In several pulses across the Devonian, ocean oxygen levels dropped precipitously, which dealt serious blows to conodonts and ancient shelled relatives of squid and octopuses called goniatites. Starting 383 million years ago, this extinction event eliminated about 75 percent of all species on Earth over a span of roughly 20 million years.
Late Devonian extinction - 383-359 million years ago The event took its hardest toll on marine organisms such as corals, shelled brachiopods, eel-like creatures called conodonts, and the trilobites. The second worst mass extinction known to science, this event killed an estimated 85 percent of all species.
Whatever life remained recovered haltingly in chemically hostile waters: Once sea levels started to rise again, marine oxygen levels fell, which in turn caused ocean waters to more readily hold onto dissolved toxic metals. Creatures living in shallow waters would have seen their habitats cool and shrink dramatically, dealing a major blow. The large-scale weathering of these freshly uplifted rocks sucked carbon dioxide out of the atmosphere and drastically cooled the planet.Īs a result, sea levels plummeted by hundreds of feet. The icy onslaught may have been triggered by the rise of North America’s Appalachian Mountains. At that time, massive glaciation locked up huge amounts of water in an ice cap that covered parts of a large south polar landmass.
Over a 30-million-year stretch, species diversity blossomed, but as the period ended, the first known mass extinction struck. The Ordovician period, from 485 to 444 million years ago, was a time of dramatic changes for life on Earth. Ordovician-Silurian extinction - 444 million years ago These eruptions ejected massive amounts of heat-trapping gases such as carbon dioxide into the atmosphere, enabling runaway global warming and related effects such as ocean acidification and anoxia, a loss of dissolved oxygen in water. The single biggest driver of mass extinctions appears to be major changes in Earth’s carbon cycle such as large igneous province eruptions, huge volcanoes that flooded hundreds of thousands of square miles with lava. Though the Cretaceous-Paleogene extinction is famous for being caused mainly by a huge asteroid, it’s the exception. Discovered in 2010 in Montana’s famed Hell Creek Formation of the late Cretaceous, the 40-foot-long fossil took four years to excavate and prepare. With 170 of its 300-odd bones preserved, this scientifically important but privately owned skeleton is currently at the Museum für Naturkunde in Berlin, Germany. This nearly whole, deep-black skull belongs to the most complete specimen of Tyrannosaurus rex on display in Europe, an individual nicknamed Tristan Otto.
0 kommentar(er)
