BP, BCE, and the problem of a moving present

The glacial chronology prompts a short discussion of archaeological dating terms. BP means before present, while BCE means before common era; the passage also contrasts these with the older BC wording. A fixed number of years BP can sound as if it should shift with the reader's own present, whether the book is read in 2021 or a century later. The preference given here is for BCE because its reference point is less likely to confuse a reader.