Before Present (BP) is a common convention used to specify a large time passage where a specific day, month, year designation wouldn't make any sense, or is inestimatable. Often used for events that occurred over a range of time with no identifiable beginning and no identifiable end.

We radiocarbon dated a hoof fragment from the Grand Canyon that dated around 30 000 years BP. It would not have made any sense to say that it dated to 28,000. BCE (Before Commin Era). Likewise, the dinosaurs became extinct 65 MYBP (Million Years Before Present). Since it took awhile for this extinction event to play itself out, it would not make sense to try and give it a specific year designation.

CE (Common Era) and BCE (Before Common Era) is replacing AD and BC.(See below). These designations are mostly used by historians, whereby we have written records that can specifically identify when an event occurred.

A.D." stands for anno domini, Latin for “in the year of the lord,” and refers specifically to the birth of Jesus Christ. "B.C." stands for "before Christ." In English, it is common for "A.D." to precede the year, so that the translation of "A.D. 2014" would read "in the year of our lord 2014."

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