Potassium 40 dating range Freemobilesix
The core also likely contains radiogenic sources, although how much is uncertain.
It has been proposed that significant core radioactivity (1-2 TW) may be caused by high levels of U, Th, and K.
In the case of potassium-argon decay, this loss of a proton causes the atom to change from a reactive alkali metal to a non-reactive noble gas, which is an important characteristic.
Because argon is an inert gas, if it is not physically trapped in a rock, it will diffuse into the atmosphere.
Argon is a gas that does not ordinarily combine with other elements.
So, when a mineral forms – whether from molten rock, or from substances dissolved in water – it will be initially argon-free, even if there is some argon in the liquid.
Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.
Because the method is primarily useful for volcanic materials, and fossils more commonly lie in sedimentary layers, the material that is dated is usually from volcanic strata (commonly volcanic ash layers) above and below that of the fossil.
The fossil is given an age limit between the dated volcanic layers.
The calcium-potassium age method is seldom used, however, because of the great abundance of nonradiogenic calcium in minerals or rocks, which masks the presence of radiogenic calcium.
On the other hand, the abundance of argon in the is relatively small because of its escape to the atmosphere during processes associated with volcanism.