Global change in Earth history: a personal point of view

The global changes of the past took place during the progress of geological cycles and marked a drastic passage from an ancient Pangaean regime of continental emergence to a new Tethyan regime of submergence. They occurred with a certain violence and rapidity, and represented critical phases in the destabilization and subsequent reorganization of the geosphere and biosphere. This process resulted in the destruction of certain assemblages (e.g. biotic mass extinctions) and the rise of new ones (e.g. the emergence of new taxa). These major phases of evolution and growth were probably connected to the upwelling of hot mantle material from great depths and a subsequent process of lateral spreading and outward migration of the mantle melt. The ensuing marked increase in mantle activity, degassing and explosive volcanicity produced catastrophic environmental perturbations with turning points in tectonics, global climate, sea level, ocean and atmospheric chemistry, palaeocirculation and palaeogeography.