Ajoy K. Geology ; 19 5 : — A basalt lava flow from the lowermost horizon yields an age of Shibboleth Sign In. OpenAthens Sign In. Institutional Sign In. Sign In or Create an Account. User Tools. Sign In.
Impact or eruptions: Are both to blame in the great end-Cretaceous whodunit?
Plants and the K—T Boundary. Its impact on plant life appears to have been of a much lesser magnitude. The authors, both on the staff of the Denver Museum of Nature and Science, have published extensively on fossil plants of Tertiary and Cretaceous age. Nichols has been mainly concerned with the palynology the microfossil record , while Johnson has concentrated on leaf assemblages megafossils of this age span. The Alvarez father-and-son team argued that the cause of the peak occurrence of that element was the result of the impact of an extra-terrestrial body.
The diverse and disastrous consequences of such an impact were, they claimed, the most likely cause for the extinctions occurring at the close of the Cretaceous Period the K—T boundary.
Using a high-precision dating technique on tektites—pebble-sized the Cretaceous and Tertiary periods—the so-called KT boundary—when.
Scientists from the Berkeley Geochronology Centre University of California , in co-operation with colleagues from Glasgow University and Vrije University Amsterdam, Holland , have concluded that an asteroid, meteorite or possibly even an object such as a comet collided with the Earth approximately Although this single event may not have been the cause of the mass extinction, the scientists conclude that if the extraterrestrial impact was not wholly responsible, it would have contributed significantly to the global extinction event.
Based on the dateline evidence that the team established, the impact of a large extraterrestrial object in the Gulf of Mexico area could have proved to have been the final blow that saw off the Dinosauria, marine reptiles and Pterosaurs. It was father and son Luis and Walter Alvarez who first published a theory , stating that a thin layer of clay enriched with the rare Earth element iridium found at the boundary between Uppermost Cretaceous strata and younger Cenozoic deposits marked the impact of a large, extraterrestrial object.
It was these two American scientists who first claimed that this was evidence of a meteorite or some other object from outer space colliding with the Earth. Although the American scientists did not know where the impact actually occurred. This was resolved when the Chicxulub crater, a geological feature that had been first identified in the s, was more thoroughly examined in the s and it was established that this feature had been created around the time of the end of the Cretaceous.
The K/T Extinction Reading Assignment
All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe.
In the San Juan Basin, 40Ar/39Ar dating of sanidine crystals from altered the K-T interface in the basin, and the magnetochron reversal boundaries from those.
A dating success story: genomes and fossils converge on placental mammal origins
Detection of a new form of carbon in volcanic rock samples from Anjar town in Gujarat in western India has revived the debate on what killed the dinosaurs. Dinosaurs and almost 80 per cent of Earth’s other organisms were wiped out 65 million ears ago at the so-called K-T boundary KTB that marks the end of Cretaceous K , and beginning of Tertiary T periods in the geological calendar. Some say it was the result of extraterrestrial objects hitting the earth, a theory originally proposed by the Nobel physicist Luis Alvarez.
The KT boundary and mass extinction was first discovered based on planktic foraminifera from volcanic eruptions based on 40K/40Ar and 40Ar/39Ar dating.
The Cretaceous—Paleogene K—Pg boundary , formerly known as the Cretaceous—Tertiary K-T boundary , [a] is a geological signature , usually a thin band of rock. K , the first letter of the German word Kreide chalk , is the traditional abbreviation for the Cretaceous Period and Pg is the abbreviation for the Paleogene Period. Its age is usually estimated at around 66 Ma million years ago ,  with radiometric dating yielding a more precise age of The K—Pg boundary is associated with the Cretaceous—Paleogene extinction event , a mass extinction which destroyed a majority of the world’s Mesozoic species, including all dinosaurs except for birds.
Strong evidence exists that the extinction coincided with a large meteorite impact at the Chicxulub crater and the generally accepted scientific theory is that this impact triggered the extinction event. In , 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 K—Pg boundary contain a concentration of iridium many times greater than normal 30 times the average crustal content in Italy and times at Stevns on the Danish island of Zealand.
As iridium remains are abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K—Pg boundary. Shocked quartz granules and tektite glass spherules, indicative of an impact event, are also common in the K—Pg boundary, especially in deposits from around the Caribbean.
All of these constituents are embedded in a layer of clay, which the Alvarez team interpreted as the debris spread all over the world by the impact. Using estimates of the total amount of iridium in the K—Pg layer, and assuming that the asteroid contained the normal percentage of iridium found in chondrites , the Alvarez team went on to calculate the size of the asteroid. One of the consequences of such an impact is a dust cloud which would block sunlight and inhibit photosynthesis for a few years.
This would account for the extinction of plants and phytoplankton and of organisms dependent on them including predatory animals as well as herbivores.
