Through a series of ^Ar-^Ar dating for terrestrial and exterrestrial samples, the results for basalts from the Japan Sea floor, Deccan Plateau and for meteorites from Antarctica give significant information concerning their formation histories. ^Ar-^Ar ages of basalts from the Japan Sea floor give a constraint that the Japan Sea floor was formed at least 20 Ma. ^Ar-^Ar ages for dyke samples from the Deccan Plateau indicate a possibility for the occurrence of a little younger ages than that of the main plateau formations by a few million years. Meteorites collected from Antarctica show some variable ^Ar-^Ar ages reflecting their different thermal histories
