These dating methods rely on a series of assumptions about the amounts of the parent-daughter elements, and a constant rate of decay. It has been accepted that a rock is formed when it first cools down from a molten or semi-molten state, which may include a variety of elements, including radioactive ones. For the last 100 years we have been able to measure the decay rate, and during this time it has been very steady, very consistent.Radioisotope dating, using the trace amounts of radioactive elements within the rock, was quickly accepted as proof the earth is millions and millions of years old. The Radioactive elements decay from heavier larger atomic elements (parent) into smaller atomic elements (daughter) that are more stable. The rate of decay and the amount of parent / daughter elements present today in a rock sample is used to calculate back to the estimated age of when the rock was first formed.And the ages assigned to the layers were derived from long age evolutionary assumptions – not from the scientific facts, – as the column was established long before we even had radiometric dating.Yet the column and its assumptions are used along with index fossils to assign dates to sedimentary rock layers and which in turn is used to date any fossil in that rock layer.Actually the assignment of a certain number of millions of years to a rock formation does not derive from the strata itself.
The Cardenas Basalt bottom layer (below the Cambrian explosion) is usually dated with Rhobidium -Strontium and calculated to be about 1 billion years old.
This is a real and common problem with radiometric dating techniques.
Consider also: ALL of the samples taken from volcanic eruptions of known times and dates are carefully collected and sent to the labs. It is the prime reason many scientists have had doubts about radiometric dating all along.
That concept began with eighteenth-century French naturalist Georges Cuvier, picked up steam with Charles Lyell, and it has been in vogue ever since.
This is despite the fact that it causes more problems for interpreting rock strata than it solves.