Abstract Significantly different assemblages of sedimentary rocks are present in the volcanic sequences of Archean greenstone belts in the Barberton Mountain Land, Pilbara block and Canadian shield. Thin sedimentary layers in the 3.55-3.3 Ga-old Onverwacht and Warrawoona Groups in the Barberton Mountain Land and eastern Pilbara, respectively, are made up of silicified volcaniclastic sediments, banded cherts, carbonaceous cherts, silicified evaporites, and locally, stromatolites deposited under shallow-water, anorogenic conditions. The volcanic sequences in these belts essentially lack terrigenous debris derived by weathering and erosion, Algoma-type iron formation, volcanogenic massive sulfide deposits, hyaloclastic breccias, and evidence for the existence during their accumulation of older sialic basement. Sedimentary rocks in the volcanic sequences of the 2.8-2.6 Ga-old Superior and Slave Provinces, Canada, and perhaps in other late Archean belts in the Rhodesian craton and Yilgarn block, include generally unsilicified volcaniclastic units, mafic hyaloclastic breccias, terrigenous clastic layers, abundant Algoma-type iron formation, and massive sulfide deposits. Sedimentation took place under relatively deep-water conditions. Local tectonic activity was widespread, and older sialic basement was present. These younger volcanic sequences contain few shallow-water deposits such as carbonaceous cherts, evaporites, and stromatolites. The volcanic sequences of both generations of greenstone belts seem to have formed platforms that stood topographically above the surrounding sea floor. Differences between older and younger greenstone-belt volcanic sequences appear to reflect the increasing abundance and influence of sialic crust from early to late Archean time and an accompanying increase in ocean-water depth over the volcanic platforms. Evolution of the sialic crust can be traced through at least five Archean and early Proterozoic stages: 1. (1) an early period of ensimatic, shallow-water greenstone belt formation 3.55-3.3 Ga ago; 2. (2) an early episode of intrusive and metamorphic activity from ca. 3.3-2.9 Ga ago during which some of the older greenstone belts were cratonized; 3. (3) a late period of greenstone belt formation, 2.8-2.6 Ga ago, during which volcanism occurred under relatively deep-water conditions upon and/or adjacent to areas of older sialic basement; 4. (4) a late Archean interval of continental crust formation during which the younger greenstone belts were cratonized, 2.7-2.5 Ga ago; 5. (5) a latest Archean and early Proterozoic period dominated by stable cratons and relatively minor greenstone belt activity.