The strontium isotopic composition of the oceans changed markedly at the Cambrian-Ordovician transition, some 500 million years ago. This isotopic shift was greatly affected by the first bio-invasion of the land and the ensuing terrestrial-surface environments in a chain reaction that included: 1) an attenuation of weathering on land, 2) changes in the outflow patterns of fluvial floods and the circulation patterns of groundwater, 3) marked regional differentiation of coastal environments, 4) the formation of soil layers, and 5) the eutrophication of estuaries by nutrient salts of terrestrial-biosphere origin. A series of these environmental changes culminated in the marine Ordovician biodiversification, an explosive flourishing of the Paleozoic evolutionary fauna that is characterized by a variety of filter and suspension feeders. The bio-invasion onto land was one of the greatest geobiological events in the Earth's history.