The probable range is the most frequently observed range of a taxon. Probable ranges are derived from a synthesis of local ranges characterized among a group of geologic sections. The local ranges provide the empirical biostratigraphic data from which the time and space distribution of a fossil is integrated. This distribution is approximated by the probable range.

The probable range concept is currently being applied to the biostratigraphy of many regions and is demonstrated using a North Atlantic Ocean data set of 228 species of Cenozoic and Mesozoic calcareous nannofossils occurring at 55 sites drilled by the Deep Sea Drilling Project. A major result of the application is a standardized range chart for the data set. Comparison of the range chart with published range data shows a good correlation. The rigorous application of the probable range concept sets no theoretical limits on the maximum size of a data set. This offers the potential of very high resolution and equally reliable alternatives to standard biostratigraphic zonations. The global application of the probable range concept will have a fundamental impact on the earth sciences by pr viding a standard biostratigraphic reference system invaluable to the interpretation of the time and paleoenvironmental relations among geologic sections.

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