Asteroid may have killed dinosaurs quicker than scientists thought
This boundary layer is well marked and recognized world-wide and has been long known to mark one of the largest mass extinctions in the fossil record. What has always clearly marked this boundary layer is the fossils above and below. In the younger, Tertiary sediments, there are only tiny, less ornate foraminifera. Other creatures, prominently the ammonites, the fish of the oceans except they are cephalopods like the octopus and the chambered nautilus in the Paleozoic and Mesozoic Eras, some to 65 million years ago, abruptly disappeared.
And of course, the terrible reptiles, the dinosaurs, disappeared from the face of the Earth.
The Cretaceous/Tertiary boundary that marks the end of the Mesozoic and the beginning of the Cenozoic had been dated to around
Few episodes in geologic history are as widely recognized as the Cretaceous-Paleogene, or K-Pg, boundary 66 million years ago. Mention it to science-interested laymen, meanwhile, and they may conjure images of tyrannosaurs peering over their shoulders in anguish as they flee from streaking meteors. These catastrophic events make for a compelling and, aside from artistic liberties taken in some recountings, mostly truthful tale. Paleontologists have long recognized from the fossil record that more than half of the species inhabiting Earth perished at the end of the Mesozoic — the most emblematic of course being the remaining nonavian dinosaurs, like T.
Possibly totaling more than 1 million cubic kilometers, these lava flows — known as the Deccan Traps — erupted over several million years, beginning before and ending after the mass extinction. The debate over the cause of the K-Pg extinction has continued to simmer through the years, boiling over at times as proponents of each explanation traded barbs in the literature and at scientific meetings.
However, improvements in rock-dating techniques and in understanding the complex and sprawling stratigraphy of the Deccan Traps and the Chicxulub impact deposits have offered the clearest views yet of the timeline of events. Shoring up this critical part of the story would be a major step, scientists say, in revising our perception of this extraordinary episode in Earth history.
Fossil records of marine plankton and terrestrial plants suggest that, in the last million years or so of the Cretaceous, the warm global climate that prevailed through the period was cooling in fits and spurts: Earth experienced a series of brief cold snaps, with average annual temperature swings of 2 to 8 degrees Celsius possibly accompanied by large sea-level fluctuations.
In addition to the dinosaurs, many other large land animals and terrestrial plants, as well as marine reptiles, mollusks and numerous ocean-dwelling microorganisms, succumbed. Other evidence from the geologic record also points to a major disturbance on Earth at about the same time as this huge pulse of extinction: A sudden shift in carbon isotopic ratios and a decrease in the amount of calcite observed in marine sediment cores indicate drastic drops in biological productivity and carbonate sedimentation in the oceans — markers traditionally taken to define the K-Pg boundary.
At certain locations on land, layers of sediment enriched in iridium and other rare metals, as well as bits of shocked quartz and droplet-shaped particles called tektites — which form when melted rock resolidifies quickly as it flies through the air — indicate that something big struck the planet around the same time that the extinctions were occurring. The position and inferred age of the crater — named after Chicxulub Puerto, the coastal town near its center — matched up with the patterns and timing of fallout observed at Gubbio and a host of other such sites.
Maybe the global climate changed, maybe they were killed by disease, volcanoes, or the rise of mammals. It was this event that pushed the dinosaurs over the edge into extinction. A thin dark line found in layers of sediment around the world; evidence that something devastating happened to the planet 65 million years ago. This line is known as the K-T boundary. What is the K-T boundary? K is actually the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period.
KT boundary exposure in Trinidad Lake State Park It is also known as the K-T extinction event and its geological signature as the K-T boundary (“K” is the traditional This dating is based on evidence collected in Northeast Mexico, detailing.
You may print out a copy for personal or educational use, and you may link to this site. Illustrations are missing from this Web version of the chapter. Cowen, R. History of Life. Blackwell Scientific Publications, Cambridge, Massachusetts. This is a freshman-level textbook published by Blackwell Science. Copyright Richard Cowen Information and updates on the 3rd edition.
See also a separate essay devoted to the general topic of major extinctions , and for an outline of Richard Cowen’s oral presentation. Updates and Web links for the essay on Extinction New references on Extinction that have appeared since History of Life was published. Paleontology in the News : Web pages of current interest. The End of the Dinosaurs: The K-T extinction Almost all the large vertebrates on Earth, on land, at sea, and in the air all dinosaurs, plesiosaurs, mosasaurs, and pterosaurs suddenly became extinct about 65 Ma, at the end of the Cretaceous Period.
At the same time, most plankton and many tropical invertebrates, especially reef-dwellers, became extinct, and many land plants were severely affected. This extinction event marks a major boundary in Earth’s history, the K-T or Cretaceous-Tertiary boundary, and the end of the Mesozoic Era.