To date rocks, scientists use
O U238
C14
O K-Pg
O Iridium

answer; (wisconsin);

explanation: the badger state. this nickname originally referred to the lead miners, of the 1830s, who worked at the galena lead mines in illinois. these mines were in northwestern illinois close to the borders of wisconsin and iowa. the wisconsin miners lived, not in houses, but in temporary caves cut into the hillsides.