Potassium argon dating problems

The Washington Post article Scientists discover hundreds of footprints left at the dawn of modern humanity describes the geological dating of stratified layers of mud by analyzing and dating minerals within each layer.But since floods jumble materials of different origins and ages together, that meant the scientists had to date dozens of different minerals.(see link) Scenario: I heard about a group of people (yes they happen to be creationists with an agenda, but this should be irrelevant to the question I am posing!) who obtained some samples of rocks from a lava flow from Mt Ngauruhoe in New Zealand.I can't exactly follow the logic, but I'm asking here about the dating process itself. I do not think that Argon-40 decays into Argon-39 as the article states, at least not all by itself. Based on the atmospheric 40-Ar/36-Ar ratio and the 36-concentration, the 40-Ar concentration at the time of formation is calculated.

There's a more basic explanation here: books.google.com/…

But whatever your passion for decaying metals and your level of chemical comprehension is now, I want to share my confidence that you can follow along just fine.

Anyone can learn technical jargon (queue Wikipedia page for Potassium Argon Dating); reading this post only requires a knack for scientific reasoning.

(see relevant bits of the link - and please ignore all agenda-based stuff in there!

) My question: Since the real age of the rocks was around 50 years, does this demonstrate that K-Ar dating is inaccurate?

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