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Geological processes implications for the duration and flux of mare basalt volcanism. In addition, knowing the distribution of in the lunar sample collection (e.g., Ryder and Spudis, 1980; directly observe any ancient volcanic deposits on the Moon because the high impact flux during the early bombardment has buried many of these deposits, known as cryptomaria (Head and Wilson, 1992), underneath a layer of crater and basin ejecta, obscuring them from view. of mare basalts is estimated to be 1 10 km (Head and Wilson, etween 30 and the volcan est fluxes a dicted by thermal evolution models to have occurred p 2 Ga, with a maximum at 4.2 Ga (1 km3/yr) (Kir Stevenson, 1989). However, these thermal model estima much higher than the derived extrusive volcanic fluxes based on unit thickness and crater model ages; these data suggest a rate of 102 km3/yr at>3.1 Ga and a maximum rate (5 102 km3/ yr) at 4.2 Ga (Basaltic Volcanism Study Project, 1981). Soon after-ward, the flux of mare basalts decreased significantly, by approxi-mately three orders of magnitude (105 km3/yr). Throughout the rest of lunar history the flux of mare basalt slowly decreased unti