They are the lower mantle (below 670km), upper mantle, continental mantle lithosphere, oceanic mantle lithosphere, continental crust and oceanic crust, the latter four constituting the earth's crust. A steady-state upper mantle model has been proposed for mass transfer of rare gases, including Ar.
K since their formation, or if some or all of it came from the mantle or from other crustal rocks and minerals.
The J value is a combined parameter incorporating the conditions of the neutron irradiation and which is obtained from simultaneously irradiated standard mineral samples of known age.
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.
magazine has been continuously published since 1978, we are publishing some of the articles from the archives for historical interest, such as this.
For teaching and sharing purposes, readers are advised to supplement these historic articles with more up-to-date ones suggested in the Related Articles and Further Reading below. At top, is fossil wood in basalt that includes—from left to right—basalt, wood and siltstone.
This is approximately 2,500 times as much Ar as is found in natural muscovite.