Before Present

Before Present (BP) is a dating convention that counts years backward from a fixed reference year of 1950 CE. It is used especially in archaeology, geology, and radiocarbon dating.

Radiocarbon dating: A method for estimating the age of once-living material from its remaining carbon-14. Radiocarbon results are conventionally reported in years Before Present.
Anno Domini: A year-numbering convention that counts from the traditional date of Jesus’s birth. Its year numbers count forward, unlike BP’s backward count from 1950.
Archaeology: The study of human pasts through the recovery and analysis of material remains. Archaeologists use BP dates to describe prehistoric sites and artifacts.
Before Present (geology): A geological age notation that counts backward from a stated or context-dependent present reference. Some geological uses do not follow radiocarbon dating’s fixed 1950 baseline.
Radiocarbon calibration: The conversion of radiocarbon ages into calendar dates using records of past atmospheric carbon-14. Calibration turns conventional BP measurements into calendar-year estimates.
Common Era: A year-numbering convention equivalent to Anno Domini but without explicitly Christian terminology. Calendar years in the Common Era provide the scale BP dates may be calibrated into.
Geochronology: The science of determining the age and sequence of Earth materials and events. Geological publications use BP-style ages for dated materials and events.
Cal BP: A label for calendar-calibrated years before 1950. The prefix distinguishes calibrated calendar dates from conventional radiocarbon BP ages.
IntCal: A series of internationally adopted calibration curves for converting Northern Hemisphere radiocarbon ages into calendar dates. IntCal curves calibrate radiocarbon ages reported on the BP scale.
Before Christ: A year-numbering convention that counts backward before the traditional date of Jesus’s birth. Its reference point differs from BP’s fixed 1950 baseline.

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