Conversation so far:
Did he make many discoveries about dinosaur extinction?
In 1980, Alvarez, Alvarez, Asaro, and Michel published a seminal paper proposing an extraterrestrial cause for the Cretaceous-Paleogene extinction .
Did he go on any digs?
During the 1970s, Walter Alvarez was doing geologic research in central Italy.

Question: What did he find on his Italy dig?
Self-contained rewrite: What did Alvarez find on his Italy dig?