Roderick Murchison in the context of "Vanity Fair (British magazine)"

The Ordovician (/ɔːrdəˈvɪʃi.ən, -doʊ-, -ˈvɪʃən/ or-də-VISH-ee-ən, -⁠doh-, -⁠VISH-ən) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period 486.85 Ma (million years ago) to the start of the Silurian Period 443.1 Ma.

The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in North Wales in the Cambrian and Silurian systems, respectively. Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received 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 Geological Congress.

Adam Sedgwick FRS (/ˈsɛdʒwɪk/; 22 March 1785 – 27 January 1873) was a British geologist and Anglican priest, one of the founders of modern geology. He proposed the Cambrian and Devonian period of the geological timescale. Based on work which he did on Welsh rock strata, he proposed the Cambrian period in 1835, in a joint publication in which Roderick Murchison also proposed the Silurian period. Later in 1840, to resolve what later became known as the Great Devonian Controversy about rocks near the boundary between the Silurian and Carboniferous periods, he and Murchison proposed the Devonian period.

Though he had guided the young Charles Darwin in his early study of geology and continued to be on friendly terms, Sedgwick was an opponent of Darwin's theory of evolution by means of natural selection.

The Permian (/ˈpɜːrmi.ən/ PUR-mee-ən) is a geologic period and stratigraphic system which spans 47 million years, from the end of the Carboniferous Period 298.9 Ma (million years ago) to the beginning of the Triassic Period 251.902 Ma. It is the sixth and last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia.

The Permian witnessed the diversification of the two groups of amniotes, the synapsids and the sauropsids (reptiles). The world at the time was dominated by the supercontinent Pangaea, which had formed due to the collision of Euramerica and Gondwana during the Carboniferous. Pangaea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors.

The Great Devonian Controversy began in 1834 when Roderick Murchison disagreed with Henry De la Beche as to the dating of certain petrified plants found in coals in the Greywacke stratum in North Devon, England. De La Beche was claiming that since Carboniferous fossils were found deep in the Greywacke stratum, which itself was older than the Carboniferous period, this method of dating rocks was not valid. Murchison, in contrast, claimed that De La Beche had not placed the fossils correctly, as they were occurring quite near the top of the stratum as opposed to deep within it. De La Beche soon agreed with Murchison's argument as to the placing of fossils but maintained that since a layer of Old Red Sandstone, present in other formations, was missing between the layer of older rock and this new formation, there was still insufficient evidence to suggest the formation was not part of the older Silurian strata.

There followed much debate and some extensive investigations which ranged as far as Russia, where in 1840 Murchison discovered a layer similar to the one found in Devon placed between well-defined Silurian and Carboniferous deposits. This discovery put an end to the controversy and led to the definition of a new period called Devonian.