Asynchrony in mammalian biochronology [Asynchronie v savčí biochronologii]
Events in earth history may be physical (e.g., earth quakes, magnetic reversals, climate change, etc.) or biological (e.g., extinction of a species, origin of a new species, dispersal of a species to a new territory, etc.). In general, physical events in earth history are usually locally synchronous although some may be globally synchronous. Some physical events (like climate change) may be gradual and/or variable by latitude. Biological events, on the other hand, are usually locally synchronous, and rarely globally synchronous. The effects of biologic events, and their recognition, tend to expand or contract over increasing geographic areas. These differences between physical and biological events in earth history are important and should be recognized when events in earth history are correlated. That is, physical events are more likely to be globally synchronous whereas biological events are more likely to be locally synchronous and globally diachronous, relative to geologic time.