Cretaceous–Paleogene extinction event

From Wikipedia, the free encyclopedia
Jump to: navigation, search
meteoroid entering the atmosphere with fireball
An artist's rendering of an asteroid a few kilometers across colliding with the Earth. Such an impact can release the equivalent energy of several million nuclear weapons detonating simultaneously.
rock hillside with rock striations
rock in museum with layering
Cretaceous Paleogene clay layer with finger pointing to boundary
Complex Cretaceous–Paleogene clay layer (gray) in the Geulhemmergroeve tunnels near Geulhem, The Netherlands. (Finger is below the actual Cretaceous-Paleogene boundary)

The Cretaceous–Paleogene (K–Pg) extinction event,[a] also known as the Cretaceous–Tertiary (K–T) extinction,[b] was a sudden mass extinction of some three-quarters of the plant and animal species on Earth,[2][3][4] approximately 66 million years ago.[3] With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived.[5] It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.

In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust, but abundant in asteroids.[6]

As originally proposed in 1980 by a team of scientists led by Luis Alvarez and Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by the impact of a massive comet or asteroid 10 to 15 km (6.2 to 9.3 mi) wide,[7][8] 66 million years ago,[3] which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton.[9][10] The impact hypothesis, also known as the Alvarez hypothesis, was bolstered by the discovery of the 180-kilometre-wide (112 mi) Chicxulub crater in the Gulf of Mexico in the early 1990s,[11] which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact.[12] The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid.[12] A 2016 drilling project into the Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, and contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region: this would have vaporized and dispersed as an aerosol into the atmosphere, initiating longer-term effects on the climate and food chain.

Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions,[13] climate change, and sea level change.

A wide range of species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs. It also destroyed a plethora of other terrestrial organisms, including certain mammals, pterosaurs, birds,[14] lizards,[15] insects,[16][17] and plants.[18] In the oceans, the K–Pg extinction killed off plesiosaurs and the giant marine lizards (Mosasauridae) and devastated fish,[19] sharks, mollusks (especially ammonites, which became extinct), and many species of plankton. It is estimated that 75% or more of all species on Earth vanished.[20] Yet the extinction also provided evolutionary opportunities: in its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular diversified in the Paleogene,[21] evolving new forms such as horses, whales, bats, and primates. Birds,[22] fish,[23] and perhaps lizards[15] also radiated.

The K–Pg boundary represents one of the most dramatic turnovers in the fossil record for various calcareous nanoplankton that formed the calcium deposits for which the Cretaceous is named. The turnover in this group is clearly marked at the species level.[24][25] Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a sharp increase in extinctions than by a decrease in speciation.[26] The K–Pg boundary record of dinoflagellates is not so well understood, mainly because only microbial cysts provide a fossil record, and not all dinoflagellate species have cyst-forming stages, which likely causes diversity to be underestimated.[27] Recent studies indicate that there were no major shifts in dinoflagellates through the boundary layer.[28]

Extinction patterns[edit]

Marine extinction intensity during the Phanerozoic
Millions of years ago

The event appears to have affected all continents at the same time. Non-avian dinosaurs, for example, are known from the Maastrichtian of North America, Europe, Asia, Africa, South America, and Antarctica,[29] but are unknown from the Cenozoic anywhere in the world. Similarly, fossil pollen shows devastation of the plant communities in areas as far apart as New Mexico, Alaska, China, and New Zealand.[18]

Despite the event's severity, there was significant variability in the rate of extinction between and within different clades. Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked sunlight and reduced the solar energy reaching the ground. This plant extinction caused a major reshuffling of the dominant plant groups.[30] Omnivores, insectivores, and carrion-eaters survived the extinction event, perhaps because of the increased availability of their food sources. No purely herbivorous or carnivorous mammals seem to have survived. Rather, the surviving mammals and birds fed on insects, worms, and snails, which in turn fed on detritus (dead plant and animal matter).[27][31][32]

Radiolaria have left a geological record since at least the Ordovician times, and their mineral fossil skeletons can be tracked across the K–Pg boundary. There is no evidence of mass extinction of these organisms, and there is support for high productivity of these species in southern high latitudes as a result of cooling temperatures in the early Paleocene.[27] Approximately 46% of diatom species survived the transition from the Cretaceous to the Upper Paleocene, a significant turnover in species but not a catastrophic extinction.[27][35]

The occurrence of planktonic foraminifera across the K–Pg boundary has been studied since the 1930s.[36] Research spurred by the possibility of an impact event at the K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary,[27] however, there is ongoing debate between groups that think the evidence indicates substantial extinction of these species at the K–Pg boundary,[37] and those who think the evidence supports multiple extinctions and expansions through the boundary.[38][39]

Marine invertebrates[edit]

spiral shell with embedded rock two centimeters across

There is significant variation in the fossil record as to the extinction rate of marine invertebrates across the K–Pg boundary. The apparent rate is influenced by a lack of fossil records, rather than extinctions.[27]

Ostracods, a class of small crustaceans that were prevalent in the upper Maastrichtian, left fossil deposits in a variety of locations. A review of these fossils shows that ostracod diversity was lower in the Paleocene than any other time in the Cenozoic. Current research cannot ascertain, however, whether the extinctions occurred prior to, or during, the boundary interval.[42][43]

Approximately 60% of late-Cretaceous Scleractinia coral genera failed to cross the K–Pg boundary into the Paleocene. Further analysis of the coral extinctions shows that approximately 98% of colonial species, ones that inhabit warm, shallow tropical waters, became extinct. The solitary corals, which generally do not form reefs and inhabit colder and deeper (below the photic zone) areas of the ocean were less impacted by the K–Pg boundary. Colonial coral species rely upon symbiosis with photosynthetic algae, which collapsed due to the events surrounding the K–Pg boundary,[44][45] however, the use of data from coral fossils to support K–Pg extinction and subsequent Paleocene recovery, must be weighed against the changes that occurred in coral ecosystems through the K–Pg boundary.[27]

The numbers of cephalopod, echinoderm, and bivalve genera exhibited significant diminution after the K–Pg boundary.[27] Most species of brachiopods, a small phylum of marine invertebrates, survived the K–Pg extinction event and diversified during the early Paleocene.

bivalve shells seven centimeters across

There are substantial fossil records of jawed fishes across the K–Pg boundary, which provide good evidence of extinction patterns of these classes of marine vertebrates. While the deep sea realm was able to remain seemingly unaffected, there was an equal loss between the open marine apex predators and the durophagous demersal feeders on the continental shelf.

Within cartilaginous fish, approximately 7 out of the 41 families of neoselachians (modern sharks, skates, and rays) disappeared after this event and batoids (skates and rays) lost nearly all the identifiable species, while more than 90% of teleost fish (bony fish) families survived.[51][52]

In the Maastrichtian age, 28 shark families and 13 batoid families thrived, of which 25 and 9 respectively, survived the K-T boundary event. 47 of all neoselachian genera cross the K/T boundary, with 85% being sharks. Batoids display with 15% a comparably low survival rate.[51][53]

There is evidence of a mass extinction of bony fishes at a fossil site immediately above the K–Pg boundary layer on Seymour Island near Antarctica, apparently precipitated by the K–Pg extinction event,[54] however, the marine and freshwater environments of fishes mitigated environmental effects of the extinction event.[55]

Terrestrial invertebrates[edit]

Insect damage to the fossilized leaves of flowering plants from fourteen sites in North America were used as a proxy for insect diversity across the K–Pg boundary and analyzed to determine the rate of extinction. Researchers found that Cretaceous sites, prior to the extinction event, had rich plant and insect-feeding diversity. During the early Paleocene, however, flora were relatively diverse with little predation from insects, even 1.7 million years after the extinction event.[56][57]

Terrestrial plants[edit]

There is overwhelming evidence of global disruption of plant communities at the K–Pg boundary.[18][18][58][59] Extinctions are seen both in studies of fossil pollen, and fossil leaves.[18] In North America, the data suggests massive devastation and mass extinction of plants at the K–Pg boundary sections, although there were substantial megafloral changes before the boundary.[18][60] In North America, approximately 57% of plant species became extinct. In high southern hemisphere latitudes, such as New Zealand and Antarctica, the mass die-off of flora caused no significant turnover in species, but dramatic and short-term changes in the relative abundance of plant groups.[56][61] In some regions, the Paleocene recovery of plants began with recolonizations by fern species, represented as a fern spike in the geologic record; this same pattern of fern recolonization was observed after the 1980 Mount St. Helens eruption.[62]

Due to the wholesale destruction of plants at the K–Pg boundary, there was a proliferation of saprotrophic organisms, such as fungi, that do not require photosynthesis and use nutrients from decaying vegetation. The dominance of fungal species lasted only a few years while the atmosphere cleared and plenty of organic matter to feed on was present. Once the atmosphere cleared, photosynthetic organisms, such as ferns and other plants, returned.[63]

Polyploidy appears to have enhanced the ability of flowering plants to survive the extinction, probably because the additional copies of the genome such plants possessed, allowed them to more readily adapt to the rapidly changing environmental conditions that followed the impact.[64]

There is limited evidence for extinction of amphibians at the K–Pg boundary. A study of fossil vertebrates across the K–Pg boundary in Montana concluded that no species of amphibian became extinct.[65] Yet there are several species of Maastrichtian amphibian, not included as part of this study, which are unknown from the Paleocene. These include the frog Theatonius lancensis[66] and the albanerpetontid Albanerpeton galaktion;[67] therefore, some amphibians do seem to have become extinct at the boundary. The relatively low levels of extinction seen among amphibians probably reflect the low extinction rates seen in freshwater animals.[68]

drawing of big plesiosaurus biting into Kronosaurus
Kronosaurus Hunt by Dmitry Bogdanov, 2008 – Large marine reptiles, including plesiosaurians such as these, became extinct at the end of the Cretaceous.

