Just because something is very old doesn’t mean it can’t still work. For instance, take the light bulb burning in a California fire station. Installed at the beginning of the 20th century, it was shining brightly well into 2017. And a family on Long Island uses an early electric stove that was built 100 years ago. But the prize for oldest useful thing may be yeast extracted from Egyptian urns. The yeast is 4,500 years old, and one man made bread with it.