In accordance with this scale, the Ordovician was divided into six series, of which the lower one, the Tremadocian, passed into the International Stratigraphic Chart (ISC) as the stage of the same name.

On the British chart, the boundaries of Ordovician subdivisions are determined by local stratigraphic and paleontological features that are poorly defined in the rest of the world.

[12] The Global Boundary Stratotype Section and Point (GSSP) of the Lower Ordovician, which is also a GSSP of the Tremadocian stage and the whole Ordovician system, is established in the Green Point section in the west of the Newfoundland, Canada (49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W / 49.6829; -57.9653) and corresponds to the first appearance datum (FAD) of the conodont Iapetognathus fluctivagus at the 101.8 m above the base of the outcrop.

[13] The GSSP of the Floian, the second and last stage of the Lower Ordovician, is established in the Diabasbrottet Quarry, Sweden, (58°21′32″N 12°30′09″E / 58.3589°N 12.5024°E / 58.3589; 12.5024) and defined by FAD of the graptolite Tetragraptus approximatus.

[15][16] Both ASSPs were approved by the Subcommission on Ordovician Stratigraphy in 2016 and 2019, respectively, but, in 2021, the International Union of Geological Sciences (IUGS) proposed to deny the use of specific points and replace them by Standard Auxiliary Boundary Stratotypes (SABS) for more "flexible" correlations with GSSPs.

[20] Laurentia was located in the tropical latitudes of the southern hemisphere; today's central Nevada and western Utah were covered by sea waters at the end of the Early Ordovician.

[21] In 2007, Bassett et al. analyzed the oxygen isotope values of Early Ordovician strata of the Lange Ranch section in central Texas and concluded that tropical sea temperatures at that time could have reached 37°C or 42°C.

[22] Similar results were recovered by Trotter et al. in 2008, after oxygen isotope analysis of conodonts from the four paleoplates located in the Early Ordovician at low latitudes.

[27] The radiation of marine life during the GOBE in the Early Ordovician was resulted by the transition from sulphidic to oxic conditions in the oceans of that time.

[20] From the Furongian to the end of the Early Ordovician, 495-470 Ma, the Ollo de Sapo magmatic event occurred on the northwestern territory of Gondwana, which is now the Iberian Peninsula.

[29] In Early Ordovician (Floian) strata of the San Juan Formation, Argentina, the oldest microfossils, known as calcisphers or calcitarchs, are present.

They already lived off the southern coast of Laurentia and Cuyania in the Early Ordovician, and later occupied an even wider range and disappeared only during the Ordovician-Silurian extinction.

[32] Echinoderm diversity increased in the Early Ordovician: new classes appeared, including asteroids, ophiuroids, crinoids and diploporitans.

[41] In the deep-water sediments of the Early Ordovician (Floian) Al Rose Formation in the Inyo Mountains, California, the trilobite fauna have been discovered.

Despite the low species diversity, this fauna is unique due to differences in the composition of families from more eastern complexes of the comparable age.