The choristoderes (semi-aquatic archosauromorphs) survived across the K–Pg boundary[27] but would die out in the early Miocene.

More than 80% of Cretaceous turtle species passed through the K–Pg boundary. Additionally, all six turtle families in existence at the end of the Cretaceous survived into the Paleogene and are represented by living species.[69]

The living non-archosaurian reptile taxa, lepidosaurians (lizards and tuataras), survived across the K–Pg boundary.[27] Living lepidosaurs include the tuataras (the only living rhynchocephalians) and the squamates.

The rhynchocephalians were a widespread and relatively successful group of lepidosaurians during the early Mesozoic, but began to decline by the mid-Cretaceous, although they were very successful in the Late Cretaceous of South America.[70] They are represented today by a single genus, located exclusively in New Zealand.[71]

The order Squamata, which is represented today by lizards, including snakes and amphisbaenians (worm lizards), radiated into various ecological niches during the Jurassic and was successful throughout the Cretaceous. They survived through the K–Pg boundary and are currently the most successful and diverse group of living reptiles, with more than 6,000 extant species. Many families of terrestrial squamates became extinct at the boundary, such as monstersaurians and polyglyphanodonts, and fossil evidence indicates they suffered very heavy losses in the KT event, only recovering 10 million years after it.[72] Giant non-archosaurian aquatic reptiles such as mosasaurs and plesiosaurs, which were the top marine predators of their time, became extinct by the end of the Cretaceous.[73][74] The ichthyosaurs had disappeared from fossil records before the mass extinction occurred.

The archosaur clade includes two surviving groups, crocodilians and birds, along with the various extinct groups of non-avian dinosaurs and pterosaurs.[75]

Ten families of crocodilians or their close relatives are represented in the Maastrichtian fossil records, of which five died out prior to the K–Pg boundary.[76] Five families have both Maastrichtian and Paleocene fossil representatives. All of the surviving families of crocodyliforms inhabited freshwater and terrestrial environments—except for the Dyrosauridae, which lived in freshwater and marine locations. Approximately 50% of crocodyliform representatives survived across the K–Pg boundary, the only apparent trend being that no large crocodiles survived.[27] Crocodyliform survivability across the boundary may have resulted from their aquatic niche and ability to burrow, which reduced susceptibility to negative environmental effects at the boundary.[55] Jouve and colleagues suggested in 2008 that juvenile marine crocodyliforms lived in freshwater environments as do modern marine crocodile juveniles, which would have helped them survive where other marine reptiles became extinct; freshwater environments were not so strongly affected by the K–Pg extinction event as marine environments were.[77]

The Choristodera, a generally crocodile-like group of uncertain phylogeny (possibly archosaurian) also survived the event, only to become extinct in the Miocene.[78] Studies on Champsosaurus' palatal teeth suggest that there were dietary changes among the various species across the KT event.[79]

One family of pterosaurs, Azhdarchidae, was definitely present in the Maastrichtian, and it likely became extinct at the K–Pg boundary. These large pterosaurs were the last representatives of a declining group that contained ten families during the mid-Cretaceous. Several other pterosaur lineages may have been present during the Maastrichtian, such as the ornithocheirids, pteranodontids, nyctosaurids, as well as, a possible tapejarid, though they are represented by fragmentary remains that are difficult to assign to any given group.[80][81] While this was occurring, modern birds were undergoing diversification; traditionally it was thought that they replaced archaic birds and pterosaur groups, possibly due to direct competition, or they simply filled empty niches,[55][82][83] but there is no correlation between pterosaur and avian diversities that are conclusive to a competition hypothesis,[84] and small pterosaurs were present in the Late Cretaceous.[85] In fact, at least some niches previously held by birds were reclaimed by pterosaurs prior to the KT event.[86]

Most paleontologists regard birds as the only surviving dinosaurs (see Origin of birds). It is thought that all non-avian theropods became extinct, including then-flourishing groups such as enantiornithines and hesperornithiforms.[87] Several analyses of bird fossils show divergence of species prior to the K–Pg boundary, and that duck, chicken, and ratite bird relatives coexisted with non-avian dinosaurs.[88] Large collections of bird fossils representing a range of different species provides definitive evidence for the persistence of archaic birds to within 300,000 years of the K–Pg boundary. The absence of these birds in the Paleogene is evidence that a mass extinction of archaic birds took place there. A small fraction of the Cretaceous bird species survived the impact, giving rise to today's birds.[14][89] The only bird group known for certain to have survived the K–Pg boundary is the Aves.[14] Avians may have been able to survive the extinction as a result of their abilities to dive, swim, or seek shelter in water and marshlands. Many species of avians can build burrows, or nest in tree holes or termite nests, all of which provided shelter from the environmental effects at the K–Pg boundary. Long-term survival past the boundary was assured as a result of filling ecological niches left empty by extinction of non-avian dinosaurs.[55]

Non-avian dinosaurs[edit]

Tyrannosaurus skeleton in museum display
Tyrannosaurus was among the dinosaurs living on Earth before the extinction.

Excluding a few controversial claims, scientists agree that all non-avian dinosaurs became extinct at the K–Pg boundary. The dinosaur fossil record has been interpreted to show both a decline in diversity and no decline in diversity during the last few million years of the Cretaceous, and it may be that the quality of the dinosaur fossil record is simply not good enough to permit researchers to distinguish between the options.[90] There is no evidence that late Maastrichtian non-avian dinosaurs could burrow, swim, or dive, which suggests they were unable to shelter themselves from the worst parts of any environmental stress that occurred at the K–Pg boundary. It is possible that small dinosaurs (other than birds) did survive, but they would have been deprived of food, as herbivorous dinosaurs would have found plant material scarce and carnivores would have quickly found prey in short supply.[55]

Whether the extinction occurred gradually or suddenly has been debated, as both views have support from the fossil record. A study of 29 fossil sites in Catalan Pyrenees of Europe in 2010 supports the view that dinosaurs there had great diversity until the asteroid impact, with more than 100 living species.[92] More recent research indicates that this figure is obscured by taphonomical biases, however, and the sparsity of the continental fossil record. The results of this study, which were based on estimated real global biodiversity, showed that between 628 and 1,078 non-avian dinosaur species were alive at the end of the Cretaceous and underwent sudden extinction after the Cretaceous–Paleogene extinction event.[93] Alternatively, interpretation based on the fossil-bearing rocks along the Red Deer River in Alberta, Canada, supports the gradual extinction of non-avian dinosaurs; during the last 10 million years of the Cretaceous layers there, the number of dinosaur species seems to have decreased from about 45 to approximately 12. Other scientists have made the same assessment following their research.[94]

Several researchers support the existence of Paleocene dinosaurs. Evidence of this existence is based on the discovery of dinosaur remains in the Hell Creek Formation up to 1.3 m (4.3 ft) above and 40,000 years later than the K–Pg boundary.[95] Pollen samples recovered near a fossilized hadrosaur femur recovered in the Ojo Alamo Sandstone at the San Juan River in Colorado, indicate that the animal lived during the Cenozoic, approximately 64.5 Ma (about 1 million years after the K–Pg extinction event). If their existence past the K–Pg boundary can be confirmed, these hadrosaurids would be considered a dead clade walking.[96] Scientific consensus, however, is that these fossils were eroded from their original locations and then re-buried in much later sediments (also known as reworked fossils).[97]

All major Cretaceous mammalian lineages, including monotremes (egg-laying mammals), multituberculates, metatherians, eutherians, dryolestoideans,[98] and gondwanatheres[99] survived the K–Pg extinction event, although they suffered losses. In particular, metatherians largely disappeared from North America, and the Asian deltatheroidans became extinct.[100] In the Hell Creek beds of North America, at least half of the ten known multituberculate species and all eleven metatherians species, are not found above the boundary.[90] Multituberculates in Europe and North America survived relatively unscathed and quickly bounced back in the Palaeocene, but Asian forms were decimated, never again to represent a significant component on mammalian faunas.[101]

Mammalian species began diversifying approximately 30 million years prior to the K–Pg boundary. Diversification of mammals stalled across the boundary.[102] Current research indicates that mammals did not explosively diversify across the K–Pg boundary, despite the environment niches made available by the extinction of dinosaurs.[103] Several mammalian orders have been interpreted as diversifying immediately after the K–Pg boundary, including Chiroptera (bats) and Cetartiodactyla (a diverse group that today includes whales and dolphins and even-toed ungulates),[103] although recent research concludes that only marsupial orders diversified after the K–Pg boundary.[102]

K–Pg boundary mammalian species were generally small, comparable in size to rats; this small size would have helped them find shelter in protected environments. In addition, it is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from K–Pg boundary environmental stresses.[55]

North American fossils[edit]

aerial view of canyon with mesas and creek in background
Hell Creek Formation

At present the most informative sequence of dinosaur-bearing rocks in the world from the K–Pg boundary is found in western North America, particularly the late Maastrichtian-age Hell Creek Formation of Montana. This formation, when compared with the older (approximately 75 Ma) Judith River/Dinosaur Park Formations (from Montana and Alberta respectively) provides information on the changes in dinosaur populations over the last 10 million years of the Cretaceous. These fossil beds are geographically limited, covering only part of one continent.[90]

The middle–late Campanian formations show a greater diversity of dinosaurs than any other single group of rocks. The late Maastrichtian rocks contain the largest members of several major clades: Tyrannosaurus, Ankylosaurus, Pachycephalosaurus, Triceratops, and Torosaurus,[104] which suggests food was plentiful immediately prior to the extinction.

