The word "paleo" is a combining form meaning "ancient" or "old." A combining form does not stand on its own as a word. It must be used in combination with either an independent word, as in paleogeology, or with another combining form, as in paleolithic.
"Paleo" comes from a Greek word, meaning "ancient." Words using paleo were first created in the early 19th century to describe new fields of scientific study.
Paleolithic and Neolithic
Paleo is often used as a contrast with neo, meaning "new" or "recent." For example, "Paleolithic" denotes the early period of the Stone Age, while "Neolithic" refers to period's final years.
"Paleontology," meaning study of the past, is among the first words to use paleo. The word was created around 1820 to describe the emerging science of early life forms through study of fossils.
Creation of New Words
New words are created as the need for them arises. The increasing specialization of scientific research in the 20th century led to such fields as paleobiogeography, paleoclimatology and paleoanthropology.
In Britain, as well as in the 19th-century United States, the preferred spelling is "palaeo," directly reflecting the Greek origin of the word.