The Ordovician is a geological period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.2 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya. TheOrdovician, named after the Celtic 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 Britain’s Cambrian and Silurian strata in different systems (the latter name was derived from ancient Welsh tribes). Lapworth recognized that the fossil fauna in each series were discontinuous across England; he also recognized that certain forms characterized one series but not the other.
Most importantly, he established an approximate timescale based on characteristic fossils for each system. The study of these types led him to define three new systems: Cretaceous, Jurassic and Triassic; which he then added to Sedgwick’s four “primary” systems (Cambrian, Devonian, Carboniferous and Permian), producing what is now known as Lapworth’s seven-part division of geological time (which has since been expanded with subsequent discoveries). Although there have been numerous revisions since its publication and many elements are now considered obsolete or incorrect, it remains an important contribution to geochronology and serves as a useful starting point for discussions about relative age dating.
The Ordovician Period began with a major extinction called the Cambrian–Ordovician boundary event about 488 million years ago (mya), which wiped out over 85% of all species that had existed during Earth’s long history up until that time including trilobites – leaving behind only a few small shelly animals such as brachiopods and archaeocyathids as well as some sponge-like organisms called demosponges From this carnage arose new groups such as cephalopods molluscs echinoderms graptolites bryozoans conodonts fish(including jawless fish)and chordates(including our own ancestors). This event set off a long interval of diversification known as an adaptive radiation where newly emerged lineages quickly fill unoccupied ecological niches resulting in an increase in biodiversity . It wasn’t until near the end of this period however around 445 mya ,that terrestrial vertebrates would make their first appearance although arthropods had already colonized land earlier .
Fossil evidence indicates that during the Early Ordovician there were two distinct biogeographic provinces separated by equatorial waters too warm for most life . Gondwana occupied southern latitudes while Laurentia lay in northern climes giving rise to what is known today as Laurussia when North America ,Greenland ,Europe and Siberia later collided forming one large continent due largely to plate tectonics . This supercontinent would remain together until late in Earth history eventually breaking up into several smaller continents we are more familiar with today towards the end of Paleozoic Era .
During much of its tenure ,the oceans were shallower than they are today averaging around 100 metres compared to present day depths exceeding 4000 metres . Also warmer conditions meant ice caps or glaciers did not exist at high latitudes during this time further contributing to lower sea levels worldwide . With less area covered by water ,there was more exposed continental shelf which resulted in shallow marine habitats ideal for life’s expansion . In fact over 90%of all species that have ever lived on Earth first appeared during this period making it one extraordinary interval in terms evolutionarily speaking! A greater variety sedimentary environments developed during this era including reefs formed from skeletal remains platforms constructed from colonial organisms like algae mud flats created excessive runoff from land plus open ocean habitats teeming pelagic creatures far away any solid ground whatsoever! All told these various ecosystems fostered evolutionary innovation leading ultimately higher levels diversity both taxonomically speaking(number different kinds organisms)as well morphologically(different body shapes sizes). Many modern groups first appearing including cnidarians gastropods bivalves brachiopods echinoderms crinoids corals cephalopods molluscs crustaceans fishes amphibians reptiles plus primitive plants fungi bacteria viruses perhaps even protozoa! So great importance placed understanding exactly what happened when why because provides critical insights how complex life evolved on planet something scientists still struggling fully comprehend.”