In addition to rich dinosaur fossils, there are also plant fossils that illustrate the reduction in plant species across the K–Pg boundary. In the sediments below the K–Pg boundary the dominant plant remains are angiosperm pollen grains, but the boundary layer contains little pollen and is dominated by fern spores.[105] More usual pollen levels gradually resume above the boundary layer. This is reminiscent of areas blighted by modern volcanic eruptions, where the recovery is led by ferns, which are later replaced by larger angiosperm plants.[106]

Marine fossils[edit]

Further analysis shows that several processes were in progress in the late Cretaceous seas and partially overlapped in time, then ended with the abrupt mass extinction.[108] The diversity of marine life decreased when the climate near the K-T boundary increased in temperature. The temperature increased about three to four degrees very rapidly between 65.4 and 65.2 million years ago, which is around the time of the extinction event. Not only did the climate temperature increase, but the water temperature decreased causing a drastic decrease in marine diversity.[109]

The scientific consensus is that the asteroid impact at the K–Pg boundary left megatsunami deposits and sediments around the area of the Caribbean Sea and Gulf of Mexico, from the colossal waves created by the impact.[110] These deposits have been identified in the La Popa basin in northeastern Mexico,[111] platform carbonates in northeastern Brazil,[112] in Atlantic deep-sea sediments,[113] and in the form of the thickest-known layer of graded sand deposits, around 100m thick, in the Chicxulub crater itself, directly above the shocked granite ejecta.

The megatsunami has been estimated to be more than 100 metres (330 ft) tall, as the asteroid fell in an area of relatively shallow sea; in deep sea it would have been 4.6 kilometres (2.9 mi) tall.[114]

The length of time taken for the extinction to occur is a controversial issue, because some theories about the extinction's causes require a rapid extinction over a relatively short period (from a few years to a few thousand years) while others require longer periods. The issue is difficult to resolve because of the Signor–Lipps effect; that is, the fossil record is so incomplete that most extinct species probably died out long after the most recent fossil that has been found.[115] Scientists have also found very few continuous beds of fossil-bearing rock that cover a time range from several million years before the K–Pg extinction to a few million years after it.[27] The sedimentation rate and thickness of K-Pg clay from three sites suggest short duration of event, perhaps less than ten thousand years.[116]

Chicxulub impact[edit]

Evidence for impact[edit]

Cretaceous–Paleogene extinction event is located in North America
Cretaceous–Paleogene extinction event
Location of Chicxulub crater, Mexico

In 1980, a team of researchers consisting of Nobel Prize–winning physicist Luis Alvarez, his son geologist Walter Alvarez, and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the Cretaceous–Paleogene boundary contain a concentration of iridium many times greater than normal (30, 160, and 20 times in three sections originally studied). Iridium is extremely rare in Earth's crust because it is a siderophile element, and therefore, most of it sank with the iron into Earth's core during planetary differentiation. As iridium remains abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the Earth at the time of the K–Pg boundary.[9] There were earlier speculations on the possibility of an impact event, but this was the first hard evidence.[117]

rock striations with dark light boundary and surveying rod

This hypothesis was viewed as radical when first proposed, but additional evidence soon emerged. The boundary clay was found to be full of minute spherules of rock, crystallized from droplets of molten rock formed by the impact.[118] Shocked quartz and other minerals were also identified in the K–Pg boundary.[119][120] Shocked minerals have their internal structure deformed, and are created by intense pressures as in nuclear blasts and meteorite impacts. The identification of giant tsunami beds along the Gulf Coast and the Caribbean also provided evidence,[121] and suggested that the impact may have occurred nearby—as did the discovery that the K–Pg boundary became thicker in the southern United States, with meter-thick beds of debris occurring in northern New Mexico.[18]

topographic diagram showing round geographic features
Radar topography reveals the 180 km –wide (112 mi) ring of the Chicxulub Crater.

Further research identified the giant Chicxulub crater, buried under Chicxulub on the coast of Yucatán, as the source of the K–Pg boundary clay. Identified in 1990[11] based on work by geophysicist Glen Penfield in 1978, the crater is oval, with an average diameter of roughly 180 kilometres (110 mi), about the size calculated by the Alvarez team.[122] The discovery of the crater—a necessary prediction of the impact hypothesis—provided conclusive evidence for a K–Pg impact, and strengthened the hypothesis that it caused the extinction.

In a 2013 paper, Paul Renne of the Berkeley Geochronology Center reported that the date of the impact is 66.043±0.011 million years ago, based on argon–argon dating. He further posits that the mass extinction occurred within 32,000 years of this date.[3][123]

In 2007, it was proposed that the impactor belonged to the Baptistina family of asteroids.[124] This link has been doubted, though not disproved, in part because of a lack of observations of the asteroid and its family.[125] It was recently discovered that 298 Baptistina does not share the chemical signature of the K–Pg impactor.[126] Further, a 2011 Wide-field Infrared Survey Explorer (WISE) study of reflected light from the asteroids of the family estimated their break-up at 80 Ma, giving them insufficient time to shift orbits and impact Earth by 66 Ma.[127]

Effects of impact[edit]

In March 2010, an international panel of 41 scientists reviewed 20 years of scientific literature and endorsed the asteroid hypothesis, specifically the Chicxulub impact, as the cause of the extinction, ruling out other theories such as massive volcanism. They had determined that a 10-to-15-kilometre (6.2 to 9.3 mi) asteroid hurtled into Earth at Chicxulub on Mexico's Yucatán Peninsula. The collision would have released the same energy as 100 teratonnes of TNT (420 ZJ), more than a billion times the energy of the atomic bombings of Hiroshima and Nagasaki.[12]

The Chicxulub impact caused a global catastrophe. Some of the phenomena were brief occurrences immediately following the impact, but there were also long-term geochemical and climatic disruptions that devastated the ecology.

The reentry of ejecta into Earth's atmosphere would include a brief (hours long) but intense pulse of infrared radiation, killing exposed organisms.[55] A paper in 2013 by a prominent modeler of nuclear winter suggested that, based on the amount of soot in the global debris layer, the entire terrestrial biosphere might have burned, iimplying a global soot-cloud blocking out the sun and creating a nuclear winter effect.[128] This is debated, however, with opponents arguing that local ferocious fires, probably limited to North America, fall short of global firestorms. This disagreement is termed the "Cretaceous-Palaeogene firestorm debate."

Aside from the hypothesized fire and/or nuclear winter effects, the impact would have created a dust cloud that blocked sunlight for up to a year, inhibiting photsynthesis.[107] Further, the asteroid struck a region of sulfur-rich carbonate rock, much of which was vaporized, thereby injecting sulfuric acid aerosols into the stratosphere, which might have reduced sunlight reaching the Earth's surface by more than 50%, and would have caused acid rain.[107][129] The resulting acidification of the oceans would kill many organisms that grow shells of calcium carbonate. At Brazos section, the paleo-sea surface temperature dropped as much as 7 °C for decades after the impact.[130] It would take at least ten years for such aerosols to dissipate, and would account for the extinction of plants and phytoplankton, and subsequently herbivores and their predators. Creatures whose food chains were based on detritus would have a reasonable chance of survival, however.[91][107]

If widespread fires occurred, they would have increased the CO
content of the atmosphere and caused a temporary greenhouse effect once the dust clouds and aerosol settled, and, this would have exterminated the most vulnerable organisms that survived the period immediately after the impact.[131]

Although most paleontologists now agree that an asteroid did hit the Earth at approximately the end of the Cretaceous, there is an ongoing dispute whether the impact was the sole cause of the extinctions.[39][132]

In a 2016 study, a team from the Potsdam Institute for Climate Impact Research announced that the main cause for mass extinction was a severe drop in global temperatures caused by large amounts sulfuric acid droplets in the atmosphere. Freezing temperatures lasted for at least three years.[133] The asteroid hit in an especially unfortunate region, having a large amount of combustible hydrocarbons and sulphur.[134]

The river bed at the Moody Creek Mine, 7 Mile Creek / Waimatuku, Dunollie, New Zealand contains evidence of a devastating event on terrestrial plant communities at the Cretaceous-Tertiary boundary, confirming the severity and global nature of the event.[58]

2016 Chicxulub crater drilling project[edit]

In 2016, a scientific drilling project obtained deep rock core samples from the peak ring around the Chicxulub impact crater. The discoveries confirmed that the rock comprising the peak ring had been shocked by immense pressure and melted in just minutes from its usual state into its present form. Unlike sea-floor deposits, the peak ring was made of granite originating much deeper in the earth, which had been ejected to the surface by the impact. Gypsum, a sulfate-containing rock usually present in the shallow seabed of the region, had been almost entirely removed, vaporized into the atmosphere. Further, the event was immediately followed by a megatsunami (a massive movement of sea waters) sufficient to lay down the largest known layer of sand separated by grain size directly above the peak ring.

These findings strongly support the impact's role in the extinction event. The impactor was large enough to create a 120-mile peak ring, to melt, shock and eject deep granite, to create colossal water movements, and to eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted for a long time. This worldwide dispersal of dust and sulfates would have affected climate catastrophically, led to large temperature drops, and devastated the food chain.[135][136]

Alternative hypotheses[edit]

Though the concurrence of the end-Cretaceous extinctions with the Chicxulub asteroid impact strongly supports the impact hypothesis, some scientists continue to suggest that other causes may have contributed. In particular, volcanic eruptions, climate change, sea level change, and other impact events have been suggested to play a role.

