147] has highlighted the fact that measurements of specimens from a 1801 lava flow near a volcano in Hualalai, Hawaii gave apparent ages (using the Potassium-Argon method) ranging from 160 million to 2.96 billion years, citing a 1968 study [Funkhouser1968].
In the particular case that Morris highlighted, the lava flow was unusual because it included numerous xenoliths (typically consisting of olivine, an iron-magnesium silicate material) that are foreign to the lava, having been carried from deep within the earth but not completely melted in the lava.
The differences actually found in the scientific literature are usually close to the margin of error, usually a few percent, not orders of magnitude!
Vast amounts of data overwhelmingly favor an old Earth.
The isochron techniques are partly based on this principle.
The use of different dating methods on the same rock is an excellent way to check the accuracy of age results.
Several hundred laboratories around the world are active in radiometric dating.
And it has been close to a hundred years since the uranium-238 decay rate was first determined.
Such failures may be due to laboratory errors (mistakes happen), unrecognized geologic factors (nature sometimes fools us), or misapplication of the techniques (no one is perfect).
We scientists who measure isotope ages do not rely entirely on the error estimates and the self-checking features of age diagnostic diagrams to evaluate the accuracy of radiometric ages.
A recent survey of the rubidium-strontium method found only about 30 cases, out of tens of thousands of published results, where a date determined using the proper procedures was subsequently found to be in error.
One question that sometimes arises here is how can scientists assume that rates of radioactivity have been constant over the great time spans involved.
Whenever possible we design an age study to take advantage of other ways of checking the reliability of the age measurements.