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
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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Antarctica served as climatic refuge in Earth's greatest extinction event
Space & Earth / Earth Sciences
56 minutes ago |
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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 ...
Kangaroos may hold skin cancer cure: study
Nov 30, 2009 |
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Kangaroos may provide the key to a potential treatment to prevent skin cancer, Australian scientists said Monday.
Pickin' Up Good Vibrations to Produce Green Electricity
Nov 30, 2009 |
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(PhysOrg.com) -- Vibrations from the environments we live and work in could be much more widely harnessed as a clean source of electricity, due to cutting-edge UK research.
Depressed women can lose weight as successfully as others do
Dec 01, 2009 |
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Women with major depression were no less likely than were women without it to have successful results with a weight loss program, according to an article in the Winter 2009 Behavioral Medicine. Group Health Research Instit ...
Pork meat grown in the laboratory
Dec 01, 2009 |
4.7 / 5 (30) |
20
(PhysOrg.com) -- Scientists from Eindhoven University in The Netherlands have for the first time grown pork meat in the laboratory by extracting cells from a live pig and growing them in a petri dish.
Physicians Explore Link Between Vitamin D Deficiency and Hypertension
Nov 25, 2009 |
5 / 5 (1) |
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(PhysOrg.com) -- Drs. William White and Pooja Luthra at the University of Connecticut Health Center are investigating a possible link between vitamin D deficiency and high blood pressure.
Elastography reduces unnecessary breast biopsies
Nov 30, 2009 |
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Elastography is an effective, convenient technique that, when added to breast ultrasound, helps distinguish cancerous breast lesions from benign results, according to an ongoing study presented today at the annual meeting ...
Overweight children may develop back pain and spinal abnormalities
Dec 01, 2009 |
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Being overweight as a child could lead to early degeneration in the spine, according to a study presented today at the annual meeting of the Radiological Society of North America (RSNA).
Obesity will snuff out health benefits gained by smoking declines
1hour ago |
5 / 5 (1) |
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If obesity trends continue, the negative effect on the health of the U.S. population will overtake the benefits gained from declining smoking rates, according to a study by U-M and Harvard researchers published today in the ...
Why a short run is better than a long walk
8 hours ago |
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(PhysOrg.com) -- Using the latest technology, researchers are uncovering evidence of exactly how major a role activity plays in the battle to keep obesity at bay. In new report published in the British Me ...
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