Deccan Traps[edit]

Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 Mya and lasted more than 2 million years. The most recent evidence shows that the traps erupted over a period of 800,000 years spanning the K–Pg boundary, and therefore may be responsible for the extinction and the delayed biotic recovery thereafter.[137]

In the years when the Deccan Traps hypothesis was linked to a slower extinction, Luis Alvarez (who died in 1988) replied that paleontologists were being misled by sparse data. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. Even Walter Alvarez acknowledged that other major changes may have contributed to the extinctions.[140]

Some geophysical models suggest a connection between the impact and the Deccan Traps. These models, combined with high-precision radiometric dating, suggest that the Chicxulub impact could have triggered some of the largest Deccan eruptions, and could have triggered eruptions at active volcanoes anywhere on Earth.[141][142]

Multiple impact event[edit]

Other crater-like topographic features have also been proposed as impact craters formed in connection with Cretaceous-Paleogene extinction. This suggests the possibility of near-simultaneous multiple impacts, perhaps from a fragmented asteroidal object similar to the Shoemaker–Levy 9 impact with Jupiter. In addition to the 180 km (110 mi) Chicxulub Crater, there is the 24 km (15 mi) Boltysh crater in Ukraine (65.17±0.64 Ma), the 20 km (12 mi) Silverpit crater in the North Sea (59.5±14.5 Ma) possibly formed by bolide impact, and the controversial and much larger 600 km (370 mi) Shiva crater. Any other craters that might have formed in the Tethys Ocean would have been obscured by the northward tectonic drift of Africa and India.[143][144][145][146]

Maastrichtian sea-level regression[edit]

There is clear evidence that sea levels fell in the final stage of the Cretaceous by more than at any other time in the Mesozoic era. In some Maastrichtian stage rock layers from various parts of the world, the later layers are terrestrial; earlier layers represent shorelines and the earliest layers represent seabeds. These layers do not show the tilting and distortion associated with mountain building, therefore the likeliest explanation is a "regression", a drop in sea level. There is no direct evidence for the cause of the regression, but the currently accepted explanation is that the mid-ocean ridges became less active and sank under their own weight.[27][147]

A severe regression would have greatly reduced the continental shelf area, the most species-rich part of the sea, and therefore could have been enough to cause a marine mass extinction; however, this change would not have sufficed to cause the extinction of the ammonites. The regression would also have caused climate changes, partly by disrupting winds and ocean currents and partly by reducing the Earth's albedo and increasing global temperatures.[108]

Multiple causes[edit]

Proponents of multiple causation view the suggested single causes as either too small to produce the vast scale of the extinction, or not likely to produce its observed taxonomic pattern.[90] In a review article, J. David Archibald and David E. Fastovsky discussed a scenario combining three major postulated causes: volcanism, marine regression, and extraterrestrial impact. In this scenario, terrestrial and marine communities were stressed by the changes in, and loss of, habitats. Dinosaurs, as the largest vertebrates, were the first affected by environmental changes, and their diversity declined. At the same time, particulate materials from volcanism cooled and dried areas of the globe. Then an impact event occurred, causing collapses in photosynthesis-based food chains, both in the already-stressed terrestrial food chains and in the marine food chains.

Recent work led by Sierra Peterson at Seymour Island, Antarctica, showed two separate extinction events near the Cretaceous-Paleogene boundary, with one correlating to Deccan Trap volcanism and one correlated with the Chicxulub impact.[148] The team analyzed combined extinction patterns using a new clumped isotope temperature record from a hiatus-free, expanded K-Pg boundary section. They documented a 7.8±3.3 °C warming synchronous with the onset of Deccan Traps volcanism and a second, smaller warming at the time of meteorite impact. They suggest "Local warming may have been amplified due to simultaneous disappearance of continental or sea ice. Intra-shell variability indicates a possible reduction in seasonality after Deccan eruptions began, continuing through the meteorite event. Species extinction at Seymour Island occurred in two pulses that coincide with the two observed warming events, directly linking the end-Cretaceous extinction at this site to both volcanic and meteorite events via climate change.".[148]

Recovery and radiation[edit]

The K–Pg extinction had a profound effect on the evolution of life on Earth. The elimination of dominant Cretaceous groups allowed other organisms to take their place, spurring a remarkable series of adaptive radiations in the Paleogene.[21] The most striking example is the replacement of dinosaurs by mammals. After the K–Pg extinction, mammals evolved rapidly to fill the niches left vacant by the dinosaurs. Also significant, within the mammalian genera, new species were approximately 9.1% larger after the K–Pg boundary.[149]

Other groups also underwent major radiations. Based on molecular sequencing and fossil dating, Neoaves appeared to radiate after the K–Pg boundary.[22][150] They even produced giant, flightless forms, such as the herbivorous Gastornis and Dromornithidae, and the predatory Phorusrhacidae. The extinction of Cretaceous lizards and snakes may have led to the radiation of modern groups such as iguanas, monitor lizards, and boas.[15] On land, giant boid and enormous madtsoiid snakes appeared, and in the seas, giant sea snakes radiated. Teleost fish diversified explosively,[23] filling the niches left vacant by the extinction. Groups appearing in the Paleocene and Eocene include billfish, tunas, eels, and flatfish. Major changes are also seen in Paleogene insect communities. Many groups of ants were present in the Cretaceous, but in the Eocene ants became dominant and diverse, with larger colonies. Butterflies diversified as well, perhaps to take the place of leaf-eating insects wiped out by the extinction. The advanced mound-building termites, Termitidae, also appear to have risen in importance.[151]

See also[edit]

Notes and references[edit]

