This impact hypothesis is known as the Alvarez hypothesis as it was put forward by Luis Alvarez and his team of scientists. This discovery provided conclusive evidence that the thin layer known as the KT boundary extinction event geologic characteristic consisting of iridium containing sediments represented the debris from the asteroid impact.
The mass extinction of the various species can be attributed to the KT mass extinction as they occurred simultaneously following the asteroid impact, and hence can be said to have been caused by the asteroid. During the drilling of Chicxulub peak ring it was confirmed that the peak ring consists of granite that must have ejected from deep inside the earth within a few minutes of the asteroid impact.
Some other factors that might have contributed to the extinction may have been the Deccan Traps and other volcanic eruptions, climate changes and changes in the sea level. Almost three quarters of the species went extinct. Of the wide range of extinctions during the KT dinosaur extinction of non-avian category is the best known extinction event. Along with the KT line dinosaur other myriad organisms like the terrestrial organisms which include mammals, birds, lizards, insects, plants and also the pterosaurs.
The KT boundary mass extinction was not limited to only the terrestrial species as mass extinction were also observed in oceanic organisms such as plesiosaurs, mosasaurs, teleost fish, sharks, mollusks and many other species of planktons.
Because of the dramatic changes in the conditions and the ample resource opportunities, many groups of living organisms underwent adaptive radiation i. Many of the species grew within the ecosystems that had been disrupted. After the loss of life due to KT boundary mass extinction, mammals diversified during the Paleogene period and many life forms evolved such as horses, whales, bats and primates.
The surviving avian dinosaur species diversified and radiated into the modern into all of the modern species of birds. Most of the evidence relating to the period of KT or K-Pg Boundary and the extinction events have been found from the North American continent. It involves two major pieces of evidence - the dinosaur fossils and the evidence of plant remains.
Currently major information regarding the dinosaur extinction and the fossils surrounding it are found in the western region of North America. Fossil beds located at Hell Creek Formation of Montana, Judith River Formation in Montana, and the Dinosaur Park Formation in Alberta, provide information about the last 10 million years of Cretaceous helping in describing the change in the dinosaur species.
The middle-late Campanian formations provide information about the diversity of the dinosaur species. The late Maastrichtian rocks at Hell Creek Formation show fossils that provide evidence of largest members of major dinosaur clades such as - Tyrannosaurus, Ankylosaurus, Triceratops, Pachycephalosaurus, and Torosaurus indicating that the food was more than enough right before the extinction.
Strong evidence comes from the rich and abundant pollen records before the extinction and the rise of the ferns post the extinction event. The sediments of the plant fossils such as the pollen grains and others around the extinction event are also indicative of the event taking place.
For example, the geological layer with plant remains that belong to the time before the event shows pollen grains from angiosperms which is a higher class of plant life.
The layer of sediments after the event show more and more fern spores. The availability of fern spores in large amounts show that ferns must have grown in abundance and they are the primary forms of vegetation that grows right after an extreme or blighting incident. They must have grown in the areas that had seen volcanic eruptions, and while studying the geologic layers it is found that there is a gradual increase in the plant remains from fern spores to pollen grains released by higher angiosperms.
Another evidence is also available from the mass extinction event. The vanishing of the planktons, an integral part of marine life, abruptly and right at the KT boundary mass extinction. Similarly the extinction of ammonite genera near the K-Pg boundary also is a sample of the effects on marine life. 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. The K-T extinctions were worldwide, affecting all the major continents and oceans.
There are still arguments about just how short the event was. It was certainly sudden in geological terms and may have been catastrophic by anyone's standards. Despite the scale of the extinctions, however, we must not be trapped into thinking that the K-T boundary marked a disaster for all living things. Most groups of organisms survived.
Insects, mammals, birds, and flowering plants on land, and fishes, corals, and molluscs in the ocean went on to diversify tremendously soon after the end of the Cretaceous. The K-T casualties included most of the large creatures of the time, but also some of the smallest, in particular the plankton that generate most of the primary production in the oceans. More bad science is described in this chapter than in all the rest of the book. For example, even in the s a new book on dinosaur extinctions suggested that they spent too much time in the sun, got cataracts, and because they couldn't see very well, fell over cliffs to their doom.
