data from bad?
The answer is where the sample fits in the
Geologic Column..
Reconstruction of an isochron from original data at:
New
Age Data of Buried Peat Deposits From the Site "Fili
Park".
This isochron of the Fili Park peat deposits indicates an age
of 89,000 years. This is the isochron presented by
the author of the paper cited above. It a fairly good five
point isochron.
Reconstructed from original data at:
New
Age Data of Buried Peat Deposits From the Site "Fili
Park".
It is also supported by additional isotope ratios. In addition
the data points were the five out of ten samples that "were
interpreted to be in the more or less closed-system."
However is was concluded that this isochron was the result of
contamination as an open system based on the fact that the date
was about 50% of the age suggest by the spore and pollen fossils
in the deposit. So this other wise good isochron was rejected
because it disagreed with the fossils.
Constructed from original data at:
New
Age Data of Buried Peat Deposits From the Site "Fili
Park".
Even when samples that were originally considered part of an open
system are added the result is still a fairly good isochron with
only two point showing significant deviation.
Constructed from original data at:
New
Age Data of Buried Peat Deposits From the Site "Fili
Park".
If the two deviating points are removed the result is an
excellent eight point isochron.
Constructed from original data at:
New
Age Data of Buried Peat Deposits From the Site "Fili
Park".
Further more all ten data points form a fairly good second
isotope ratio plot.
The result is that contamination can form good looking isochron
data and uniformitarian geolgists know it. The real way a
"true" isochron is distingquished from a false isochron
is by how well it agrees with how old the fossils aleged to
be.
Reference: New
Age Data of Buried Peat Deposits From the Site "Fili
Park".