Before Present (BP) years, or years before present is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred before the origin of practical radiocarbon dating in the 1950s.

How did they come up with carbon dating?

In 1946, Willard Libby proposed an innovative method for dating organic materials by measuring their content of carbon-14, a newly discovered radioactive isotope of carbon. Known as radiocarbon dating, this method provides objective age estimates for carbon-based objects that originated from living organisms.