geologia: Late Ordovician mass extinction

Evidence: 100 • authority: 72

The Late Ordovician mass extinction (LOME), sometimes referred to as the end-Ordovician mass extinction or the Ordovician–Silurian extinction, is the first of the "big five" major mass extinction events in Earth's history, occurring roughly 445 million years ago (Ma). It is often considered to be the second-largest-known extinction event, behind only the end-Permian mass extinction, in terms of the percentage of genera that became extinct. Extinction was global during this interval, eliminating 49–60% of marine genera and nearly 85% of marine species. Under most tabulations, only the Permian–Triassic mass extinction exceeds the Late Ordovician mass extinction in biodiversity loss. The extin…

Evidence: 45 • authority: 72

The Late Ordovician is the third and final epoch of the Ordovician period, lasting 15.1 million years and spanning from around 458.2 to 443.1 million years ago. The rocks associated with this epoch are referred to as the Upper Ordovician Series. At this time, Western and Central Europe and North America collided to form Laurentia, while glaciers built up in Gondwana, which was positioned over the South Pole. This caused a drop in global temperatures, resulting in "ice house" conditions. For most of this time, life continued to flourish, but at and near the end of the period, there were mass-extinction events that seriously affected planktonic forms like conodonts, graptolites, and some grou…

Evidence: 45 • authority: 72

The Triassic–Jurassic (Tr-J) extinction event, often called the Triassic–Jurassic mass extinction (TJME) or end-Triassic extinction, marks the boundary between the Triassic and Jurassic periods, 201.4 million years ago. It represents one of five major extinction events during the Phanerozoic, profoundly affecting life on land and in the oceans. In the seas, about 23–34% of marine genera disappeared; corals, bivalves, brachiopods, bryozoans, and radiolarians suffered severe losses of diversity and conodonts were completely wiped out, while marine vertebrates, gastropods, and benthic foraminifera were relatively unaffected. On land, all archosauromorph reptiles other than crocodylomorphs, din…

Evidence: 43 • authority: 88

Extinction: Late Ordovician Mass Extinction. Abstract The Late Ordovician mass extinction was one of the five outstanding mass extinctions in Earth history. It was caused by environmental changes linked to exceptionally large climatic shifts and resulted in a massive elimination of species, but no major lasting changes in ecological structure or evolutionary direction.

Evidence: 43 • authority: 72

The Ordovician ( 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 43.75 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…

Evidence: 38 • authority: 72

Background extinction rate (BER), also known as the normal extinction rate, refers to the standard rate of extinction in Earth's geological and biological history, excluding major extinction events, such as the current human-induced Holocene extinction. There have been five mass extinction events throughout Earth's history.

Evidence: 38 • authority: 72

An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the background extinction rate and the rate of speciation. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.

Evidence: 33 • authority: 88

What Conditions Accompanied the Late Ordovician Mass Extinction?. The second-largest mass extinction in Earth’s history took place in a period of stresses from non-sulfidic anoxia in shelf areas, together with glacioeustatic sea-level change and climatic cooling.