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An illustration depicting Cameroceras shells sticking out of the mud as a result of draining seaways during the Ordovician-Silurian Extinction event. The cause of the glaciation is heavily debated. The late Ordovician glaciation was preceded by a fall in atmospheric carbon dioxide (from 7,000 ppm to 4,400 ppm).
As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out.
Most scientists believe that this climatic oscillation caused the major extinction event that took place during this time. In fact, the Hirnantian (also known as the End Ordovician and the Ordovician-Silurian) mass extinction event represents the second largest such event in geologic history. Approximately 85% of marine (sea-dwelling) species died.
The cause for the end of the Late Ordovician Glaciation is a matter of intense research, but evidence shows that the deglaciation in the terminal Hirnantian may have occurred abruptly, as Silurian strata marks a significant change from the glacial deposits left during the Late Ordovician. [66]
In the geological timescale, the Llandovery Epoch (from 443.8 ± 1.5 million years ago to 433.4 ± 0.8 million years ago) occurred at the beginning of the Silurian Period. . The Llandoverian Epoch follows the massive Ordovician-Silurian extinction events, which led to a large decrease in biodiversity and an opening up of ecosyste
Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician-Silurian Extinction Events may have been caused by an ice age that occurred at the end of the Ordovician period as the end of the Late Ordovician was one of the coldest ...
Dresbachian extinction event 486.85: Cambrian–Ordovician extinction event: 450–440: Ordovician–Silurian extinction event, in two bursts, after cooling perhaps caused by tectonic plate movement 450: Andean-Saharan glaciation: 360–260: Karoo Ice Age: 305: Cooler climate causes Carboniferous rainforest collapse: 251.9: Permian–Triassic ...
Permian–Triassic extinction event: 252 Ma Large igneous province (LIP) eruptions [23] from the Siberian Traps, [24] an impact event (the Wilkes Land Crater), [25] an Anoxic event, [26] an Ice age, [27] or other possible causes End-Capitanian extinction event: 260 Ma: Volcanism from the Emeishan Traps, [28] resulting in global cooling and ...