147-406: The Deccan Traps are a large igneous province of west-central India (17–24°N, 73–74°E). They are one of the largest volcanic features on Earth, taking the form of a large shield volcano . They consist of many layers of solidified flood basalt that together are more than about 2,000 metres (6,600 ft) thick, cover an area of about 500,000 square kilometres (200,000 sq mi), and have
294-449: A consequence of the initial hot-spot activity in ocean basins as well as on continents. It is possible to track the hot spot back to the flood basalts of a large igneous province; the table below correlates large igneous provinces with the track of a specific hot spot. Eruptions or emplacements of LIPs appear to have, in some cases, occurred simultaneously with oceanic anoxic events and extinction events . The most important examples are
441-465: A diverse group of large predatory marine reptiles, also became extinct. Fossil evidence indicates that squamates generally suffered very heavy losses in the K–Pg event, only recovering 10 million years after it. The extinction of Cretaceous lizards and snakes may have led to the evolution of modern groups such as iguanas, monitor lizards, and boas. The diversification of crown group snakes has been linked to
588-413: A few species of ground and water fowl, which radiated into all modern species of birds. Among other groups, teleost fish and perhaps lizards also radiated. The K–Pg extinction event was severe, global, rapid, and selective, eliminating a vast number of species. Based on marine fossils, it is estimated that 75% or more of all species became extinct. The event appears to have affected all continents at
735-423: A high proportion of dykes relative to country rocks, particularly when the width of the linear field is less than 100 km. The dykes have a typical width of 20–100 m, although ultramafic dykes with widths greater than 1 km have been reported. Dykes are typically sub-vertical to vertical. When upward flowing (dyke-forming) magma encounters horizontal boundaries or weaknesses, such as between layers in
882-517: A large proportion (>75%) of the total igneous volume has been emplaced. They are dominantly mafic, but also can have significant ultramafic and silicic components, and some are dominated by silicic magmatism." This definition places emphasis on the high magma emplacement rate characteristics of the LIP event and excludes seamounts, seamount groups, submarine ridges and anomalous seafloor crust. The definition has since been expanded and refined, and remains
1029-668: A large slowing of the rate of counterclockwise rotation of Africa. The close correlations between the plate motions suggest that they were both driven by the force of the Réunion plume. When comparing the Na 8 , Fe 8 , and Si 8 contents of the Deccan to other major igneous provinces, the Deccan appears to have undergone the greatest degree of melting suggesting a deep plume origin. Olivine appears to have fractionated at near- Moho depths with additional fractionation of gabbro ~6 km below
1176-534: A period in the earliest part of the Cenozoic of decreased acanthomorph diversity, although acanthomorphs diversified rapidly after the extinction. Teleost fish diversified explosively after the mass extinction, filling the niches left vacant by the extinction. Groups appearing in the Paleocene and Eocene epochs include billfish, tunas, eels, and flatfish. There is limited evidence for extinction of amphibians at
1323-419: A planktonic strategy of reproduction (numerous eggs and planktonic larvae), which would have been devastated by the K–Pg extinction event. Additional research has shown that subsequent to this elimination of ammonoids from the global biota, nautiloids began an evolutionary radiation into shell shapes and complexities theretofore known only from ammonoids. Approximately 35% of echinoderm genera became extinct at
1470-490: A range of different species provide 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. The most successful and dominant group of avialans , enantiornithes , were wiped out. Only a small fraction of ground and water-dwelling Cretaceous bird species survived
1617-527: A result of cooling temperatures in the early Paleocene . 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. The occurrence of planktonic foraminifera across the K–Pg boundary has been studied since the 1930s. Research spurred by the possibility of an impact event at
SECTION 10
#17327725510841764-441: A sedimentary deposit, the magma can flow horizontally creating a sill. Some sill provinces have areal extents >1000 km. A series of related sills that were formed essentially contemporaneously (within several million years) from related dikes comprise a LIP if their area is sufficiently large. Examples include: Volcanic rifted margins are found on the boundary of large igneous provinces. Volcanic margins form when rifting
1911-454: A small phylum of marine invertebrates, survived the K–Pg extinction event and diversified during the early Paleocene. The numbers bivalve genera exhibited significant diminution after the K–Pg boundary. Entire groups of bivalves, including rudists (reef-building clams) and inoceramids (giant relatives of modern scallops ), became extinct at the K–Pg boundary, with the gradual extinction of most inoceramid bivalves beginning well before
2058-500: A solid convective mantle above a liquid core . The mantle's flow is driven by the descent of cold tectonic plates during subduction and the complementary ascent of mantle plumes of hot material from lower levels. The surface of the Earth reflects stretching, thickening and bending of the tectonic plates as they interact. Ocean-plate creation at upwellings, spreading and subduction are well accepted fundamentals of plate tectonics, with
2205-627: A volcanic province), and volcanic rifted margins . Mafic basalt sea floors and other geological products of 'normal' plate tectonics were not included in the definition. Most of these LIPs consist of basalt, but some contain large volumes of associated rhyolite (e.g. the Columbia River Basalt Group in the western United States); the rhyolite is typically very dry compared to island arc rhyolites, with much higher eruption temperatures (850 °C to 1000 °C) than normal rhyolites. Some LIPs are geographically intact, such as
2352-530: A volume of about 1,000,000 cubic kilometres (200,000 cu mi). Originally, the Deccan Traps may have covered about 1,500,000 square kilometres (600,000 sq mi), with a correspondingly larger original volume. This volume overlies the Archean age Indian Shield , which is likely the lithology the province passed through during eruption. The province is commonly divided into four subprovinces:
2499-554: A work in progress. Some new definitions of LIP include large granitic provinces such as those found in the Andes Mountains of South America and in western North America. Comprehensive taxonomies have been developed to focus technical discussions. Sub-categorization of LIPs into large volcanic provinces (LVP) and large plutonic provinces (LPP), and including rocks produced by normal plate tectonic processes, have been proposed, but these modifications are not generally accepted. LIP