But no matter how convincing or how silly they are, any of the theories that try to explain only the extinction of the dinosaurs ignore the fact that extinctions took place in land, sea, and aerial faunas, and were truly worldwide. The K-T extinctions were a global event, so we should examine globally effective agents: geographic change, oceanographic change, climatic change, or an extraterrestrial event. The most recent work on the K-T extinction has centered on two hypotheses that suggest a violent end to the Cretaceous: a large asteroid impact and a giant volcanic eruption.
An Asteroid or Cometary Impact? A meteorite big enough to be called a small asteroid hit Earth precisely at the time of the K-T extinction. The evidence for the impact was first discovered by Walter Alvarez and colleagues.
They found that rocks laid down precisely at the K-T boundary contain extraordinary amounts of the metal iridium Figure It doesn't seem to matter whether the boundary rocks were laid down on land or under the sea. In the Pacific Ocean and the Caribbean the iridium-bearing clay forms a layer in ocean floor sediments; it is found in continental shelf deposits in Europe; and in North America, from Canada to New Mexico, it occurs in coal-bearing rock sequences laid down on floodplains and deltas.
The dating is precise, and the iridium layer has been identified in more than places around the Earth. Where the boundary is in marine sediments, the iridium occurs in a layer just above the last Cretaceous microfossils, and the sediments above it contain Paleocene microfossils from the earliest part of the Cenozoic.
The iridium is present only in the boundary rocks and therefore was deposited in a single large spike: a very short event. Iridium occurs in normal seafloor sediments in microscopic quantities, but the iridium spike at the K-T boundary is very large. Iridium is rare on Earth, and although it can be concentrated by chemical processes in a sediment, an iridium spike of this magnitude must have arisen in some unusual way.
Iridium is much rarer than gold on Earth, yet in the K-T boundary clay iridium is usually twice as abundant as gold, sometimes more than that. The same high ratio is found in meteorites. Starvation was another possibility: Large dinosaurs required vast amounts of food and could have stripped bare all the vegetation in their habitat. But many of these theories are easily dismissed. Also, plants do not have brains nor do they suffer from the same diseases as animals, so their simultaneous extinction makes these theories less plausible.
But in the late Mesozoic Era that corresponds with the extinction of the dinosaurs, evidence shows that the planet slowly became cooler. Lower temperatures caused ice to form over the North and South poles and the oceans to become colder. Because the dinosaurs were cold-blooded—meaning they obtained body heat from the sun and the air—they would not have been able to survive in significantly colder climates.
Yet some species of cold-blooded animals, such as crocodiles, did manage to survive. Also, climate change would have taken tens of thousands of years, giving the dinosaurs sufficient time to adapt. In , Russian astronomer Joseph Shklovsky became the first scientist to consider the extinction was due to a single catastrophic event when he theorized that a supernova the explosion of a dying star showered the earth in radiation that could have killed the dinosaurs.
Once again, the problem with the theory was explaining why dinosaurs died out and other species did not. Also, scientists said that such an event would have left evidence on the surface of the earth—trace amounts of radiation dating back to the Cretaceous Period.
None was found. Enter Luis Alvarez, a Nobel Prize-winning physicist, inventor and pioneer in the field of radiation and nuclear research. He and his son, noted geologist Walter Alvarez, were conducting research in Italy when they discovered a centimeter-thick layer of iridium-enriched clay at the K-T boundary. Iridium is rare on earth, but more common in space. The Alvarezes published their findings in , postulating that the thin layer of iridium was deposited following the impact of a large meteor, comet or asteroid with the earth.
At the time, the Alvarez theory was so far removed from prevailing hypotheses that it was ridiculed. Slowly, though, other scientists began finding iridium evidence at various places around the globe that corroborated the Alvarez theory. There was, however, no smoking gun in the form of an impact site.
The Chicxulub Crater, as it was dubbed, was named for a nearby village. Scientists believe the bolide that formed it was roughly 6 miles in diameter, struck the earth at 40, miles per hour and released 2 million times more energy than the most powerful nuclear bomb ever detonated. Miles-high tsunamis would have washed over the continents, drowning many forms of life. Shock waves would have triggered earthquakes and volcanic eruptions.
The resulting darkness could have lasted for months, possibly years.
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