It was Wellhausen, with Karl Heinfrich Graf, who did much to delineate and date the four strands of the Pentateuch known as J.P.E and D. See the following articles in Bible Review: Joseph Blenkinsopp, “Julius Wellhausen,” and “The Documentary Hypothesis in Trouble,” Fall 1985; Victor Hurowitz, “P—Understanding the Priestly Source,” June 1996; Rolf Rendtorff, “What We Miss By Taking the Bible Apart,” February 1998.