2646-400: Is a common geochemical proxy used to detect massive volcanism in the geologic record, although its foolproofness has been called into question. Jameson Land Thulean Plateau Brazilian Highlands These LIPs are composed dominantly of felsic materials. Examples include: These LIPs are comprised dominantly of andesitic materials. Examples include: This subcategory includes most of
2793-462: Is accompanied by significant mantle melting, with volcanism occurring before and/or during continental breakup. Volcanic rifted margins are characterized by: a transitional crust composed of basaltic igneous rocks, including lava flows, sills, dikes, and gabbros , high volume basalt flows, seaward-dipping reflector sequences of basalt flows that were rotated during the early stages of breakup, limited passive-margin subsidence during and after breakup, and
2940-740: Is an extremely large accumulation of igneous rocks , including intrusive ( sills , dikes ) and extrusive ( lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics . The formation of some of the LIPs in the past 500 million years coincide in time with mass extinctions and rapid climatic changes , which has led to numerous hypotheses about causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems. In 1992, Coffin and Eldholm initially defined
3087-537: Is an impact crater suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early Paleogene . However, the current consensus in the Earth science community is that this feature is unlikely to be an actual impact crater. 18°51′N 73°43′E / 18.850°N 73.717°E / 18.850; 73.717 Large igneous province A large igneous province ( LIP )
SECTION 20
#17327725510843234-561: Is associated with subduction zones or mid-oceanic ridges, there are significant regions of long-lived, extensive volcanism, known as hotspots , which are only indirectly related to plate tectonics. The Hawaiian–Emperor seamount chain , located on the Pacific Plate , is one example, tracing millions of years of relative motion as the plate moves over the Hawaii hotspot . Numerous hotspots of varying size and age have been identified across
3381-476: Is clearly marked at the species level. 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 . Major spatial differences existed in calcareous nannoplankton diversity patterns; in the Southern Hemisphere, the extinction was less severe and recovery occurred much faster than in
3528-537: Is estimated that 75% or more of all species on Earth vanished. However, 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 , evolving new forms such as horses , whales , bats , and primates . The surviving group of dinosaurs were avians,
3675-475: Is influenced by a lack of fossil records, rather than extinctions. 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 whether the extinctions occurred prior to, or during,
3822-515: Is marked by a thin layer of sediment called the K–Pg boundary, Fatkito boundary or K–T boundary , which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium , which is more common in asteroids than in the Earth's crust . As originally proposed in 1980 by a team of scientists led by Luis Alvarez and his son Walter , it
3969-494: 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. The growing consensus about
4116-618: Is not now observable. The upper basalt layers of older LIPs may have been removed by erosion or deformed by tectonic plate collisions occurring after the layer is formed. This is especially likely for earlier periods such as the Paleozoic and Proterozoic . Giant dyke swarms having lengths over 300 km are a common record of severely eroded LIPs. Both radial and linear dyke swarm configurations exist. Radial swarms with an areal extent over 2,000 km and linear swarms extending over 1,000 km are known. The linear dyke swarms often have
4263-652: Is now frequently used to also describe voluminous areas of, not just mafic, but all types of igneous rocks. Further, the minimum threshold to be included as a LIP has been lowered to 50,000 km . The working taxonomy, focused heavily on geochemistry, is: Because large igneous provinces are created during short-lived igneous events resulting in relatively rapid and high-volume accumulations of volcanic and intrusive igneous rock, they warrant study. LIPs present possible links to mass extinctions and global environmental and climatic changes. Michael Rampino and Richard Stothers cite 11 distinct flood basalt episodes—occurring in
4410-515: Is now generally thought that the K–Pg extinction was caused by the impact of a massive asteroid 10 to 15 km (6 to 9 mi) wide, 66 million years ago causing the Chicxulub crater , which devastated the global environment, mainly through a lingering impact winter which halted photosynthesis in plants and plankton . The impact hypothesis, also known as the Alvarez hypothesis ,
4557-451: 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. After the K–Pg extinction, mammals evolved to fill the niches left vacant by the dinosaurs. Some research indicates that mammals did not explosively diversify across
Deccan Traps - Misplaced Pages Continue
4704-560: Is postulated that the Deccan Traps eruption was associated with a deep mantle plume . High He/He ratios of the main pulse of the eruption are often seen in magmas with mantle plume origin. The area of long-term eruption (the hotspot ), known as the Réunion hotspot , is suspected of both causing the Deccan Traps eruption and opening the rift that separated the Mascarene Plateau from India. Regional crustal thinning supports
4851-472: Is thought that ammonites were the principal food of mosasaurs , a group of giant marine reptiles that became extinct at the boundary. 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, causing a remarkable amount of species diversification during the Paleogene Period. After
4998-526: Is thought that body sizes of placental mammalian survivors evolutionarily increased first, allowing them to fill niches after the extinctions, with brain sizes increasing later in the Eocene . Plant fossils illustrate the reduction in plant species across the K–Pg boundary. There is overwhelming evidence of global disruption of plant communities at the K–Pg boundary. Extinctions are seen both in studies of fossil pollen, and fossil leaves. In North America,
5145-756: The Baffin Island flood basalt about 60 million years ago. Basalts from the Ontong Java Plateau show similar isotopic and trace element signatures proposed for the early-Earth reservoir. Seven pairs of hotspots and LIPs located on opposite sides of the earth have been noted; analyses indicate this coincident antipodal location is highly unlikely to be random. The hotspot pairs include a large igneous province with continental volcanism opposite an oceanic hotspot. Oceanic impacts of large meteorites are expected to have high efficiency in converting energy into seismic waves. These waves would propagate around
