Usage and Grammar

Q. Dear CMOS, What is your opinion of the contraction “there’s” for “there has”? A sample sentence is “There’s been an explosion of scientific knowledge.” One on-line source says “there’s” has two meanings, “there is” and “there has.” If contractions were appropriate in a document, would you use “there’s” in both ways in the same document? Same paragraph? And by the way, when did the second usage creep in? Thanks.

A. (1) Seems fine to me. (2) Sure. (3) Can’t think why not. (4) I don’t know, but the online concordance to Shakespeare shows 401 occurrences, so it must have crept in some time ago. (5) You’re most welcome.