Isochron dating methods forummember phpu

Note that the error estimates (the ± numbers) are small compared with the age.They are also small compared with the variation in ages between samples.

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Clearly, there is a problem with the assumptions on which the K-Ar ‘ages’ are calculated.The isotopic results other than potassium-argon (K-Ar), namely rubidium-strontium (Rb-Sr), samarium-neodymium (Sm-Nd) and lead-lead (Pb-Pb), were used to calculate ages for the rock formation utilizing isochrons.It is important to realize that the laboratories do not measure the ‘age’ of the rocks but the isotopes in them at the present time.Geologists calculate an ‘age’ using the measured amount of a ‘daughter’ isotope (e.g.argon) and its corresponding ‘parent’ isotope (e.g. However, before this calculation can be made, it is necessary to assume how much of the ‘daughter’ and ‘parent’ were present when the rock formed.

It is also necessary to assume that no isotopes were gained or lost over time and that the rate of radioactive decay has remained constant at the very slow rate measured today.

Routinely, if the data set is large, a few outlying data points are ignored if they don’t plot on the line.

Geologists justify this, saying that some geochemical alteration in the past disturbed the radioisotopes in those samples.

But the quest to test this belief by sampling rocks from deep within Grand Canyon has found it is not true.

Both laboratories use standard, best-practice procedures on state-of-the-art equipment and routinely provide accurate and repeatable measurements of the required isotopes.

Furthermore, the seven samples from the small amphibolite unit near Clear Creek, which should be even closer in age because they belong to the same metamorphosed basalt lava flow, yielded K-Ar model ‘ages’ ranging from 1,060.4 ± 28 Ma to 2,574.2 ± 73 Ma (figure 6).