I liked this quote, attributed to Rebecca Solnit, from this article ruminating on the longevity of trees(external link):

There’s an Etruscan word, saeculum, that describes the span of time lived by the oldest person present, sometimes calculated to be about a hundred years. In a looser sense, the word means the expanse of time during which something is in living memory. Every event has its saeculum, and then its sunset when the last person who fought in the Spanish Civil War or the last person who saw the last passenger pigeon is gone.