5292-433: The Chicxulub impact was the primary cause of the extinction. While some scholars suggest that the eruptions may have been a contributing factor in the extinctions, others suggest that the role of the Deccan Traps in the extinction may have been negligible or even partially negated the effects of the impact. The Deccan Traps are thought to have been produced in major part by the still active Réunion hotspot , responsible for
5439-518: The Deccan Traps of India were not antipodal to (and began erupting several Myr before) the Chicxulub impact in Mexico. In addition, no clear example of impact-induced volcanism, unrelated to melt sheets, has been confirmed at any known terrestrial crater. Aerally extensive dike swarms , sill provinces, and large layered ultramafic intrusions are indicators of LIPs, even when other evidence
5586-629: 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 . The scientific consensus is that these fossils were eroded from their original locations and then re-buried in much later sediments (also known as reworked fossils ). Most paleontologists regard birds as
5733-458: The molluscan class Cephalopoda became extinct at the K–Pg boundary. These included the ecologically significant belemnoids , as well as the ammonoids , a group of highly diverse, numerous, and widely distributed shelled cephalopods. The extinction of belemnites enabled surviving cephalopod clades to fill their niches. Ammonite genera became extinct at or near the K–Pg boundary; there was a smaller and slower extinction of ammonite genera prior to
5880-451: 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, but 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. Most species of brachiopods ,
6027-459: The Chicxulub peak ring confirmed that the peak ring comprised granite ejected within minutes from deep in the earth, but contained hardly any gypsum , the usual sulfate-containing sea floor rock in the region: the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, causing longer-term effects on the climate and food chain . In October 2019, researchers asserted that
Deccan Traps - Misplaced Pages Continue
6174-522: The Chicxulub event" found in the gills of fish fossils and embedded in amber , an iridium -rich top layer that is considered another signature of the event, and an atypical lack of evidence for scavenging perhaps suggesting that there were few survivors. The exact mechanism of the site's destruction has been debated as either an impact-caused tsunami or lake and river seiche activity triggered by post-impact earthquakes, though there has yet been no firm conclusion upon which researchers have settled. Within
6321-606: The Cretaceous. Along with the aforementioned mosasaurs, plesiosaurs , represented by the families Elasmosauridae and Polycotylidae , became extinct during the event. The ichthyosaurs had disappeared from fossil record tens of millions of years prior to the K-Pg extinction event. Ten families of crocodilians or their close relatives are represented in the Maastrichtian fossil records, of which five died out prior to
6468-665: The Deccan Traps ( Cretaceous–Paleogene extinction event ), the Karoo-Ferrar ( Pliensbachian-Toarcian extinction ), the Central Atlantic magmatic province ( Triassic-Jurassic extinction event ), and the Siberian Traps ( Permian-Triassic extinction event ). Several mechanisms are proposed to explain the association of LIPs with extinction events. The eruption of basaltic LIPs onto the earth's surface releases large volumes of sulfate gas, which forms sulfuric acid in
6615-532: The Deccan Traps at least 95% of the lavas are tholeiitic basalts . Major mineral constituents are olivine , pyroxenes , and plagioclase , as well as certain Fe-Ti-rich oxides. These magmas are <7% MgO. Many of these minerals are observed however, as highly altered forms. Other rock types present include: alkali basalt , nephelinite , lamprophyre , and carbonatite . Mantle xenoliths have been described from Kachchh (northwestern India) and elsewhere in
6762-492: 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. There are fossil records of jawed fishes across the K–Pg boundary, which provide good evidence of extinction patterns of these classes of marine vertebrates. While
6909-606: The Hell Creek Formation shows a minimum of 75% of turtle species survived. Following the extinction event, turtle diversity exceeded pre-extinction levels in the Danian of North America, although in South America it remained diminished. European turtles likewise recovered rapidly following the mass extinction. The rhynchocephalians which were a globally distributed and diverse group of lepidosaurians during
7056-443: The Indian tectonic plate and the eruptive history of the Deccan traps show strong correlations. Based on data from marine magnetic profiles, a pulse of unusually rapid plate motion began at the same time as the first pulse of Deccan flood basalts, which is dated at 67 million years ago. The spreading rate rapidly increased and reached a maximum at the same time as the peak basaltic eruptions. The spreading rate then dropped off, with
7203-548: The Jurassic and continued to diversify throughout the Cretaceous. They are currently the most successful and diverse group of living reptiles, with more than 10,000 extant species. The only major group of terrestrial lizards to go extinct at the end of the Cretaceous were the polyglyphanodontians , a diverse group of mainly herbivorous lizards known predominantly from the Northern Hemisphere. The mosasaurs ,
7350-506: The K-Pg boundary known as the Main Fossiliferous Layer (MFL) containing a thanatocoenosis of disarticulated vertebrate fossils, which was likely also caused by a catastrophic flood from the impact. 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
7497-538: The K–Pg boundary subsequently becoming extinct in the Miocene . The gharial-like choristodere genus Champsosaurus ' palatal teeth suggest that there were dietary changes among the various species across the K–Pg event. More than 80% of Cretaceous turtle species passed through the K–Pg boundary. All six turtle families in existence at the end of the Cretaceous survived into the Paleogene and are represented by living species. Analysis of turtle survivorship in
SECTION 50
#17327725510847644-672: The K–Pg boundary resulted in numerous publications detailing planktonic foraminiferal extinction at the boundary; there is ongoing debate between groups which think the evidence indicates substantial extinction of these species at the K–Pg boundary, and those who think the evidence supports a gradual extinction through the boundary. There is strong evidence that local conditions heavily influenced diversity changes in planktonic foraminifera. Low and mid-latitude communities of planktonic foraminifera experienced high extinction rates, while high latitude faunas were relatively unaffected. Numerous species of benthic foraminifera became extinct during
7791-445: The K–Pg boundary, although taxa that thrived in low-latitude, shallow-water environments during the late Cretaceous had the highest extinction rate. Mid-latitude, deep-water echinoderms were much less affected at the K–Pg boundary. The pattern of extinction points to habitat loss, specifically the drowning of carbonate platforms , the shallow-water reefs in existence at that time, by the extinction event. Atelostomatans were affected by
