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BP

Small caps, no periods or space; should be explained if used.

Use comma with five digits or more. The older date should come first:
            47,000 to 43,000 BP.

A date expressed as ''11,000 BP'' means 11,000 years before the present, using 1950 as the benchmark.

Dates given as BP—especially if determined by radiocarbon decay—may be in radiocarbon years, which do not exactly match calendar dates.

Scientists, using tree-ring and coral dates, have created calibration scales to convert radiocarbon ages to calendar dates. For instance, 20,000 radiocarbon years equals 23,700 calendar years.

If possible, specify whether or not you are using calibrated dates.

See also A.D., B.C., C.E., B.C.E.