CREATE TABLE table_23537091_1 (copper_age VARCHAR2, ubaid_period_in_mesopotamia VARCHAR2)

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