7938-421: The K–Pg boundary, despite the ecological niches made available by the extinction of dinosaurs. 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 ), although recent research concludes that only marsupial orders diversified soon after
8085-506: The K–Pg boundary. Deposit feeders were the most common bivalves in the catastrophe's aftermath. Abundance was not a factor that affected whether a bivalve taxon went extinct, according to evidence from North America. Veneroid bivalves developed deeper burrowing habitats as the recovery from the crisis ensued. Except for nautiloids (represented by the modern order Nautilida ) and coleoids (which had already diverged into modern octopodes , squids , and cuttlefish ) all other species of
8232-521: The K–Pg boundary. 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. Crocodyliform survivability across
8379-412: The K–Pg boundary. However, morphological diversification rates among eutherians after the extinction event were thrice those of before it. Also significant, within the mammalian genera, new species were approximately 9.1% larger after the K–Pg boundary. After about 700,000 years, some mammals had reached 50 kilos (110 pounds), a 100-fold increase over the weight of those which survived the extinction. It
8526-493: The K–Pg boundary. A study of fossil vertebrates across the K–Pg boundary in Montana concluded that no species of amphibian became extinct. 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 and the albanerpetontid Albanerpeton galaktion ; therefore, some amphibians do seem to have become extinct at
8673-555: 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. Based on molecular sequencing and fossil dating, many species of birds (the Neoaves group in particular) appeared to radiate after the K–Pg boundary. The open niche space and relative scarcity of predators following the K-Pg extinction allowed for adaptive radiation of various avian groups. Ratites , for example, rapidly diversified in
8820-418: The K–Pg event. 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. There
8967-532: The K–Pg extinction event as marine environments were. Among the terrestrial clade Notosuchia , only the family Sebecidae survived; the exact reasons for this pattern are not known. Sebecids were large terrestrial predators, are known from the Eocene of Europe, and would survive in South America into the Miocene. Tethysuchians radiated explosively after the extinction event. Two families of pterosaurs, Azhdarchidae and Nyctosauridae , were definitely present in
SECTION 60
#17327725510849114-663: The K–Pg extinction event, although they suffered losses. In particular, metatherians largely disappeared from North America, and the Asian deltatheroidans became extinct (aside from the lineage leading to Gurbanodelta ). 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. Multituberculates in Europe and North America survived relatively unscathed and quickly bounced back in
9261-496: The K–Pg extinction event, biodiversity required substantial time to recover, despite the existence of abundant vacant ecological niches . Evidence from the Salamanca Formation suggests that biotic recovery was more rapid in the Southern Hemisphere than in the Northern Hemisphere. Despite the massive loss of life inferred to have occurred during the extinction, and a number of geologic formations worldwide that span
9408-522: The LIP-triggered changes may be used as cases to understand current and future environmental changes. Plate tectonic theory explains topography using interactions between the tectonic plates, as influenced by viscous stresses created by flow within the underlying mantle . Since the mantle is extremely viscous, the mantle flow rate varies in pulses which are reflected in the lithosphere by small amplitude, long wavelength undulations. Understanding how
9555-601: The Lilliput effect. Insect damage to the fossilized leaves of flowering plants from fourteen sites in North America was 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, flora were relatively diverse with little predation from insects, even 1.7 million years after
9702-541: The Maastrichtian age, 28 shark families and 13 batoid families thrived, of which 25 and 9, respectively, survived the K–T boundary event. Forty-seven of all neoselachian genera cross the K–T boundary, with 85% being sharks. Batoids display with 15%, a comparably low survival rate. Among elasmobranchs, those species that inhabited higher latitudes and lived pelagic lifestyles were more likely to survive, whereas epibenthic lifestyles and durophagy were strongly associated with
9849-417: The Maastrichtian, and they likely became extinct at the K–Pg boundary. Several other pterosaur lineages may have been present during the Maastrichtian, such as the ornithocheirids , pteranodontids , a possible tapejarid , a possible thalassodromid and a basal toothed taxon of uncertain affinities, though they are represented by fragmentary remains that are difficult to assign to any given group. While this
9996-604: The Northern Hemisphere. Following the extinction, survivor communities dominated for several hundred thousand years. The North Pacific acted as a diversity hotspot from which later nannoplankton communities radiated as they replaced survivor faunas across the globe. 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. Recent studies indicate that there were no major shifts in dinoflagellates through
10143-447: The Paleocene, but Asian forms were devastated, never again to represent a significant component of mammalian fauna. A recent study indicates that metatherians suffered the heaviest losses at the K–Pg event, followed by multituberculates, while eutherians recovered the quickest. 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. It
10290-548: The adaptations of many dinosaurs to cold environments. Whether the extinction occurred gradually or suddenly has been debated, as both views have support from the fossil record. A highly informative sequence of dinosaur-bearing rocks from the K–Pg boundary is found in western North America, particularly the late Maastrichtian-age Hell Creek Formation of Montana . Comparison with the older Judith River Formation (Montana) and Dinosaur Park Formation ( Alberta ), which both date from approximately 75 Ma, provides information on
10437-461: The asteroid impact and not volcanism . A wide range of terrestrial species perished in the K–Pg extinction, the best-known being the non-avian dinosaurs, along with many mammals, birds, lizards, insects , plants, and all the pterosaurs . In the oceans, the K–Pg extinction killed off plesiosaurs and mosasaurs and devastated teleost fish, sharks , mollusks (especially ammonites , which became extinct), and many species of plankton. It
