mass extinction

(noun)

a sharp decrease in the total number of species in a relatively short period of time

Related Terms

Examples of mass extinction in the following topics:

  • Biodiversity Change through Geological Time

    • Biodiversity has been affected by five mass extinction periods, which greatly influenced speciation and extinction rates.
    • There are many lesser, yet still dramatic, extinction events, but the five mass extinctions have attracted the most research.
    • The Ordovician-Silurian extinction event is the first-recorded mass extinction and the second largest.
    • The transitions between the five main mass extinctions can be seen in the rock strata.
    • Describe how biodiversity has changed through geological time as a result of mass extinctions

  • Post-Cambrian Evolution and Mass Extinctions

    • The post-Cambrian era was characterized by animal evolution and diversity where mass extinctions were followed by adaptive radiations.
    • Such periods of mass extinction have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind .
    • The end of the Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth's history, a loss of roughly 95 percent of the extant species at that time.
    • Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end.
    • Differentiate among the causes of mass extinctions and their effects on animal life

  • Present-Time Extinctions

    • Human activities probably caused the Holocene mass extinctions; many methods have been employed to estimate these extinction rates.
    • The sixth, or Holocene, mass extinction appears to have begun earlier than previously believed and is mostly due to the activities of Homo sapiens.
    • The list is not complete, but it describes 380 extinct species of vertebrates after 1500 AD, 86 of which were made extinct by over-hunting or overfishing.
    • One contemporary extinction rate estimate uses the extinctions in the written record since the year 1500.
    • Secondly, the number of recently-extinct species is increasing because extinct species now are being described from skeletal remains.

  • Loss of Biodiversity

    • In fact, there were several factors that played a role in the extinction of perhaps 200 cichlid species in Lake Victoria.
    • Extinction, a natural process of macroevolution, occurs at the rate of about one out of 1 million species becoming extinct per year.
    • The fossil record reveals that there have been five periods of mass extinction in history with much higher rates of species loss.
    • The rate of species loss today is comparable to those periods of mass extinction.
    • However, there is a major difference between the previous mass extinctions and the current extinction we are experiencing: human activity.

  • The Cambrian Explosion of Animal Life

    • These fossils (a–d) belong to trilobites, extinct arthropods that appeared in the early Cambrian period 525 million years ago and disappeared from the fossil record during a mass extinction at the end of the Permian period about 250 million years ago.

  • Newly Discovered Eukaryotes

    • Due to the advent of mass sequencing tools, thousands of new viral species have been identified in metagenomics studies, while at the same time hundreds of new viral species have been found.
    • Of course we may never truly identify many eukaryotic species, since the rate of extinction has increased.
    • Many extant species may become extinct before they are described.

  • Past and Present Effects of Climate Change

    • Results of climate change, past and present, have been documented and include species extinction, rising sea levels, and effects on organisms.
    • Global warming has been associated with at least one planet-wide extinction event during the geological past.
    • The Permian extinction event occurred about 251 million years ago toward the end of the roughly 50-million-year-long geological time span known as the Permian period.
    • Scientists estimate that approximately 70 percent of the terrestrial plant and animal species and 84 percent of marine species became extinct, vanishing forever near the end of the Permian period.
    • Similarly, the mass of the ice sheets in Greenland and the Antarctic is decreasing: Greenland lost 150–250 km3 of ice per year between 2002 and 2006.

  • The Pleistocene Extinction

    • The Pleistocene Extinction is one of the lesser extinctions and a relatively-recent one.
    • The extinction appears to have happened in a relatively-restricted time period between 10,000–12,000 years ago.
    • It seems probable that over-hunting was a factor in extinctions in many regions of the world.
    • In general, the timing of the Pleistocene extinctions correlated with the arrival of humans and not with climate-change events, which is the main competing hypothesis for these extinctions.
    • It seems clear that even if climate played a role, human hunting was an additional factor in the extinctions.

  • Problems

    • An optically thin cloud surrounding a luminous object is estimate to be 1 pc in radius and to consist of ionized plasma.Assume that electron scattering is the only important extinction mechanism and that the luminous object emits unpolarized radiation.
    • A particle of mass $m$, charge ${q}$, moves in a plane perpendicular to a uniform, static, magnetic field $B $.
    • A particle of mass $m$ and charge $q$ moves in a circle due to a force ${\bf F} = -\hat{\bf r} \frac{q^2}{r^2}.$ You may assume that the particle always moves non-relativistically.
    • Consider ionized hydrogen gas.Each electron-proton pair has a mass more or less equal to the mass of the proton ($m_p$) and a cross section to radiation equal to the Thompson cross-section ($\sigma_T$).
    • The mass of the sun is $2 \times 10^{33}$g.What is the Eddington luminosity of the sun?

  • Early Hominins

    • Australopithecus ("southern ape") is a genus of hominin that evolved in eastern Africa approximately 4 million years ago and became extinct about 2 million years ago.
    • The brain size of Australopithecus relative to its body mass was also smaller than modern humans and more similar (although larger) to that seen in the great apes.
    • These hominids became extinct more than 1 million years ago and are not thought to be ancestral to modern humans, but rather members of an evolutionary branch on the hominin tree that left no descendants.