Table schema:
CREATE TABLE table_23537091_1 (copper_age VARCHAR, ubaid_period_in_mesopotamia VARCHAR)

Question: When hittite old kingdom , minoan eruption is the  ubaid period in mesopotamia what is the copper age?
SQL: SELECT copper_age FROM table_23537091_1 WHERE ubaid_period_in_mesopotamia = "Hittite Old Kingdom , Minoan eruption"