  2. ^ The former designation includes the term 'Tertiary' (abbreviated as T), which is now discouraged as a formal geochronological unit by the International Commission on Stratigraphy.[1]
  2. ^ "International Chronostratigraphic Chart". International Commission on Stratigraphy. 2015. Archived from the original on May 30, 2014. Retrieved 29 April 2015.
  5. ^ Muench, David; Muench, Marc; Gilders, Michelle A. (2000). Primal Forces. Portland: Graphic Arts Center Publishing. p. 20. ISBN 1-55868-522-7.
  6. ^ Schulte, Peter (March 5, 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary". Science. American Association for the Advancement of Science. 327 (5970): 1214–1218. Bibcode:2010Sci...327.1214S. doi:10.1126/science.1177265. JSTOR 40544375. PMID 20203042.
  7. ^ Sleep, Norman H.; Lowe, Donald R. (9 April 2014). "Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast". American Geophysical Union. Retrieved 30 December 2016.
  8. ^ Amos, Jonathan (15 May 2017). "Dinosaur asteroid hit 'worst possible place'". BBC News Online. Retrieved 16 March 2018.
  10. ^ Vellekoop, J.; Sluijs, A.; Smit, J.; et al. (May 2014). "Rapid short-term cooling following the Chicxulub impact at the Cretaceous-Paleogene boundary". Proc. Natl. Acad. Sci. U.S.A. 111 (21): 7537–41. Bibcode:2014PNAS..111.7537V. doi:10.1073/pnas.1319253111. PMID 24821785.
  11. ^ a b Hildebrand, A. R.; Penfield, G. T.; et al. (1991). "Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatán peninsula, Mexico". Geology. 19 (9): 867–871. Bibcode:1991Geo....19..867H. doi:10.1130/0091-7613(1991)019<0867:ccapct>;2.
  14. ^ a b c Longrich, Nicholas R.; Tokaryk, Tim; Field, Daniel J. (2011). "Mass extinction of birds at the Cretaceous–Paleogene (K–Pg) boundary". Proceedings of the National Academy of Sciences. 108 (37): 15253–15257. Bibcode:2011PNAS..10815253L. doi:10.1073/pnas.1110395108. PMC 3174646Freely accessible. PMID 21914849.
  15. ^ a b c Longrich, N. R.; Bhullar, B.-A. S.; Gauthier, J. A. (December 2012). "Mass extinction of lizards and snakes at the Cretaceous-Paleogene boundary". Proc. Natl. Acad. Sci. U.S.A. 109 (52): 21396–401. Bibcode:2012PNAS..10921396L. doi:10.1073/pnas.1211526110. PMC 3535637Freely accessible. PMID 23236177.
  16. ^ Labandeira CC; Johnson KR; et al. (2002). "Preliminary assessment of insect herbivory across the Cretaceous-Tertiary boundary: major extinction and minimum rebound". In Hartman JH; Johnson KR; Nichols DJ. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the Northern Great Plains: An Integrated Continental Record of the End of the Cretaceous. Geological Society of America. pp. 297–327. ISBN 978-0-8137-2361-7.
  17. ^ Rehan, Sandra M.; Leys, Remko; Schwarz, Michael P. (2013). "First Evidence for a Massive Extinction Event Affecting Bees Close to the K-T Boundary". PLoS ONE. 8 (10): e76683. Bibcode:2013PLoSO...876683R. doi:10.1371/journal.pone.0076683. ISSN 1932-6203. PMC 3806776Freely accessible. PMID 24194843.
  19. ^ Friedman M (2009). "Ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction". PNAS. 106 (13): 5218–5223. Bibcode:2009PNAS..106.5218F. doi:10.1073/pnas.0808468106. PMC 2664034Freely accessible. PMID 19276106.
  20. ^ a b Jablonski, D.; Chaloner, W. G. (1994). "Extinctions in the fossil record (and discussion)". Philosophical Transactions of the Royal Society of London, Series B. 344 (1307): 11–17. doi:10.1098/rstb.1994.0045.
  21. ^ a b Alroy J (1999). "The fossil record of North American Mammals: evidence for a Palaeocene evolutionary radiation". Systematic Biology. 48 (1): 107–118. doi:10.1080/106351599260472. PMID 12078635.
  22. ^ a b Feduccia A (1995). "Explosive evolution in Tertiary birds and mammals". Science. 267 (5198): 637–638. Bibcode:1995Sci...267..637F. doi:10.1126/science.267.5198.637. PMID 17745839.
  23. ^ a b Friedman M (2010). "Explosive morphological diversification of spiny-finned teleost fishes in the aftermath of the end-Cretaceous extinction". Proceedings of the Royal Society B. 277 (1688): 1675–1683. doi:10.1098/rspb.2009.2177. PMC 2871855Freely accessible. PMID 20133356.
  24. ^ Pospichal JJ (1996). "Calcareous nannofossils and clastic sediments at the Cretaceous–Tertiary boundary, northeastern Mexico". Geology. 24 (3): 255–258. Bibcode:1996Geo....24..255P. doi:10.1130/0091-7613(1996)024<0255:CNACSA>2.3.CO;2.
  25. ^ Bown P (2005). "Selective calcareous nannoplankton survivorship at the Cretaceous–Tertiary boundary". Geology. 33 (8): 653–656. Bibcode:2005Geo....33..653B. doi:10.1130/G21566.1.
  27. ^ a b c d e f g h i j k l m n o p MacLeod N; Rawson PF; Forey PL; Banner FT; Boudagher-Fadel MK; Bown PR; Burnett JA; Chambers P; Culver S; Evans SE; Jeffery C; Kaminski MA; Lord AR; Milner AC; Milner AR; Morris N; Owen E; Rosen BR; Smith AB; Taylor PD; Urquhart E; Young JR (1997). "The Cretaceous–Tertiary biotic transition". Journal of the Geological Society. 154 (2): 265–292. doi:10.1144/gsjgs.154.2.0265.
  28. ^ Gedl P (2004). "Dinoflagellate cyst record of the deep-sea Cretaceous-Tertiary boundary at Uzgru, Carpathian Mountains, Czech Republic". Geological Society, London, Special Publications. 230: 257–273. Bibcode:2004GSLSP.230..257G. doi:10.1144/GSL.SP.2004.230.01.13.
  34. ^ Kauffman E (2004). "Mosasaur Predation on Upper Cretaceous Nautiloids and Ammonites from the United States Pacific Coast". PALAIOS. Society for Sedimentary Geology. 19 (1): 96–100. doi:10.1669/0883-1351(2004)019<0096:MPOUCN>2.0.CO;2. ISSN 0883-1351. Retrieved 2007-06-17.
  35. ^ MacLeod N (1998). "Impacts and marine invertebrate extinctions". Geological Society, London, Special Publications. 140 (1): 217–246. Bibcode:1998GSLSP.140..217M. doi:10.1144/GSL.SP.1998.140.01.16.
  37. ^ Arenillas I, Arz JA, Molina E, Dupuis C (2000). "An independent test of planktic foraminiferal turnover across the Cretaceous/Paleogene (K/P) boundary at El Kef, Tunisia: catastrophic mass extinction and possible survivorship". Micropaleontology. 46 (1): 31–49. JSTOR 1486024.
  39. ^ a b Keller G, Adatte T, Stinnesbeck W, Rebolledo-Vieyra, Fucugauchi JU, Kramar U, Stüben D; Adatte; Stinnesbeck; Rebolledo-Vieyra; Urrutia Fucugauchi; Kramar; Stüben (2004). "Chicxulub impact predates the K–T boundary mass extinction". PNAS. 101 (11): 3753–3758. Bibcode:2004PNAS..101.3753K. doi:10.1073/pnas.0400396101. PMC 374316Freely accessible. PMID 15004276.
  40. ^ Galeotti S, Bellagamba M, Kaminski MA, Montanari A (2002). "Deep-sea benthic foraminiferal recolonisation following a volcaniclastic event in the lower Campanian of the Scaglia Rossa Formation (Umbria-Marche Basin, central Italy)" (PDF). Marine Micropaleontology. 44: 57–76. doi:10.1016/s0377-8398(01)00037-8. Retrieved 2007-08-19.
  41. ^ Kuhnt W, Collins ES; Collins (1996). "8. Cretaceous to Paleogene benthic foraminifers from the Iberia abyssal plain" (PDF). Proceedings of the Ocean Drilling Program, Scientific Results. Proceedings of the Ocean Drilling Program. 149: 203–216. doi:10.2973/ Retrieved 2007-08-19.
  42. ^ Coles, GP; Ayress MA; Whatley RC (1990). "A comparison of North Atlantic and 20 Pacific deep-sea Ostracoda". In RC Whatley; C Maybury. Ostracoda and global events. Chapman & Hall. pp. 287–305. ISBN 978-0-442-31167-4.
  43. ^ Brouwers EM, De Deckker P; Deckker (1993). "Late Maastrichtian and Danian Ostracode Faunas from Northern Alaska: Reconstructions of Environment and Paleogeography". PALAIOS. 8 (2): 140–154. doi:10.2307/3515168. JSTOR 3515168.
  44. ^ Vescsei A, Moussavian E; Moussavian (1997). "Paleocene reefs on the Maiella Platform Margin, Italy: An example of the effects of the cretaceous/tertiary boundary events on reefs and carbonate platforms". Facies. 36 (1): 123–139. doi:10.1007/BF02536880.
  45. ^ Rosen BR, Turnšek D (1989). Jell A; Pickett JW, eds. "Extinction patterns and biogeography of scleractinian corals across the Cretaceous/Tertiary boundary". Memoir of the Association of Australasian Paleontology. Proceedings of the Fifth International Symposium on Fossil Cnidaria including Archaeocyatha and Spongiomorphs. Brisbane, Queensland (8): 355–370.
  48. ^ Neraudeau D, Thierry J, Moreau P (1997). "Variation in echinoid biodiversity during the Cenomanian–early Turonian transgressive episode in Charentes (France)". Bulletin de la Société Géologique de France. 168: 51–61.
  50. ^ MacLeod KG (1994). "Extinction of Inoceramid Bivalves in Maastrichtian Strata of the Bay of Biscay Region of France and Spain". Journal of Paleontology. 68 (5): 1048–1066.
  51. ^ a b Kriwet, Jürgen; Benton, Michael J. (2004). "Neoselachian (Chondrichthyes, Elasmobranchii) Diversity across the Cretaceous–Tertiary Boundary". Palaeogeography, Palaeoclimatology, Palaeoecology. 214 (3): 181–194. doi:10.1016/j.palaeo.2004.02.049.
  53. ^ Noubhani, Abdelmajid (2010). "The Selachians' Faunas of the Moroccan Phosphate Deposits and the K-T Mass Extinctions". Historical Biology. 22: 71–77. doi:10.1080/08912961003707349.
  57. ^ Wilf P, Labandeira CC, Johnson KR, Ellis B; Labandeira; Johnson; Ellis (2006). "Decoupled Plant and Insect Diversity After the End-Cretaceous Extinction". Science. 313 (5790): 1112–1115. Bibcode:2006Sci...313.1112W. doi:10.1126/science.1129569. PMID 16931760.
  58. ^ a b c Vajda Vivi, Raine J Ian, Hollis Christopher J; Raine; Hollis (2001). "Indication of Global Deforestation at the Cretaceous–Tertiary Boundary by New Zealand Fern Spike". Science. 294 (5547): 1700–1702. Bibcode:2001Sci...294.1700V. doi:10.1126/science.1064706. PMID 11721051.
  59. ^ Wilf, P.; Johnson, K. R. (2004). "Land plant extinction at the end of the Cretaceous: a quantitative analysis of the North Dakota megafloral record". Paleobiology. 30 (3): 347–368. doi:10.1666/0094-8373(2004)030<0347:lpeate>;2.
  62. ^ Schultz PH, D'Hondt S; d'Hondt (1996). "Cretaceous–Tertiary (Chicxulub) impact angle and its consequences". Geology. 24 (11): 963–967. Bibcode:1996Geo....24..963S. doi:10.1130/0091-7613(1996)024<0963:CTCIAA>2.3.CO;2. Retrieved 2007-07-05.
  63. ^ Vajda V, McLoughlin S; McLoughlin (2004). "Fungal Proliferation at the Cretaceous–Tertiary Boundary" (PDF). Science. 303 (5663): 1489–1490. doi:10.1126/science.1093807. PMID 15001770. Archived from the original (PDF) on 2007-09-26. Retrieved 2007-07-07.
  65. ^ Archibald JD, Bryant LJ (1990). "Differential Cretaceous–Tertiary extinction of nonmarine vertebrates; evidence from northeastern Montana". In Sharpton VL, Ward PD. Global Catastrophes in Earth History: an Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality. Geological Society of America, Special Paper. 247. pp. 549–562. doi:10.1130/spe247-p549. ISBN 0-8137-2247-0.
  66. ^ Estes, R (1964). "Fossil vertebrates from the Late Cretaceous Lance Formation, Eastern Wyoming". University of California Publications, Department of Geological Sciences. 49: 1–180.
  67. ^ Gardner J. D. (2000). "Albanerpetontid amphibians from the Upper Cretaceous (Campanian and Maastrichtian) of North America". Geodiversitas. 22 (3): 349–388.
  69. ^ Novacek MJ (1999). "100 Million Years of Land Vertebrate Evolution: The Cretaceous-Early Tertiary Transition". Annals of the Missouri Botanical Garden. 86 (2): 230–258. doi:10.2307/2666178. JSTOR 2666178.
  70. ^ Apesteguía Sebastián; Novas Fernando E (2003). "Large Cretaceous sphenodontian from Patagonia provides insight into lepidosaur evolution in Gondwana". Nature. 425 (6958): 609–612. Bibcode:2003Natur.425..609A. doi:10.1038/nature01995. PMID 14534584.
  73. ^ Chatterjee S, Small BJ; Small (1989). "New plesiosaurs from the Upper Cretaceous of Antarctica". Geological Society, London, Special Publications. 47 (1): 197–215. Bibcode:1989GSLSP..47..197C. doi:10.1144/GSL.SP.1989.047.01.15. Retrieved 2007-07-04.
