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.
What did he find on his Italy dig?
There he had located an outcrop on the walls of a gorge whose limestone layers included strata both above and below the Cretaceous-Paleogene boundary.

Question: What was the significance of that find?
Self-contained rewrite: What was the significance of the find of the finding of the layers found at the boundary?