Extinction event
hideAn 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:
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 as it marks the extinction of nearly all dinosaur species, which were the dominant animal class of the period. 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.
For more information about Extinction event, read the full article at
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News tagged with mass extinction
Study shows loss of 15-42 percent of mammals in North America
Dec 17, 2009 |
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If the planet is headed for another mass extinction like the previous five, each of which wiped out more than 75 percent of all species on the planet, then North American mammals are one-fifth to one-half the way there, according ...
Antarctica served as climatic refuge in Earth's greatest extinction event
Space & Earth / Earth Sciences
Dec 02, 2009 |
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A new fossil species suggests that some land animals may have survived the end-Permian extinction by living in cooler climates in Antarctica. Researchers have identified a distant relative of mammals that apparently survived ...
Superior Super Earths
Space & Earth / Space Exploration
Nov 30, 2009 |
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Super Earths are named for their size, but these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life. They could also provide an answer to ...
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As shuttle's career nears an end, NASA turns focus to satellites
Space & Earth / Space Exploration
Dec 26, 2009 |
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NASA heads into 2010 with the bittersweet assignment of retiring the space shuttle after nearly three decades. But that's not all the agency has planned: There are also launches of three new satellites aimed at better understanding ...
Keck Telescopes Take Deeper Look at Planetary Nurseries
Dec 23, 2009 |
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(PhysOrg.com) -- Astronomers using the W. M. Keck Observatory have peered far into a young planetary system, giving an unprecedented view of dust and gas that might eventually form planets similar to Jupiter, ...
Scientists map speed of climate change
Dec 23, 2009 |
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New study finds that the average ecosystem will need to shift about a quarter mile per year to keep pace with global climate change.
Vampires and collisions rejuvenate stars
Dec 23, 2009 |
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Stars in globular clusters are generally extremely old, with ages of 12-13 billion years. However, a small fraction of them appear to be significantly younger than the average population and, because they ...
Scientists discover how the brain encodes memories at a cellular level
Dec 23, 2009 |
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Scientists at UC Santa Barbara have made a major discovery in how the brain encodes memories. The finding, published in the December 24 issue of the journal Neuron, could eventually lead to the development ...
Adverse consequences of obesity may be greater than previously thought
Dec 23, 2009 |
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The link between obesity and cardiovascular mortality may be substantially underestimated, while some of the adverse consequences of being underweight may be overstated, concludes a study published in the British Medical ...
Tracing the traces: Nanogram concentrations of a toxic compound detected in chlorinated tap water
Chemistry / Analytical Chemistry
Dec 23, 2009 |
5 / 5 (4) |
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(PhysOrg.com) -- Drinking water can transmit a number of diseases, including typhoid, dysentery, cholera, and diarrhea, which can then spread explosively throughout an entire service area. To avoid this problem, drinking ...
Student-Made 'Sustain-a-Bear' Puts Green Spin on Timeless Toy
Dec 22, 2009 |
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Most teddy bears, regretfully, face a lonesome retirement once their owners grow up or move on.
Elpida Begins Mass Production of 40nm 2-Gigabit DDR3 SDRAM
Dec 22, 2009 |
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Elpida Memory, Japan's leading global supplier of Dynamic Random Access Memory (DRAM), today announced that its Hiroshima Plant has begun volume production of 40nm process 2-gigabit DDR3 SDRAMs. Since completing development ...
Physiologic factors linked to image quality of multidetector computed tomography scans
Dec 22, 2009 |
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A large multicenter international trial found that the image quality of multi-detector computed tomography (MDCT) scans, used for the noninvasive detection of coronary artery disease, can be significantly affected by patient ...
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