  75. ^ "The Great Archosaur Lineage". University of California Museum of Paleontology. Retrieved 2014-12-18.
  76. ^ Brochu CA (2004). "Calibration age and quartet divergence date estimation". Evolution. 58 (6): 1375–1382. doi:10.1554/03-509. PMID 15266985.
  79. ^ Morphology and function of the palatal dentition in Choristodera Journal of Anatomy 228(3):n/a-n/a · November 2015 doi:10.1111/joa.12414
  80. ^ Company J.; Ruiz-Omeñaca J. I.; Pereda Suberbiola X. (1999). "A long-necked pterosaur (Pterodactyloidea, Azhdarchidae) from the Upper Cretaceous of Valencia, Spain". Geologie en Mijnbouw. 78 (3): 319–333.
  81. ^ Barrett P. M.; Butler R. J.; Edwards N. P.; Milner A. R. (2008). "Pterosaur distribution in time and space: an atlas" (PDF). Zitteliana. 28: 61–107.
  83. ^ Penny D, Phillips MJ; Phillips (2004). "The rise of birds and mammals: are microevolutionary processes sufficient for macroevolution". Trends Ecol Evol. 19 (10): 516–522. doi:10.1016/j.tree.2004.07.015. PMID 16701316.
  84. ^ Butler Richard J.; Barrett Paul M.; Nowbath Stephen; Upchurch Paul (2009). "Estimating the effects of sampling biases on pterosaur diversity patterns: implications for hypotheses of bird/pterosaur competitive replacement". Paleobiology. 35 (3): 432–446. doi:10.1666/0094-8373-35.3.432.
  85. ^ Prondvai E.; Bodor E. R.; Ösi A. (2014). "Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity". Paleobiology. 40 (2): 288–321. doi:10.1666/13030.
  86. ^ Longrich, N. R.; Martill, D. M.; Andres, B. (2018). "Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary". PLoS Biology. 16 (3): e2001663. doi:10.1371/journal.pbio.2001663.
  87. ^ Hou L, Martin M, Zhou Z, Feduccia A; Martin; Zhou; Feduccia (1996). "Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China". Science. 274 (5290): 1164–1167. Bibcode:1996Sci...274.1164H. doi:10.1126/science.274.5290.1164. PMID 8895459.
  90. ^ a b c d e David, Archibald; David Fastovsky (2004). "Dinosaur Extinction" (PDF). In Weishampel David B; Dodson Peter; Osmólska Halszka. The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 672–684. ISBN 0-520-24209-2.
  91. ^ a b Ocampo, A; Vajda V; Buffetaut E (2006). "Unravelling the Cretaceous–Paleogene (K–T) turnover, evidence from flora, fauna and geology in biological processes associated with impact events". In Cockell C; Gilmour I; Koeberl C. Biological Processes Associated with Impact Events. SpringerLink. pp. 197–219. ISBN 978-3-540-25735-6.
  92. ^ Rieraa V, Marmib J, Omsa O, Gomez B; Marmi; Oms; Gomez (March 2010). "Orientated plant fragments revealing tidal palaeocurrents in the Fumanya mudflat (Maastrichtian, southern Pyrenees): Insights in palaeogeographic reconstructions". Palaeogeography, Palaeoclimatology, Palaeoecology. 288 (1–4): 82–92. doi:10.1016/j.palaeo.2010.01.037.
  93. ^ Loeuff Le J (2012). "Paleobiogeography and biodiversity of Late Maastrichtian dinosaurs: how many dinosaur species became extinct at the Cretaceous-Tertiary boundary?". Bulletin de la Société Géologique de France. 183 (6): 547–559. doi:10.2113/gssgfbull.183.6.547.
  94. ^ Ryan MJ, Russell AP, Eberth DA, Currie PJ; Russell; Eberth; Currie (2001). "The taphonomy of a Centrosaurus (Ornithischia: Ceratopsidae) bone bed from the Dinosaur Park Formation (Upper Campanian), Alberta, Canada, with comments on cranial ontogeny" (PDF). PALAIOS. 16 (5): 482–506. doi:10.1669/0883-1351(2001)016<0482:ttoaco>;2. Archived from the original (PDF) on 2009-07-20.
  96. ^ Fassett JE, Lucas SG, Zielinski RA, Budahn JR; Lucas; Zielinski; Budahn (2001). "Compelling new evidence for Paleocene dinosaurs in the Ojo Alamo Sandstone San Juan Basin, New Mexico and Colorado, USA" (PDF). International Conference on Catastrophic Events and Mass Extinctions: Impacts and Beyond, 9–12 July 2000, Vienna, Austria. 1053: 45–46. Bibcode:2001caev.conf.3139F. Retrieved 2007-05-18.
  98. ^ Gelfo JN, Pascual R (2001). "Peligrotherium tropicalis (Mammalia, Dryolestida) from the early Paleocene of Patagonia, a survival from a Mesozoic Gondwanan radiation" (PDF). Geodiversitas. 23: 369–379. Archived from the original (PDF) on 2012-02-12.
  99. ^ Goin FJ, Reguero MA, Pascual R, von Koenigswald W, Woodburne MO, Case JA, Marenssi SA, Vieytes C, Vizcaíno SF (2006). "First gondwanatherian mammal from Antarctica". Geological Society, London, Special Publications. 258: 135–144. Bibcode:2006GSLSP.258..135G. doi:10.1144/GSL.SP.2006.258.01.10.
  102. ^ a b Bininda-Emonds OR, Cardillo M, Jones KE, MacPhee RD, Beck RM, Grenyer R, Price SA, Vos RA, Gittleman JL, Purvis A (2007). "The delayed rise of present-day mammals" (PDF). Nature. 446 (7135): 507–512. Bibcode:2007Natur.446..507B. doi:10.1038/nature05634. PMID 17392779.
  103. ^ a b Springer MS, Murphy WJ, Eizirik E, O'Brien SJ (2003). "Placental mammal diversification and the Cretaceous–Tertiary boundary" (PDF). PNAS. 100 (3): 1056–1061. Bibcode:2003PNAS..100.1056S. doi:10.1073/pnas.0334222100. PMC 298725Freely accessible. PMID 12552136.
  105. ^ "Online guide to the continental Cretaceous–Tertiary boundary in the Raton basin, Colorado and New Mexico". U.S. Geological Survey. 2004. Archived from the original on 2006-09-25. Retrieved 2007-07-08.
  107. ^ a b c d Pope KO, D'Hondt SL, Marshall CR (1998). "Meteorite impact and the mass extinction of species at the Cretaceous/Tertiary boundary". PNAS. 95 (19): 11028–11029. Bibcode:1998PNAS...9511028P. doi:10.1073/pnas.95.19.11028. PMC 33889Freely accessible. PMID 9736679.
  109. ^ Keller, Gerta (July 2001). "The end-cretaceous mass extinction in the marine realm: year 2000 assessment". Planetary and Space Science. 49 (8): 817–830. Bibcode:2001P&SS...49..817K. doi:10.1016/S0032-0633(01)00032-0.
  110. ^ Bourgeois J (2009). "Chapter 3. GEOLOGIC EFFECTS AND RECORDS OF TSUNAMIS". In Robinson, A.R.; Bernard, E.N. The Sea, Volume 15: Tsunamis (Sea: Ideas and Observations on Progress in the Study of the Seas) (pdf). Boston: Harvard University. ISBN 978-0-674-03173-9. Retrieved 2012-03-29.
  113. ^ Norris, R. D.; J. Firth; J. S. Blusztajn & G. Ravizza (2000). "Mass failure of the North Atlantic margin triggered by the Cretaceous-Paleogene bolide impact". Geology. 28 (12): 1119–1122. Bibcode:2000Geo....28.1119N. doi:10.1130/0091-7613(2000)28<1119:MFOTNA>2.0.CO;2. Retrieved 2012-03-29.
  114. ^ Bryant, Edward (June 2014). Tsunami: The Underrated Hazard. Springer. p. 178. ISBN 9783319061337.
  115. ^ Signor III, PW; Lipps, JH (1982). "Sampling bias, gradual extinction patterns, and catastrophes in the fossil record". In Silver LT; Schultz PH. Geological implications of impacts of large asteroids and comets on the Earth. Special Publication 190. Boulder, Colorado: Geological Society of America. pp. 291–296. ISBN 0-8137-2190-3. OCLC 4434434112.
  116. ^ Mukhopadhyay, S.; et al. (2001). "A Short Duration of the Cretaceous-Tertiary Boundary Event: Evidence from Extraterrestrial Helium-3". Science. 291: 1952–1955. doi:10.1126/science.291.5510.1952. PMID 11239153.
  117. ^ De Laubenfels MW (1956). "Dinosaur extinction: One more hypothesis". Journal of Paleontology. 30 (1): 207–218. JSTOR 1300393.
  118. ^ Smit J., Klaver J. (1981). "Sanidine spherules at the Cretaceous-Tertiary boundary indicate a large impact event". Nature. 292 (5818): 47–49. Bibcode:1981Natur.292...47S. doi:10.1038/292047a0.
  119. ^ Bohor B. F., Foord E. E., Modreski P. J., Triplehorn D. M. (1984). "Mineralogic evidence for an impact event at the Cretaceous-Tertiary boundary". Science. 224 (4651): 869. Bibcode:1984Sci...224..867B. doi:10.1126/science.224.4651.867. PMID 17743194.
  120. ^ Bohor B. F.; Modreski P. J.; Foord E. E. (1987). "Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution". Science. 236 (4802): 705–709. Bibcode:1987Sci...236..705B. doi:10.1126/science.236.4802.705. PMID 17748309.
  121. ^ Bourgeois J., Hansen T. A., Wiberg P. A., Kauffman E. G. (1988). "A tsunami deposit at the Cretaceous-Tertiary boundary in Texas". Science. 241 (4865): 567–570. Bibcode:1988Sci...241..567B. doi:10.1126/science.241.4865.567. PMID 17774578.
  125. ^ Majaess DJ, Higgins D, Molnar LA, Haegert MJ, Lane DJ, Turner DG, Nielsen I (February 2009). "New Constraints on the Asteroid 298 Baptistina, the Alleged Family Member of the K/T Impactor" (PDF). The Journal of the Royal Astronomical Society of Canada. 103 (1): 7–10. arXiv:0811.0171Freely accessible. Bibcode:2009JRASC.103....7M. Archived from the original (PDF) on 2010-11-29.
  126. ^ Reddy V, Emery JP; Gaffey, MJ; Bottke, WF; Cramer A, Kelley MS (December 2009). "Composition of 298 Baptistina: Implications for the K/T impactor link". Meteoritics & Planetary Science. 44 (12): 1917–1927. Bibcode:2009M&PS...44.1917R. doi:10.1111/j.1945-5100.2009.tb02001.x.
  129. ^ Ohno, S.; et al. (2014). "Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification". Nature Geoscience. 7: 279–282. doi:10.1038/ngeo2095. Retrieved 22 January 2014.
  130. ^ Vellekoop, J.; et al. (2013). "Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary". Proceedings of the National Academy of Sciences. 111: 7537–41. doi:10.1073/pnas.1319253111. PMID 24821785.
  131. ^ Pope KO, Baines KH, Ocampo AC, Ivanov BA (1997). "Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact". Journal of Geophysical Research. 102 (E9): 21645–21664. Bibcode:1997JGR...10221645P. doi:10.1029/97JE01743. PMID 11541145.
  133. ^ Brugger Julia, Feulner Georg, Petri Stefan (2016). "Baby, it's cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous". Geophysical Research Letters. doi:10.1002/2016GL072241.
  134. ^ Kunio Kaiho & Naga Oshima (2017). Site of asteroid impact changed the history of life on Earth: the low probability of mass extinction. Scientific Reports 7, Article number: 14855. doi:10.1038/s41598-017-14199-x
  135. ^
  136. ^
  139. ^ Courtillot, Vincent (1990). "A volcanic eruption". Scientific American. 263 (4): 85–92. doi:10.1038/scientificamerican1090-85. PMID 11536474.
  141. ^ Renne, P. R.; et al. (2015). "State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact". Science. 350 (6256): 76–78. Bibcode:2015Sci...350...76R. doi:10.1126/science.aac7549. PMID 26430116.
  142. ^ Richards, M. A.; et al. (2015). "Triggering of the largest Deccan eruptions by the Chicxulub impact". Geological Society of America Bulletin. 127 (11–12): 1507–1520. Bibcode:2015GSAB..127.1507R. doi:10.1130/B31167.1.
  146. ^ Chatterjee, Sankar (August 1997). "Multiple Impacts at the KT Boundary and the Death of the Dinosaurs". 30th International Geological Congress. 26. pp. 31–54. ISBN 978-90-6764-254-5.
  147. ^ Li, Liangquan; Keller, Gerta (1998). "Abrupt deep-sea warming at the end of the Cretaceous". Geology. 26 (11): 995–998. Bibcode:1998Geo....26..995L. doi:10.1130/0091-7613(1998)026<0995:ADSWAT>2.3.CO;2.
  148. ^ a b Petersen Sierra V., Dutton Andrea, Lohmann Kyger C. (2016). "End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change". Nature Communications. 7: 12079. doi:10.1038/ncomms12079.
  149. ^ Alroy J (May 1998). "Cope's rule and the dynamics of body mass evolution in North American fossil mammals". Science. 280 (5364): 731–4. Bibcode:1998Sci...280..731A. doi:10.1126/science.280.5364.731. PMID 9563948.
  150. ^ Ericson PG; Anderson CL; Britton T; et al. (December 2006). "Diversification of Neoaves: integration of molecular sequence data and fossils". Biol. Lett. 2 (4): 543–7. doi:10.1098/rsbl.2006.0523. PMC 1834003Freely accessible. PMID 17148284.