10584-552: The atmosphere; this absorbs heat and causes substantial cooling (e.g., the Laki eruption in Iceland, 1783). Oceanic LIPs can reduce oxygen in seawater by either direct oxidation reactions with metals in hydrothermal fluids or by causing algal blooms that consume large amounts of oxygen. Large igneous provinces are associated with a handful of ore deposit types including: Enrichment in mercury relative to total organic carbon (Hg/TOC)
10731-794: The basaltic Deccan Traps in India, while others have been fragmented and separated by plate movements, like the Central Atlantic magmatic province —parts of which are found in Brazil, eastern North America, and northwestern Africa. In 2008, Bryan and Ernst refined the definition to narrow it somewhat: "Large Igneous Provinces are magmatic provinces with areal extents > 1 × 10 km , igneous volumes > 1 × 10 km and maximum lifespans of ~50 Myr that have intraplate tectonic settings or geochemical affinities, and are characterised by igneous pulse(s) of short duration (~1–5 Myr), during which
10878-484: The beds of fossils that have been found between layers of lava. Particularly well known species include the frog Oxyglossus pusillus (Owen) of the Eocene of India and the toothed frog Indobatrachus , an early lineage of modern frogs, which is now placed in the Australian family Myobatrachidae . The Infratrappean Beds (Lameta Formation) and Intertrappean Beds also contain fossil freshwater molluscs . It
11025-402: The biotic recovery in the aftermath of the K-Pg extinction event. Pan-Gekkotans weathered the extinction event well, with multiple lineages likely surviving. ∆ Ca values indicate that prior to the mass extinction, marine reptiles at the top of food webs were feeding on only one source of calcium, suggesting their populations exhibited heightened vulnerability to extinctions at the terminus of
11172-402: The boundary associated with a late Cretaceous marine regression, and a small, gradual reduction in ammonite diversity occurred throughout the very late Cretaceous. Researchers have pointed out that the reproductive strategy of the surviving nautiloids, which rely upon few and larger eggs, played a role in outsurviving their ammonoid counterparts through the extinction event. The ammonoids utilized
11319-495: The boundary interval. Ostracods that were heavily sexually selected were more vulnerable to extinction, and ostracod sexual dimorphism was significantly rarer following the mass extinction. Among decapods , extinction patterns were highly heterogeneous and cannot be neatly attributed to any particular factor. Decapods that inhabited the Western Interior Seaway were especially hard-hit, while other regions of
11466-498: The boundary layer. There were blooms of the taxa Thoracosphaera operculata and Braarudosphaera bigelowii at the boundary. 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
11613-450: The boundary may have resulted from their aquatic niche and ability to burrow, which reduced susceptibility to negative environmental effects at the boundary. 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
11760-780: The boundary, only a few fossil sites contain direct evidence of the mass mortality that occurred exactly at the K-Pg boundary. These include the Tanis site of the Hell Creek Formation in North Dakota , USA, which contains a high number of well-preserved fossils that appear to have buried in a catastrophic flood event that was likely caused by the impact. Another important site is the Hornerstown Formation in New Jersey , USA, which has prominent layer at
11907-418: The boundary. The relatively low levels of extinction seen among amphibians probably reflect the low extinction rates seen in freshwater animals. Following the mass extinction, frogs radiated substantially, with 88% of modern anuran diversity being traced back to three lineages of frogs that evolved after the cataclysm. The choristoderes (a group of semi-aquatic diapsids of uncertain position) survived across
12054-487: 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. 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 , which suggests food
12201-438: The circumstances of food chain disruption previously mentioned, non-avian dinosaurs died out, while some crocodiles survived. In this context, the survival of other endothermic animals, such as some birds and mammals, could be due, among other reasons, to their smaller needs for food, related to their small size at the extinction epoch. Prolonged cold is unlikely to have been a reason for the extinction of non-avian dinosaurs given
12348-471: The core; roughly 15–20% have characteristics such as presence of a linear chain of sea mounts with increasing ages, LIPs at the point of origin of the track, low shear wave velocity indicating high temperatures below the current location of the track, and ratios of He to He which are judged consistent with a deep origin. Others such as the Pitcairn , Samoan and Tahitian hotspots appear to originate at
12495-530: The creation of the modern Mascarene Islands in the Indian Ocean. The term trap has been used in geology since 1785–1795 for such rock formations . It is derived from the Swedish word for stairs ( trapp ) and refers to the step-like hills forming the landscape of the region. The name Deccan has Sanskrit origins meaning "southern". The Deccan Traps began forming 66.25 million years ago , at
12642-404: The current consensus among the scientific community is that the extinction was primarily triggered by the Chicxulub impact event in North America, which would have produced a sunlight-blocking dust cloud that killed much of the plant life and reduced global temperature (this cooling is called an impact winter ). A 2014 study suggested the extinction may have been caused by both the volcanism and
12789-423: 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. 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
12936-413: The decrease occurring around 63 million years ago, by which time the main phase of Deccan volcanism ended. This correlation is seen as driven by plume dynamics. The motions of the Indian and African plates have also been shown to be coupled, the common element being the position of these plates relative to the location of the Réunion plume head. The onset of accelerated motion of India coincides with
13083-498: 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. In
13230-530: The destruction from the impact alone, however. In a March 2019 article in the Proceedings of the National Academy of Sciences , an international team of twelve scientists revealed the contents of the Tanis fossil site discovered near Bowman, North Dakota , that appeared to show a devastating mass destruction of an ancient lake and its inhabitants at the time of the Chicxulub impact. In the paper,
13377-643: The early Mesozoic , had begun to decline by the mid-Cretaceous, although they remained successful in the Late Cretaceous of southern South America . They are represented today by a single species, the tuatara ( Sphenodon punctatus ) found in New Zealand . Outside of New Zealand, one rhynchocephalian is known to have crossed the K-Pg boundary, Kawasphenodon peligrensis , known from the earliest Paleocene (Danian) of Patagonia. The order Squamata comprising lizards and snakes first diversified during
