The extinction of a large number of species within a relatively short period of geological time, thought to be due to factors such as a catastrophic global event or widespread environmental change that occurs too rapidly for most species to adapt. At least five mass extinctions have been identified in the fossil record, coming at or toward the end of the Ordovician, Devonian, Permian, Triassic, and Cretaceous Periods. The Permian extinction, which took place 245 million years ago, is the largest known mass extinction in the Earth’s history, resulting in the extinction of an estimated 90 percent of marine species. In the Cretaceous extinction, 65 million years ago, an estimated 75 percent of species, including the dinosaurs, became extinct, possibly as the result of an asteroid colliding with the Earth. Compare background extinction.
Any of several events in the Earth’s past in which large numbers of species (in some cases, up to eighty percent) became extinct.
Note: The most famous mass extinction included the destruction of the dinosaurs sixty-five million years ago. (See Alvarez hypothesis.)
- Massey hope
language, functional programming A refinement of Hope+C by Nigel Perry of Massey University, NZ, with improved syntax. Concurrent Massey Hope is derived directly from Massey Hope. (1999-08-04)
noun, Psychology. 1. a condition affecting a group of persons, characterized by excitement or anxiety, irrational behavior or beliefs, or inexplicable symptoms of illness. mass hysteria n.
[mas-i-kot] /ˈmæs ɪˌkɒt/ noun 1. monoxide of lead, PbO, in the form of a yellow powder, used as a pigment and drier. /ˈmæsɪˌkɒt/ noun 1. a yellow earthy secondary mineral consisting of lead oxide. Formula: PbO
[ma-seef, mas-if; French ma-seef] /mæˈsif, ˈmæs ɪf; French maˈsif/ noun 1. a compact portion of a mountain range, containing one or more summits. 2. a large elevated block of old complex rocks resistant to both erosion and crustal folding. 3. a band or zone of the earth’s crust raised or depressed as a unit and […]