Further reading[edit]

External links[edit]


8 Pages
Unlock Document

Supply Chain Management

Chapter 8—Process Management: Lean Production and Six Sigma Quality Issues in Supply Chain Management TRUE/FALSE 1. Lean production is an operating philosophy or mindset that essentially attempts to minimize the impact of system variability and flaws in forecasting through the use of high safety stock inventories. ANS: F PTS: 1 2. Lean production and Six Sigma quality are essentially two terms that mean the same thing. ANS: F PTS: 1 3. Channel integration is a supply chain term which refers to how a manufacturing firm within a supply chain attempts to create strategic alliances not only with their immediate suppliers but also with the suppliers' suppliers and in the other direction not only reaching out to its immediate customers but also the customer's customers. ANS: T PTS: 1 4. Manufacturing layouts for an organization practicing lean manufacturing principles seek to maximize operator visibility, maintain an effective and efficient flow of people and materials, and minimize the distance that work in process must travel from one processing center to another processing center. ANS: T PTS: 1 5. Organizations practicing lean production often increase their inventory levels in the long-run in order to create a cushion against variability so that they can investigate and eliminate the weaknesses of their system. ANS: F PTS: 1 6. The objective of the Deming Prize is to stimulate quality and productivity improvement among US firms. ANS: F PTS: 1 7. W. Edwards Deming and Shigeo Shingo were two of the notables who helped Toyota develop the Toyota Production System. ANS: T PTS: 1 8. When designing a manufacturing or service process, or even during the reengineering of such a process, a Pareto chart would be an essential tool for evaluating the process in terms of its action elements, waiting periods, and process flow. ANS: F PTS: 1 9. Statistical process control uses control charts to monitor the outputs of a process to identify variations due to assignable causes from variations due to common causes. ANS: T PTS: 1 10. The five S's refer to various safety activities practiced by Toyota. ANS: F PTS: 1 11. The primary design objective with lean layouts is to reduce wasted movements of workers, customers, and/or work-in-process ANS: T PTS: 1 12. Carbon neutral organizations do not produce any carbon emissions. ANS: F PTS: 1 13. Six Sigma is a quality improvement concept developed by Motorola. ANS: T PTS: 1 14. Deming's 14 points actually conflict with many Six Sigma concepts. ANS: F PTS: 1 15. For a certain loaf of bread it was found that it measured 16 inches in length, 4 inches in height, and 4 inches across, it was also found to weigh 1 pound; all of these measures can be considered attribute data. ANS: F PTS: 1 16. Acceptance sampling is a statistical technique that enables a reject or accept decision to be made based on information obtained from a representative sample drawn from the population. ANS: T PTS: 1 MULTIPLE CHOICE 1. Modern supply chains simultaneously pursue the goals of high-quality, fast response, and low cost because customers nowadays want both high levels of quality and responsiveness. A key manufacturing philosophy that emphasizes waste elimination and minimizing inventories to expose problems is: a. Just-in-time b. Quick Response c. Efficient Consumer Response d. Total Quality Management ANS: A PTS: 1 2. Japanese manufacturing firms sometimes create cooperative coalitions with their suppliers in order to provide the suppliers with a certain degree of financial support. What are these cooperative coalitions called? a. Jidoka Networks b. Keiretsu Networks c. Kanban Networks d. Kaizen Networks ANS: B PTS: 1 3. Which of the following are among the most important elements of the lean production philosophy? a. Quality inspections and a standardized product line b. Fully automated assembly lines and a large supplier base c. Large inventories and quality inspections d. Waste reduction and value enhancement ANS: D PTS: 1 4. Which company probably played the largest role in the development of the Toyota Production System? a. General Motors b. Ford c. Chrysler d. Boeing ANS: B PTS: 1 5. Lean production systems are sometimes referred to as pull systems because demand from customers activates the production actions of the manufacturing facilities. In order for this demand to be communicated to everyone in the supply chain/manufacturing facility a signal must be passed from downstream processing centers to the upstream processing centers. This system of relaying signals is referred to as a: a. Kanban Pull System b. Semaphore System c. Keiretsu Network d. TQM Network ANS: A PTS: 1 6. Which of the following is NOT consistent with the lean philosophy? a. Cross-training employees to increase processing flexibility b. Developing a culture of continuous improvement within the organization c. Increasing batch size to take advantage of economies of scale d. Positioning WIP inventories near each processing center ANS: C PTS: 1 7. Which of the following is NOT one of Toyota's seven wastes? a. Excess inventories b. Environmental waste c. Waiting time d. Scrap and rework ANS: B PTS: 1 8. Which of the following best describes the five S's? a. These were originally Japanese words relating to industrial housekeeping b. Five ways to reduce inventories on the shop floor c. These are five different kinds of manufacturing layouts d. Refer to methods for reducing setup times ANS: A PTS: 1 9. While the philosophy of Six Sigma means different things to different people and is practiced differently in different companies, according to the textbook, two of the more important and agreed- upon elements of Six Sigma are: a. Minimizing inventories and increasing material flow b. Focusing on the customer and workforce involvement c. Rewarding employees and keeping defect rates below 2% d. Minimizing inventories and keeping defect rates below 1% ANS: B PTS: 1 10. Calculate the number of inventory containers required, given the following: Demand rate = 10 parts per hour, Safety stock required = 15% Container size = 5 parts, Time to cycle through entire system = 6 hours a. 12 b. 13 c. 14 d. 15 ANS: C PTS: 1 11. Calculate the inventory container size required given the following: Demand rate = 10 parts per hour, Safety stock required = 15% Number of containers = 14, Time to cycle through entire system = 6 hours a. 2 parts b. 3 parts c. 4 parts d. 5 parts ANS: D PTS: 1 12. Calculate the defects per million opportunities (DPMO) given the following: Blake, owner of Blakester's T-shirt Shoppe, keeps track of customer complaints. For each T-shirt sold, there are four possible complaints: T-shirt shrinks, poor quality, design wears off, and doesn't fit right. Each week, Blake calculates the rate of T-shirt "defects" per total T-shirts sold, and then uses this information to determine his company's DPMO. During the past week, his company sold 1200 T- shirts. His company received 22 customer shrinkage complaints, 16 poor quality complaints, 12 design wears off complaints, 8 doesn't fit right complaints. Calculate his firm's DPMO. a. 69,600 b. 0.193 c. 58 × 106 d. 12,083 ANS: D PTS: 1 13. Which of the following quality gurus believed that companies should strive for zero defects and that quality was, in a sense, free since quality improvement programs invariably paid for themselves? a. Juran b. Deming c. Baldrige d. Crosby ANS: D PTS: 1 14. The ISO certification standard for environmental management is: a. ISO 9000 b. ISO 9005 c. ISO 14000 d. ISO 19000 ANS: C PTS: 1 15. A company that produces 8 pound bags of rice gathered 5 samples of 6 bags each. The weights of each bags' contents are listed below. Bag Number Sample 1 2 3 4 5
More Less

Related notes for 33:799:301

Log In

Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Add your courses

Get notes from the top students in your class.


