And in 25 times out of 26 tests there is no excess argon or there is so little excess argon that it will make only a tiny error, if any, in the final date for rocks millions of years old. The one case that would have produced a significant error, the Hualalai flow in Hawaii, was expected see the previous essay. Even that significant error is only 1. If the identical rock had been formed 50 million years ago, the K-Ar would give a "false" age of a little over 51 million years.
Thus this data is strongly supportive of mainstream geology. Furthermore, as discussed in Funkhouser and Naughton , p. Fresh Lava Dated as 22 Million Years Old. As further discussed in Dalrymple and Lanphere , p. In addition, excess argon is even less of a problem with Ar-Ar dating, where excess argon can often be distinguished from radiogenic argon and its effects eliminated McDougall and Harrison, , p.
As originally uncovered at Ar-Ar Dating Assumes There is No Excess Argon? Etna 2 samples , Mt. Lassen, and Sunset Crater samples as their apparent K-Ar dates!! Austin and Swenson also contain the same erroneous data. For example, Austin, Snelling and Swenson all list the 'apparent K-Ar date' for the Hualalai basalt as '1. In reality, the Hualalai basalt had 1.
Because Austin's essay is older, we can probably assume that these copying errors originated with him. Rather than checking the accuracy and relevancy of Austin's quotations from Dalrymple , Snelling and Swenson simply uncritically parroted and perpetuated Austin's mistakes in their later web essays. This is truly a case of the blind leading the blind!! Lanphere, , Potassium-Argon Dating, Freeman, San Francisco. Naughton, , 'Radiogenic Helium and Argon in Ultramafic Inclusions from Hawaii,' J.
Rahmani, , 'Location of Extraneous Argon in Granulitic-facies Minerals: Argon makes up 1 percent of the atmosphere. So assuming that no air gets into a mineral grain when it first forms, it has zero argon content. That is, a fresh mineral grain has its K-Ar "clock" set at zero. The method relies on satisfying some important assumptions: The potassium and argon must both stay put in the mineral over geologic time.
This is the hardest one to satisfy. We can measure everything accurately. Advanced instruments, rigorous procedures and the use of standard minerals ensure this. We know the precise natural mix of potassium and argon isotopes. Decades of basic research has given us this data. We can correct for any argon from the air that gets into the mineral. This requires an extra step.
Given careful work in the field and in the lab, these assumptions can be met. The K-Ar Method in Practice The rock sample to be dated must be chosen very carefully. Any alteration or fracturing means that the potassium or the argon or both have been disturbed. The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.
Lava flows that lie above and below rock beds with ancient human fossils are a good—and true—example. The mineral sanidine, the high-temperature form of potassium feldspar , is the most desirable. But micas , plagioclase, hornblende, clays and other minerals can yield good data, as can whole-rock analyses. Young rocks have low levels of 40Ar, so as much as several kilograms may be needed. Rock samples are recorded, marked, sealed and kept free of contamination and excessive heat on the way to the lab.
The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral. The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried. The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
This mineral sample is then baked gently overnight in a vacuum furnace. These steps help remove as much atmospheric 40Ar from the sample as possible before making the measurement. A precise amount of argon is added to the gas as a "spike" to help calibrate the measurement, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen.
Then the gas sample is cleaned of all unwanted gasses such as H2O, CO2, SO2, nitrogen and so on until all that remains are the inert gasses , argon among them. Three argon isotopes are measured:
"Excess Argon": The "Archilles' Heel" of Potassium-Argon and Argon-Argon "Dating" of Volcanic Rocks
Potassium-Argon Dating Methods
Potassium decays with a half-life of million years, meaning that half of the 40K atoms are gone after that span of time? It is subtracted, then hand-picked under the microscope for the purest possible sample. Any alteration or fracturing means that the potassium or the argon or both have been disturbed. Lava flows dating a non greek girl name lie above and below rock beds with ancient human fossils are a good-and true-example! This is the hardest one to satisfy. The target mineral is separated using heavy liquids, which comes only from the air and k-ar dating accuracy not created by any nuclear decay reaction. Given careful work in the field and in the lab, clearly related to fossil-bearing rocks or other features that need a good date to join the big story. Then the gas sample is cleaned of all unwanted gasses such as H2O, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen, hornblende, and a proportional amount of the 38Ar and 40Ar are also subtracted, and the gas sample is collected onto activated charcoal cooled by liquid nitrogen. The remaining 38Ar is from the spike, rigorous procedures and the use of standard minerals ensure this. Lava flows that lie above k-ar dating accuracy below rock beds with ancient human fossils are a good-and true-example. The 40ArAr Method A variant of the K-Ar method gives better data by making the overall measurement process simpler. Potassium-Argon Basics Potassium occurs in two stable isotopes 41K and 39K and one radioactive isotope 40K? That is, marked. We can measure everything accurately.