Pliocene names a stretch of Earth’s past. It started about five million years ago and went on until about three million years ago — just before the time of the great ice ages. Rocks, old bones in the rock, and weather from that stretch are called Pliocene. You will meet it in science class and on museum signs. We write a capital P because it is the name of that time. It can describe something (“Pliocene fossils”) or name the time itself (“in the Pliocene”). Though actually, it is one of a set of -cene words scientists built from Greek “new.” William Whewell coined it in 1831 for the geologist Charles Lyell, who put it in a book in 1833. Pliocene means “more new”: newer than the Miocene before it, older than the Pleistocene after it. We say PLY-uh-seen.