Marvel boss Kevin Feige confirms 'Black Panther 2,' considering spinoffs

Kelly Woo

Wakanda forever! The blockbuster, record-breaking "Black Panther" will be getting a sequel, surprising nobody and delighting us all.

Marvel boss Kevin Feige confirmed the studio has already begun planning a follow-up film. As he told Entertainment Weekly, "We absolutely will do that."

Feige didn't allude to possible storylines, though the end of the first movie left things wide open — literally, since T'Challa (Chadwick Boseman) was starting to open the doors of Wakanda to the rest of the world.

And what about the very loud demands for spinoffs featuring the badass female characters of "Black Panther," like tech wizard Shuri (Letitia Wright), warrior Okoye (Danai Gurira), and spy Nakia (Lupita Nyong'o)?


Your questions answered: Electric motor basics

The Sept. 27, 2017, “Electric motor basics” webcast presenter addressed questions not covered during the live event.

Reece Robinson, Grundfos Pumps Corp.Rotation is an essential part in the act of pumping thus making the motor an essential component of any pump. The purpose of the electric motor is to create this rotation by converting electrical energy into mechanical energy. This webcast is an introduction into how motors work. Viewers will learn the basic principles of magnetism, electromagnetism, and magnetic flux; how the two primary components, the stator and rotor, form the basic operating principle of an induction motor; the operating principles for 3-phase and single-phase motors; the difference between synchronous and asynchronous motors; and motor torque and power—where torque and speed come from.

Presenter Reece Robinson, senior technical training specialist, Grundfos Pumps Corp., responded to questions not answered during the live Electric motor basics webcast on Sept. 27, 2017.

Moderated by Jim Swetye, technical training expert, Grundfos Pumps Corp.

Question: What materials are used for laminations? Which is best for producing the strongest field of magnetism?

Reece Robinson: Laminations are made of steel, specifically silicon steel, also known as electrical steel. The addition of silicon to steel makes the steel more efficient and faster in terms of building and maintaining magnetic fields.

Q: I’ve read that motors act as generators during a fault. What exactly happens during a fault that causes the motor to act as a generator?

Robinson: Actually, when the motor spins in the opposite direction, it essentially becomes a generator. Some controls use braking to slow motors down, which can cause a fault or trip of the control. In pump applications, if water flow is going back through a pump discharge, this can cause the pump to spin in the opposite direction. This can be due to a check valve not functioning or in some cases, sever water hammer can cause a sudden reverse of pump shaft direction.

Q: What is the reason again to use variable frequency drives (VFDs) for permanent magnet synchronous motors (PMSMs)?

Robinson: PMSMs are not designed for across-the-line starting, and require a drive. To provide the right amount of torque at a given current, the rotor position must be known. Currently, there is research being done for line-start permanent magnet motors.

Q: Are PMSMs single-phase or 3-phase?

Robinson: The motor itself is based on 3-phase power but the control (VFD) can be designed for single-phase or 3-phase input. For commercial pumps, for example, PMSMs are available for single-phase supply from fractional size motors to 3 hp; 3-phase sizes range up to around 15 hp.

Q: For PMSMs, do you need to install stray current protection for the motor/pump bearings?

Robinson: I have seen no evidence showing that PMSMs reduce or eliminate problems associated with bearing currents. I will say that bearing damage due to these stray currents (called “fluting”) occurs predominantly in larger motors (above 50 hp). Fluting also is more common in equipment that is poorly grounded and/or has a flexible type coupling between the driven equipment and motor. Many flexible type couplings result in a break in the metal-to-metal contact, which results in having a poor path to ground for those stray currents.

Q: Did you say it is not necessary to worry about motor overheating at low speeds, and did you mean lower than 25% speed?

Robinson: For variable torque loads (centrifugal pumps and fans), the torque reduces with the square of the speed, so, even though the fan at the end of the motor shaft is only spinning at 25% of the motor’s rated speed, the torque has been reduced to only 6.25% of the full-load torque. Motor overheating concerns have originated from constant torque type applications where high torque is required at all speeds.

Q: Can you discuss implications running a 50 Hz, 380 V induction motor at 460 V, 60 Hz and vice versa?

Robinson: If a motor is rated/nameplated at 50 Hz/380 V, it should not be operated at 60 Hz/460 V. For example, if the motor was rated at 10 hp (7.5 kW) at 50 Hz/380 V and had a rated speed of 2,900 rpm, it could certainly overload at 60 Hz/460 V as it would be spinning at approximately 3,480 rpm. The horsepower increases with the cube of the speed so that 10 hp (7.5 kW) could become 17.3 hp (12.9 kW). It’s generally more feasible to go down from 60 Hz/460 V to 50 Hz/380 V, especially because most modern induction motors are rated for variable speed. When controlled by a VFD, a 60 Hz/460 V motor will periodically operate at 50 Hz/380 V during the normal duty cycle. Many motors have dual ratings, both at 50 Hz and 60 Hz. It is always best to consult the motor manufacturer and also check with the driven equipment manufacturer as well to ensure operation is advisable.

Q: All other things being equal, which has a higher initial cost: an 1,800-rpm motor or a 3,600-rpm motor?

Robinson: A 4-pole (1,800 rpm) motor will require more material and cost to produce therefore will have a higher initial cost. The 1,800-rpm motor will also be heavier, which may incur a higher shipping cost as well, as possible increased cost to mount and support. But on the other hand, 4-pole (1,800 rpm) motors generally are more efficient, from 1% to 2% higher than 2-pole (3,600 rpm) motors. But remember that the initial cost and efficiency of the driven equipment must also be taken into consideration.

Q: How does the switching frequency/carrier frequency of the VFD affect motor operation and expected life?

Robinson: When the switching/carrier frequency of a VFD is increased, this will result in a rise in temperature for both the motor and drive, which will result in lower efficiency for both as well. The most common reason for increasing the switching frequency is to decrease the audible noise (sometimes known as “VFD whine”). If the equipment is of good quality and sized to allow for some wiggle room, carrier frequencies can be adjusted up with only minor impacts on added heat or loss of efficiency. As always, it is best to consult with the drive and equipment manufacturers (or industry experts) before making those changes.

Q: How do you determine a motor's load?

Robinson: The load on the motor is based on the equipment connected to the motor. So, if the motor is connected to a pump, there will be a corresponding brake horsepower curve for that pump. If the pump is driven by a 10 hp (7.5 kW) motor for example, the actual load on the motor might only be 8 hp (6 kW). The amount of flow going through the pump will determine the load on the motor and that load will be shown on the pump performance curve (or fan curve if you’re looking at fans). If you’re evaluating a motor in the field for example, you can get an idea of the approximate load on the motor by measuring the current and voltage. If the full load amps (FLA) of a motor is 10 and the average current draw on each phase is 8, then that motors is running somewhere between 7.5 and 8.5 brake horsepower (bhp). There are formulas to determine motor performance in publications such as the Electricians Handbook and the Cameron Hydraulic Data Book, etc. Most motor suppliers can supply a motor performance curve that shows volts, amps, efficiency, rpm, and power factor as a function of load.

click me


Which chat app?

27-Nov-14 18:47
Hey guys!

I have one question and I believe I will find people to answer it here.

I am looking for a chat service to use on my algo-trading website. It needs to have option for adding youtube videos and posting charts and also I want to be able to edit design a bit.

I came across Rumbletalk and Envolv but I am still finding more options.

Which one you recommend?
06-Nov-16 12:47
iHelpDesk or Chatango.

New posts
Old posts

Follow Elated


Giaran Inc.

Giaran Inc. is a Northeastern University spinoff and founded by serial entrepreneurs and world-renowned Artificial Intelligence expert. The company takes the big data mining principles of digital makeup visualization and provides real-time augmented reality displays using advanced machine learning and computer vision technologies. Giaran's most current prototype, the "Giaran Mirror," enables users to experience a highly realistic smart real-life makeup try-on in augmented reality.


Shang han lun / Wen bing

Books about shang han lun and wen bing

The Shang Han Lun, a treatise on cold diseases, is considered the oldest treatise in the history of medicine. Unfortunately, only the TCM books by Mitchel and Young are available.
Check also our video on Shang Han Lun formulas, 6 important basic formulations, construction and use of Wortman and Simon. A DVD from the presentation at the SMS Congress 2011 in Tutzing (Germany). The topic is 6 important basic formulations, their structure and use. The two therapists discuss the structure of the book and its translation. In the further course, Wortman and Simon introduce constitutional types. Finally, practical exercises will be performed to show how a stomach is being examined. Shang Han Lun in Mitchell and Wiseman’s cold diseases show that Shang Han Lun is the main therapy for almost 200 years. Its author, Zhang Zhong Jing, is also called the Chinese Hippocrates and represents the depth and breadth of his contribution to traditional Chinese herbal medicine. This issue contains the Chinese texts, the Pinyin translation and an English translation of the entire Song Dynasty. The contents and texts were mainly used in Asia. As with Chinese-language editions, it’s full of comments and comments. The notes describe the clinical symptoms that Zhang Zhong Jing has associated with Chinese phrases. For example, modern interpretations often describe a moderate pulse with the speed of the beat. The same description, when used in the Shang Han Lun, refers to a pulse that is gentle and harmonious. Such comments provide practitioners with clinical observations that are important to the information. The comments expand the clinical applicability of the text, through the theoretical and practical justification found behind the lines of text. The comments in this issue serve exactly the same purpose to extend their usability as much as possible. The appendices are written for those who study Chinese to give them an easy start.