Conversation so far:
What did Michael Shermer earn his PhD in?
Michael Shermer lost interest in psychology and switched to studying the history of science.
Where did Michael Shermer earn his PhD?
Michael Shermer lost interest in psychology and switched to studying the history of science, earning his PhD at Claremont Graduate University.

Question: In what year did he earn his PhD?
Self-contained rewrite: In what year did Michael Shermer earn his PhD?