Clocks in the Rocks
Chronological Methods 9 - Potassium-Argon Dating. Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating. potassium–argon dating* A dating technique  for certain rocks that depends on the decay of the radioisotope potassium–40 to argon–40, a process with a. Potassium-Argon dating has the advantage that the argon is an inert gas that to 40Ar, Dalrymple and Lanphere point out that potassium-argon dating was.
The ratio of K to Ar is plotted. Note that time is expressed in millions of years on this graph, as opposed to thousands of years in the C graph.
Click on the "Show Movie" button below to view this animation. How are Samples Processed? Clicking on the "Show Movie" button below will bring up an animation that illustrates how a K-Ar sample is processed and the calculations involved in arriving at a date. This is actually a mini-simulator, in that it processes a different sample each time and generates different dates.
Potassium-argon dating | planetaokon.info
K-Ar Processing Limitations on K-Ar Dating The Potassium-Argon dating method is an invaluable tool for those archaeologists and paleoanthropologists studying the earliest evidence for human evolution. As with any dating technique, there are some significant limitations. The technique works well for almost any igneous or volcanic rock, provided that the rock gives no evidence of having gone through a heating-recrystallization process after its initial formation.
For this reason, only trained geologists should collect the samples in the field.
This technique is most useful to archaeologists and paleoanthropologists when lava flows or volcanic tuffs form strata that overlie strata bearing the evidence of human activity. Dates obtained with this method then indicate that the archaeological materials cannot be younger than the tuff or lava stratum.
As the simulation of the processing of potassium-argon samples showed, the standard deviations for K-Ar dates are so large that resolution higher than about a million years is almost impossible to achieve. By comparison, radiocarbon dates seem almost as precise as a cesium clock! Potassium-argon dating is accurate from 4. Atyears, only 0. The time of 65 million years was associated with the K-T boundary from these studies.
Other large impact craters such as the Manson crater in Iowa dated to 74 My were examined carefully as candidates for the cause of the extinction, but none were close to the critical time. Chicxulub was not so obvious as a candidate because much of the evidence for it was under the sea. More attention was directed to the Yucatan location after published work by Alan Hildebrand in demonstrated the chemical similarity of Chicxulub core samples with material found distributed in the K-T boundary layer.
Carl Swisher organized a team to produce three independent measurements of the age of intact glass beads from the C-1 core drill site in the Chicxulub impact area. The measurements were done by the argon-argon method.
Even this extraordinary matching with the age of the K-T boundary was insufficient to convince many geologists. The team proceeded to date spherules of glass found in Haiti to provide another bit of evidence. Many pieces of glass ejecta had been found on Haiti, which is over a thousand miles from the impact point currently.
- Potassium-Argon Dating
But geologists project a much smaller distance between the points at the time of the impact because of measured sea floor expansion.