Potassium argon dating range

Potassium-Argon Dating

Most of the chronometric dating methods in use today are radiometric. That is to say, they are based on knowledge of the rate at which certain radioactive isotopes within dating samples decay or the rate of other cumulative changes in atoms resulting from radioactivity. Isotopes are specific forms of elements. The various isotopes of the same element differ in terms of atomic mass but have the same atomic number. In other words, they differ in the number of neutrons in their nuclei but have the same number of protons. The spontaneous decay of radioactive elements occurs at different rates, depending on the specific isotope.

REGISTER TO VIEW

Official websites use. Share sensitive information only on official, secure websites. More than potassium-argon apparent ages on minerals from crystalline rocks, chiefly from the San Bernardino and eastern San Gabriel Mountains and the southern Mojave Desert, define an area greater than 10, km 2 in which the potassium-argon isotopic systematics have been highly disturbed. The disturbance or disturbances appear to have culminated at different times in different parts of the region, ranging from 57 m. The region can be subdivided into three parts on the basis of potassium-argon dating: 1 An inner area of anomalous ages in which the rocks yield apparent potassium-argon ages that indicate complete or nearly complete resetting of the isotopic system. This discordant zone varies in width from about 6 to 12 km and grades inward to rocks reset to the degree that they yield concordant potassium-argon apparent ages on coexisting mineral pairs and outward toward rocks that yield near-concordant apparent ages.

REGISTER TO VIEW

Most people envision radiometric dating by analogy to sand grains in an hourglass: the grains fall at a known rate, so that the ratio of grains between top and bottom is always proportional to the time elapsed. In principle, the potassium-argon K-Ar decay system is no different. Of the naturally occurring isotopes of potassium, 40K is radioactive and decays into 40Ar at a precisely known rate, so that the ratio of 40K to 40Ar in minerals is always proportional to the time elapsed since the mineral formed [ Note: 40K is a potassium atom with an atomic mass of 40 units; 40Ar is an argon atom with an atomic mass of 40 units]. In theory, therefore, we can estimate the age of the mineral simply by measuring the relative abundances of each isotope.

REGISTER TO VIEW

Potassium–argon dating

Potassium-Argon dating has the advantage that the argon is an inert gas that does not react chemically and would not be expected to be included in the solidification of a rock, so any found inside a rock is very likely the result of radioactive decay of potassium. Since the argon will escape if the rock is melted, the dates obtained are to the last molten time for the rock. Since potassium is a constituent of many common minerals and occurs with a tiny fraction of radioactive potassium, it finds wide application in the dating of mineral deposits.

REGISTER TO VIEW

REGISTER TO VIEW