The Cause of Anomalous Potassium-Argon Ages

Andrew A. Snelling,

Snelling, A.A. 1998. The Cause of Anomalous Potassium-Argon Ages for Recent Andesite Flows at Mt. Ngauruhoe, New Zealand, and the Implications for Potassium-Argon Dating. In R.E. Walsh (editor), Proceedings of the Fourth International Conference on Creationism, pp. 503-526. Pittsburgh, Pennsylvania: Creation Science Fellowship.

I remember that I was on an itinerant creation ministry speaking trip around New Zealand back in the mid-1990s and staying in the Taupo area on the central North Island when I had a free day. I had seen from maps and reports that the historic lava flows on the sides on Mt Ngauruhoe could be clearly distinguished, and in my research, I also knew that recent lava flows sometimes gave falsely old K-Ar dates, similar to what Dr. Steve Austin had found at Mount St. Helens. So, in a borrowed vehicle I headed south on the highway, then east on a rough gravel road to near the Ngauruhoe volcano, parked and walked the rest of the way. After a day of trekking and sampling the easily identified historic lava flows, I started back in the car, only to experience a deflated tire. The available spare was one of those small spacer tires, so it was a slow and cautious drive all the way back to our accommodation.

Back home in Brisbane with the andesite samples I had to find a suitable laboratory that would date the samples using the potassium-argon (K-Ar) method without questioning who I was and asking what ages I was expecting. From my contact with colleague Dr. Steve Austin at ICR I chose the Geochron Laboratories in Cambridge, Massachusetts because they offered a commercial service and the staff being so distant from my outpost in the Antipodes would not know me. Fortunately, they accepted my samples and payment without question.

Months later the results came. As anticipated, most samples yielded grossly older ages up to 3.5 million years, in contrast to the true ages of 1949, 1954 and 1975. Now came the task of reporting these results and exploring the reasons for them. That involved a literature search. It was well documented as to how extraneous argon would be brought up in the volcanic gases and extruded in the lavas then was trapped in the lavas during their cooling. This is because congealing of the lavas does not allow the relatively heavy argon gas to totally escape. However, being a noble gas, which is chemically inert, the argon atoms are not bonded within the lattices of any of the andesite’s constituent minerals. Nevertheless, during standard potassium-argon dating procedures the argon gas is bled out of the crushed samples and analyzed as though it had been produced by radioactive decay of the potassium in the andesite’s minerals. Then based on that assumption the analytical results are plugged into the potassium-argon model age equation to yield the erroneously old ages.

The outcome was very satisfying. In documenting these problems with potassium-argon dating care had to be taken to be thorough so as cover any angles that opponents would exploit in defending this dating method. However, the fact that erroneously old K-Ar dates for historic lavas was already well known in the literature made that task easier. Of course, that implied that if the K-Ar method produced erroneous dates on historic lavas of known ages due to extraneous or inherited argon, then how could we trust the K-Ar dates obtained for ancient lavas whose true ages were not known. It also opened to me the huge literature on the geochemistry of the mantle sources of magmas that affects all the radioisotope dating of the lavas erupted from them.

This all started a long journey to explore and understand the problems with the radioisotope dating methods and how we explain the grossly old ages that systematically occur in the rock record in the apparent right superpositional order. It soon resulted in me being invited to participate in the very successful, landmark, ICR-led, Radioisotopes and the Age of The Earth (RATE) research initiative. And that quest continues to this day, when we have even more reasons to doubt the validity of the vast ages purportedly yielded by the radioisotope dating methods.

The location of Mt Ngauruhoe in the Taupo Volcanic Zone (TVZ), New Zealand, showing the main structural features. The shaded area is the andesite arc, and the inset shows the major components of the boundary between the Australian and Pacific Plates in the New Zealand region (arrows indicate relative motions). Solid triangles are basalt-andesite volcanoes.

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