Sir John Tapps questions whether I believe the fossil dating method is the only dating method I know about.

He is referring to my article GULO and other irrational atheist arguments - Part 2 where I describe how old earth advocates use fallacious circular reasoning to support an old age for the earth (billions of years) and fossils (millions of years).  I pointed out that their reasoning is flawed - they used a circular process to date the fossils - dating the fossils by the layer they are found in, and dating the layers by the fossils in the layers as this diagram shows:

So since I only mentioned one dating method, naturally Mr. Tapps supposes that's the only dating method I know about.
In response, obviously there are other dating methods - the most popular of which is radiometric dating.  But radiometric dating methods are subject to the following errors:

1. Unfounded assumptions
2. Circular reasoning.

To elaborate:
1. Unfounded assumptions:
Radiometric dating methods (Potassium-argon, Rubidium-strontium, Uranium-thorium, etc.) make assumptions about the age of an item based on the amount of a daughter element found in the item in question. What the tester must assume is:

1. The Initial amounts of parent and daughter element (typically it is assumed no daughter element is present)
2. The rate of change is constant (there was nothing that influenced the rate of change.)
3. The system is closed (there were no contaminants introduced that changed the amount of parent or daughter element in the sample in question.)

2. Circular Reasoning
These assumptions have been the cause of so many inaccurate dates, that the actual dating of items has led to a circular process where the age is actually estimated based on what the submitting scientist(s) assumes (or wants) it to be. Thus dates obtained by radiometric dating are not "absolute" dates, and in fact are not even used if the date does not come out to be what the old earth believer wants them to be as creationist physical, chemist,  spectroscopist and author Jonathan Sarfati, PH.D., FM  points out:

Radiometric dates are not regarded as absolute:

For all the talk about 'absolute' dating methods, they are not regarded as such in practice. When samples are submitted to radiodating labs, the forms usually have an entry for 'estimated age'. But why should this be, if the method were absolute? One expert admitted:

"If a C14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in a foot note. And if it is completely 'out of date,' we just drop it."¹

 And if the dates are rejected, the difference can be explained away - the technical term is 'interpreted'.²

So even the highly vaunted radiometric dating methods are not the silver bullet for old earth belief as evolutionists, big bangers and other deniers of the biblical account believe them to be. They don't actually date anything - they determine the amount of a daughter element and attempt to base an age based on that - which as noted above - is fraught with many errors. The inherent uncertainty and errors then lead them to estimate what the date should be, making the whole process an exercise in circular reasoning.

- DC 2/21/2015

Notes:

1 Quoted by Säve-Söderberg., T. and Olsson, I.U., (Institute of Egyptology and Institute of Physics, respectively, University of  Uppsala, Sweden), "C14 dating and Egyptian chronology"; in Olsson, I.U., (ed.) Radiocarbon Variations and Absolute Chronology, the 12th Nobel Symposium, p. 35, John Wiley & Sons, Inc. New York, 1970.

2 This entire quoted referenced from:
Sarfati, Jonathan The Greatest Hoax on Earth? Refuting Dawkins on Evolution  Atlanta, GA, Creation Book Publishers, 2010 p. 194
(emphasis his)