CHICXULUB: THE IMPACT CONTROVERSY

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 impact was cataclysmic, some scientists estimate that the collision released energy equivalent to million hydrogen bombs.

Cretaceous–Paleogene boundary

Scientists determine most precise dates yet for dinosaur extinction 66 million years ago. Rock strata in northeastern Montana; they span the time of the dinosaur extinction. This material is available primarily for archival purposes.

The K-T boundary was the climax of a climate change initiated ca. Formation, as also supported by absolute U-Pb dating of inter-fingered volcanic ashes.

The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance. This layer was found many places around the globe and came to be associated with the boundary between the Cretaceous and Tertiary Periods, referred to as the K-T Boundary on the geological age scale.

The fact that a layer like this has been found at several locations scattered around the world suggests a large-scale atmospheric suspension of the material, such as would occur upon the impact of a sizable asteroid. Coupled with the presence of dinosaur fossils below this layer, but not above, this evidence has led to the asteroid model for the extinction of the dinosaurs. This cross-section of the strata containing the iridium-rich layer is on display at the Smithsonian Museum of Natural History.

The thickness of the layer appeared to be cm. Iridium-Rich Layer The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance. Index Frankel, “The End of the Dinosaurs”.

PHYSICAL STRATIGRAPHY OF K-T BOUNDARY STRATA

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 new extinction date is precise to within 11, years. SUERC Renne and his colleagues also dated rocks above the KT boundary where.

According to abundant geological evidence, an asteroid roughly 10 km 6 miles across hit Earth about 65 million years ago. This impact made a huge explosion and a crater about km roughly miles across. Many asteroids of this type are now known; their orbits pass through the inner solar system and cross Earth’s orbit. Some of these could potentially hit Earth in the future. Most, but not all are smaller than the one that hit us 65 million years ago. Fossils found in soil layers of different ages show a record of slow, gradual changes in species, with simple organisms gradually being replaced by more complex organisms, apparently by evolutionary processes driven by natural selection.

For example, million years abbreviate My ago, the oceans held only simple organisms like algae, while the land was relatively lifeless. Fish fossils appear in strata after about My ago; dinosaurs and giant reptiles were on the land by My ago.

Refining the date of the K/T boundary and the dinosaur extinction

The beginning of the end started with violent shaking that raised giant waves in the waters of an inland sea in what is now North Dakota. Then, tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.

The KT boundary falls right at the border of the Cretaceous period and the the rock that was melted by the impact could be dated by a number of laboratories.

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.

Plants and the K–T Boundary

You’ve read 1 of 2 free monthly articles. Learn More. B uilt upon the slopes of Mount Ingino in Umbria, the ancient town of Gubbio boasts many well-preserved structures that document its glorious history. Founded by the Etruscans between the second and first centuries B. It is one of those special destinations that draws tourists to this famous part of Italy. It was not the ancient architecture but the much longer natural history preserved in the rock formations outside the city walls that brought Walter Alvarez, a young American geologist, to Gubbio.

K-T Event. Sixty-five million years ago about 70% of all species then living on Earth have caused enormous fires, and indeed soot is found in the boundary clays. The Chicxulub crater has been age dated (by the 40Ar/39Ar method) at

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. Clearly, something happened 65 million years ago to cause a mass extinction. A core sample of rock, taken across the boundary layer but not from Gubbio is shown here:. Alvarez brought samples of the boundary layer back to his lab at Berkeley and ran some standard tests. Iridium is an element that has very few uses: one of these is as a hardening agent for gold. So the initial tests were thought contaminated by material sloughing off the gold wedding bands worn by the scientists working with the clay.

The Impact That Wiped Out the Dinosaurs

Both were vilified and ostracized by the increasingly vocal group of impact hypothesis supporters. The Cretaceous-Tertiary boundary KTB mass extinction is primarily known for the demise of the dinosaurs, the Chicxulub impact, and the frequently rancorous thirty years-old controversy over the cause of this mass extinction. In a perverse twist of fate, this discovery also began the decline of this hypothesis, because for the first time it could be tested directly based on the impact crater and impact ejecta in sediments throughout the Caribbean, Central America and North America.

present there are no accurately dated impact craters contemporaneous to Chicxulub (and thus to the K/T boundary). While this suggests that Chicxulub may be.

The Yacoraite Formation corresponds to a mixed carbonate-siliciclastic lacustrine sedimentary system, deposited during the sag phase post-rift and also records the K-T boundary. An integrated S2S approach was applied using sedimentary, geochronology, geochemical and isotopic datasets at basin scale ca. These data are used here to discuss the high-resolution time step ca. Results show that the Yacoraite Formation recorded major climate changes that can be documented in terms of catchment dynamic, erosion processes, carbonate accumulation trends, lacustrine dynamic and source rock quality.

The K-T boundary was the climax of a climate change initiated ca. It was followed by a major pulse in paleo-productivity, in turn followed by a major pulse in TOC 0 wt.

The Day the Dinosaurs Died

The iridium anomally that they described has now been detected at many other K-T boundary locations throughout the world. The hypothesis that an impact was the cause of extinctions at the K-T boundary is still being debated, and a competing hypothesis suggests that the extinctions and many features of the K-T boundary layer can best be explained to be a result of large-scale volcanism. One of the uncertainties regarding the impact hypothesis is the location of the impact crater. Using the concentrations detected, Alvarez et al.

The impact of a bolide of this size would have resulted in a crater [is approx. Geochemical data on material from the K-T boundary interval in marine sections suggested that the impact was probably in oceanic crust, in which case it may have been subducted.

Other articles where K–T boundary is discussed: dinosaur: The K–T boundary shells), for rocks dating from the Carboniferous through the Permian Period.

Was it a comet or asteroid impact? Volcanic eruptions? Climate change? In an attempt to resolve the issue, an international team of scientists have determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known impact that occurred around the same time. The new extinction date is precise to within 11, years. The revised dates clear up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures.

The new date for the impact — 66,, years ago — is the same within error limits as the date of the extinction, said Renne, making the events simultaneous. Argon-argon dating uses a mass spectrometer to measure the ratio of radioactive potassium in a sample of rock to its decay product, argon. The amount of argon in a sample allows researchers to use rocks as incredibly slow clocks.

Many people think precision is just about adding another decimal place to a number, but it’s far more exciting than that.

Cretaceous–Paleogene boundary – Video Learning – 7


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