Plants and the K–T Boundary

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. In that introduction, Keller et al. The discovery of similar anomalies elsewhere and the proposition that these anomalies and the KT extinctions resulted from the impact of a large extraterrestrial bolide have spurred over a decade of unparalleled research on the physical and biological events at and near the KT boundary. Chicxulub had become the KTB impact crater. This foregone conclusion only lacked the evidence.

Re: Precise K-T boundary dating

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.

The ‘K–T Boundary’ or ‘end Cretaceous event’, which marks the extinction of the events close to the K–T boundary, very precise stratigraphic control (dating of.

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. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts. In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center BGC at the University of California, Berkeley, and at universities in the Netherlands and the United Kingdom, have determined that an impact event occurred at about the same time as the mass extinction of the dinosaurs.

Using a recalibrated technique for dating Earth minerals, the researchers hypothesize that impact happened 66,, years ago, and that it produced the final atmospheric conditions needed to wipe out the dinosaurs.

Cretaceous–Paleogene boundary

Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs’ extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils. The argon-argon dating method has been widely used to determine the age of rocks, whether they’re thousands or billions of years old.

Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2. Renne and his colleagues in Berkeley and in the Netherlands now have lowered this uncertainty to 0. As a result, argon-argon dating today can provide more precise absolute dates for many geologic events, ranging from volcanic eruptions and earthquakes to the extinction of the dinosaurs and many other creatures at the end of the Cretaceous period and the beginning of the Tertiary period.

AGE LIMITATIONS ON THE K-T BOUNDARY IN NEW JERSEY The precise Owens and Sohl () used potassium-argon dating on the glauconites, and.

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. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region.

Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. Subsequent tectonism has complicated the picture. Shocked quartz and more: Impact signatures in K-T boundary clays and claystones. Quartz grains displaying multiple sets of planar features are described from numerous Cretaceous-Tertiary K-T boundary clays and claystones at both marine and nonmarine depositional sites around the world.

All these sites also show anomalously high amounts of iridium and enrichments of other siderophile elements in cosmic ratios within these boundary units. This combination of mineralogical and geochemical features are used in support of an impact hypothesis for the end-Cretaceous event. Recently, it was suggested that some combination of explosive and nonexplosive volcanism associated with the formation of the Deccan traps in India could be responsible for the mineralogy and geochemistry seen in the K-T boundary units.

Besides the obvious contradition of simultaneous explosive and nonexplosive volcanism from one locality during an instant of geologic time, there remains the difficulty of spreading both iridium and trace elements in cosmic proportions and quartz grains around the world by volcanic atmospheric transport.


Whether the platinum group elements PGE can be taken as the indicators of extraterrestrial materials is a very important and interesting scientific problem. It is discussed on the basis of systematic investigation and study of a great amount of related literature. The following conclusions can be obtained: i extraterrestrial impact event can cause the PGE anomaly; conversely, the PGE anomaly may not represent the existence of extraterrestrial impact event, because the PGE anomaly can be caused by many terrestrial events e.

This is a preview of subscription content, log in to check access. Alvarez, L.

not at) the K-T boundary (dated at about Ma). Hofmann et al. [] collected and analyzed samples from close to the bottom and top of the main lava pile in.

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.

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.

K/T boundary: Discussion of the platinum group elements as indicators of Hildebrand, A.R., Chicxulub crater: A possible K-T boundary impact crater on the​.

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.

Others blame it on vast clouds of climate-altering gases released by eruptions that buried western India under layer upon layer of basaltic lava flows nearly 3, meters thick. Now, researchers from India’s three national laboratories have joined the fray. They report that their discovery of a new phase of fullerene or Carbon in the Anjar sedimentary rocks bolsters the impact theory. According to this theory, a meteorite the size of a small city that landed in Chicxulub in Mexico 65 million years ago, coinciding with KTB, kicked up so much dust that it caused a global blackout triggering mass extinction.

The key evidence of impact, besides the crater, is the abnormally high concentration of element Iridium found at K—T boundaries across the world. Iridium is more abundant in meteorites than in Earth’s crust and so it was hypothesized that the meteorite vaporized after crashing into Mexico and spread the Iridium into the atmosphere. Since Alvarez and his team proposed the impact hypothesis in , over one hundred KTB sections have been identified worldwide based on the presence of anomalously high Iridium.

The Anjar volcano-sedimentary sequence located in the Kutch region of Gujarat consists of nine lava flows covering a time span from

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.

To date biostratigraphic, magnetostratigraphic, stable isotope, or iridium data do not support a K-T boundary age for the Chicxulub impact.

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”.

Carbon clues to dino extinction

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 , [2] 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.

This is called the KT boundary, because it marks the dividing line finding his own fossilized bones from mammals dating back to the Ice Age.

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.

So the K-T boundary is the point in between the Cretaceous and Tertiary periods.


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.

Shocked quartz and more: Impact signatures in K-T boundary clays and U-Pb isotopic dating of single 1 – 3 micrograms zircons from K/T distal ejecta from a.

If you watched for an hour or two, the star would have seemed to grow in brightness, although it barely moved. Sixty hours later, the asteroid hit. The air in front was compressed and violently heated, and it blasted a hole through the atmosphere, generating a supersonic shock wave. In that moment, the Cretaceous period ended and the Paleogene period began. The result was a slow-motion, second-by-second false-color video of the event.

Within two minutes of slamming into Earth, the asteroid, which was at least six miles wide, had gouged a crater about eighteen miles deep and lofted twenty-five trillion metric tons of debris into the atmosphere.

Iridium-Rich Layer

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.

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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.

At the K-T boundary.