| rdfs:comment
| - An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic classes present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:
* extinction of an unusually large number of species in a short period.
* a sharp drop in the rate of speciation.
- An extinction event (also known as: mass extinction; extinction-level event, ELE) is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:
* extinction of an unusually large number of species in a short period.
* a sharp drop in the rate of speciation.
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| abstract
| - An extinction event (also known as: mass extinction; extinction-level event, ELE) occurs when there is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic classes present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:
* extinction of an unusually large number of species in a short period.
* a sharp drop in the rate of speciation. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Since life began on Earth, a number of major mass extinctions have greatly exceeded the background extinction rate present at other times. Though there were undoubtedly mass extinctions in the Archean and Proterozoic, it is only during the Phanerozoic Eon that the emergence of bones and shells in the evolutionary tree has provided a sufficient fossil record from which to make a systematic study of extinction patterns. There are differing estimates of the number of major mass extinctions in the last 540 million years, ranging from as few as five to more than twenty discrete extinctions. These differences stem primarily from: (a) the threshold chosen for describing an extinction event as "major"; and, what set of data one chooses as the best measure of past diversity.
- An extinction event (also known as: mass extinction; extinction-level event, ELE) is a sharp decrease in the number of species in a relatively short period of time. Mass extinctions affect most major taxonomic groups present at the time — birds, mammals, reptiles, amphibians, fish, invertebrates and other simpler life forms. They may be caused by one or both of:
* extinction of an unusually large number of species in a short period.
* a sharp drop in the rate of speciation. Over 99% of species that ever lived are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because they are more plentiful and cover a longer time span than fossils of land organisms. Since life began on earth, several major mass extinctions have significantly exceeded the background extinction rate. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others because it killed the dinosaurs. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were mass extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record. 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 the threshold chosen for describing an extinction event as "major", and the data chosen to measure past diversity.
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