BC, AD, BCE, BP Abbreviation(s), Latin phrase, Meaning
Abbreviation(s) Latin phrase Meaning
BC * (Christian calendar concepts)

before Christ
Before Common Era
Years are designated as before the Christ's birth.
AD ** (Christian calendar concepts) Anno Domino
Year of the Lord
in the year of the Lord

Years are designated as after the Christ's birth.
BP ***
"Before Present" means before 1950. The most commonly used convention in radiocarbon dating. "Present" referring to the year 1950 AD.
1950 is the date that the calibration curves were established.
It also predates atmospheric testing of the atom bomb, which significantly upset C12/C14 ratios in the following years.
  • * In the Gregorian Calendar, which we use, there is no year zero and the sequence of years near the start runs as follows: ..., 4BC, 3BC, 2BC, 1BC, 1AD, 2AD, 3AD, 4AD ...
  • ** Since 2000 AD is the 2000th year of the Christian calendar, it was the last year of the 2nd millennium. So the 3rd millennium and the 21st century began at the same moment - on January 01, 2001.
  • *** If a radiocarbon lab reports an age of 13000 years BP, they are implying that the fossil would have died 13000 years before 1950 AD.

Note: Read A.M. and P.M. Meaning. Noon and Midnight. Converting from AM / PM to 24 hour clock.

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