Potassium dating fossils
This is approximately 2,500 times as much Ar as is found in natural muscovite.Thus under certain conditions Ar can be incorporated into minerals which are supposed to exclude Ar when they crystallize.If so, then the K-Ar and Ar-Ar "dating" of crustal rocks would be similarly questionable.When muscovite (a common mineral in crustal rocks) is heated to 740°-860°C under high Ar pressures for periods of 3 to 10.5 hours it absorbs significant quantities of Ar, producing K-Ar "ages" of up to 5 billion years, and the absorbed Ar is indistinguishable from radiogenic argon ( In other experiments muscovite was synthesized from a colloidal gel under similar temperatures and Ar pressures, the resultant muscovite retaining up to 0.5 wt% Ar at 640°C and a vapor pressure of 4,000 atmospheres.That corn cob found in an ancient Native American fire pit is 1,000 years old.Geologic age dating—assigning an age to materials—is an entire discipline of its own.The observation that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century.The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods" in the Age of the Earth FAQ and Isochron Dating FAQ).
Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages.
Potassium argon (40K-40Ar) dating is a form of radiometric dating widely used because of the range of dates for which it is useful.
The technique can be used for dates ranging from earth's beginning, 4550 mya (4.55bn in US terminology) to about 100,000 years ago.
The half-life of carbon-14 is only 5,730 years, so carbon-14 dating is only effective on samples that are less than 50,000 years old.
Evolution places severe demands upon fossils used to support it.It is not about the theory behind radiometric dating methods, it is about their , and it therefore assumes the reader has some familiarity with the technique already (refer to "Other Sources" for more information).