Geologic Time Scale: Ordovician Period
(485.4 to 443.8 million years ago)
The Ordovician Period is the second of six periods in the Paleozoic Era. The name is derived from the Welsh tribe of the Ordovices. Charles Lapworth named it in 1879 to reslove a dispute between followers of Adam Segwich (British geologist and Anglican proest, one of the founders of modern geology) and Roderick Murchison (Scottish geologist who served as director-general of the British Geologic Survey from 1855 until his death in 1871), who were placing the same rock beds in North Wales in the Cambrian and Silurian systems. Lapworth recognised that fossils fauna in disrupted strata (rock layers) were different than those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician recieved international approval in 1960 (forty years after Lapworth’s death) when it was adopted as an official period of the Paleozoic Era by the International Geologic Congress.
The first land plants appear in the Ordovician, while the seas were dominated by arthropods and molluscs with a a considerable increase fish (the world’s first true vertebrates).