K–T boundary

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 heaving sea turned into a foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish — sturgeon and paddlefish — onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud.


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.

Cambridge Core – Plant Sciences – Plants and the K-T Boundary – by Douglas J. Publisher: Cambridge University Press; Online publication date: August

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.

That boundary had previously been dated at Renne noted that the greater precision matters little for recent events, such as the emergence of human ancestors in Africa 6 million years ago, because the uncertainty is only a few tens of thousands of years. One major implication of the revision involves the formation of meteorites, planetessimals and planets in the early solar system, he said.

Argon-argon dating was giving a lower date than other methods for the formation of meteorites, suggesting that they cooled slowly during the solar system’s infancy. Argon-argon dating is now no longer at odds with that evidence, but is very consistent with it. Renne has warned geologists for a decade of uncertainty in the argon-argon method and has been correcting his own data since , but it took a collaboration that he initiated in with Jan R.


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.

Rare-earth-element diagram of K-T boundary interval rocks from North been collected for K-Ar dating (J.D. Obradovich, oral commun., ). It is clear that an​.

This formation forms the striking, massive, m high vertical cliffs along the south side of the San Juan River on the south side of the city of Farmington in the west-central part of the basin Figure 1. The Ojo Alamo is a coarse-grained, conglomeratic sandstone that crops out around the periphery of most of the New Mexico part of the San Juan Basin but is absent in the northern part mostly in Colorado, Figure 1.

The Ojo Alamo was deposited on a basin-wide erosion surface in early, but not quite earliest, Paleocene time by south-to-southeasterly flowing, high energy, braided streams Fassett , Fassett et al. A hiatus of nearly 8 m. The Ojo Alamo is a multi-storied conglomeratic sandstone with highly varied internal architecture and thicknesses throughout the basin Fassett et al. Conglomerate clasts range from near-boulder size in the northwest part of the basin to small pebbles and grit in the southeast part.

The rock-stratigraphic definition and age of the formation have been characterized differently by various workers over the years as discussed in numerous papers; those discussions are summarized and referenced in Fassett et al. Figure 2 shows the principal differences in the ways the Ojo Alamo has been characterized in its type area and the way the name is used in this report.

The so-called middle, “shaly” part of the Ojo Alamo in the type area of the Ojo Alamo Sandstone is a mischaracterization of this interval because it contains multiple sandstone beds, and these sandstones represent a significant part of the interval. In the type area, the sandstones of the middle part of the Ojo Alamo are white and relatively friable rather than having the rusty-brown color of the harder lower and upper benches, thus these beds do not typically form cliffs or ledges.

Photographs of the Ojo Alamo Sandstone at several outcrop localities are included in this report and show the nature and variability of the lithology of this formation.

Carbon clues to dino extinction

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 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​.

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. Mammals were not common until after 65 My ago, and humanlike creatures appeared only in the last 4 My.

Fundamentalists are defined as people who believe that the primary way of learning about nature should not be the scientific method, or compilation of evidence tested in different labs in different countries, but rather interpretation of ancient manuscripts, such as the Koran, the Old Testament of the Bible, the New Testament, or other ancient writings. The scientific method was hammered out mainly in the s, when naturalists of that period agreed that information about nature could best be determined by direct observations of nature, and experiments, which would be published openly, in international literature.

Re: Precise K-T boundary dating

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.

The date of the impact coincides precisely with the Cretaceous–Paleogene boundary (K–Pg boundary), slightly less than 66 million years ago, and a widely​.

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.

The massive formation is composed of many layers that span about meters in total. Not all of the more than million specimens and artifacts that Kirk Johnson oversees as director of the Smithsonian National Museum of Natural History can be seen or touched. For 20 years, Johnson has been collecting stories along with Geologists have long used fossils to help identify parts of the rock record from around the world and Walter employed this strategy in studying the formations around Gubbio.

But in one centimeter of clay that separated two limestone layers, he found no fossils at all. Furthermore, in the older layer below the clay, the forams were more diverse and much larger than in the younger layer above the clay See Foraminifera. Everywhere he looked around Gubbio, he found that thin layer of clay and the same difference between the forams below and above it. Walter was puzzled.

The Day the Mesozoic Died

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.

Later tests confirmed that the iridium level is enhanced in the K/T boundary Typically, a sedimentary rock from the Cretaceous-Tertiary eras can be dated to.

All rights reserved. New insights about the asteroid thought to have killed off the dinosaurs suggest it may have just been the final blow, and that the reptiles were already suffering from a finicky climate prompted by volcanic eruptions long before the meteorite struck. The research, detailed in the February 8 issue of the journal Science , adds to the ongoing scientific debate over what exactly killed off the dinosaurs.

That debate, which once revolved around the question of whether the culprit was an asteroid or volcano-induced climate changes, has evolved to consider the possibility that perhaps multiple environmental factors were involved. Using a high-precision dating technique on tektites—pebble-sized rocks formed during meteorite impacts—from Haiti that were created during the event, the team concluded that the impact occurred 66,, years ago—slightly later than previously thought.

When error limits are taken into account, the new date is the same as the date of the extinction, the team says, making the events simultaneous. Renne said the new findings should lay to rest any remaining doubts about whether an asteroid was a factor in the dinosaurs’ demise. That is not to say, however, that the asteroid—which carved out the so-called Chicxulub crater—was the sole cause of the dinosaurs’ extinction. Evidence now suggests massive volcanic eruptions in India that predated the asteroid strike also played a part, triggering climate changes that were already killing off some dinosaur groups.

For example, “nobody has ever found a non-avian dinosaur fossil exactly at the impact layer,” Renne said in an email.

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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.

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.

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.

In ca. The obtained results suggest that the Yacoraite Formation can be considered as a world-class example to illustrate how the K-T boundary is recorded in lacustrine sediments. In particular, it could be used as reference to address key questions related to cross-scale interactions, feedback loops and temporal dynamics in the sedimentary record. How to cite: Rohais, S. This work is distributed under the Creative Commons Attribution 4.

Plants and the K–T Boundary

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.

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​.

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.

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.

What survived the KT event?

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