13524-422: The early Paleocene provided the food source to support large benthic foraminiferal assemblages, which are mainly detritus-feeding. Ultimate recovery of the benthic populations occurred over several stages lasting several hundred thousand years into the early Paleocene. There is significant variation in the fossil record as to the extinction rate of marine invertebrates across the K–Pg boundary. The apparent rate
13671-630: The early Paleogene and are believed to have convergently developed flightlessness at least three to six times, often fulfilling the niche space for large herbivores once occupied by non-avian dinosaurs. Mammalian species began diversifying approximately 30 million years prior to the K–Pg boundary. Diversification of mammals stalled across the boundary. All major Late Cretaceous mammalian lineages, including monotremes (egg-laying mammals), multituberculates , metatherians (which includes modern marsupials), eutherians (which includes modern placentals), meridiolestidans , and gondwanatheres survived
13818-474: The end of the Cretaceous period, although it is possible that some of the oldest material may underlie younger material. The bulk of the volcanic eruption occurred at the Western Ghats between 66 and 65 million years ago when lava began to extrude through fissures in the crust known as fissure eruptions. Determining the exact age for Deccan rock is difficult due to a number of limitations, one being that
13965-642: The end of the Cretaceous and underwent sudden extinction after the Cretaceous–Paleogene extinction event. 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
14112-405: The endothermy of dinosaurs (see dinosaur physiology ) helps to understand their full extinction in contrast with their close relatives, the crocodilians. Ectothermic ("cold-blooded") crocodiles have very limited needs for food (they can survive several months without eating), while endothermic ("warm-blooded") animals of similar size need much more food to sustain their faster metabolism. Thus, under
14259-458: The event rapidly acidified the oceans and produced long-lasting effects on the climate, detailing the mechanisms of the mass extinction. Other causal or contributing factors to the extinction may have been the Deccan Traps and other volcanic eruptions, climate change , and sea level change. However, in January 2020, scientists reported that climate-modeling of the extinction event favored
14406-422: 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. Omnivores , insectivores , and carrion -eaters survived
14553-409: The event, presumably because they depend on organic debris for nutrients, while biomass in the ocean is thought to have decreased. As the marine microbiota recovered, it is thought that increased speciation of benthic foraminifera resulted from the increase in food sources. In some areas, such as Texas, benthic foraminifera show no sign of any major extinction event, however. Phytoplankton recovery in
14700-449: The extinction event is best represented by the marked discrepancy between the rich and relatively abundant late-Maastrichtian pollen record and the post-boundary fern spike. 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
14847-586: The extinction event, perhaps because of the increased availability of their food sources. Neither strictly herbivorous nor strictly 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). In stream communities and lake ecosystems , few animal groups became extinct, including large forms like crocodyliforms and champsosaurs , because such communities rely less directly on food from living plants, and more on detritus washed in from
14994-471: The extinction event. Studies of the size of the ichnotaxon Naktodemasis bowni , produced by either cicada nymphs or beetle larvae, over the course of the K-Pg transition show that the Lilliput effect occurred in terrestrial invertebrates thanks to the extinction event. The extinction event produced major changes in Paleogene insect communities. Many groups of ants were present in the Cretaceous, but in
15141-461: The extinction of all non-avian dinosaurs . Most other tetrapods weighing more than 25 kg (55 lb) also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians . It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the current era, the Cenozoic . In the geologic record , the K–Pg event
15288-526: The gases released during the formation of the Deccan Traps played a major role in the Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary or K–T extinction). It has been theorized that sudden cooling due to sulfurous volcanic gases released by the formation of the traps and toxic gas emissions may have contributed significantly to the K–Pg mass extinction. However,
15435-618: The group reports that the geology of the site is strewn with fossilized trees and remains of fish and other animals. The lead researcher, Robert A. DePalma of the University of Kansas , was quoted in the New York Times as stating that "You would be blind to miss the carcasses sticking out... It is impossible to miss when you see the outcrop". Evidence correlating this find to the Chicxulub impact included tektites bearing "the unique chemical signature of other tektites associated with
15582-414: The impact event. This was followed by a similar study in 2015, both of which consider the hypothesis that the impact exacerbated or induced the Deccan volcanism, since the events occurred approximately at antipodes . A 2020 study questioned the idea that the Deccan Traps were a contributory factor at all, suggesting that the Deccan Traps eruptions may have even partially negated the climatic change induced by
15729-467: The impact, giving rise to today's birds. The only bird group known for certain to have survived the K–Pg boundary is the Aves. 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
15876-399: The impact. A major criticism of the Deccan Traps as the primary cause of the extinctions is that the extinction event appears to be globally geologically instantaneous and simultaneous in both marine and terrestrial environments, as would be expected from an impact cause, rather than staggered as would be expected from an LIP cause. A more recent discovery appears to demonstrate the scope of
16023-401: The interaction between mantle flow and lithosphere elevation influences formation of LIPs is important to gaining insights into past mantle dynamics. LIPs have played a major role in the cycles of continental breakup, continental formation, new crustal additions from the upper mantle , and supercontinent cycles . Earth has an outer shell made of discrete, moving tectonic plates floating on
16170-414: The land, protecting them from extinction. Modern crocodilians can live as scavengers and survive for months without food, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms for their first few years. These characteristics have been linked to crocodilian survival at the end of the Cretaceous. Similar, but more complex patterns have been found in the oceans. Extinction
16317-493: The landscape for centuries after the event. 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. 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. In North American terrestrial sequences,
