The primordial atmosphere on the Earth originated from the secondary expulsion from the interior of the Earth. This hypothesis comes from the high deficiency factors of rare gases. An argon isotope ratio of 295.5 in the present atmosphere suggests that degassing of more than 85 percent of the volatile matter present on the Earth might have occurred within 0.5 billion years after the birth of the Earth. This is known as the catastrophic early degassing hypothes is.
There appear, however, some doubts on this hypothesis from the study of Archean geology. Extremely low abundance of carbonate rocks in the Archean，constant δ^(13)C difference between the carbonate and organic carbons throughout geologic time and other geological evidences seem to support the intermittent degassing hypothesis (Akiyama，1984;1985b).
Determination of an argon isotope ratio of the Archean atmospheric gas enclosed in the Iyengra quartzite in the Siberian Pla，tform is expected as one of the possible methods for the solution of this problem.