An extinction event is a widespread and rapid decrease in the biodiversity on Earth.
Earth is the third planet from the Sun, the densest planet in the Solar System, the largest of the Solar System's four terrestrial planets, and the only astronomical object known to harbor life.
Biodiversity, a contraction of "biological diversity," generally refers to the variety and variability of life on Earth.
In biology and ecology, extinction is the end of an organism or of a group of organisms, normally a species.
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Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms.
Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms.
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It occurs when the rate of extinction increases with respect to the rate of speciation.
Speciation is the evolutionary process by which biological populations evolve to become distinct species.
Because most diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity and abundance of life.
A microorganism or microbe is a microscopic organism, which may be single-celled or multicellular.
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 animals every million years.
Marine life, or sea life or ocean life, refers to the plants, animals and other organisms that live in the salt water of the sea or ocean, or the brackish water of coastal estuaries.
Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past.
Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land animals.
Terrestrial animals are animals that live predominantly or entirely on land, as compared with aquatic animals, which live predominantly or entirely in the water, or amphibians, which rely on a combination of aquatic and terrestrial habitats.
The Great Oxygenation Event was probably the first major extinction event.
The Great Oxygenation Event was the biologically induced appearance of dioxygen in Earth's atmosphere.
Since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate.
The Cambrian explosion or Cambrian radiation was the relatively short span event, occurring approximately 541 million years ago in the Cambrian period, during which most major animal phyla appeared, as indicated by the fossil record.
Background extinction rate, also known as the normal extinction rate, refers to the standard rate of extinction in earth's geological and biological history before humans became a primary contributor to extinctions.
The most recent and debatably best-known, the Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago, was a large-scale mass extinction of animal and plant species in a geologically short period of time.
The Cretaceous–Paleogene extinction event, also known as the Cretaceous–Tertiary extinction, was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time approximately 66 million years ago.
The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period 145 million years ago to the beginning of the Paleogene Period 66 mya.
Plants, also called green plants, are multicellular eukaryotes of the kingdom Plantae.
In addition to the five major mass extinctions, there are numerous minor ones as well, and the ongoing mass extinction caused by human activity is sometimes called the sixth extinction.
The Holocene extinction, otherwise referred to as the Sixth extinction or Anthropocene extinction, is the ongoing extinction event of species during the present Holocene epoch, mainly due to human activity.
Mass extinctions seem to be a mainly Phanerozoic phenomenon, with extinction rates low before large complex organisms arose.
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed.
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.