16464-411: The large-scale plate tectonic circulation in which they are imbedded. Images reveal continuous but convoluted vertical paths with varying quantities of hotter material, even at depths where crystallographic transformations are predicted to occur. A major alternative to the plume model is a model in which ruptures are caused by plate-related stresses that fractured the lithosphere, allowing melt to reach
16611-412: The likelihood of perishing during the extinction event. 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; the marine and freshwater environments of fishes mitigated the environmental effects of the extinction event. The result was Patterson's Gap,
16758-457: The lower efficiency of kinetic energy conversion into seismic energy is not expected to create an antipodal hotspot. A second impact-related model of hotspot and LIP formation has been suggested in which minor hotspot volcanism was generated at large-body impact sites and flood basalt volcanism was triggered antipodally by focused seismic energy. This model has been challenged because impacts are generally considered seismically too inefficient, and
16905-673: The main Deccan, the Malwa Plateau , the Mandla Lobe, and the Saurashtran Plateau. The eruptions occurred over a 600–800,000 year time period between around 66.3 to 65.6 million years ago, spanning the Cretaceous–Paleogene boundary . While some authors have suggested that the eruptions were the primary cause of the Cretaceous–Paleogene mass extinction event , which dates to around 66.05 million years ago, this has been strongly disputed, with many authors suggesting that
17052-444: The number of flowering plants. However, phylogenetic evidence shows no mass angiosperm extinction. 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
17199-426: 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 . 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. Large collections of bird fossils representing
17346-564: The order of 1 million cubic kilometers. In most cases, the majority of a basaltic LIP's volume is emplaced in less than 1 million years. One of the conundra of such LIPs' origins is to understand how enormous volumes of basaltic magma are formed and erupted over such short time scales, with effusion rates up to an order of magnitude greater than mid-ocean ridge basalts. The source of many or all LIPs are variously attributed to mantle plumes, to processes associated with plate tectonics or to meteorite impacts. Although most volcanic activity on Earth
17493-410: The overall flow volume. It can be difficult, however, to locate the largest dikes as they are often located towards the west coast and are therefore believed to currently reside under water. Although the Deccan Traps began erupting well before the impact , in a 2015 study it was proposed based on argon–argon dating that the impact may have caused an increase in permeability that allowed magma to reach
17640-603: The past 250 million years—which created volcanic provinces and oceanic plateaus and coincided with mass extinctions. This theme has developed into a broad field of research, bridging geoscience disciplines such as biostratigraphy , volcanology , metamorphic petrology , and Earth System Modelling . The study of LIPs has economic implications. Some workers associate them with trapped hydrocarbons. They are associated with economic concentrations of copper–nickel and iron. They are also associated with formation of major mineral provinces including platinum group element deposits and, in
17787-558: The presence of a lower crust with anomalously high seismic P-wave velocities in lower crustal bodies, indicative of lower temperature, dense media. The early volcanic activity of major hotspots, postulated to result from deep mantle plumes, is frequently accompanied by flood basalts. These flood basalt eruptions have resulted in large accumulations of basaltic lavas emplaced at a rate greatly exceeding that seen in contemporary volcanic processes. Continental rifting commonly follows flood basalt volcanism. Flood basalt provinces may also occur as
17934-493: The provinces included in the original LIP classifications. It is composed of continental flood basalts, oceanic flood basalts, and diffuse provinces. Cretaceous%E2%80%93Paleogene extinction event The Cretaceous–Paleogene ( K–Pg ) extinction event , also known as the K–T extinction , was the mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event caused
18081-489: The relative abundance of plant groups. European flora was also less affected, most likely due to its distance from the site of the Chicxulub impact. In northern Alaska and the Anadyr-Koryak region of Russia, the flora was minimally impacted. Another line of evidence of a major floral extinction is that the divergence rate of subviral pathogens of angiosperms sharply decreased, which indicates an enormous reduction in
18228-494: The same assessment following their research. Several researchers support the existence of Paleocene non-avian 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. Pollen samples recovered near a fossilized hadrosaur femur recovered in the Ojo Alamo Sandstone at
18375-531: The same time. Non-avian dinosaurs , for example, are known from the Maastrichtian of North America, Europe , Asia, Africa , South America, and Antarctica , 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 . Nevertheless, high latitudes appear to have been less strongly affected than low latitudes. Despite
18522-500: The sequence of events in Deccan extrusion, it is now more widely accepted that these horizons relate more closely to paleo topography and distance from the eruption site. The release of volcanic gases , particularly sulfur dioxide , during the formation of the traps may have contributed to climate change . An average drop in temperature of about 2 °C (3.6 °F) was recorded during this period. Because of its magnitude, some scientists (notably Gerta Keller ) have speculated that
18669-407: The silicic LIPs, silver and gold deposits. Titanium and vanadium deposits are also found in association with LIPs. LIPs in the geological record have marked major changes in the hydrosphere and atmosphere , leading to major climate shifts and maybe mass extinctions of species. Some of these changes were related to rapid release of greenhouse gases from the lithosphere to the atmosphere. Thus
18816-464: The size of modern India . The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 500,000 km (200,000 sq mi). The Deccan Traps are segmented into three stratigraphic units: the Upper, Middle, and Lower traps. While it was previously interpreted that these groups represented their own key points in
18963-464: The suggestion as being "convenient interpretations based on superficial and cursory observations." A geological structure that exists in the sea floor off the west coast of India has been suggested as a possible impact crater, in this context called the Shiva crater . It was also dated approximately 66 million years ago, potentially matching the Deccan traps. The researchers claiming that this feature
