Open up the main panel and take the picture and post on here, along with any writing on the sheath of the cable. Most like at that age, it can be Aluminum. If it is, and you take care to put No-Ox on the wiring, and use the proper receptacle's, light switches, breakers, etc, Aluminum is safe. Problems arise when people use the wrong fixtures, switches, receptacle's, etc. The latest NEC also recommends using AFCI breakers with Aluminum wiring for all points.