What is the origin of "This is the Word of the Lord" and "Thanks be to God? In the past I attended a church where at the end of the Scripture reading, the reader would say:

This is the Word of the Lord

And the congregation would respond:

Thanks be to God

Does anyone know the origins of this tradition?
"Thanks be to God" is, in its Latin form "Deo gratias", used after the epistle reading in the traditional Catholic (Latin) mass, which was codified by Pope St. Pius V in the 16th century, but which actually goes back much farther.  I'm not sure how much older this particular usage is, but I wouldn't be surprised if it went back another thousand years or so.  In the traditional mass, this "Deo Gratias" is not said aloud by the whole congregation (though we may, and I do, "say" it mentally) but by the altar servers.  

"This is the Word of the Lord", on the other hand, seems to have been introduced in the aftermath of the Second Vatican Council in the 1960's, though it may have been in use earlier in some Protestant denominations.