19110-412: The surface and produced the most voluminous flows, accounting for around 70% of the volume. The combination of the asteroid impact and the resulting increase in eruptive volume may have been responsible for the mass extinctions that occurred at the time that separates the Cretaceous and Paleogene periods, known as the K–Pg boundary . However this proposal has been questioned by other authors, who describe
19257-465: The surface from shallow heterogeneous sources. The high volumes of molten material that form the LIPs is postulated to be caused by convection in the upper mantle, which is secondary to the convection driving tectonic plate motion. It has been proposed that geochemical evidence supports an early-formed reservoir that survived in the Earth's mantle for about 4.5 billion years. Molten material is postulated to have originated from this reservoir, contributing
19404-432: The surface topography. The convective circulation drives up-wellings and down-wellings in Earth's mantle that are reflected in local surface levels. Hot mantle materials rising up in a plume can spread out radially beneath the tectonic plate causing regions of uplift. These ascending plumes play an important role in LIP formation. When created, LIPs often have an areal extent of a few million square kilometers and volumes on
19551-404: The surface. Features such as widespread faulting , frequent diking events, high heat flux, and positive gravity anomalies suggest that the extrusive phase of the Deccan Traps is associated with the existence of a triple junction which may have existed during the Late Cretaceous, having been caused by a deep mantle plume. Not all of these diking events are attributed to large-scale contributions to
19698-458: The term "large igneous province" as representing a variety of mafic igneous provinces with areal extent greater than 100,000 km that represented "massive crustal emplacements of predominantly mafic (magnesium- and iron-rich) extrusive and intrusive rock, and originated via processes other than 'normal' seafloor spreading." That original definition included continental flood basalts , oceanic plateaus , large dike swarms (the eroded roots of
19845-482: The theory of this rifting event and likely encouraged the rise of the plume in this area. Seafloor spreading at the boundary between the Indian and African Plates subsequently pushed India north over the plume, which now lies under Réunion island in the Indian Ocean , southwest of India. The mantle plume model has, however, been challenged. Data continues to emerge that supports the plume model. The motion of
19992-472: The top of large, transient, hot lava domes (termed superswells) in the mantle. The remainder appear to originate in the upper mantle and have been suggested to result from the breakup of subducting lithosphere. Recent imaging of the region below known hotspots (for example, Yellowstone and Hawaii) using seismic-wave tomography has produced mounting evidence that supports relatively narrow, deep-origin, convective plumes that are limited in region compared to
20139-488: The transition between eruption events may have lasted only a few thousand years and the resolution of dating methods isn't sufficient to pinpoint these events. In this way, determining the rate of magma emplacement is also difficult to constrain. This series of eruptions may have lasted for less than 30,000 years. The original area covered by the lava flows is estimated to have been as large as 1.5 million km (0.58 million sq mi), approximately half
20286-399: The upwelling of hot mantle materials and the sinking of the cooler ocean plates driving the mantle convection. In this model, tectonic plates diverge at mid-ocean ridges , where hot mantle rock flows upward to fill the space. Plate-tectonic processes account for the vast majority of Earth's volcanism . Beyond the effects of convectively driven motion, deep processes have other influences on
20433-433: The western Deccan and contain spinel lherzolite and pyroxenite constituents. While the Deccan traps have been categorized in many different ways including the three different stratigraphic groups, geochemically the province can be split into as many as eleven different formations. Many of the petrologic differences in these units are a product of varying degrees of crustal contamination. The Deccan Traps are famous for
20580-399: The world and reconverge close to the antipodal position; small variations are expected as the seismic velocity varies depending upon the route characteristics along which the waves propagate. As the waves focus on the antipodal position, they put the crust at the focal point under significant stress and are proposed to rupture it, creating antipodal pairs. When the meteorite impacts a continent,
20727-597: The world's oceans were refugia that increased chances of survival into the Palaeocene. Among retroplumid crabs, the genus Costacopluma was a notable survivor. Approximately 60% of late-Cretaceous scleractinian 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
20874-415: The world. These hotspots move slowly with respect to one another but move an order of magnitude more quickly with respect to tectonic plates, providing evidence that they are not directly linked to tectonic plates. The origin of hotspots remains controversial. Hotspots that reach the Earth's surface may have three distinct origins. The deepest probably originate from the boundary between the lower mantle and
21021-457: Was bolstered by the discovery of the 180 km (112 mi) Chicxulub crater in the Gulf of Mexico 's Yucatán Peninsula in the early 1990s, which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact . The fact that the extinctions occurred simultaneously provides strong evidence that they were caused by the asteroid. A 2016 drilling project into
21168-527: Was more severe among animals living in the water column than among animals living on or in the sea floor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton , while animals on the ocean floor always or sometimes feed on detritus. Coccolithophorids and mollusks (including ammonites , rudists , freshwater snails , and mussels ), and those organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, it
21315-480: 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, but there is no correlation between pterosaur and avian diversities that are conclusive to a competition hypothesis, and small pterosaurs were present in the Late Cretaceous. At least some niches previously held by birds were reclaimed by pterosaurs prior to
21462-614: Was plentiful immediately prior to the extinction. 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. More recent research indicates that this figure is obscured by taphonomic biases 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
21609-428: Was present. Once the atmosphere cleared photosynthetic organisms returned – initially ferns and other ground-level plants. 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 . Just two species of fern appear to have dominated
#83916